The ferruginous district of Beni Bou Ifrour-Ouixane is located in northern Morocco. This mining area includes three abandoned iron mines: Ouixane, Axara, and Setolazar, where the tailings and rock waste have been oxidizing for over 32 years. The intensive mining of ore deposits has generated deep acidic pit lakes.

Geochemical and mineralogical techniques were used to characterize the tailings (Setolazar) and sediments from the open-pit lakes (Axara and Ouixane). Surface water samples were collected from the Axara open-pit lake to examine the hydrochemistry and heavy metal pollution characteristics. PHREEQC software was used to simulate the forms of heavy metals in the water and to better understand the interactions between the sediment and water in the open-pit lake.

The mineralogy of the tailings is dominated by jarosite (14–88%), gypsum (2–80%), and quartz (10–13%). Low quantities of hematite, magnetite, and tetanomagnetite were also identified. Lake floor sediments were composed mainly of gypsum (53-74%), quartz (10-32%), and langbeinite (15%). Wixane lake sediment contains morenosite (32%), bianchite (26%), and dolomite (9%), suggesting the presence of nickel and Zn-sulfates. Copiapite and jarosite are indicators of extreme acidic conditions. Ouiksane pit lake sediment contains more aluminosilicate minerals related to the local lithology, particularly the microdiorite. Fe and S constitute the main elements of the chemical composition of the studied samples. Mn is the predominant metal for mine tailings with values ranging from 198.49 to 638.65 µg/g, followed by As (606.93 to 16.12 µg/g); Cu (576.24 to 40.70 µg/g); Co (411.22 to 31.54 µg/g); Ni (144.70 to 16.94 µg/g); Zn (120.31 to 30.92 µg/g); and Pb (70.83 to 6.05 µg/g). The highest Mn, Zn, and Pb contents were recorded in lake sediments. Waters from Axara pit lake are characterized by acidic pH (3.12) with high conductivity (29.16 mS/cm), and very high sulfate contents (31506.2264 mg/l). High Fe (30.33 mg/l) and moderate Zn content (3.09 mg/l), Cu (1.15 mg/l), and Ni (1.59 mg/l) were recorded in Axara, indicating high contamination potential. This may be related to sulfate dissolution. PHREEQC modeling of sampled waters shows that Fe, Zn, and Cu exist in solution on FeSO4, FeCl, ZnSO4, and CuSO4 species, respectively. The dissolution kinetics of sulfate minerals control the distribution of the potentially toxic elements in water. The acquired data could be of great interest in managing potentially toxic element contamination and taking necessary remediation measures in this area.

The treatment of acid mine drainage (AMD) is an urgent issue due to mainly the economic burden of the treatment. The treatment of AMD using limestone emits CO₂ gas, which will become a major issue soon for carbon neutrality. Also, for carbon neutrality, expectations for enhanced rock weathering (ERW) have increased as negative emission technologies (NETs). The ERW has been applied in agricultural and marine sites which are moderately acidic to alkaline environments. In contrast, it is well known that the dissolution of most silicate minerals is enhanced by an order of magnitude in strongly acidic environments such as AMD. In this context, as a case study, geochemical reactive transport modeling of ERW with basalt at the AMD site in Japan was conducted to calculate the annual mass of weatherable minerals in the basalt and subsequent CDR. After that, a life cycle assessment (LCA) and techno-economic assessment (TEA) of ERW in the AMD were also conducted. This is the first study to evaluate both the effectiveness of ERW in AMD as one of NETs and its co-benefit in providing passive treatment for AMD with LCA/TEA.

Our research introduces an innovative approach by combining a one-dimensional reactive transport model (1D-RTM) of crushed basalt dissolution in AMD with LCA/TEA assessment to evaluate the effectiveness of basalt ERW in AMD. Additionally, arsenic adsorption by schwertmannite, a sulfuric iron oxyhydroxide known to precipitate under acidic conditions was predicted using a surface complex model (SCM) in 1D-RTM to assess the potential for passive treatment.

The results demonstrate that AMD substantialy accelerates weathering of basalt, leading to substantial net CO₂ removal within a year and ERW on AMD can be economical. Furthermore, the schwertmannite precipitation offers an efficient arsenic removal as an adsorbent, while the providing proton during schwertmannite precipitation could maintain the strongly acidic conditions for ERW. These two results indicate that passive treatment of AMD could be technically integrated with CDR by ERW in AMD.

The practical implications are twofold: the potential for large-scale CO₂ sequestration and the simultaneous passive treatment of AMD. This dual benefit could offer substantial economic incentives, particularly for AMD sites dealing with arsenic, iron, and sulfuric acid contamination. Future research should apply to active treatment to compare the active treatment using limestone currently carried out at AMD treatment plants with the proposed active treatment that combines ERW.

Releasing toxic metals from mining waste heaps presents environmental challenges, particularly in regions with a long history of ores processing. The mining industry produces vast amounts of waste, often stored in open conditions and exposed to changing weather. For this reason, post-mining areas risk becoming sites of enhanced microbial activity, especially at acidic pH, where weathering and bioleaching occur. Microorganisms, when they adhere to solid surfaces, contribute to acid mine drainage (AMD) and acid rock drainage (ARD) by facilitating the release of toxic elements into surrounding ecosystems. Studying how bacteria interact with minerals within porous media is crucial to understanding and mitigating these processes.

There is still little information on the mechanism of metal transformations due to the acidophiles' activities in mixed wastes. Surfactants and biosurfactants can accelerate the leaching rate by changing solid-liquid interfacial properties such as surface charge and wettability. In bioleaching, where interactions occur at the interfaces between microbes, solids, solution, and other components, modification of the mineral surface, already applied in ore beneficiation, can improve the adhesion of bacterial cells, enhancing the leaching process. Depending on the surface-active agent, it can also inhibit AMD formation by increasing cell mobility in the heap.

Acidophilic microorganisms play a major role in the extraction of metals from mineral deposits, and one belonging to the genus Acidithiobacillus was dominant in the post-mining heaps studied. Bioleaching experiments were conducted to evaluate the potential for toxic element release and the possibility of using post-mining waste as a secondary resource. It has been shown that up to 1000 mg/L of arsenic can be leached depending on process conditions. Adhesion, movement and retention of microorganisms in the mineral bed can affect the release of metals and metalloids. Therefore, bacterial mobility was studied in untreated waste bed and the ones with adsorbed surfactants. Tests were performed at constant temperature. Experiments were carried out in a column filled with solid and closed circuits.

This insight into microbial-mineral interactions highlights the importance of controlling bacterial activity in mining waste management. An improved understanding of these processes could lead to more effective strategies for minimising environmental contamination from mining heaps and optimising metal recovery through biotechnological applications.

Coal holds an important position within South Africa's commodities due to its current role as the primary energy source. Nevertheless, the beneficiation and processing of South African coals result in substantial wastes in the form of discards and ultrafine coal slurries. Previous research has shown the potential of coal ultrafines to serve as an energy resource if suitably beneficiated, given their comparable quality to run-of-mine coal. The issue of long-term environmental impact from these ultrafine coals also comes to the forefront, particularly concerning the substantial sulfidic content in coal ultrafines, which can contribute to the generation of acid rock drainage (ARD). In addressing these complexities, froth flotation is seen as a promising technique for the beneficiation of ultrafine coal waste. However, this technique is not without its challenges. Coal ultrafines often encompass a significant proportion of clay minerals, with kaolinite being a prominent phyllosilicate clay mineral. The prevalence of kaolinite as a gangue mineral in South African coal ultrafines adds an intricate layer to the beneficiation process, as effectively depressing kaolinite during flotation can prove intricate. Efficient depression of kaolinite is thus necessary to separate it from ultrafine coal particles during flotation. Furthermore, considerations of pulp chemistries, such as process water quality in ultrafine coal flotation would be of paramount importance, especially given that there is water scarcity in regions within which coal mining occurs in South Africa. Because of this, the implementation of closed water circuits in flotation and effective dewatering of tailings for water recovery and dry stacking of tailings have gained much prominence owing to the need to minimise water consumption and enhance waste management practice in line with SDG 6, 9, 12, 13, 14 and 15. Therefore, it stands to reason that effective depression of kaolinite during ultrafine coal flotation is crucial in achieving high-quality coal products with reduced impurities with an understanding of the influence of different flotation chemistries. This research considers kaolinite depression and dewatering characteristics in inorganic electrolyte concentrated process water in view of process water recirculation in coal flotation and the need for the dewatering of tailings. Laboratory scale tests such as zeta potential measurements and depressant adsorption studies were considered. Understanding the behaviour of kaolinite in these contexts is vital for sustainable coal processing and environmental stewardship.

In this study, direct CO₂ emissions from mine drainages and indirect CO₂ emissions from the potential consumption of hydrated lime were modeled using PHREEQ-N-AMDTreat based on chemical compositions and flow rates at most mine drainage sites (n = 395) across South Korea. When considering CO₂ emissions, passive treatment methods were found to be substantially more advantageous than (semi-)active treatment methods using hydrated lime. Additionally, implementing pre-aeration is a preferable approach for most mine drainages from the perspective of CO₂ emission reduction.

In recent decades, dozens of abandoned sulphide mines have been closed in the Ural pyrite belt (the second largest after the Iberian belt). Some of them still produce acid mine drainage (AMD). Their contribution to hydrosphere pollution is very substantial. More than a quarter of highly and extremely highly polluted groundwater and surface waters in the Sverdlovsk region (Middle Urals, Russia) are located in catchments where minerals were previously mined.The chemical composition of AMD is unstable over many years (the first flush is observed in the first years with a slow gradual decrease over decades), relevant changes occur depending on climatic factors.

Long-term monitoring data are used to assess the effectiveness of AMD treatment. Using the example of 2 mines (Levikhinsky and Degtyarsky), an analysis of the observation results was performed over a period of 30 years; 1) the composition of AMD, and 2) the quality of wastewater (after neutralization and settling). These waters enter the river basins and then into reservoirs that are used to water supply of large cities, population of .4 million people (Nigniy Tagil) and 1.5 (Ekaterinburg).

The treatment of AMD at both sites is carried out in two stages: neutralization with lime milk and settling in clarification ponds. The efficiency of mine water treatment at the Degtyarsky mine reaches 99% for the main pollutants. At the Levikhinsky mine, a similar treatment scheme is used, but it is much less effective - from 59% for manganese to 93% for iron and copper. Despite the same treatment system, at the Levikhinsky mine, the quality of water discharged into the Tagil river system does not reach the standard indicators, the excess factor reaches hundreds and thousands for manganese, copper, zinc, aluminum. The reasons for this discrepancy are: 1) higher values of pollutants in mine water (2 times) and 2) insufficient time for settling (10 times).

To improve the efficiency of treatment at Levikhinsky mine, it is necessary to modernize the existing system (neutralization plus settling) and supplement it with a passive purification stage. Such a three-stage system will reduce the pollution of surface waters to standardized values, relevantly improve the environmental situation. To ensure this possibility, it will be necessary to create a cascade of ponds with an area of several thousand hectares.

To reduce the cost of active treatment of manganese (Mn) rich mine drainage, a pilot-scale passive treatment system utilizing an existing Mn(II)-oxidizing bioreactor was installed at Legacy Mine X. This system achieved over 95% Mn(II) removal efficiency without the need for additional organic substrates. To ensure stable operation and assess its applicability to other mine drainage sources, a laboratory-scale bioreactor was set up to evaluate the effects of temperature and pH across different mine drainage sources.

The acid mine drainage from Legacy Mine X was continuously used as the source for the lab-scale bioreactor, with varying temperature at 15°C, 10°C and 6°C. For pH evaluation, acid mine drainage from Mine Y, with an initial pH of 2.6 and Mn(II) concentration of 10 mg/L, was used. The limestone medium with Mn(II)-oxidizing microbes in the bioreactor was sourced from the pilot-scale system at Legacy Mine X. Mn(II) concentrations were measured at both the inlet and outlet of the bioreactor. Sludge precipitated on the limestone medium was collected for 16S rRNA gene amplicon sequencing at the end of each experimental run.

The evaluation of temperature effects revealed that a decrease in temperature from 15°C to 6°C reduced the Mn(II) removal rate from 95% to 88% on average in the lab-scale reactors. In the investigation of the effect of pH, a strong positive correlation (r = 0.92) was observed between pH and Mn(II) removal rate, indicating that pH substantially influences Mn(II) removal of the bioreactor. At a low flow rate of Hydraulic Retention Time (HRT) = 4 days, the pH of the mine drainage increased to above 7 because of reaction with limestone in the reactor, and more than 90% Mn(II) removal was achieved. Based on Bray-Curtis dissimilarity calculated from amplicon sequencing variants, the decrease in pH from 7 to 4 caused more than 2.5 times greater changes in the microbial community compared to the temperature decrease from 15°C to 6°C.

In many cases, mine drainage is acidic and poor in organic matter. The lab-scale bioreactor removed Mn(II) even from acidic mine drainage (pH2.6) thanks to neutralization effect of limestone. It suggests that the Mn(II)-oxidizing bioreactors operating without organic substrate, has broad applicability for mine drainage treatment.

Mine drainages, particularly in abandoned sites, are a widespread environmental issue requiring continuous treatment. Passive treatment systems have emerged as an effective method for managing these drainages, necessitating a deeper understanding of the geochemical processes involved. Japan, with its abundance of abandoned mines, offers an ideal setting to study these processes. Insights gained from these studies can inform the design and optimization of passive treatment systems worldwide.

This research focuses on two distinct mine drainage sites in Japan: the Ainai mine in Akita, with a neutral pH (≈7.3), and the acidic Shojin River in Hakodate (pH ≈3.1). Both sites are rich in iron (Fe), a common characteristic of many mine drainages globally. Due to its chemical properties, Fe has the potential to sequester other potentially toxic elements, such as arsenic (As), zinc (Zn), and lead (Pb). The role of Fe nanoparticles and colloids in this sequestration process was a particular focus of this study.

Field measurements, water chemistry analyses, and solid-phase observations indicated that Fe colloids were present in both systems, though they differed in composition. Ferrihydrite colloids were more prevalent in the Ainai system, while schwertmannite colloids were found to dominate the Shojin drainage system. In the neutral pH conditions of the Ainai system, Fe colloids were stable, promoting the efficient incorporation and removal of As from the wastewater. However, in the acidic Shojin River, the colloids were relatively unstable, limiting their effectiveness in treating the water.

To enhance treatment in the Shojin River, we implemented the addition of basalt to the river, a technology that also contributes to CO₂ reduction, called enhanced rock weathering (ERW). By adding 1 ton of basalt to the river, we aimed to increase the pH of the wastewater, thereby improving the stability of the Fe colloids and enhancing their ability to sequester toxic elements. This approach demonstrates the potential for combining passive treatment systems with CO2 reduction strategies to improve water quality in acidic mine drainage systems.

This abstract elaborates upon a top-down perspective and history of AMD, while progressing towards modern day solutions.

Utilizing centrifugation, acid mine drainage treatment systems (both fixed and mobile/temporary) are able to take advantage of technolgoy which until recent years had been untested and not familiar in the industry.

As our water constraints increase globally, legacy and active mines require options which provide a long-term solution. We share some information on this technology, in both how it operates, and it's placement in an AMD treatment flow diagram.

Water management has already been a major issue for miners globally over the past decades. Global weather changes, focus on environmental, social & governance (“ESG”) issues, and new legislation on water management are going to make this even more critical. A crisis, that goes by many names, Acid Mine Drainage (AMD) requires the attention of community, government, academia, and miners to create long-term solutions. This presentation provides an overview of available treatments, while providing insightful spotlight on history and critical regions.

Mining activities and the processing of ores have left a legacy of environmental contamination. Radionuclides can migrate into surrounding aquifers and soils, thus represent a human health risk. Conventional technologies based on physicochemical treatments are traditionally used to remediate contaminated mine water. However, these approaches are cost-intensive and ineffective for instance for low uranium concentrations. Findings from the present study suggest a promising method to support or outperform the physico-chemical treatments. By harnessing the magnetic properties of magnetotactic bacteria, it appears possible to bio-remediate uranium-contaminated mine water, even at low-uranium concentrations.

Magnetospirillum magneticum AMB-1 cells were treated in laboratory experiments with 24 mg/L uranium in tap water at different pH (3.5–7.5) under aerobic conditions. In a unique combination of analytical methods and transmission electron and fluorescence microscopy as well as various spectroscopic techniques, the ability of these bacteria of adsorbing uranium was tested. Significant hints were gained on possible binding sites in the bacteria cell`s wall.

The removal efficiency of dissolved uranium(VI) by Magnetospirillum magneticum AMB-1 cells from contaminated water appears to be very effective, independent of the pH. High amounts (86–96%) of uranium were removed from the suspension already in the first hours of exposure and bound in the bacteria`s cell wall showing a stable immobilization of uranium. Parallel factor analysis of time-resolved laser-induced fluorescence spectra reveals that peptidoglycan, a key ligand in the cell wall, plays a crucial role in uranium adsorption. This discovery regarding magnetotactic bacteria is both novel and unexpected for Gram-negative bacteria. M. magneticum AMB-1 cells also show a high level of tolerance towards uranium. In an aqueous environment containing 24 mg/L uranium(VI), most of the bacteria were still alive after one day's exposure.

An outstanding feature however, is the formation of nanoscopic magnetic crystals within the cell of magnetotactic bacteria, which were proved by transmission electron microscopy. These magnetic properties could be harnessed for straightforward magnetic separation of uranium-loaded bacteria from contaminated water. Thus, a simple technical water purification process could be realized, not only for uranium(VI), but probably also for other metals with the objective of potential industrial applications in the field of microbiological purification of water.

Nickel extraction through open-pit mining presents crucial environmental challenges, especially in regions with high annual precipitation, such as Indonesia, a tropical nation which has the world's largest nickel reserves. The entry of mine water into rivers severely effect aquatic ecosystems, as these water bodies serve as critical pathways for the transport and biochemical transformation of pollutants. Given the essential role that rivers play in maintaining ecological balance and supporting communities, it is crucial to find effective, sustainable solutions to manage and mitigate mining-related water contamination. This study explores the potential of aquatic plants to naturally remediate metal-contaminated water, offering an eco-friendly approach to managing mine runoff.

This study introduces a novel application of the Bioaccumulation Factor (BAF) and Translocation Factor (TF) to evaluate the phytoremediation potential of aquatic plants in nickel-contaminated rivers. By identifying and analyzing the metal uptake and translocation capabilities of local plant species, specifically the grass family Poaceae (Echinochloa sp.) in the Akelamo River of Obi Island, the research sheds light on the natural resilience of these plants in mitigating metal pollution. This dual assessment provides insight into the plant's ability to accumulate and translocate metals such as Fe, Mn, Cr, Ni, Zn, and Cu, contributing to the advancement of phytoremediation strategies.

The results indicate that Echinochloa sp. shows high potential as a hyperaccumulator of metals, particularly for Fe, Mn, and Ni, with bioaccumulation levels (%BAF) peaking at 541.03 for Fe. The translocation sequence from roots to stems (%TF) for metals was determined to be Ni > Zn > Cu > Fe > Cr > Mn. These findings highlight the plant's ability to concentrate and move metals within its structures, making it a promising candidate for removing metals from contaminated environments and reducing environmental risks associated with nickel mining.

The hyperaccumulation and translocation properties of Echinochloa sp. have essential implications for post-mining land restoration and erosion control. Their natural abundance and effectiveness in absorbing and redistributing metals make them suitable for phytoremediation applications, particularly in nickel mining regions. The study's outcomes pave the way for implementing sustainable environmental management practices in tropical mining regions, contributing to ecosystem restoration and improving water quality in nickel-contaminated rivers.

The uranium (U) contamination from mining activities in East Germany is a major concern. This study introduces an ecological and scalable approach that offers an effective microbiological technology to complement conventional remediation techniques, which are often more costly and less sustainable. This innovative microbiological solution is a promising response to environmental challenges associated with low-level U contamination.

A comprehensive investigation was conducted in the laboratory using microcosms filled with water samples from former U mines and supplemented with glycerol as an electron donor to stimulate the growth of bacteria involved in U(VI) reduction. A multidisciplinary approach was employed, integrating analytical, spectroscopic, and microscopic techniques. For the first time, High Energy-Resolution Fluorescence Detection Spectroscopy (HERFD) was used to obtain quantitative information about the oxidation state of U in mine water samples amended with an electron donor. Information about the structure of U species was given by Extended X-Ray Absorption Fine Structure (EXAFS) analyses. Advanced microscopic techniques, such as High-Resolution Transmission Electron Microscopy (HRTEM), localized U species in the samples. The findings demonstrated the reduction of U(VI) to U(V) and U(IV) within the anoxic microcosms supplemented with 10 mM glycerol.

During the experiment, the monitoring of the physicochemical parameters of the water samples showed a decrease in the redox potential, accompanied by a remarkable decrease of the U, Fe, and SO₄^2- concentrations by 98%, 96%, and 68%, respectively. A black precipitate formed at the bottom of the microcosms was collected and studied by spectroscopy and microscopy. EXAFS spectra revealed the reduction of soluble U(VI) to insoluble U(IV) dioxide (uraninite) and U(VI)/U(V)-carbonates. HERFD analysis combined with Iterative Transformation Factor Analysis estimated the oxidation states in the black precipitates, revealing U(IV) as dominant oxidation state. A notable finding was the identification of U(V) in the samples with a proportion ranging from 21% to 32% and a long-term U(V) phase even under oxic conditions. By HRTEM we were able to localize U(IV) and U(V) as nanoparticles in the membrane of the bacteria.

This research gives rise to further investigations for the development of an applicable process approach for a cost-effective solution for remediating water contaminated with low U concentrations and co-contaminants such as Fe, and SO₄^2- and even As, through biostimulation of native microbial communities using glycerol. Additionally, biogenic U(V), as a reduction product, provides a noteworthy advantage over uraninite due to its greater stability and resistance to reoxidation.

The closure of pit lakes as aquatic ecosystems is a viable, sustainable and economically responsible option for post-mining land use. Riparian vegetation and littoral areas are critical ecosystem components that cannot be established before the lake is full. Pits may take decades to centuries to fill, creating a long period where the aquatic ecosystem is unlikely to meet regulator and public expectations. We aimed to investigate the potential for artificial floating islands (AFIs) to provide a source of plant propagules that could seed the lakes edges during and post filling, allowing riparian plants to become established without a need for direct planting or seeding in saline coal pit lakes.

AFIs replicate naturally occurring islands of floating vegetation, using a constructed floating base where emergent plants can grow through the island, and their roots sit in and interact with the water column. AFIs have been used to treat stormwater quality issues in lakes and provide habitat for waterbirds. In a one-year pilot study, a set of six (3 ‘vegetated’ and 3 ‘unvegetated’) small AFIs (3 m²) were installed at two saline (3 and 12 mS cm^-1) pit lakes in Queensland (Australia). Vegetated islands were planted with four local species (<1 m tall) in approximately equal proportions. Plant survival rates, growth and biomass were measured twice and sedimentation rates in the lake and under the AFIs were measured once.

Only two of the four plant species grew successfully on the islands which spread across the island via propagules. A range of terrestrial insects were noted within the plants. Evidence was found of extensive bird usage of both vegetated and unvegetated islands, yet no bird species were observed nesting on them. Multiple aquatic organisms (particularly macroinvertebrates and fish) were noted within the plant roots. The AFIs had no significant impact on the total sedimentation in the lakes with no significant difference between vegetated or unvegetated islands.

Key findings of the experiment were: 1) emergent plants can grow successfully on AFIs in pit lake 2) plants have the potential to increase aquatic and terrestrial biodiversity; 3) plants at least after less than 1 year do not alter natural sedimentation within the lake; 4) islands are used by birds. Based on these results we have commenced a full-scale trial of large (100 m²) AFIs as more intensive sources of biodiversity and propagules for pit lakes.

This work explores the role of diatoms in assessing hydrological connectivity between groundwater and surface water in wetlands affected by coal mining activities. The study aimed to establish whether phytoplankton assemblages, specifically diatoms, can improve our understanding of the interactions between terrestrial and aquatic environments in mining areas. Benthic diatoms were postulated to constitute appropriate bioindicators of groundwater-surface water connectivity, as their responsiveness to changes in water chemistry, flow, and important nutrient dynamics provides valuable insights into hydrological conditions, making them key to monitoring ecosystem health in groundwater-dependent environments.

By using field and laboratory assessments of hydrochemistry, isotopic analysis, and benthic diatom assemblages, the influence of coal mining activities on wetland ecosystems and the hydrological connectivity between wetlands and groundwater was investigated. Samples of water and diatoms were collected from wetland surface water, wetland piezometers, local boreholes and benthic vegetation, respectively. Hydrochemistry results were analyzed using standard graphical groundwater quality plots (Piper, Durov, Stiff and biplot diagrams). Cannonical correspondence analysis and cluster analysis were used to identify relationships between chemical parameters and diatom species. This multidisciplinary approach allows for result verification and generating robust findings on interactions between biotic and abiotic parameters in complex wetland ecosystems.

The study findings indicated that wetlands closer to mining operations had more acidic water (low pH), higher electrical conductivity (EC), total dissolved solids (TDS), and isotopic signatures resembling nearby boreholes. Additionally, these areas were dominated by diatom species characteristic of industrial and mining-related pollution, suggesting that the wetlands were largely supported by mine-affected groundwater. In contrast, wetlands further from mining zones were characterized by cosmopolitan diatom species associated with nutrient pollution, implying a different water source or lesser influence from mining-derived groundwater. In these wetlands, isotopic signatures were characteristic of atmospherically derived recharge.

These findings highlight the value of diatom assemblages as reliable bio-indicators of hydrological connectivity in coal mining affected landscapes. Diatoms, when combined with hydrochemistry and isotope data, provide a clearer picture of groundwater-surface water interactions. This approach is crucial for managing and conserving wetlands in coal mining regions, where understanding the influence of groundwater on surface water systems is essential for ecosystem health.

This paper investigates the overburden bed separation evolution and grouting propagation in the Menkeqing coal mine, China, using laboratory test, numerical, and field monitoring methods. Bed separation develops vertically from low-order to high-order and aligns with the mined-out area horizontally, forming stable separations in the Zhidan Formation. A comprehensive evaluation of water inrush disaster risk was conducted for the panel 11-3101. Grouting with coal gangue slurry effectively mitigated groundwater inrush and surface subsidence. Results confirm grouting as a viable measure for controlling bed-separation water inrush hazards.

The environmental assessment and management of mines in South Australia frequently relies on groundwater modelling. These models are reviewed by government hydrogeologists to ensure that the environmental impacts of mining are assessed and predicted as reliably as possible. Often government reviewers repeatedly see the same avoidable shortcomings in these models. The identification of common shortcomings is important to improve modelling and provide confidence to decision makers that a project can be responsibly developed. This is particularly important in South Australia, where groundwater resources are limited and mining is economically important. The mining and energy sector in South Australian contributed $7 billion of the state’s total $18 billion of exports in 2023. The majority of the state’s groundwater is allocated, and competition is developing even for saline groundwater in the arid northern part of the state.

To improve model assessments, five hydrogeologists from two government departments, with a combined experience of 150 years, compiled a list of common errors and omissions in mining applications and operational programs for existing mines, related to groundwater. The list is based on state, national, and international experience, with a focus on more than 40 models. Each of the five hydrogeologists identified the most common and important issues in their experience. Those that were identified by at least two of the hydrogeologists are presented here.

The following common errors and omissions were identified:

• inconsistency between the conceptual hydrogeology and its numerical model representation;
• insufficient model-independent groundwater potentiometric head maps for each aquifer to inform model boundary conditions;
• lack of consideration of groundwater dependent ecosystems;
• little focus on the damage that rising saline groundwater can cause to ecosystems in arid areas;
• sensitivity or uncertainty analysis used in place of field data or good conceptual hydrogeology; and,
• environmental compliance criteria that are linked to model predictions and are unnecessarily complex and difficult to monitor or enforce.

The findings from this review are already used in workshops with hydrogeologists working on behalf of mining companies, will be considered in mining guidelines and may contribute towards a new Australian groundwater modelling guideline. It is envisaged that by highlighting the common errors and omissions of numerical groundwater flow models to modellers and miners, models will be improved and better documented (adhering to the Australian modelling guideline). Ultimately, these will help to ensure that potential environmental impacts are reliably identified, and appropriate regulatory controls applied.

In the drive to secure the world’s supply of critical minerals, mining projects are being developed in more complex locations and at greater depth. Bulk mining methods such as caving are becoming increasingly popular to allow the production rates necessary to secure appropriate return on investment and to provide the urgently needed near term supply of critical minerals to support the energy transition. Should appropriate geotechnical conditions exist, cave mining methods can allow high production rates following a period of initial investment in substantial development required to support this mining method. Consideration of water is essential for the successful development of these types of mining operations, both to limit production risks, costs, and safety as well as to minimise or meet Environmental, Social, and Governance (ESG) targets.

When undertaking water management studies and design at deep underground cave mines, it is fundamental to consider geotechnical conditions throughout every aspect of the mine water study. In this light, we have developed a workflow to support full integration of geotechnical considerations into mine water aspects of cave mining studies. The workflow supports all aspects of a typical mine water study from site investigation through development of the Conceptual Site Model (CSM), hydrogeologic modelling, risk management, planning and engineering of the water management scheme.

Although the integration of geotechnical and hydrogeological field investigations is common practice in the industry to limit drilling costs, the key value of this study was the production of a tested workflow which allows geotechnical integration through every aspect of a cave mining focused mine water study.

The developed workflow contained in this paper is expected to be used as a checklist to guide future mine water studies supporting the development of cave mines. A case study is used as an example of the workflow, applied to advance the development of a cave mining study and demonstrating the effect and importance of geotechnical integration to the outcomes of the mine water study.

Tharisa Minerals is a chrome and platinum group metals (PGM) open-pit mine near Rustenburg, South Africa. The mine dewaters three pits and a planned underground mine. Historic workings under the mine’s active East pit also require proactive water management to ensure safe mining operations.

Tharisa’s dewatering strategy integrates stormwater control, in-pit pumping (boreholes and sumps), and pit perimeter dewatering boreholes. Automated monitoring of water levels record success in meeting drawdown targets. Water re-use enables a phased approach to zero discharge.

Tharisa is a good example of pro-active dewatering design. There are valuable insights on dewatering for surface and underground transition mines.

Monitoring data is crucial for effective resource management, as it helps validate management actions, reduce risk, and improve decision-making. However, gathering data on groundwater resources can be expensive. Focusing on targeted data collection allows for the allocation of resources toward obtaining high-value information, thus avoiding unnecessary spending on data with limited or redundant value.

This study introduces a workflow aimed at optimizing an existing groundwater monitoring program of a well-field supporting an operating mine in an arid region. The project is expected to last for several decades, with uncertainties surrounding the sustainability of the well-field yield and its potential effects on nearby environmental receptors. The current monitoring program involves collecting data from hundreds of sites, leading to substantial projected monitoring costs over time.

To evaluate how effectively collected data can reduce uncertainty in this complex, non-linear problem, we demonstrate the use of an Ensemble Variance Analysis method. This method was integrated into a multi-objective optimization framework using particle swarm optimization and the NSGA-II algorithm. The entire workflow is implemented using the open-source software PESTPP-MOU. The goal was to minimize monitoring costs while maximizing the informational value of the collected data, thereby reducing uncertainty across multiple key predictions.

The process allowed us to identify the most valuable monitoring locations and analyze the trade-offs between cost, uncertainty reduction, and the duration of the monitoring program. Results show that an 80% reduction in uncertainty is possible at just 25% of the anticipated costs of the current monitoring approach. Outcomes enabled a rationalization of the monitoring program and incurring substantial savings over the mines projected lifespan.

Arsenic (As) and sulfate (SO₄) concentrations are important indicators of surface water quality, particularly in areas influenced by mining activities. This study investigates the use of remote sensing to detect As and SO₄ in water bodies through Earth Observation (EO) data, focusing on a case study from the Chalkidiki peninsula in Greece, where are three active surface mines—Olympias, Stratoni, and Skouries (operated by Hellas Gold).

We employed a VNIR hyperspectral sensor (STS Spectrometer, Ocean Optics with a spectral range of 337–823 nm) mounted on a DJI Phantom 3 drone to capture spectral data at 15 sites across three streams linked to the mines. This data was complemented by in situ water sampling and laboratory analysis at Hellas Gold's facilities.

Due to the limitations in directly detecting As and SO₄ using imaging spectroscopy, we focused on indirect detection via optically active substances, specifically targeting Total Suspended Solids (TSS). TSS showed a substantial correlation with As (in situ sampling data: R² = 0.434) and, at selected sites, with SO₄ (long-term water quality measurements: R² = 0.471 or higher). These correlations were further validated using Hellas Gold's public water quality monitoring data (https://environmental.hellas-gold.com/).

To directly estimate TSS and indirectly determine As and SO₄ levels, a spectral sensitivity analysis was conducted using drone-based hyperspectral data. The red-band wavelength range of 670-680 nm exhibited the strongest correlation with TSS (R² = 0.512), leading to the calculation of spectral indices such as NDVI (R² = 0.442), NDWI1 (R² = 0.353), and WRI1 (R² = 0.403). In order to scale up the results from the drone-based data, equivalent indices were derived from satellite multispectral PlanetScope imaging data utilizing bands B4, B6, and B7. The PlanetScope data also displayed substantial correlations with TSS (for NDVI is R² = 0.561, for NDWI1 is R² = 0.659, and for WRI is R² = 0.668), highlighting its potential for broader spatial and temporal monitoring purposes.

Our results indicate that these indices, which respond to spectral changes in water caused by TSS, could serve as proxies for As and SO₄ concentrations. This study demonstrates the potential of integrating in situ, drone-based and satellite data for comprehensive water-quality monitoring contributing to more effective environmental management practices.

Spectral absorption feature parameters (SAFPs) derived from airborne hyperspectral imaging (HSI) (396.0–2453.5 nm) were used to predict Pb contents in coalfield overbank sediments. The derived SAFPs were associated with goethite (~500 nm) and kaolinite (~1448 nm) in sediments. Sediment Pb contents correlated strongest with goethite-related absorption-depth (r = 0.6). The calibration model had a R² = 0.69 and standard error of estimation (SEE) = 3.97, after outlier removal. The validation model had a R² = 0.65 and SEE = 3.90. Overall, the results suggest that airborne HSI can complement conventional geochemical methods of detecting Pb contents in overbank sediments.

According to official figures, aggregate extraction has intensified along the Guaviare River to meet Colombia’s growing infrastructure demands, raising concerns about its geomorphological stability and the socio-environmental wellbeing of riverine communities. This study combines multitemporal Landsat imagery (1984–2023) with official mining data to evaluate channel migration, erosion, and deposition across a 230 km river reach. Seven meanders were classified according to their distance from principal mining hotspots—high, medium, and low influence—revealing that meanders nearest to extraction sites exhibit up to 60–70 % higher migration rates and nearly double the erosion observed in more distant meanders. A distinct peak in deposition at a medium-influence meander (24.5 km downstream) further underscores the heterogeneity of fluvial responses, which are affected by both direct mining impacts and localized sediment accumulation. Temporal analyses demonstrate a threefold increase in erosion between 2008 and 2013, coinciding with the onset of heightened production (~2012), followed by elevated deposition from 2013 to 2018 and a renewed surge in erosion after 2018. Minimal correlation with deforestation or river discharge levels suggests that aggregate mining is the primary driver of these channel adjustments. However, potential unreported or illicit extraction beyond officially documented sites complicates the assessment, indicating that official records may underestimate the full extent of mining-related impacts. The results highlight an urgent need for integrated management and enforcement strategies that balance economic imperatives with ecological and cultural preservation along the Guaviare River.

Keywords: Alluvial mining, Guaviare river, Remote sensing, Gravel extraction, fluvial dynamics, river water

A significant proportion of the environmental challenges associated with mining are related to the waste produced during the extraction process, with pit lakes being one of the most difficult mining legacies to manage. These water bodies are susceptible to physico-chemical changes due to prolonged exposure to minerals (such as pyrite), which can create acidic conditions and increase sulphate and trace element concentrations in the pit lake and the surrounding water bodies. This study aims to develop a robust methodology and numerical dataset of these water bodies to analyse, monitor and determine the physico-chemical characteristics of pit lakes in Chile using satellite imagery.

The novelty of this research lies in its development of a low-cost methodology for monitoring pit lakes through satellite imagery and water colour analysis in the HSV (Hue, Saturation, Value) space. The true colour of water, influenced by the absorption, reflection, and transmission of specific wavelengths of sunlight through dissolved ions and suspended particles, serves as a proxy for understanding its chemistry. Transition metals create distinctive coloured complexes—such as olive-green for Fe²⁺ and blue-green for Cu²⁺—while fine colloids scatter sunlight in specific ways, revealing information about the water's pH and redox conditions. This study calculates time series of HSV values for each pit lake using surface reflectance data from Landsat and Sentinel-2, processed via the Google Earth Engine with Python. A supervised machine learning technique, Random Forest, was employed for the identification and segmentation of pit lakes over time, successfully leveraging the Normalized Difference Water Index (NDWI) to enhance the accuracy of the monitoring approach. Overall, this methodology provides a scalable solution for assessing the dynamic physico-chemical characteristics of pit lakes.In situ physicochemical parameters (pH, EC, Cu and Fe) were collected from publicly available documents. These two datasets are then integrated and compared.

The results of this study confirm that it is possible to obtain HSV parameters from pit lakes. Furthermore, the HSV parameters and their variations over time are directly associated with the physico-chemical characteristics of the pit lakes.

This method provides an accessible and efficient tool for continuous monitoring of water quality in pit lakes, without relying solely on costly and safety compromising in situ sampling campaigns. It has direct applications in the management of mines undergoing closure or already closed, enabling compliance with international environmental regulations. This methodology can be adopted globally, promoting sustainability in mining and protecting water resources.

In the past decade, unmanned aerial vehicles (UAVs), or drones, have become invaluable tools in the mining industry, supporting applications ranging from mineral exploration to environmental remediation. When equipped with high-resolution image sensors, UAVs enable high spatial and temporal resolution surveying, making them particularly effective for monitoring abandoned mining sites. This paper presents a case study demonstrating the application of UAV technology for monitoring an abandoned mining site affected by acid mine drainage (the Trimpancho mining complex in the Iberian Pyrite Belt, southwestern Spain).

The study was conducted on two selected waste dumps: one at the beginning and the other at the end of the mining complex. The primary objective was to estimate the volume of waste material accumulated in these areas. To achieve this, a DJI Phantom 4 RTK UAV was employed to conduct comprehensive aerial surveys of the sites. The imagery collected enabled the generation of orthophotomaps and digital surface models (DSMs), which provided detailed spatial information for accurately delimiting waste accumulations and identifying dominant runoff zones contributing to the degradation of the Trimpancho stream.

The three-dimensional models and orthomosaics produced from the UAV data provided an in-depth visualization of the waste distribution. This enabled precise volume estimations that are essential for long-term monitoring and management of the mining system. By comparing these models with future surveys, it is possible to track changes in waste dump morphology over time. Additionally, the models offer a valuable tool for assessing the potential valorization of critical materials accumulated in the abandoned dumps.

The results confirm that UAV technology is highly effective in obtaining the detailed and accurate data needed for monitoring abandoned mining sites. This information is crucial for planning and implementing remediation strategies adapted to the site's specific topography, hydrology, and geology. UAVs present an innovative, efficient solution that optimizes safety, accuracy, and cost-effectiveness. By enhancing assessment precision and enabling targeted reclamation strategies, UAVs technology contributes to the restoration and sustainable management of degraded mining areas, while also advancing environmental monitoring efforts.

The Iberian Pyrite Belt (IPB) is located in the southwest of the Iberian Peninsula, hosting the largest concentration of polymetallic massive sulfide deposits in the world. Due to heavy mining and processing of ores since the times of Romans, large amounts of mining wastes are dispersed along this geographical area, which are called as “legacy sites”. Many of these wastes contain huge levels of toxic metals and metalloids (e.g. As, Cd, Cu.) and are also potentially NORM (Naturally Occurring Radioactive Materials) wastes, which can constitute an important environmental threat and a substantial potential public health and safety problem.

Therefore, a novel radioactive and physicochemical characterization of the most relevant mining wastes located at different points of the IPB was performed. To this end, wastes have been sampled in different mines, and a multi-elemental, mineralogical and natural radionuclide analysis has been done on each of the samples collected. Forced leaching experiments have also been done to assess the release capacity of contaminants when they come into contact with water. Finally, a diagnosis of potential lines of valorization was made to provide a solution and viability for the environmental effects caused by mining wastes.

The radionuclides activity concentrations of both ²³⁸U and ²³²Th decay series, and ⁴⁰K, were in the same order of magnitude as those expected for undisturbed soils in this geographical area, about 30, 50 and 700 Bq/kg, respectively. In addition, some disequilibria radioactive between long-lived radionuclides from the same series were found, mainly produced by the physicochemical process where they are produced. On the other hand, highly toxic elements such as As, Cu, Pb or Zn, in few wastes, exceed the concentrations in μg/g for uncontaminated soils by 3-4 orders of magnitude. Finally, wastes have an equivalent radius value (Ra_eq), external radiological hazard index (H_ex) and activity concentration index for emitted gamma radiation (Ic) lower than the threshold values stablished.

The potential valorization lines for the use of these mining wastes have been also analysed. From a radiological point of view, wastes would comply with the marketing regulations in the USA, and EU regulation to be reused in construction materials.

Hydrogeological studies in mining are traditionally aimed at tackling problems of safer development of mineral deposits. In recent years, a large number of deposits have been decommissioned both around the world and in Russia, which has made it imperative to solve the problems of post-closure management of sites disturbed by long-term mining operations. The principal types of influence are almost identical in different countries and do not depend on the type of mineral: these are changes in the condition of the underground and surface waters, instability of the earth's surface, and leakages of toxic gases or hazardous substances into the environment. Management of depleted deposits, especially old and abandoned mines, has necessitated the development of special laws and investment of substantial funds in mining area remediation.

In the early 21st century, coal mining in the Chelyabinsk coal basin (Southern Urals, Russia) was terminated. Mining operations in this area of 1,300 km² had continued for over a century, accompanied by dewatering (700 L/s). During that time, a number of towns and settlements with a population of about 300,000 people appeared near the mines. The cessation of the dewatering process has been accompanied by a number of phenomena: the groundwater balance is changing; the sources of surface water recharge are being redistributed; the settlement areas are exposed to flooding; landslides occur on the pit slopes, and sinkholes are forming in subsidence areas.

The first-ever regional groundwater flow model has been developed, which has enabled us to assess the consequences of mine and open-pit flooding; maximum groundwater levels and a time frame for reaching them have been determined. The forecasts consider the influence of climate changes both in the longer term and annually with reference to the probability of precipitation redistribution. The filling of the depression cone is almost complete, and the groundwater levels have stabilized. The open pit workings will continue flooding over the next 70 to 200 years.

Studies have established that at the post-closure stage, the duration of which is estimated at tens and even hundreds of years, new hydrogeoecological conditions are emerging: the lakes that existed due to mine drainage are drying up, and a relevant deterioration of water quality in them is taking place. The complexity of the processes at the post-closure stage is determined by a combination of structural geological features and geomorphological conditions, hydrometeorological factors and mining methods.

Over a hundred lignite-mining pit lakes exist in East Germany, most of them flooded for more than a decade. A specially developed monitoring program tracks their hydrological and chemical conditions and, encouragingly, many lakes show progress towards stable conditions. In recognition, 16 pit lakes were included in a preliminary monitoring under the European Water Framework Directive, which provides a standardized framework for assessing lake water quality across Europe. The coexistence of these two monitoring systems has prompted consideration of potential synergies. However, a comparison reveals differences in frequency, parameters, and quality requirements. Ultimately, defining ‘stable lake water quality’ remains the key relinquishment criterion to conclude the mining-hydrological monitoring.

Designing robust stormwater management infrastructure at mining sites requires accurate estimates of runoff rates in response to design storm events. Standard practice for event runoff estimation is to develop a surface water hydrology model that is calibrated to reproduce the runoff response for historical storm events at gaged locations in the catchment. The calibration lends confidence to the model’s ability to predict conditions during a future event. At mine sites where reclamation is in progress, model calibration is complicated as the reclamation work can change the landforms and surface cover in ways that modify the surface water response characteristics.

This study evaluated the changes in catchment response to progressive reclamation of the Upper Wanagon overburden stockpiles at the Grasberg Mine in Indonesia. The stockpiles occupy approximately 350 hectares. Progressive reclamation of the stockpiles commenced when overburden placement ended in 2018. As of 2024, reclamation work has been completed for approximately 250 hectares. Reclamation includes regrading to direct surface runoff into engineered channels that are armored with riprap. To mitigate erosion, the overland surfaces are covered with a rock armor and vegetated.

These closure activities alter surface water runoff. For example, regrading of the stockpiles has altered flow paths and reduced surface depressions. Also, installation of rock cover and vegetation has roughened the overburden pile surface. These activities alter the runoff volumes and the rate at which runoff flows are conveyed. Accounting for these alterations in predictive runoff models is a challenge for the Upper Wanagon reclamation design.

Rainfall gauges and a surface water flume at the catchment outlet provide rainfall and runoff measurements for the Upper Wanagon area pre- and post-reclamation. Review of this data and subsequent model calibration provides insight on how reclamation affects the runoff responses. This work explores these impacts, and the findings are used to inform reclamation design and post reclamation stormwater management.

Historic salt mining at Carrickfergus, Northern Ireland has left a legacy of hazards including surface subsidence and land contamination through brine water discharges. An area of three abandoned mines, hydrologically connected to facilitate solution mining, underlies a public road network, public water supply intake and gas transmission pipeline. Post closure, the site is undergoing active subsidence resulting in crown-hole development and a series of large brine discharges at surface contaminating the surrounding lands and watercourses.

Multi-geophysical techniques using seismic and electrical resistivity surveys combined with electrical self-potential surveys were conducted to characterize the geological and hydrological processes driving the mining hazards. Water and salinity levels within the connected mines are recorded through a network of monitoring boreholes. Surface motion data is measured using terrestrial levelling and satellite Interferomatic synthetic-aperture radar (InSAR). Using these combined methods, we have been able to characterize the linkages between mine water levels and surface instability and, in turn, surface subsidence and highly saline brine migration to surface.

Results from the geophysical surveys identified compositional changes and deformation altering the geochemistry of the groundwater. Water ingress to the underlying strata from crown holes has led to gravitational slumps as a result of dissolution of the halite bearing strata. This has resulted in deformation and stepped thrusts coincident with brine migration to surface. The occurrence of brine migration to surface is more prevalent following surface subsidence as a hydraulic head in the deep mine induced by freshwater injection to the crown hole at surface promotes the movement of saline waters through pathways created by weaknesses within the strata, boreholes and shafts leading to extensive land contamination events. Ground motion data acquisitions combined with water level data show a correlation with decreasing water levels within the mine as a result of surface brine emissions and increased subsidence at surface, which, in turn, lead to further water ingress pathways in a repeated cycle.

Presently, a high-density network of satellite InSAR reflectors, GNSS stations and precise levelling points are developing across the site to gain an increased understanding of mine water level controls on surface instability. Combined with mine water data, information will enable early escalated actions to be taken to mitigate mining hazards.

This study is based on a waste management company that operates a hazardous waste landfill site and has a challenge with the production of leachate. Leachate is produced when water percolates through the waste disposal site, accumulating the contaminants, which creates the highly concentrated hazardous liquid. This leachate must be effectively treated by concentration and solidification, and accommodate larger volume increases as the landfill capacity increases. The main aim of this study was to develop a practical, feasible and economically viable technology to solidify the concentrated leachate from the effluent treatment plant, comprising approximately 8750 m³ per annum.

A 300 L/h cooling demonstration plant was developed which consisted of various equipment for freeze crystallization method such as the chiller, secondary refrigerant mixture (40% ethylene glycol, in water), clarifier, reactor and pumps. The following samples were collected at the waste management company to be used at the demonstration plant: (i) 1000 L concentrate after evaporation, (ii) 2000 L leachate (feed to the evaporator). This demonstration plant was developed with the aim of recovering clean water and Na₂SO₄ through ice formation.

OLI software simulations were used to predict the amount of salt and ice that should be recovered. The predicted results were confirmed by actual runs on the demonstration plant. Salt production was monitored over time when 302 L of concentrate was recycled. A mass of 102.9 kg of salt (Na₂SO₄.10H₂O) was recovered over a period of 6 hours, which amounts to 339.8 g/L (as Na₂SO₄.10H₂O). This corresponds well with the OLI prediction of 353.9 g/L. Ice production was monitored over time when 273 L of leachate was recycled. A mass of 118.7 kg ice was removed over a period of 5.5 hours, with the ice purity having 4.0 g/L TDS, which is substantially lower than the 46.0 g/L TDS of the feed. Energy consumption amounted to 171 kWh/ton ice, which compares well with the theoretical value of 91 kWh/ton ice for a COP of 1.

This study proved that pipe freeze crystallization is a low cost method for treating leachate. To put it in context, the total cost of waste transportation and disposal amounts to ZAR2 500/m³, while freeze crystallization only costs ZAR524.07/m³. Therefore, this study recommends that a freeze crystallization plant be built for the waste management company to save costs in treating the leachate and to also recover valuable resources.

Mineral development carries an increasing expectation for protection of water resources as focus on water supplies continues to grow. Integrating projections of anticipated mine water chemistry early in the mine design process—prior to when project specific data are available—provides the greatest opportunity for improving environmental outcomes at the lowest increase to overall schedule and cost.

An approach derived from behavioral economics, “Reference Class Forecasting” (RCF), is used in project management disciplines to empirically estimate costs and schedule by establishing a reference class of similar projects and adjusting based on project-specific characteristics. This paper applies RCF in a mine water quality context to identify a preliminary design basis for rock stockpiles. It requires a relatively low level of project definition and eliminates the inherent sources of optimism and misrepresentation bias present in bottom-up estimates. It was applied here to a scoping-level project to: (1) screen out constituents that are unlikely to influence design, (2) identify constituents that are likely to drive design, including a scale of the reductions required, and (3) identify constituents for which further review is necessary.

A hypothetical mine rock stockpile from a magmatic nickel-copper-PGE deposit located in a humid continental climate region was evaluated as follows: 1) a reference class of mines was identified based on shared characteristics that drive mine water chemistry (e.g., deposit model, climate); 2) a database was created of operational water quality data for the mine stockpile class containing approximately 5,700 individual records; 3) acceptance criteria were established that reflected project-specific risk tolerance and regional water quality standards; and 4) a statistical evaluation was conducted to compare observations from the reference class to the acceptance criteria. The RCF process narrowed the list of constituents of interest from an initial twenty-two to eight; three were likely to inform mine water quality design; five for which further evaluation was recommended. The remaining fourteen were unlikely to pose water quality risks for the project. An anticipated scale of required reduction was established for the eight remaining constituents of interest.

By narrowing the constituent list and identifying necessary reductions during mine scoping, projects can more fluidly integrate water management strategies into the early mine design. The broad application of this approach is limited by the availability of data to form a reference class of operational mine water chemistry; however, as existing repositories of data continue to become available, opportunities to leverage RCF may become more prevalent.

The leachate from coal waste dumps is the most polluted stream and poses significant environmental challenges. The current practice involves storing the leachate in evaporation ponds to evaporate and facilitate iron(II)-oxidation. This method is aimed at reducing the immediate environmental impact. If treated separately salt removal already take place in the pre-treatment stage. This method would enhance the effectiveness of subsequent treatment and help mitigate long-term environmental risks.

This research introduces a novel approach that utilizes evaporation to minimize leachate volume and facilitate the oxidation of Fe²⁺ to Fe³⁺. By exposing leachate to oxygen and iron-oxidizing bacteria, we achieve the necessary oxidation while simultaneously adjusting pH using Na₂CO₃/CaCO₃/Ca(OH)₂/NaOH. This method not only simplifies the treatment process but also allows for the direct recovery of magnetite from the solution. The study utilized HDPE pipes for solar heating, OLI software for vapour concentration predictions, and beaker studies to assess magnetite formation under varying conditions.

The findings reveal several key insights: solar energy effectively evaporates water; Fe²⁺ can be oxidized to Fe³⁺ to meet a 1:2 molar ratio; and both Fe(OH)₃ and Fe(OH)₂ can be precipitated using Na₂CO₃/CaCO₃ and Ca(OH)₂/NaOH, respectively. Additionally, the conversion of Fe(OH)₃/Fe(OH)₂ sludge to Fe₃O₄ occurs at 100°C, with magnetite formation happening in the presence or absence of gypsum. Notably, the settling rate of Fe₃O₄-rich sludge surpasses that of Fe(OH)₃-rich sludge, indicating improved separation characteristics.

The implications of this research are significant for the mining industry and environmental management. By optimizing AMD treatment, this innovative technology reduces energy costs associated with Fe²⁺ oxidation, allows for the feasible recovery of magnetite under varying conditions, and enhances sludge settling rates, leading to greater operational efficiency. Furthermore, the streamlined treatment process minimizes complications related to managing multiple slurries, thereby reducing post-treatment handling challenges. Future studies are recommended to explore magnetic separation techniques for efficient magnetite and gypsum separation, further contributing to sustainable practices in mining. Overall, this research presents a promising strategy for advancing AMD treatment and mitigating its environmental effects.

This article deals with the water resource legacies we in the mining realm are creating and leaving it behind in semi-arid regions and how some of these legacies are already monuments for future food security plans. In semi-arid regions water resources are often a fatal flaw to start new mining operations and therefore new resources needs to be developed, however once the mineral resources are depleted then the water resources will still be available and these remaining water resources will become an integrate part of a water/food security network for many millennia to come.

The most common water resources developed forming part of new mining projects are dams and wellfields and as a result during feasibility studies we never really considers the default water resources developed as a result mining and associated infrastructure. This is most probably as a result of the “naughty” minerals in the classroom for example gold and coal and over years created a stigma that the water resources legacies from mining is one of acid mine drainage linked with unwanted elements for example uranium. There is more water-friendly mineral resources for example the Bushveld Igneous Complex (BIC) with chrome and platinum and together with phosphate and potassium mines all creating new vast water resources that can be converted into food security options.

The water resources typically left behind range from underground mines fill with water and new modified aquifers or anthropogenetic aquifers. The case studies discussed specifically deals with the BIC and the AAs already developed, the phosphate aquifer now created in the west-coast of Southern Africa, potassium mine in Ethiopia transforming hypersaline alluvial fan aquifers in the Danikal Desert to fresh water aquifers and even how large gold TSF’s are now harvested to aggressively reuse tailings water and reduce the consumptive use of fresh water.

Finally, we take a brave step into the future and consider how salt water reclamation in greenhouse in the Nethe erlands can be combined with injection wells to harvest and clean our seepage water derived from scavenger wells at larges gold tailings facilities in South Africa.

Hard coal mining ended in Germany in the Ruhr Area in December 2018. The cessation of mining activities and the associated changes in mine water management lead to a controlled mine water rebound. The geochemical composition of mine water is fundamentally influenced by sulfur cycling. Research results enable a deeper understanding of the sulfur and carbon cycles in mine water, and thus provide important information about ongoing biogeochemical processes in the now inaccessible underground mine workings. This in turn allows projecting expected biogeochemical changes into the future which is important for risk assessment.

A controlled mine water rebound is conducted in former hard coal mines of the Ruhr and Saar regions. To avoid risks for humans and the environment, the identification of old mine workings, which are prone to hydrogen sulfide (H₂S) formation is important. Thus, the sulfur content in coal is implemented in a geochemical model to assess future H₂S formation. Given the natural variability within a coal seam, mean sulfur contents for each mine water management province shall be used. For the southern Ruhr area, no significant correlation of precipitation and mine water geochemistry is discernible from the data available.

The lignite-mining region of Lusatia is characterized by i) low precipitation (compared to the German average), ii) a negative climatic water balance in most years, iii) predominantly sandy soils with a low water storage capacity covered by highly managed ecosystems (forest and agricultural monocultures), and iv) long-term, large-scale open cast lignite mining activities. The lignite mining activities have substantially affected the water resources, both in terms of water quantity and quality, in the Lusatian river basins. Recent extreme heatwaves, coupled with low precipitation, have exacerbated water management challenges in this already water-scarce region.

To refine the understanding of hydrological processes in watersheds strongly affected in lignite mining, we combine the analysis of extreme climate indicators with the isotopic signatures of precipitation, groundwater and surface water bodies (rivers, streams, post-mining lakes). In a first step, we quantified long-term changes in climate and drought indicators (1948-2022) as well as the isotopic composition (δ¹⁸O, δ²H, d-excess) of precipitation (1978-2022, station located in Berlin). In the second step, more than 1000 water samples, consisting of ≈400 groundwater, ≈260 channels and streams and ≈450 post-mining lake samples, are collected in 2024 and analyzed to assess the groundwater-surface water interactions and evaporation losses of the post-mining lakes. The survey covers an area of approximately 4000 km².

The analysis of the climate indicators show substantial increases in the temperature-related indices. The frequency of severe and extreme droughts has increased. The observed climatic changes coincide with a positive trend in the 45-year record of isotopic composition (δ¹⁸O, δ²H) of precipitation, which is statistically significant (p>0.05) on the annual basis as well as during spring (only δ¹⁸O) and summer. We show that the positive trend in the isotopic composition of precipitation is strongly correlated (r > 0.5) with air temperature during winter and moderately (0.3 < r < 0.5) during all seasons except autumn (September-November). A screening of the first samples suggest distinct difference between the isotopic signatures of the different water sources depending on the location as well as the mining influence.

Our study shows the potential of combining stable isotope tracers with hydroclimatic records to investigate the spatial and temporal variability of the dominant hydrological processes in watersheds affected by large-scale lignite mining. For the Lusatian mining region, the results suggest that multiple water-related challenges are overlapping and that climate change needs to be considered in regional water management.

Acid Mine Drainage (AMD) is a substantial source of water pollution, especially in regions with active mining operations. This phenomenon occurs when sulfide minerals in mined rock come into contact with air and water, resulting in the formation of sulfuric acid. The acidic runoff can dissolve Potentially Toxic Elements and other harmful substances from the surrounding rock, contaminating nearby water sources like rivers and streams. To tackle AMD effectively, mining operations must adopt measures such as proper handling and treatment of extracted materials, as well as implementing robust water management systems. Utilizing imaging spectroscopy offers a practical approach for mine assessment and characterization, serving as a valuable alternative to traditional chemical analyses. It focuses on identifying minerals that indicate subaerial oxidation of pyrite ("hot spots") and the resulting formation of sulfate minerals (such as jarosite) and their oxidation products (such as oxy-hydroxides and oxides).

Our cutting-edge approach is dedicated to enhancing the development of robust monitoring systems for Acid Mine Drainage (AMD) through the utilization of Machine Learning techniques applied to multi-temporal optical multispectral, and hyperspectral data. Specifically, our research delves into the utilization of hyperspectral data (PIKA L) obtained at various time points via Unmanned Aerial Vehicles (UAVs) and multi-temporal datasets from the Sentinel-2 satellite. This investigation has been conducted at the Lítov post-mine dump in the western region of the Sokolov lignite basin, Czech Republic. The Lítov dump stands out due to its highly acidic substrates, sparse vegetation, and the presence of a unique semi-desert environment. The accuracy of our Machine Learning classifications has been validated using ground truth data (mineralogy resolved by X-ray diffraction), demonstrating that the Radial Basis Function Support Vector Machine (RBF SVM) and Random Forest (RF) models surpass other ML approaches in performance when effectively identifying the main AMD hotspots and providing good separation between classes. More specifically, when using both hyperspectral Pika L and Sentinel-2 data RBF SVM and RF classifiers excel at detecting the AMD discharge, as well as mixtures between different mineral classes indicating the increasing pH e.g. oxy-hydroxides and oxides.

Future work will focus on testing ML techniques on extended multi-temporal data and evaluating the transferability of the model to other geographical locations (e.g., Greece).

The increasing demand for metals essential for net-zero technologies has led to as surge of intense mining activities, resulting in substantial waste production. Effectively managing this waste is crucial for minimizing environmental impacts and reducing greenhouse gas (GHG) emissions. This study investigates the potential for carbon sequestration in mine waste through mineral carbonation, focusing on silicate-rich waste from ultramafic ore deposits in Northern Europe.

Mine Environment Management Ltd. in collaboration with Geochemic Ltd., and Cardiff University, are developing innovative methods to measure CO₂ sequestration and emissions from mine waste. Based on previous work (e.g., Shiimi et al., 2023; Schoen et al., 2023), this project brings new insights to waste characterisation and properties, using closed-system experiments coupled with open-system equipment testing to simulate future field trials. Waste characterisation involves detailed mineralogical, elemental, geotechnical, and geochemical analyses, while closed-system experiments utilize bespoke sealed cells and Xylem-WTW Oxitop® devices to monitor CO₂ and O₂ flux.

Key findings from the closed-system sealed cell experiments revealed dynamic changes in CO₂ and O₂ concentrations in ultramafic waste rock over a two-year monitoring period. Initially, O₂ concentration decreased from atmospheric 21% to a negligible concentration, reflecting sulfide oxidation. To date, O₂ levels remain negligible, indicating a depletion of O₂ within the closed system. Conversely, CO₂ levels increased from 399 mg/L to 14,983 mg/L due to carbonate dissolution, before steadily declining as carbonation processes became dominant within the closed system. These results highlight the potential for enhanced weathering and effective CO₂ sequestration over time.

To upscale monitoring to mine site field conditions, an open barrel (OB) equipment test has been developed to examine the gas flux and geochemical behaviour of mine tailings under partially controlled, open-atmospheric conditions. This system integrates sensors to monitor CO₂ and O₂ levels, temperature, pH, and moisture content, yielding key data for real-world applications. The field trials aim to inform carbon sequestration strategies and contribute to the EU-funded C-SINK project by establishing Monitoring, Reporting, and Verification (MRV) protocols for future carbon dioxide removal (CDR) efforts. This study demonstrates that carbonation in mine waste has the potential to reduce CO₂ emissions, supporting the development of scalable carbon management strategies in the mining industry.

Mining environments involve complex hydro-bio-geochemical systems. Reactive transport modeling (RTM) is essential to rigorously describe these processes. Yet, process-based RTM is computationally intensive and limited in practical applications. To mitigate such challenges, this paper provides a novel deep learning-based surrogate accelerator, hidden-reactive-transport-neural-network (HRTNet), to simulate pyrite oxidation, a process of key importance for acid mine drainage. HRTNet relies on a flexible two-network architecture integrating chemical and physical equations. The model can effectively capture the desired spatio-temporal dynamics in a considerably reduced computation time (almost eight-fold). Additionally, HRTNet shows a good generalization capability covering a wide range of conditions beyond the training datasets.

Due to the natural conditions, the Smolník deposit (Slovakia) was one of the few where mine waters were intensively used for the extraction of copper from the Middle Ages. In favourable periods, it was possible to obtain more metal from mine the water than from the ore (Jaško 1998). Cementation technology was unique in the world at that time. According to historical records, China (1086 A.D.) was the first in the world to use this technology (Lung 1986), but it is the Smolník location that holds this primacy within the Europe. The oldest written mention of copper production by cementation in Smolník is from 1346 (Juck 1984). The record itself was therefore the second in the world that mentions the practice of copper cementation.

The mining activities on the site ceased in 1994, and the area was subsequently flooded. The mining complex itself began to behave like a bioreactor, producing large amounts of acid mine drainage where the predominant microorganism of the given waters is the genus Gallionella (Bártová, 2020). The primary pollutants within AMD in Smolník are iron, sulfates, manganese, aluminum, copper, zinc and arsenic. Under normal conditions, the flow of mine water reaches 10 L/s^-1 with an average temperature of 14 °C. Sulfates and ferrous iron, which are products of pyrite leaching, are the dominant ions in this water (Kupka et al. 2012).

The precipitates themselves, iron ochre, are mainly formed on surfaces that are in contact with mine water. Larger pieces can be observed in places where the flow slows down and the mineral (ochre) has room to form. The main mineral in the outflow is Schwertmannite (Fe₈O₈ (OH) ₈–2x(SO₄)x • nH₂O. Along with elements such as iron and sulfur, also metalloids such as arsenic or antimony coprecipitate here. Schwertmannite has an interesting reddish color and there is a possibility of its use as a natural pigment. After drying, it is brittle and easily crushed into a fine powder. It can be easily mixed with a base medium, such as oil, and the resulting colour is intense and well usable. Smolník mine waters are currently a rare raw material, which has the potential to be used for obtaining natural pigments and metals, with the help of biohydrometallurgical approaches.

Intensive research is currently underway. Preliminary results show a great potential in a novel use of this old mining site.

Wetlands altered by mining activities are often critical ecosystems that provide essential services such as water purification, biodiversity support, and flood regulation. However, traditional monitoring tools used to assess ecosystem health are often inadequate in capturing the complex interactions between natural and ecologically engineered systems within these altered environments. This study presents an innovative framework, combining the Ecological Integrity Index (EII) and the Ecological Engineering Index (EEI), which allows for more accurate assessments of ecological health and prioritization of interventions in mine-altered wetlands. This approach addresses an existing gap in current ecosystem monitoring practices, particularly in the mining sector, where environmental degradation have long-term consequences for both ecosystems and mining operations.

The novelty of this approach lies in the integration of the EII and EEI, which offer a comprehensive, scientifically robust method for evaluating ecosystem health. The EII assesses baseline ecological conditions, focusing on biological and physical integrity of natural systems, while the EEI provides a tailored approach for evaluating and guiding interventions in ecologically engineered systems, such as constructed wetlands. For the first time, these indices are applied together to both natural and engineered environments, offering a holistic view of wetland functionality and resilience. The assessment was conducted at the Leeuspruit wetland near South Deep Gold Mine, where baseline conditions were evaluated, and targeted ecological engineering interventions were proposed based on indices’ findings.

The main findings of the study revealed that the Leeuspruit wetland, categorized as critically modified (Ecological Category E), exhibited impaired water quality, with uranium concentrations and total dissolved solids (TDS) well above acceptable levels. Biodiversity had declined, with invasive species dominating large areas. The application of the EEI identified key areas for ecological regeneration and restoration, including implementation of constructed wetlands, bioremediation systems, and buffer zones. These interventions are projected to reduce uranium levels by 50% and improve water quality within five years, while also promoting biodiversity recovery.

The implications of this work are far-reaching for the mining industry. By integrating the EII and EEI, mining operations can more effectively prioritize regeneration and restoration efforts, meet regulatory compliance, and contribute to long-term sustainability. This approach not only enhances ecological resilience but also positions mining companies as stewards of biodiversity conservation. The combined application of these indices offers a replicable model for sustainable mine water management, which can be adapted across different mining landscapes worldwide, aligning with global biodiversity and environmental sustainability goals.

In Chile, coal was extracted from underground mines beneath the Pacific Ocean, in the Arauco Basin in the Southern Biobío Region, with the operation ceasing in 1997. The mine “Chiflón del Diablo” is an abandoned coal mine and part of the Lota mining complex, registered on the tentative list to be awarded UNESCO World Heritage status. The mine has been a tourist attraction due to the exploitation beneath the coastal area. Unfortunately, since the last massive earthquake that hit the Biobio Region (February 2010), flooding of the mine was observed, requiring saline groundwater to be dewatered directly into the nearshore zone to maintain tourist activities. This water pumped from the mine out onto the beach, possessed a high concentration of chloride (~600 mM) as a consequence of the seawater intrusion process into the shafts, a phenomenon reported at many mines near the coast. The mine water discharged to the sea from the Chilean mine additionally contained elevated ferrous iron (between 2-5 mM) and sulfate (~33 mM) due to the oxidation of pyrite, the main sulfide mineral associated with the Arauco Basin. This study describes the removal of iron and sulfate in mine water with high chloride concentration by using a continuous sulfidogenic biofilm reactor inoculated with sediment samples from the “Salar of Huasco”, Chile. In the samples analyzed in the biofilm, Desulfomicrobium, a genus belonging to the order Desulfovibrionales, was the most abundant SRB, with a relative abundance of about ~30%. Feeding the mine water, with a hydraulic retention time of 25 h, it was possible to remove more than 95% of sulfate and iron by using lactate as electron and carbon source. This study highlights the use of a halophilic sulfate-reducing consortium to promote sulfidogenesis in mine water with a high chloride concentration.

Effluents, surface water, and groundwater were analyzed, and a detailed mineralogical investigation was conducted aiming the hydrogeochemical characterization of acidic effluents and waters from areas surrounding a uranium waste rock pile. Additionally, gases circulating in the surface layer of the pile, such as O₂, CO₂, H₂, and Ar, were characterized to understand the influence of oxidation and mineral dissolution processes.

The conceptual model, through spectral analysis of hydrochemical samples, revealed that manganese (Mn), uranium (U), and sulfate begin to be released into the effluents after three months of exposure. These compounds, under supersaturation conditions, precipitate in the porous medium and accumulate during the dry season. With increased rainfall, these elements are mobilized and discharged. The pH of the waters remains between 3 and 4 throughout the hydrological year, exhibiting little variation until the onset of the next rainy season, indicating the prolonged effect of acidification processes.

The results showed that the primary contribution of effluents from the pile occurs through groundwater recharge rather than surface infiltration. Water percolating through the tailings mass carries dissolved compounds along the profile, releasing ions such as sulfate, iron, and aluminum. The western portion of the pile is particularly critical, exhibiting reduced pH and high concentrations of dissolved solids, iron, and sulfate, characteristics typical of acid mine drainage (AMD). The ions present in this region are found to be in a state of supersaturation or near saturation limits. In contrast, the waters circulating in the eastern portion exhibit characteristics of natural waters, with less influence from sulfide minerals and saturation in iron oxides. The difference in oxidation patterns between the two areas was corroborated by measurements of partial pressures of O₂, CO₂, and H₂, as well as the isotopic signature of argon, confirming distinct geochemical processes.

To evaluate the dynamics of these processes, a numerical model was developed and calibrated using the PHREEQC software. The model allowed for the simulation of different hydrogeochemical scenarios, validating the observed precipitation and mobilization patterns. A sensitivity analysis of the parameters was conducted to identify the most influential variables in the oxidation and transport processes. This research provides a detailed understanding of the hydrogeochemical processes in uranium tailings piles and highlights the importance of groundwater recharge in the generation and mobilization of effluents, contributing to more effective environmental management in the area.

This work aims to minimize Acid Mine Drainage influence on two mining areas located in the Iberian Pyritic Belt, a Volcanogenic Massive Sulfide province of high historical importance regarding the mining exploration activities. Both the Caveira mine (Grândola, Portugal) and the Trimpancho mining complex (Spain), located on opposite sides of the Portuguese South Zone, ceased operations in the 1960’s. Since then, the region has been under the influence of acid drainage from waste piles, left in aerial exposure with poor coverage, without supervision, which releases potential toxic elements (PTE) to waterways adjacent to the mining areas, subsequently leading to the dissemination of these PTE to more distant lands, causing scattered contamination.

In a first step, laboratory-scale tests have been conducted to evaluate the best conditions of environmental remediation of both mining areas, by applying mining water samples, in contact with different alternative materials such as paper, marble and limestone sludges, iron oxides, clays and industrial activated carbon. In this first step, it was verified that paper sludge had a great potential on pH increment, since a composed mining water with pH of 1.64 increased to 6.23 in 11 days of contact, in a proportion of 1g of material for 50mL of mining water.

Analysis of 18 water samples from Caveira and other 18 from Trimpancho, collected in February 2023 showed extremely high values of As, Fe, Cu, Pb, and Zn with peaks of 17.66 mg/L, 2831.7 mg/L, 33.1 mg/L, 2.3 mg/L and 146.0 mg/L, respectively, in Caveira’s mining waters, and <0.1 mg/L, 2958.0 mg/L, 206.6 mg/L, 0.2 mg/L and 2402.1 mg/L, in Trimpancho’s mining waters. The highest values are associated to pH of ≈ 1,22 (Caveira) and ≈ 1.11 (Trimpancho). In addition, we tested the removal of PTEs through column tests, with different combinations of geomaterials and wastes, simulating reactive barriers, to verify which set is most effective for containing and remediating these acidic drainage waters rich in toxic metals.

These laboratory-scale tests showed that the three sludges and the industrial activated carbon, are the most suitable materials for PTEs retention, such as As, Fe, Cu, Pb, and Zn. Also, due to the diversity of PTEs, there is geochemical competition between the alternative materials versus chemical elements, so a multilayered reactive barrier shows to be the most suitable way for future applications in a large-scale treatment out in the field, while attempting water remediation.

The oxidation of pyrite-bearing waste rock is a critical environmental concern, as it leads to the generation of acid mine drainage (AMD), which releases acidic and metal-rich waters into the surrounding environment. AMD poses a significant threat to water resources, making it essential to reduce the oxidation of sulfides, such as pyrite (FeS₂), to mitigate its environmental impacts. Stabilizing waste rock using Ordinary Portland Cement (OPC) is a promising approach, as it serves as a physical barrier against oxygen and moisture, thereby limiting pyrite oxidation and, consequently, reducing the risk of AMD generation. However, the high carbon emissions associated with cement production highlight its environmental drawbacks, making OPC less ideal for this stabilization technique. Thus, there is a need to identify and develop effective alternatives to OPC.

In this study, we explore the potential of slag-blended cement as an alternative to Ordinary Portland Cement (OPC) for stabilizing pyrite-bearing waste rock. Pyrite-bearing waste rock was fully encapsulated with OPC and slag-blended cement and then cured for 28 days under controlled conditions. The specimens were subsequently placed in a climate-controlled chamber for 64 days allowing interactions between the cement and waste rock.

Throughout a 64-day leaching experiment, OPC-treated waste rocks produced leachates with slightly higher pH levels and generally higher major ion release. This is likely due to the faster reactivity of OPC and the early-stage dissolution of soluble cement hydrate phases. In contrast, slag mix-treated waste rocks exhibited slower ion leaching, which may be attributed to the slower reactivity of slag, highlighting the need for a longer curing period. Some dissolved trace element concentrations (Cu, Mn, Ni, Pb) are slightly higher in the leachate from untreated waste rock signifying the early-stage performance of both cementitious materials in immobilizing metal(loids).

Further research involving extended leaching durations and microstructural analysis is required to evaluate the long-term effectiveness of slag-mix cement, particularly under conditions where waste rock oxidation occurs. This research seeks to provide a comprehensive understanding of the geochemical interactions within the cemented matrix, contributing to the identification of the most effective and sustainable alternative material for stabilizing sulfidic waste rock.

Characterization of metamorphic rocks to evaluate waste material acid rock drainage potential is particularly challenging as commonly used laboratory methods can result in substantial underprediction of acid generation potential (AGP) and overprediction of acid neutralization potential (ANP); this combination can lead to considerable underprediction of overall material acid rock drainage potential. Legacy waste and ore sulfur assays from the Touro copper project in Galicia, Northwestern Spain frequently relied on methods insufficient to fully digest metamorphosed sulfides. Additionally, the presence of both graphite and manganese–iron carbonates in Touro added considerable risk of ANP overestimation. Environmental characterization tests conducted on newer ore and waste samples aim to properly address these risks.

Innovative machine learning algorithms were employed to correct over 60,000 erroneous sulfur data points. When Atalaya Mining, Cobre San Rafael began exploring the Touro project, it inherited multiple legacy assay datasets with noticeable inconsistencies in sulfur assay data. The cost of such re-analysis is typically very high when such errors are repeated over the scale of thousands of samples. The innovative approach relied on re-analysis of a small subset of samples, and training an algorithm to 1) recognize relationships between the corrected parameter and other assay parameters in the subset, and 2) estimate corrected values for the larger dataset. Environmental characterization methods employed towards new waste and ore samples included Leco sulfur for full digestion of metamorphosed sulfides and correct AGP estimation. For improved ANP estimation, the Modified Sobek method was employed to more accurately account for the buffering capacity of non-metal carbonates while ignoring graphite and metal carbonates (although aluminosilicate dissolution rates need to be evaluated in the context of sulfide oxidation rates).

Machine learning algorithms trained on a dataset with correct sulfur data were able to derive a relationship between other assay variables which enabled reproducing the sulfur concentrations with 93% accuracy. Predictive success is largely a function of 1) the number of samples, 2) the number of assay parameters, and 3) material/deposit geochemistry. Additionally, use of LECO and Modified Sobek to quantify AGP and ANP resulted in considerable improvements over legacy data.

The innovative supervised sulfur prediction, LECO digestion and Modified Sobek titration methods employed in this study indicate that erroneous data generated from use of improper laboratory tests does not necessarily need to be discarded. Rather, such methods offer a pathway to correction of erroneous data.

Water quality data is collected throughout the mine project life cycle. During early stages, water quality is collected for baselining purposes. During feasibility, permitting, and mine planning, water quality data collected from material characterization tests is combined with baseline data to develop models predicting water quality associated with future mining activities. Prediction outcomes support material and water management strategies. During operations, water quality data is collected to monitor mine facility seepage, water treatment performance, and mine boundary compliance. At closure, water quality is collected to assess closure strategy effectiveness and employ adaptive management strategies. Water quality data is ubiquitous through the project life cycle and yet remains highly underutilized.

The abundance of this data is ideally suited to using machine learning approaches to maximize its value. It is typically collected at regular intervals throughout the mine life cycle. Furthermore, compliance and operational requirements dictate that water quality be collected at sufficient spatial density. Finally, water quality data is multi-dimensional, commonly including measurements for 20 to 40 (or more) different parameters. The large number of parameters makes for a “wide” dataset with considerable statistical variance, which facilitates application of innovative unsupervised machine learning methods.

Application of unsupervised methods to water quality data in four different parts of the mine project life cycle indicates that the multivariate approach is highly effective in identifying different water quality domains, breakthrough of MIW, mixing effects and various reactive processes that occur in water.

The four use cases have application and implications as follows:

• Baseline and compliance: machine learning methods are applied to separate pre-mining water quality in different hydrostratigraphic units and to detect vertical transmissivity between units.
• Feasibility and permitting: interpretation of a large laboratory humidity cell dataset to understand the formation and timing of acid conditions; this information can be applied at the field scale to predict acidic conditions in mine waste facilities and assess regional groundwater patterns in mineralized zones.
• Operations: forensic study to detect mine process water influence in both surface and groundwater, and to separate MIW from natural acid rock drainage.
• Closure planning: coupled unsupervised machine learning and isotope study is used to identify natural acid rock and neutral drainage and to separate these chemical fingerprints from groundwater influenced by pit and waste rock generated acid rock drainage; this work is all in support of development of the long-term site closure strategy.

In 2015, Minera La Zanja S.R.L. (a subsidiary of Compañía de Minas Buenaventura) began the planning, design and subsequent execution (2018) of the pilot closure project based on improved soils (Tecnosoles) over an area of approximately 8 ha, which proposed to refocus the criteria for coverings based on the Peruvian Ministry of Energy and Mines' mine closure guide.

Nature does not design or segment layers of materials in the soil, as proposed in the Peruvian closure guidelines, on the contrary, it is the soil itself that brings together the properties of waterproofing, water retention and evapotranspiration, so this pilot focused on working the soil properties in order to test its effectiveness in a waste deposit within an area of the San Pedro Sur open pit, operated at the La Zanja mine, in the Cajamarca region, Peru.

To test the effectiveness of the improved soil cover, a monitoring system was designed and installed. This monitoring system consists of 1) near-surface boreholes, just below the soil cover and isolated from the waste rock by a layer of quartz gravel; 2) deep boreholes, the purpose of which is to collect any water that may be present at the base of the reservoir after circulation through the reservoir; 3) instrumented wells, which are wells with a series of sensors (for continuous measurement of temperature, conductivity, suction pressure, humidity, oxygen and CO2) and suction lysimeters at different depths within the reservoir; and 4) external piezometers upstream and downstream of the reservoir and at different depths to monitor the potential effect on the aquifer. This project started reporting water quality indicators since 2018.

The evolution of water quality indicators, infiltration, runoff and evapotranspiration, have been similar or better than those obtained by traditional systems of layers with low permeability materials such as clays, which are used in many cases of mine closure in Peru, but without the added cost of their acquisition (often outside the mining units), transport and disposal, becoming a living pilot that continues to yield results that can be used to focus other cases of closure based on sustainable solutions.

Coal mining has been occurring in the United States for nearly two hundred years. Prior to the passage of the 1977 Surface Mining Control and Reclamation Act (SMCRA), there was no regulatory oversight over coal mining activities and what happened to those mine sites once mining stopped. With the passage of SMCRA, states and tribes are given abandoned mined land reclamation grants, generated by active mining production.

Marshal Equipment, Richardson Coal Company and Beecher Williams No. 1, were three different abandoned coal mined sites, located in Saline County, within the drainage basin of the South Fork of the Saline River, in southern Illinois and eligible for reclamation, under SMCRA, by the Abandoned Mined Land Reclamation Division (AMLRD), in the state of Illinois.

All three abandoned mined sites were contour surface mined, with some auger mining also occurring, to remove the number two coal, known as the Davis/Dekoven coal seam, at a depth varying from 1,5 to 35 meters. These three coal mine sites were in operation from the early 1950s to the early 1960s.

These sites had acid mine drainage seeps, with average flows of under approximately 40 liters per minute. While the seeps have low water flows, the water chemistry of the Davis/Dekoven seam has proven to be extremely destructive. This seam produces highly acidic seepage, with high iron and aluminum concentrations, proving to be challenging to treat with traditional passive treatment. A Lime Compost Drain (LCD) consists of a two-layer system, separated by filter fabric, with the bottom most layer containing 7,6 centimeter, coarse aggregate, with a minimum thickness of 0,3 meters, followed by another 0,3 meter layer, of a well-blended layer that consist of 50% compost, 50% of, 2,5 centimeters, coarse aggregate mixture. Both layers vary in width, depending on the flow and slight variation on the water chemistry at each site. Both layers are then draped by a polyethylene liner, followed by carefully placed backfill material.

The main concept of the LCD is to create a low oxygen alkaline drain through which acid seepage is directed, with any oxygen present being consumed by the slow degradation of the mulch. Keeping the drain composition as anoxic as possible, preventing the iron from precipitating out, minimizing coating of the high alkalinity coarse aggregate. This LCD system was constructed on all three sites with great improvement to chemistry of the coal acid mine drainage discharging from the constructed LCD.

Coal mining generates coal mine waste rock (CMWR), which can pose environmental risks like acid mine drainage (AMD), contaminated neutral drainage (CND), or saline drainage, depending on pH and metal(loids) concentration. The Jerada T08 CMWR pile, deposited over 50 years, exemplifies this issue. To assess its environmental impact, a geo-environmental characterization was conducted, leading to a 3D model establishment highlighting zones prone to acidity. Results identified 3.8 Mt of potentially acid-forming (PAF) materials, distributed heterogeneously mainly in highly oxidized upper zones. This approach enhances management strategies, reducing costs by enabling targeted mitigation and minimizing expensive remediation efforts.

This study evaluates the environmental quality of river water and sediments in the Caudal River basin (NW Spain), historically affected by Hg and Cu mining. Initial sampling revealed high metal(oid) concentrations, especially downstream of former Hg mines. A second campaign used DGT (Diffusive Gradients in Thin Films) passive samplers to assess bioavailable fractions at selected points. Results showed a strong correlation between As and Cu in DGT and pore water, with As showing up to 75% transfer at low concentrations, indicating its nearly fully bioavailable chemical form. This highlights the usefulness of DGT samplers for determining bioavailability.

Mine water geothermal energy presents a unique opportunity for former mining regions to become hubs for renewable energy production and storage, particularly as part of 5th generation energy networks. This supports sustainable energy goals and also revitalizes former mining areas. Northwestern Europe, with its coal mining history, offers an ideal environment for these systems. This abstract highlights the Walloon region's efforts in Belgium to harness this untapped resource to support renewable energy and regional development. A key milestone of these efforts is the 2019 study assessing mine water regional potential for geothermal applications. The methodology for regional assessment and the modeling approaches applied at the local scale is presented.

First, the innovative methodology developed to assess the geothermal potential of abandoned mines at a regional scale for thermal energy production and storage is introduced. Second, the modeling approaches applied during feasibility studies to assess the actual local potential are discussed. A detailed modeling framework, designed to evaluate the energy production and storage capacity of mine water systems in relation to surface demand, is also explained. By considering local factors such as subsurface characteristics and energy requirements, this work offers a new perspective on how former mines can be effectively repurposed for renewable energy projects.

The study's key finding is that, under conservative assumptions, Wallonia has the potential to develop several geothermal projects like the pioneering mine water geothermal project in Heerlen, the Netherlands. Based on this, the Walloon Administration launched three feasibility studies for mine geothermal projects in the most important mining districts — Couchant de Mons, Charleroi, and Liège. Depending on local conditions, the studies showed that either demand or the subsurface can limit the development of geothermal projects using mine water. The study also highlights the value of various modeling approaches and the challenges of collecting, digitizing, georeferencing mine maps and related data to build usable 3D models incorporating mine galleries, shafts and panels.

The implications of this work are relevant for the future of renewable energy in former mining regions. The findings have led to a call to implement a pilot geothermal project in the Liège mining basin, which could serve as a model for similar initiatives across Wallonia or Europe. This research highlights the potential for abandoned mines to play a central role in the energy transition, providing both a sustainable energy source and storage solution while addressing environmental and economic challenges in post-mining areas.

Geothermal use of flooded mines has become increasingly established in recent years. In addition to research projects, there are dozens of applications exploiting warm mine water for heating purposes. One of the recently implemented projects is the use of the former Dannenbaum colliery in Bochum, Germany, where mine water is to be utilised for heating and cooling applications. As the hydrodynamic and geochemical changes in mine water associated with geothermal applications are largely unknown to date, the abandoned Dannenbaum colliery was selected as a case study for analogue modelling in the “Agricola Model Mine” in Pretoria, South Africa.

Analogue modelling is used to simulate hydrodynamic and hydrochemical processes on a model scale. Configured to represent the conditions at the Dannenbaum colliery, the 4 × 6 metre large, analogue “Agricola Model Mine” was implemented for a mine water geothermal experiment. For this purpose, conditions such as water temperature, density stratification and pumping rates were set up to match those at the colliery, with warm mine water being pumped and re-injected into the flooded mine. Continuous monitoring of parameters (temperature, electrical conductivity, tracer concentration) throughout the mine water body and the use of tracers have allowed changes in the system to be recorded.

As in most flooded underground mines, the analogue model initially contained stratification between different water bodies, similar to the one at the Danneborg colliery. However, the reinjection of the lower warm mineralised water into the upper cold freshwater body caused the density stratification to collapse. This was accompanied by a change in the water composition throughout the entire flooded model mine. At the discharge point itself, the water quality initially deteriorated due to the breakdown of the stratification. In addition, the water temperature changed as a result of the mixing in the entire model mine, forming a mixed water body.

It is expected that these phenomena observed in the analogue model will also occur at the Dannenbaum colliery and the nearby mine water discharge point at the Friedlicher Nachbar colliery. Yet, detailed studies will have to be done in the coming months and years to investigate these effects. Experiments in the analogue model indicate that a change in the water chemistry is likely. These early findings will allow consideration of measures to be taken on site. In addition, attention should be paid to the collapse of density stratification in future geothermal mining water applications.

Groundwater and surface water quality around a mine constitutes a major part of a mine environmental permit. Understanding mine water quality and its environmental impacts are something that must be investigated not just during the mine operation but also even 100 years or more after closure.

In this study, groundwater and surface water quality was modelled around a mine site with the goal of understanding the effect on water quality around the mine during its current operation, mine production expansion, and closure. The groundwater hydrology of the mine was first modelled using MIKE-SHE while the surface water hydrology was modelled using MIKE-HYDRO. A multi-component reactive transport modelling was performed using PHREEQC incorporating the transport parameters obtained from the results of the groundwater hydrology. The reactive transport modeling subdivided the study area into different zones that have specific geochemical and hydrological characteristics. These zones are the tailings dam, dam crest, moraine and glacial sediments. Input parameters used in these models are: material properties of the geologic units and mine facilities (tailings dam, dam crest, clarification pond); geochemical mineralogy data; surface and groundwater analyses; meteorological data; and hydrogeological parameters. These input parameters are based on the mine database, field sampling and observations as well as publicly available sources. Calibration of the models was carried out using existing water quality data downstream of the modeled areas. Once calibrated, the models were run for other time scenarios.

Modelling results show good agreement with the existing water quality. A potential increase in mine production will also increase constituent elements in the modelled groundwater and surface water. Attenuation of metal transport was notable in the moraine and glacial sediments due to the strong presence of hydrous ferric oxides. The closure and post-closure scenarios of the mine shows lowering concentration of all constituents.

The results from these models provide a basis for a mine environmental permit application. These models also provide guidance on potential water quality risks that must be addressed and water management measures that must be implemented to make sure water quality around the mine remains within the set limits of regulatory agencies. In addition, these models provide a good picture of the hydrodynamics and water quality, their effect to mine operation, natural ecosystems surrounding the mine, communities and other stakeholders.

The Hg-district of Mt. Amiata (Tuscany, central Italy) has been one of the most famous mining areas worldwide for the production of liquid mercury from cinnabar(HgS)-bearing ore deposits and the mining site of Abbadia San Salvatore was by far the largest exploiting and productive center of the whole district. Since 2010, a reclamation project started and operated by the local municipality. To date, the most contaminated represents about 9% of the 65 ha into which the mining structures and metallurgic plant were deployed, i.e. where furnaces (Gould, Nesa and the already demolished Cermak-Spirek), condensers and driers occur. Here, the remediation is expected to be completed next year. Presently, no solutions have been proposed to reduce the concentration of dissolved and particulate Hg in the surface waters and the shallow aquifer system.

Since 2013 a large dataset of geochemical parameters, including Hg, As and Sb, has been compiled and including about 40 geochemical surveys carried out for upstream and downstream waters, as well as those occurring within the mining area. Interestingly, a great seasonal variability in terms of geochemical facies and concentrations of main and trace solutes was observed. Setting aside a few exceptions, the pH values are mostly circumneutral with relatively low total dissolved solids (TDS) that in most cases was <1000 mg/L).

Nevertheless, strikingly high concentrations of Hg were determined in the filtered (up to 2-300 mg/L) and unfiltered (up to 650 mg/L) aliquots whereas those of As and Sb were only occasionally above 10 mg/L. The construction of a channel that crosscuts the whole Hg-contaminated area has limited the interaction between meteoric waters and ore deposits and tailings occurring all over the mining area.

Thus, the new hydrogeological conceptual model and the geochemical data suggested that the Hg-contamination is presently limited to the mining area, since Hg concentrations >1 mg/L were only rarely measured in the surface waters and shallow aquifer downstream the mining area. Additionally, the terrains that host the shallow aquifer have a very low transmittivity and the amount of water to actually be treated is thought to be relatively low. All these hydrogeochemical data were preparatory for testing specific adsorbent materials able to remove mercury according to the pH and TDS values and geochemical facies of the analyzed waters. A pilot site is indeed planned shortly to apply the encouraging laboratory results directly in the field.

Waste rock is a ubiquitous mining waste often produced in large quantities as rock mass surrounding the orebody is extracted from the subsurface. The waste rock is frequently stored at the land surface in piles that may be more than 100 m in height and cover several square kilometers. These piles may be temporary features during active mining operations with the waste rock ultimately backfilled into open pits and underground workings at the cessation of mining; however, more often they become permanent fixtures in the landscape. As the waste rock piles are constructed, fresh rock surfaces are exposed to atmospheric conditions with the potential for the development of poor-quality water. Mine permitting and development require estimation of water quantities emanating from these facilities which, together with geochemical assessment of water-rock interactions within the waste, allow effective short- and long-term planning for water management and treatment. As part of mine planning and operation of waste rock facilities, a large number of scenarios may need to be evaluated to address variants in mine development schedules and permitting requirements. Furthermore, extensive sensitivity analyses of predicted seepage quantities are commonly needed to adequately account for uncertainty in waste rock properties and climate variability.

Within this framework, this study presents efficient methodology for estimating waste rock water balance components (e.g., overland flow, evapotranspiration, infiltration, and basal drainage) using HydroGeoSphere, a physically based, fully integrated, groundwater-surface water numerical code. A suite of numerical simulations was developed to illustrate key concepts and considerations affecting the waste rock water balance during construction and closure for a range in waste rock parameters and climatic conditions. Simulations were conducted using quasi-1-dimensional vertical columns of waste rock material; however, the methodology is easily extendable to two- and three-dimensions. Results of the study indicate the importance of both considering the transient build-out of the waste rock pile during construction and the influence of cover materials at closure on predicted drainage rates reporting to the base of the simulated piles. The analysis framework presented in this study can readily be applied at mine sites in various climatic conditions and waste rock types ranging from “soil-like” materials commonly encountered in coal operations to “rock-like” materials characteristic of hard rock settings.

Mining activities can affect water quality long after the mines have closed. This study focuses on the current status of water in two abandoned gold mines - Crocette and Pestarena - in the Western Alps (Piedmont, Italy). Surface and groundwater samples were collected in three monitoring campaigns in 2024. The results showed arsenic contamination in 75% of the samples. Contamination by aluminium, iron, lead, manganese and nickel was also found in groundwater close to the tailings. These results highlight the long-term impact of abandoned mining activities and the need for continuous monitoring to assess environmental and human health risks.

The nature of groundwater flow and solute transport modelling at and near mine sites has evolved because the objectives (the questions) have changed, simulation software has improved, model resolution has increased, graphical interfaces have become very powerful and stakeholders are asking more challenging questions, especially related to prediction uncertainty. Computing performance has increased by a factor of 10⁶ or more (cf. Moore’s Law and its corollaries), but stakeholder expectations have increased dramatically, so the time required to develop, test and apply a simulation model is not significantly less than it was 40 years ago. High-level modellers still need programming skills to extend available simulation software.

Drainages from two mines in the Ancash region of Peru were enriched with Al, As, Fe, and Mn, and Zn. Both pilot-scale and laboratory-scale slag reactors were employed to remove Mn and Zn. The column system effectively reduced Mn and Zn concentrations to <0.1 mg/L for both mines, with a residence time of 14.4 hrs in the slag reactor. Additionally, As was removed to <0.09 mg/L, likely due to coprecipitation and adsorption by Fe, even in the absence of a dedicated As adsorption reactor. These results suggest efficacy of the complex passive treatment system to treat Al, As, Fe, Mn, and Zn as well as possible utilization of coprecipitation-adsorption by Fe to reduce As and Zn concentrations in passive treatment system. The adsorption efficiency can be further enhanced by design improvement in the future.

Mine water treatment is carried out in about 100 abandoned mines in Japan, which costs a large amount of money each year through active treatment (AT). There are only a few domestic examples of passive treatment (PT), therefore Japan has been researching PT for implementation. This study aimed to develop PT technology for manganese (Mn) using a contact oxidation method with Mn-oxidizing bacteria (MnOB) as a sustainable alternative to AT.

The test site was in cold district in Japan, where there is heavy snowfall and temperatures drop to around -10°C in winter (from December to March). The average water chemistry of the targeted mine water was pH 7.1, 65.8 mg/L soluble Mn, and 10.2 mg/L soluble zinc (Zn). The system was divided into two sequential biological processes: a bioreactor filled with limestone (20-40 mm) for pH stabilization and a bioreactor using fiber filter materials as inorganic carriers for enhancement of microbial activity. The test was conducted from September 2023 at a mine water flow rate of 30 to 570 mL/min (hydraulic retention time (HRT) in limestone bioreactor from 1 to 7 days) with air pump aeration at the bottom of the two sequential bioreactors.

After acclimating MnOB in each reactor, soluble Mn average removal rates in the effluent of limestone bioreactor and the following bioreactor using fiber filter reached 89.0 % and 96.5 % to the original concentration in the mine water respectively during the non-winter period (from April to November), associated with remarkable removal rate of soluble Zn. In the limestone bioreactor, the maximum soluble Mn removal efficiency was 40.0 g/m³-reactor/day during the non-winter period. In the winter period, the limestone bioreactor achieved a maximum soluble Mn removal efficiency of 15.5 g/m³-reactor/day, due to low water temperatures below 5°C, possibly causing to less microbial activity.

The findings of this study suggest that a PT system using the contact oxidation method with MnOB is capable of removal of soluble Mn and Zn without chemical reagents use. This system, despite microbial process, showed applicability in various mine sites in cold district. However, the relationship between water temperature, HRT, and the soluble Mn removal rate has not been fully understood. Therefore, further tests are being on-going under different conditions to reveal the relationship above and assess the sustainability of Mn and Zn removal in the system.

This paper explores the application of mine water injection and storage technology in the Ordos Basin, focusing on its hydro-geological framework and practical implementation strategies. 15 hydro-geological framework of mine water injection and storage are systematically delineated. Based on the projects, the study also evaluates six different well construction methods and operational modes. And the case study of the MC-1 well in the Muduchaideng coal mine provides insights into the challenges and successes of long-term mine water injection. The detailed implementation plans, hydro-geological testing, operation timelines and consideration for re-operation were presented to provide the option methodology for sustainable mine water resource management in the arid and semi-arid areas.

Continuous mine water treatment is carried out in approximately 100 abandoned mines by active treatment in Japan. The research and development of passive treatment techniques have been conducted to reduce the treatment costs, especially focusing on a treatment process with short hydraulic retention time (HRT) applicable to a limited area available for the treatment in Japan.

A large-scale passive treatment test has been performed with a water flow rate of 100 L/min in a domestic abandoned mine site since 2020. The targeted acid mine drainage (AMD) has a pH of 3.6, and contains 38 mg/L Fe, 16 mg/L Zn, 4.6 mg/L Cu and 0.06 mg/L Cd. The AMD was initially pre-treated for Fe using an Fe oxidizing/removal process with Fe oxidizing bacteria in media composed of a mixture of rice husk and limestone (20-40 mm). The effluent from this process was then introduced into two vertical flow bioreactors (VFRs) of sulfate-reduction. The VFRs of sulfate-reducing process were filled with a mixture of rice husk and limestone (20-40 mm) at a 1.5 m thickness (HRT of 22.5 hours).

In this study, appropriate nutrient conditions for sulfate-reducing process with short HRT were investigated. At one of the VFRs, three different nutrient conditions with continuous ethanol feed were tested from 2020. The first test was conducted by feeding only ethanol (final concentration of 36 mg/L). The second and third conditions involved feeding ethanol (final concentration of 24 mg/L) with an initial addition of rice bran on the surface of the media as a supplemental nutrient. The weight of rice bran for second and third conditions were 300 kg (0.3wt% of media) and 1000 kg (0.8wt% of media) for approximately 26000 m³ of annual water flow, respectively.

Total Zn removal was shown to be effective in non-winter period (from April to November) under the three conditions. In winter season (from December to March), concentration of total Zn in effluents were sharply up to 7.4 mg/L under only ethanol addition condition, whereas the conditions with initial rice bran addition gradually resulted in total Zn conc. of 1.9 mg/L (300 kg) and 0.03 mg/L (1000 kg) at most in effluents. The test is continuously conducted to evaluate appropriate nutrient condition for metal removal and its sustainability.

Pilot-scale trials using Dispersed Alkaline Substrate (DAS) reactors for the treatment of AMD at a closed Sb mine in Abbaretz, France have been conducted (). The experiments demonstrated substantial iron precipitation leading to progressive head loss, which was an indicator of clogging over time. In this study, to better managed this phenomenon, we develop a method to estimate the volume occupied by iron precipitate. This information was then used for modelling the pilot-scale experiments (iron precipitation, system performance, and long-term operational viability).

To define the volume occupied by iron precipitate, a fixed-bed limestone reactor (0.25 L) was used to simulate AMD treatment over a time period. The reactor was analyzed using X-ray tomography, which allowed precise measurement of porosity variation and the in-situ volume of iron precipitate. This in-situ measurement is critical, as determining the volume of iron oxyhydroxide precipitates is typically challenging due to their low density. The ability to correlate dissolved iron concentrations directly with the volume of precipitate provides valuable insights into the operational lifespan of passive treatment systems, including both DAS reactors and other structures such as settling ponds.

To better understand the chemical interactions at play, a geochemical model was developed using PHREEQC software, paired with the Thermoddem database. The reactive transport model simulated key processes such as calcium carbonate dissolution and iron precipitation, as well as the resulting effect on porosity and metal retention under varying residence times. The model illustrated the neutralization of the AMD acidity by the DAS, through calcite dissolution. As consequences, the increasing pH of the effluent allowed Iron, Cobalt and Zinc to precipitate in the form of hydroxide. Different scenarios were modelled, including 24, 36, and 48-hour residence times in the DAS, to predict system efficiency and lifespan. The simulations reproduce correctly experimental data, showing strong agreement for parameters such as pH, iron removal rates, and the accumulation of precipitates.

These findings are crucial for improving the design and performance of full-scale DAS reactors. The insights gained from both the laboratory experiments and the reactive transport modeling will inform future applications, enabling more efficient AMD treatment and extending the operational lifespan of passive treatment systems.

The importance of total inorganic carbon (TIC) chemistry in passive mine water treatment is well understood and is supported by numerous publications. However, there is less published information on how TIC effects active treatment both negatively and positively. For example, on raising the pH to promote iron oxidation with air, dissolved carbon dioxide is converted into bicarbonate/carbonate increasing alkali demand and sludge generation -effectively fighting against the process. Conversely with net alkaline waters the TIC can be beneficially used to maintain the pH reduce sludge generation provided an alternative oxidant (such as hydrogen peroxide) is used for iron precipitation.

The paper uses the following 4 mine water projects to demonstrates how by carrying out a series of carbon speciation analyses the plant performance can be improved:

Mine A – Highly acidic metalliferous mine water - Analysis revealed the water contained around 37 mg/L TIC present in the form dissolved CO_2. Modelling revealed that as a result around 50% of the added lime was consumed in converting this to bicarbonate and carbonate. In comparison the back calculated figure using actual plant data showed 47% wastage. Further calculations revealed that by air stripping the carbon dioxide, this could be reduced to less than 25%

Mine B – Circum neutral pH metalliferous mine water. Understanding the carbon chemistry for this application was crucial in reducing the lime demand and sludge generation rate 82.8% and 62.4% respectively.

Mine C – Circum neutral pH coal mine water with degassing followed by HDS iron precipitation. Understanding carbonate chemistry allowed a 50% reduction in lime by simply degassing prior to iron precipitation. Modelling demonstrated that by switching to peroxide iron oxidation, the water could be treated without the need for carbon dioxide stripping and lime addition- substantially reducing the operating cost

Mine D - circum neutral pH coal mine water with iron and manganese consents. By means of simply modelling the carbon chemistry it was possible to optimise the process at design stage, with the predicted savings subsequently confirmed by on-site pilot testing.

In conclusion, by carrying out carbon species analysis it is possible to not only understand the negative effect this can have on alkali demand and sludge generation but also develop an understanding of how these can be reduced these by working with thetic chemistry rather than fighting against it.

The Sustainable Active Treatment (SAT) system being developed by Cambrian Environmental Technologies (CET) presents a meaningful advancement in the treatment of circum-neutral mine water (CNMW). The process offers a rapid, sustainable, and cost-effective approach that not only improves water quality, but also provides the potential for the recovery of valuable metals.

The initial step of the SAT system is to degas dissolved CO₂ from CNMW, in order to elevate the pH to allow removal of Zn and other metals present via precipitation. The most recent advancements to the CET SAT system involved constructing a low-cost device to pre-strip carbon dioxide (CO₂) from compressed air before utilising the CO₂-depleted air to raise CNMW pH to 8.3.

Ocean acidification (pH reduction) is a well-known consequence of elevated gaseous CO₂ concentrations at the surface of water. The opposite phenomenon, removal of dissolved CO₂ from water, therefore, increases the pH. It was proposed that a steeper partial pressure differential be introduced to remove the dissolved CO₂ from CNMW. Initially this theory was tested using nitrogen gas rather than air as the gas supply in the SAT system high-shear degassing step to decarbonise the CNMW from Nant-y-Mwyn Mine, Mid-Wales.

The removal of CO₂ by chemical scrubber is a well-known practice to remove excess CO₂ in enclosed breathing spaces such as spacecraft, submarines or scuba-divers’ rebreathing apparatus. A ‘chemical scrubber’ using crushed waste concrete was constructed in the laboratory. Air was passed through the column to strip the CO₂ from compressed air by reaction with the residual lime in the concrete. Results demonstrated that degassing with this CO₂-depleted air more effectively increased the pH in CNMW from circum-neutral to a pH above 8 than using compressed air, leading to the precipitation of metal compounds. The use of waste concrete as the CO₂ scrubbing media was successful, further enhancing the system's sustainability.

This work highlights the potential of waste concrete as a sustainable reagent for gas scrubbing for high-shear degassing applications and the SAT system as a practical solution for mitigating environmental impacts of abandoned mine sites.

The mining activities in the Le Cetine di Cotorniano Sb-mine (Southern Tuscany, Italy) ceased in 1948 and the site was abandoned, but there are still residential buildings near the mine. The surface and drainage waters, that drained the mine, are convoyed into a reactive permeable barrier (PRB) with the aims to reduce the concentration of Sb.

The reclamation works has commenced last year. A geochemical characterization was conducted in 2011, while a geochemical survey has been ongoing since June 2024. In this work, full-scale and a laboratory-scale PRB models, the latter built by a 3D printer with inert material to the Sb-rich waters, are working in parallel. The PRB design comprises four cascade boxes, each one divided into three further boxes. Each box is filled with gravels and alternating layers of calcite and biochar. In addition, different packaging and materials are tested to improve the PRB efficiency up to 90%. Currently, laboratory experiments are going on to test whether the PRB is able to remove other chalcophile elements such as As, Tl, Hg and Se.

The 2024 geochemical characterization of the surface water near the ore bodies had showed Sb contents up to 700 µg/L, while 20 mg/L of dissolved Sb were measured in the water of a piezometer upstream of the tailing pile. Downstream of the mine, the Sb concentration is much lower, since the water of the Rosia River had concentrations of <10 µg/L. The laboratory-scale PRB models had showed that the filling material was found to reduce up to 75% of the initial Sb content.

If this technique succeeds in reducing the other chalcophilic elements, in addition to Sb, this technique could be exported to other sites in southern Tuscany where remediation has recently started or is about to start. This could minimize both the risk of exposure to people living nearby and the environmental impact to the aquatic ecosystem.

Iron ore has been periodically mined in Stripa, Sweden, since the Middle Ages. Mining operations ceased in 1977, and the 490-meter-deep mine was later repurposed by the Swedish Nuclear Fuel and Waste Management Company (SKB) as a research facility until 1991 Afterward, the mine was flooded, and the above-ground facilities were repurposed for industrial use. In 2006, the remaining structures were listed as buildings with historical value.

The area surrounding the mine is relatively densely populated by Swedish standards, and many private wells have been drilled in the vicinity. The possibility of using water from the old mine shaft prompted a scientific investigation summarized here. Water samples were collected from streams near the site, from the mine shaft overflow, and from within the mine shaft itself (down to a depth of 200 meters). All samples underwent general geochemical analysis, including measurements of pH, dissolved oxygen, metals, and anions. Given the site's history, a wealth of historical data is also available from previous reports and research articles.

From the literature, three types of groundwater have been identified in the area:

1. Deep anoxic water, with a Na-Ca-Cl composition, high salinity, and a pH above 9.
2. Intermediate anoxic water, characterized by Ca-HCO3, low salinity, and a pH of 7-8.
3. Shallow oxic water, with traces of surface water, low salinity, and a pH of 5-7.

The deeper water (below 330 meters) is 8,000 to 30,000 years old, while the shallow water is more recent and heavily influenced by infiltrating surface water.

During the most recent sampling campaign, several notable changes were observed compared to historical data.. Notably, uranium concentrations in the mine shaft have increased to nearly 1 mg/L at a depth of 200 meters, compared to previous averages of 10 µg/L. Dissolved oxygen measurements indicated relatively high oxygen saturation for such deep water, ranging from 37% at 15 meters to 23% at 200 meters depth, which suggest water mixing and oxidation of uranium(IV) minerals.

These findings suggest that the water quality in wells surrounding the site may be unsuitable for consumption, which requires further verification through analysis. The outflow of uranium from the mine is estimated at 10-100 kg annually, is likely driven by increased dissolved oxygen and poses a regional environmental concern.

The current study focused on identifying valuable elements that can be recovered from Lancaster Dam and gold mine dumps in Krugersdorp, a city in Gauteng Province, South Africa. The mine dumps considered are from closed and abandoned mines and have been existing for many decades. The area is also known for high volumes of acid mine drainage. The concentrations of valuable and base elements were measured. Rare earth elements (REEs), Ni, Co, Ag, Li, Cu and Cr among others were detected and found to be in concentrations that can be recovered to help meet their demand. Salvaging REEs and other valuable elements from mine waste can help improve the economies of many countries since, the elements are in demand due to improving technologies and growing population. Other elements including those that are toxic at very low concentrations were also detected. Thus, suitable techniques for the recovery of valuable elements in the study area, are those that have high selectivity and efficiency.

After their decommissioning and the accompanying natural flooding, mines represent large water reservoirs. Because of the contact with the rock, the mine water is thermally well coupled to the underground. The large storage mass activated in this way correlates with a high heating or cooling capacity. However, harnessing this energy is associated with high costs due to the drilling and securing of boreholes or shafts. This makes an accurate design of the plant essential in order to optimize energy utilization. Herein lies an obstacle for many potential project initiators. Administrations of mining regions and local energy suppliers most often are not able to conduct detailed thermohydraulic modeling of the mining structures to determine the energetic potential. Subsequently, the scope of this paper is the advancement of a reduced model that will be integrated into a user-oriented tool to allow for preliminary thermodynamical assessments.

As a basis for this development, literature models suitable for mine water geothermal use were reviewed. Simplified analytical models have the advantage of producing fast results compared to extensive mine structure modeling. However, the lack of flexibility or accuracy poses obstacles in the unrestricted integration in a practice-oriented tool. To address these weaknesses, a separate reduced numerical model was developed using a one-dimensional implicit finite volume method.

This developed implicit Finite-Volume-Method (FVM) model was tested against an analytical model as well as against a three-dimensional computational fluid dynamics (CFD) mine water model, the latter being used as a verification benchmark. Reference calculations show that in the case of laminar water flow, the heat extraction power between the self-developed model and the CFD simulation differs by less than 2.5% in the reference scenario. This demonstrates a higher level of accuracy than that achieved by the comparison model. Furthermore, the model can be adapted to accommodate varying heat loads, thereby facilitating the integration of cooling in addition to heating.

The model will be subsequently used to create an easy-to-access tool which is able to yield accurate results for a wide variety of boundary conditions, including properties of the fluid and the underground as well as heat load requirements. This opens up new opportunities for stakeholders in the application of reduced models for the planning of geothermal mine water systems.

Mine water geothermal and thermal energy storage are efficient solutions to re-use subsurface infrastructure and contribute to the decarbonisation of heating. The understanding of groundwater flow and heat transport in flooded mines and the prediction of system behaviour over the long-term operation is key for a successful implementation of the technology and sustainable use of the resource. However, the combined uncertainty about the post-closure mining conditions and the physical processes occurring in the subsurface limits the prediction of the flow and heat preferential pathways and long-term behaviour of the system.

This work describes the results of heat tracer tests performed at the UK Geoenergy Observatory (UKGEOS) in Glasgow (UK), a unique at-scale research facility to study mine water geothermal and thermal energy storage. The observatory includes a geothermal infrastructure, with multi-physical monitoring capabilities and boreholes drilled to different depths in and above a coal mine closed in the 1930s. Six boreholes intersected a variety of mine working types including coal pillars and voids, backfilled, collapsed and fractured zones and roadways, with variable hydraulic and thermal properties. Four of these boreholes are equipped with infrastructure that allow for multiple combinations of abstraction-reinjection and geothermal experimentation.

We present and compare the results of the heat tracer experiments and discuss the influence of the mine geometry and working types on the groundwater flow and heat transfer processes. The analysis of old mine working plans in combination with the data collected after drilling has been used to inform, delineate and parameterise site numerical models used to help in the interpretation of the hydraulic and thermal observations. Data from single-borehole pumping tests and abstraction-reinjection experiments have been used for model calibration and obtain a spatial distribution of hydraulic and thermal properties. Hydro-thermal models were then run to compare outputs with the heat tracer experiments.

Understanding the spatial variability of these elements and their influence on groundwater flow and heat transport processes is fundamental to assess the viability of a mine water geothermal project. Learnings from this work at an extensively monitored site can be applied to other sites. For example, to understand the responses to characterisation pumping tests, to improve the understanding of flow and heat transport processes in various flow regimes, and to predict, and avoid, rapid thermal breakthrough of the reinjected water in the abstraction borehole that would decrease the efficiency of the installation.

As part of the energy and heating transition away from fossil fuels and towards renewable energies, it is important to offer local energy suppliers as many functional and economically competitive options for renewable energies as possible. In former coal mining regions, the geothermal use of mine water can be a substantial building block that can be accessed both as a source and as a storage option when converting the heat supply. The development and implementation of projects for the thermal utilization of mine water present a number of challenges that must be addressed, in order to make such utilization both feasible and economical.

In previous projects that investigated the feasibility of utilizing mine water, a wide range of challenges were identified, necessitating the development of appropriate solutions where possible. Recognizing and compiling these important findings is essential in order to create better conditions for future projects so that obstacles that arise again can be dealt with more effectively using the lessons learned.

The challenges that may arise in mine water utilization projects can be diverse and range from legal, technical, contractual and social to economic challenges. The findings from previous projects clearly show that legal and contractual issues in particular should be clarified as early as possible in the project. Although solving legal problems can be very time-consuming, a solution can usually be found with the right planning and appropriate contracts. Depending on the complexity, technical obstacles can sometimes be very cost-intensive or result in the project being not feasible and alternative heat sources have to be developed. Social challenges are often based on the prejudices and personal impressions of individuals, so they need to be persuaded with sound, scientifically proven arguments to overcome them.

As part of the ongoing heat transition, mine water is intended to play a vital role as a geothermal source in the former mining regions to offer suppliers another sustainable option. It is therefore essential to evaluate and systematically categorize the experience gained, providing an ideal basis for future projects. Leveraging this existing knowledge effectively will enhance both the efficiency, profitability and speed of future project implementation.

The feasibility study for the foreseen development area Richtericher-Dell in Aachen, Germany aims at the supply of heating and cooling via mine water with the focus on the underground development and mine water utilization concept.

The planned heating grid within the Richtericher-Dell development area is around 37 ha with approx. 850-900 new residential units. A maximum grid capacity of approx. 4.2 MW with a simultaneity of 83 % was based on the net energy balance of the foreseen buildings (with an anticipated annual consumption of approx. 9.5 GWh). As an innovation, it should be emphasized that the influence of an additional underground storage system was specifically investigated and evaluated within the feasibility study. This could significantly support the approx. 40 °C network during peak loads by providing an additional hydraulically separated temperature circuit for more than 24 hours at a time. In combination with an underground storage system, the output of the mine water system and the heat pumps could be significantly reduced.

Thanks to an up to 100% sustainable, low-energy and efficient mine water system with regeneration of the heat source through the possible use of surplus heat from cooling in summer and the integration of an underground storage system, there is no need for additional fossil heat sources. Only a power-to-heat system is only planned to be integrated into the system as a backup.

The results of this preliminary study for a so-called 5^th generation heating network (5GDHC) should be seen as a “blueprint” for heating grid expansions in the Aachen city region. This integral concept aims at the reutilization of mine water for the supply of decentralized energy systems, including the integration of additional storage systems. Based on the size and interconnectivity of the abandoned hard coal mines in the Aachen area, an extension of the foreseen heating grid is feasible.

A challenge in the decarbonisation of heating systems is the seasonal mismatch between heat production and heat demand. Mine thermal energy storage (MTES) is an innovative solution that uses mine water as heat carrier to store heat in abandoned, flooded mine workings. In these systems, hot water is injected during summer, when heat demand is low, and extracted during winter to support peak demand, improving efficiency and reducing costs. However, as with the implementation of mine water geothermal (for heating), the commercial uptake of mine thermal energy storage is relatively slow due to multiple technical, economic and regulatory barriers.

The EU-funded project PUSH-IT (Piloting Underground Storage of Heat In geoThermal reservoirs) is piloting the implementation of high-temperature thermal energy storage in aquifers (ATES), boreholes (BTES) and in two mines (MTES) in Bochum (Germany) and Cornwall (UK). In Bochum, an abandoned coal mine will be used to store high temperature waste heat from the university data centre at the Ruhr University Bochum. In Cornwall (UK), the project is evaluating solutions to store the residual heat from deep geothermal power production at United Downs in nearby flooded metal mines. Investigations are being carried out at these sites as part of the project, including water sampling, tracer testing, temperature logging and numerical modelling.

In parallel with the scientific and technical activities at each site, the project aims to understand public knowledge and perception of the technology. As with other new technologies, limited technology awareness and the lack of specific legislation are factors that can prevent faster market upscaling. In this work we investigate how MTES systems are regulated, focusing on regulations relevant to the respective countries and sites. The research involves literature studies as well as semi-structured interviews with operators, permitting authorities and regulators.

By analysing the regulatory frameworks and assessing experiences from the regulatory and operational sides of MTES permitting and construction, we develop an understanding of the benefits and challenges associated with the different approaches for regulating MTES. Through discussing and comparing specific examples, we develop recommendations for good regulatory practices that maintain public participation and environmental protection objectives without creating unnecessary barriers to the development of MTES systems.

Looking back over 50 years of studying acid mine drainage and the mineral deposits and mining activities that produce it, several lessons that should be universally recognized are often not.

(1) Conceptualization of a mine site begins with one’s background and experience with geology, hydrology, natural water chemistry, microbiology, mining, and mineral processing. Because these are typically not courses covered by civil engineering curricula, consulting companies, mining companies, and regulatory agencies must either hire this expertise or learn these skills through training. Progress has been made in this direction, but more is needed. If the conceptualization of a site is inadequate, costly mistakes are inevitable.

(2) Characterization of a site requires some of the same skill set and includes detailed knowledge of best practices for sampling procedures, time and costs needed to do adequate characterization, how to incorporate data into a site model that addresses fluxes and reservoirs of contaminant substances. Water analyses should be “reasonably” complete with major ions, trace elements, redox species, and preferably a few relevant isotopes. Seasonal trends and storm event trends should be sampled to determine how precipitation events and change of seasons affects aqueous contaminant mobility.

(3) Modeling is often a guessing activity full of assumptions and misconceptions that become clearer and improved through hypothesis testing and further data collection. The type of models, the inherent assumptions, their limitations, and the codes used to implement the models should all be transparent to the stakeholders. Sometimes nothing beyond a conceptual model is needed for a site, and sometimes a site can be so complex that different models should be developed, and the experts should discuss dissimilar conclusions and plot a path forward that clears up any controversial concerns.

Specific examples will be presented from actual case studies that emphasize these factors including the study of "natural background." Of all the skill sets, one of the most important is a solid knowledge of natural and man-made water contaminants and how water interacts with minerals and waste materials. Along with that knowledge, an expert should be humble enough to recognize that these sites are very complex and can perplex even the best experts, requiring a cautious iterative approach to find the most cost-efficient remediation.

This study addresses a critical environmental challenge, Acid Mine Drainage (AMD) in pit lakes, by exploring the potential of fly ash (FA) as a neutralizing agent. AMD in open-pit mines creates acidic water bodies that threaten ecosystems, demanding innovative and cost-effective treatment solutions. Fly ash, a coal combustion byproduct with alkaline properties, offers a promising alternative for in-situ neutralization of AMD, with the added benefit of better FA waste management practices. This research investigates the settling characteristics and physic-geochemical stability of FA when applied to neutralize AMD.

A novel aspect of this study is the usage of FA for AMD treatment and also its focus on controlled laboratory experiments using acrylic tubes containing different volumes of AMD (5, 10, and 15 liters), which simulate varying depths in pit lakes while maintaining a consistent FA-to-water ratio of 1:5. During a 24-hour settling period, FA’s behavior in AMD was analyzed by observing settling velocity, particle stratification, and pH change. Post-treatment water samples underwent Ion Chromatography (IC) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) analyses, with geochemical modeling conducted using PHREEQC software to understand secondary mineral formation and long-term stability.

The results showed significant improvements in water quality, with pH levels increasing from 2.77 to 6.24, 6.81, and 7.65 in the three acrylic tubes. Fe and Al concentrations decreased by over 100%, while manganese levels dropped by 19.88% to 40.06%, demonstrating FA’s effectiveness as a neutralizing agent for AMD. Notably, pH levels improved to near-neutral within the first hour and remained stable over the next 24 hours. The contact time between FA and AMD was directly proportional to water quality improvement, as smaller FA particles with larger surface areas took longer to settle. Settling velocities of FA particles ranged from 15.38 to 21.88 cm/s. Following neutralization, iron precipitated as goethite (FeOOH), hematite (Fe₂O₃), and hydrohematite; aluminum precipitated as gibbsite (Al(OH)₃); and manganese as pyrolusite (Mn(OH)₂) and manganite (MnOOH).

This research implies that FA can serve as an effective, sustainable solution for AMD neutralization, offering both a feasible treatment method and an environmentally beneficial use for FA waste. Implementing FA as a treatment agent in pit lakes could substantially enhance AMD-affected water bodies, aligning with broader environmental management goals for mining operations.

At a coal mine in north-eastern British Columbia, Canada, three lysimeters were constructed to evaluate the relative performance of covers placed on run of mine rock as a mitigation option. Mine rock covers are required as part of the approved reclamation plan for the coal mine, therefore progressive reclamation, including application of covers, is being contemplated to mitigate contaminant loadings at the site.

Each lysimeter consists of a 5 m tall mine rock pile built on a 17 m x 17 m pad, complete with liner systems, a network of collection pipes, and containment berms. Any percolation through the surface of the bare or covered mine rock pile is piped to a collection system where water volumes are measured, and water quality samples can routinely be taken. Regarding placed materials and cover systems: Lysimeter 1 (L1) is a control pile, Lysimeter 2 (L2) has a soil reclamation cover, whereas Lysimeter 3 (L3) has an engineered soil cover.

Data collected thus far confirms the research hypothesis that percolation through the L3 lysimeter is systematically lower than at L1 and L2, while noting that much of the total seepage measured at all three lysimeters is attributed to relatively infrequent, but high magnitude, convective rainfall events (>30 mm/day). Consistent with initial research hypotheses, seepage at L2 lysimeter was also typically less than L1 lysimeter (i.e., 90% of the time). However, measured seepage at L2 following extreme rainfall events was routinely higher than at L1, and in aggregate, total seepage at L2 and L1 was essentially the same over the study period. Since 2019, sulfate and selenium concentrations have consistently been highest at L1 lysimeter, lowest at L2 lysimeter, but intermediate at L3 lysimeter.

Study outcomes will eventually be used to inform site reclamation planning, in keeping with best management practices for mitigating contaminants of concern at the mine site. To date, the uncovered L1 lysimeter is characterized by high runoff volumes and elevated seepage concentrations for key parameters (e.g., sulphate and selenium) when compared to L2 and L3 lysimeters which are covered. Contaminant loading from L2 and L3 lysimeters is lower than at L1, but conclusions are mixed at L2 and L3 in terms of overall performance: L2 lysimeter yields higher runoff volumes compared to L3, but seepage concentrations at L2 are lower than at L3 lysimeter.

Around the world, both mining and underground civil works require excavating tunnels or ramps, whether for access, ore mining, rail or road connectivity, ventilation, water supply, among many other applications. During this process, it is common to find groundwater, which must necessarily be removed to achieve the final objectives of the excavation.

If the slope of the tunnel or ramp is positive or zero, drainage can be done through a lateral channel or pipe without major impacts. However, when the slope of the ramp or tunnel is negative, the water must be removed as soon as possible to avoid its accumulation, always overcoming gravity. It is common that when the depth reached exceeds the hydraulic capacities of a simple pumping system, pumping stations must be used to drain the water in stages to the surface or to the final accumulation or drainage site.

This paper develops a methodology for the design, sizing and planning of pumping stations for underground drainage in mines with depths that require the use of pumping stations, due to the high hydraulic pressures required by a pumping system above 10 bar. The methodology consists of the use of hydraulic design variables for the system that are initially proposed, according to the maximum expected infiltration flow and the maximum depth that would be reached in the project. With the latter, and the total head losses estimated by the proposed design variables, the total head loss to be overcome is determined and then subdivided according to the number of pumping stations proposed based on the height and flow to be overcome by each one.

The application of this methodology efficiently takes advantage of available resources, maintenance, geological conditions of the site and drainage needs in terms of flow and depth, considering potential anomalous situations and response capacities in the event of emergencies or faults. It also allows the treatment and reuse of water to be used as "industrial water". This methodology can be used for all types of underground works, whether civil, mining, military or others that require the management and use of water resources found underground during the excavation process and/or in its subsequent operation.

The importance of this work lies in addressing the increasing risks posed by dams, whose failures have led to environmental disasters, operational disruptions, safety issues and security problems that put lives and the population close to the mining operation at risk. The mining industry faces increasing pressure to monitor these dams more effectively, especially given their proximity to communities. This paper emphasizes the need for strict real-time monitoring systems to manage geotechnical risks and prevent structural failures, ensuring the safety of both personnel and nearby populations. Using advanced technology to improve risk management in mining operations is critical to mitigating potential catastrophes.

What sets this approach apart is the integration of 3D laser scanning technology with dedicated software. This novel method provides continuous monitoring and real-time data reporting on changes in the dam surface and stability. The system can detect minute deformations, track moisture levels and alert engineers to any potential risks. Furthermore, the technology allows for the creation of new monitoring zones after initial scans, enabling adaptive risk management even in areas that were previously unmonitored. This flexibility and the system’s ability to perform retrospective analysis make it an advanced tool for predictive and preventative monitoring.

In this study, an innovative and precise remote monitoring system for tailings dam stability control was implemented using a combination of 3D laser scanners and software that processes point cloud data using Gaussian weighting. The system was able to capture detailed data on dam walls, allowing geotechnical engineers to analyze deformation patterns and predict potential areas of failure. It also provided real-time alerts for immediate action when critical changes are detected. The method demonstrated the system’s ability to track millimeter-level movements and offered flexible visualization and reporting options to suit various operational needs. Being able to recreate failure scenarios and critical areas for re-evaluating situations and decision making is key to geotechnical tasks in tailings stability.

The key findings show that this innovative control system is a cost-effective and flexible solution for tailings dam monitoring. Its applications extend beyond safety monitoring, as the system can be used for routine operational measurements and risk assessments in mining. The implications of this work highlight the importance of advanced monitoring technologies to improve safety and operational efficiency in the mining sector, while also addressing environmental concerns related to dam failures.

Understanding long-term hydrometeorological conditions is essential for assessing water resource availability and variability for mining projects. Current practices often rely on conceptual models with empirical relationships and generalized parameters. While these approaches are easier to implement and often have lower data requirements compared to process-based models, they may not perform well outside the conditions for which they were calibrated, limiting their spatial transferability to un-monitored sites and their applicability to changing climate conditions.

This study aims to assess climate change impacts on water availability for a planned mine project in Eastern Canada. A process-based hydrological model was developed to simulate the current and future hydrology of a natural catchment near the mine site. The model was configured with publicly available topographical and meteorological data. Model performance in simulating streamflow was evaluated using the Kling-Gupta Efficiency metric, optimized through the Dynamically Dimensioned Search algorithm. The potential impacts of climate change on catchment hydrology were assessed using an ensemble of CMIP6 simulations for the SSP2-4.5 (moderate) and SSP3-7.0 (high) climate change scenarios.

Kling-Gupta Efficiency for simulating streamflow exceeded 0.8 during both the calibration and validation periods, demonstrating the model's reliability in generating representative hydrographs. The model effectively captures the magnitude and timing of observed snow accumulation and ablation, which is encouraging given that snowmelt runoff largely dominates the streamflow in the region. Projections show an increase in mean annual temperature of 2-4°C by the 2050s and 4-8°C by the 2100s, along with annual precipitation rising by 5-10% by the 2050s and 10-15% by the 2100s. These climatic changes will significantly alter catchment hydrology, with peak discharge projected to decline by approximately 40% and shift from May to April by the 2050s under the high emission scenario. While winter flows are anticipated to increase due to enhanced rainfall and mid-winter melt events, summer water availability is expected to decrease by 20-40%, depending on the emission scenario and projection period.

The outcomes of this study provide essential insights for the planned mine project, highlighting the need for proactive management of water resources. By quantifying anticipated changes in water availability, this study supports the formulation of targeted adaptation strategies, such as optimizing water storage and usage practices, enhancing runoff management in winter, and implementing measures to cope with reduced summer flow. These strategies will be crucial for ensuring sustainable mining operations, maintaining operational efficiency, and minimizing potential environmental impacts in the face of climate variability.

Underwater mine exploration is a challenging task due to confined spaces, the need for high precision, and extreme environmental conditions. Traditional human-based methods are not only risky but also inefficient in submerged environments. This abstract introduces UNEXMIN Georobotics' underwater robotic technology, which provides a safe, non-invasive, and highly efficient alternative to manual exploration, particularly in abandoned, flooded, or hard-to-access mine workings. Our robotic system allows us to collect valuable geological and structural data while substantially reducing human exposure to dangerous conditions. This work is important as it addresses the growing need for cost-effective, automated solutions in the mining industry.

Our approach is centred around a novel underwater robotic platform designed for confined and extreme environments, specifically tight mine shafts that are often submerged and inaccessible by traditional means. The UX robotic technology incorporates advanced navigation systems, including a Doppler Velocity Log (DVL), inertial measurement units (IMU), multibeam sonar, 360° imaging sonar and high-precision laser modules. Our robots are equipped with six cameras and optical cable connection to ensure precise, real-time data acquisition up to 1500 m water depth. What sets our approach apart is the combination of these technologies in a modular, compact egg-shaped design that can access areas as small as 1 meter in diameter.

Our key findings include successful deployments in several test environments and active mine sites, where our robotic system demonstrated its ability to navigate complex underwater environments, collect high-resolution 3D data, and perform tasks autonomously. In 2022, our robot set a world record by reaching 450 meters in depth during a dive in the Hranice Abyss, the world’s deepest underwater cave, showcasing its capability to operate in extreme conditions.

The implications of our work are broad. Our technology can be applied to flooded mine exploration, water management in underground environments, geological surveys, and archaeological missions to preserve submerged historical structures. Additionally, it has the potential to substantially shorten the process of reopening flooded mines by providing detailed, real-time data without the need for dewatering or large-scale manual inspections. This technology enhances safety and efficiency. It offers new avenues for industries and governments to explore submerged environments while decreasing the risk and high cost associated with traditional and mostly non-applicable diving methods. As such, UNEXMIN Georobotics' underwater robots represent a breakthrough in the way we approach and manage flooded and confined spaces in mining and beyond.

A material’s potential to generate acidity is predicted based on the balance of acid-generating and acid-neutralizing minerals. The standard acid-base accounting and depletion calculations assume that pyrite and calcite are the primary reactive phases and that the relative rates of pyrite oxidation and calcite dissolution follow a specific reaction pathway associated with a defined pH and carbon dioxide partial pressure. This paper evaluates the effects of changes in system conditions on acid-base accounting using results from both laboratory-kinetic testing and reactive-transport modeling.

Mine sites throughout the world are similar but different. They have different topography, climate, geology, target minerals, mining methods and processing methods, but mining and processing are always affected by water, and water in the environment is always affected by mining and processing on site. At every stage in the project pipeline, from Conceptual to Order of Magnitude Study (OoM) to Pre-Feasibility Study (PFS), from Feasibility Study (FS) to Engineering, Procurement and Construction Management (EPCM), from commissioning to operations, and then to expansion and closure studies, there are reasons to consider water management holistically, in an integrated way, to ensure success in operations and to mitigate risks. Simulation modelling can be used to support decisions during design and operations, and with 25 years of evolution of integrated water balance modelling, there are now clear patterns that show when integrated balance modelling is especially useful.

Using constructed wetlands (CWs) for treatment of acidic and neutral waters is well documented, but their application for treatment of alkaline drainage has received less focus. In addition, there is limited available data for long-term employment of CWs treating alkaline drainage, with most studies in small scale systems or pilots <5 years old.
Bauxite residue (BR) formed as a waste of alumina production, is inherently alkaline (pH 9-13) and contains elevated concentrations of Al , As and V, with Na the dominant cation. Leachates from Bauxite Residue Disposal Areas (BRDAs) have similar characteristics and will be generated for decades, thus requiring appropriate treatment prior to discharge.

A pilot scale single cell leachate treatment system has been operational for 10 years, with influent and effluent monitoring to assess its ability to reduce pH. Sediment and water analyses across the operating period give insight to system performance (pH, conductivity, soil elemental fractionation, microbial community) with this system possibly having one of the longest running datasets for an alkaline leachate CW.

Results indicate the 10-year-old system consistently reduces pH in the BRDA leachate to an average of 7.14 (±0.18) at outflow, far below the target of pH<9, with average reductions in concentrations of Al (96%), As (85%) and V (71%). Sodium also decreased (22%), with Na mostly found in soluble forms in the substrate (up to 60% of total).

New, larger multicell CWs have been constructed on a separate site on the same BRDA. The two new systems (3 cells each) began operating in spring 2024, using differing substrate organic matter content to investigate the effects of substrate content on pH and metal reduction, and whether lab-based trace element removal studies are replicated in the field.

The new system with the higher organic content has to date shown a greater pH reduction in the effluent (pH = 7.1) when compared with the system with the lower organic content (pH=7.41). Analysis is ongoing to establish whether effluent elemental concentrations differ, with longer monitoring needed over the first year and further to determine whether pH reduction across time is maintained as the systems age.

Current results of the pilots demonstrate CWs are an effective treatment method for at least a decade for alkaline BRDA leachates. Future monitoring of the new CWs will ascertain whether performances are affected using different substrate mixes, but initial findings indicate increased organic content improves the extent of pH reduction.

Acid mine drainage (AMD) is widely recognized for its environmental impact, but in carbonate-rich systems, neutral mine drainage (NMD) can occur, posing distinct risks to water quality despite its neutral pH. Effectively managing post-mining sites in the long term requires a deep understanding of the hydrogeochemical processes governing the water chemistry. While numerous studies have explored abandoned iron and coal mines, the geochemical processes are often highly site-specific. Therefore, extensive localized studies are essential to determine the main water-rock interactions, sources of dissolved elements, and the role of bacterial populations in the geochemical cycles of each abandoned mine.

This work focuses on the Gardanne lignite mine, located near Marseille (Southern France), which operates in an NMD context. The flooding of galleries in 2003 caused a noticeable deterioration in water quality, notably with substantial increases in iron and sulfate concentrations. Currently, water is pumped through the Gérard shaft, the main outlet for the mine water reservoir, to control water levels and avoid overflow into the former discharge gallery, which directly leads to the port of Marseille. To identify the main spatial sources of mineralized water in the mine, physico-chemical measurements are conducted throughout the water column of the Gérard shaft, from the water table surface down to a depth of 700 m. Based on these results, samples are collected at specific depths for detailed chemical, isotopic, dissolved gas (CFCs, SF6) and microbiological analysis.

A previous similar physico-chemical log, conducted in 2011, identified four gallery levels likely contributing water to the Gérard shaft. The current campaign aims to confirm those results or detect any changes in the groundwater flow regime within the mine reservoir. Furthermore, chemical and isotopic analyses will be interpreted in light of similar studies from nearby aquifers, which could potentially sustain the mine system through deep underground sources.

To complement this study, column and batch leaching experiments will simulate water-rock interactions using rocks from the Gardanne mine, refining our understanding of these processes. The ultimate goal is to develop a geochemical model of the mine, either semi- or fully spatialized, by integrating fieldwork and laboratory results. This work is expected to provide essential insights for the long-term management of flooded lignite mines, particularly in neutral mine drainage contexts.

In areas affected by mining, such as the Ruhr region (Germany), mine gas releases are regularly observed at the surface. These gases are composed of mixtures of methane, carbon dioxide, carbon monoxide, oxygen, nitrogen and other higher hydrocarbons emitted from a fossil deposit. Methane in particular is a very climate-harmful greenhouse gas.

Mine gas release does not end with the closure of the coal mine and can continue for decades. After the shutdown of a mine, the mine water pumps are stopped or at least continued to be operated at a reduced pumping rate. The result is a rise of the mine water level in the underground mine. As the mine water level rises, the cavity volume decreases. Mine gas will therefore be pushed to the surface by a piston effect. The migrating gas will either be caught in traps or migrate further upwards through mine workings/shafts, permeable strata or faults. The emission on the surface and release into the atmosphere can either be wide spread and diffuse or focused.

In August 2024, the EU regulation 2024/1787 on the reduction of methane emissions in the energy sector went into force. Companies are now obliged to continuously measure and quantify methane emissions and develop measures to reduce these methane emissions into the atmosphere. Against the background of several thousand locations in the former coalfield in the Ruhr area alone where methane is degassing, this requirement represents a major challenge for companies in the European Union. Only a few techniques for dealing with mine gas, even in low concentrations, have been tested and utilised to date.

An integrated monitoring, which includes hydraulic and geochemical monitoring, can help to explain the mine gas release at the surface and can identify the processes in the mine workings that influence the gas during the mine water rebound. A comparison with maps of the mine workings and continuous measurements of the mine water level provides conclusions about potential migration pathways for the mine gas. Measurements of the gas concentration and composition as well as the analysis of isotopic markers reveal processes that consume or generate methane. The evaluation of the integral monitoring can make an important contribution to optimise future mine water rebounds with regard to the regulation of mine gas release behaviour and thus directly contribute to the requirements of the EU methane regulation.

Underground mine flooding is an important consideration of mine closure due to discharges that can occur when the water table reaches specific outlets as this has potential to modify the water quality of local water sources. Understanding the rate of reflooding is important to inform water management strategies. Presented in this study is a comparison between an analytical and a numerical method for estimating the natural flooding of an underground mine.

Using an Excel-based analytical method, the flooding rate was estimated by dividing the total underground void volume by the current total groundwater inflow. This method, however, assumes a constant inflow rate which is not akin to natural conditions in the study area due to a reducing hydraulic gradient developing as water level rises in the mine relative to the water level in the surrounding rock. Therefore, numerical modelling was incorporated to scrutinise this initial estimate considering inflow rate decreases as the mine floods.

The flooding process was simulated using the existing calibrated FEFLOW model and a Python script (FEFLOW API) that relies on Volume-Elevation curves estimated from available mine wireframes. The FEFLOW-based workflow estimates a total flooding time of around 4.5 years. This result contrasts with the 1-year flooding period estimated using the analytical method, due to the assumption of a constant inflow of 5,900 m3/d which is considered too conservative. According to the simulation, the mean inflow during the first 4.5 years of flooding will be approximately 1,300 m3/d. Additionally, FEFLOW also accounts for the required time to re-saturate the surrounding rock.

Although there were benefits to the analytical method such as lower computational costs, data requirements and assumptions, the conservative approach resulted in an overestimation of the daily inflow rate. Representing more realistic conditions via transient simulations has been effectively demonstrated using numerical modelling, increasing confidence in the estimation.

The formation of pit lakes during coal mine closure poses complex environmental, hydrological, geological, and socio-economic challenges that require integrated and proactive planning. This study develops a strategic framework for pit lake formation in Indonesia by combining hydrological modelling, geochemical assessment, and regulatory analysis. A key focus is the use of nearby river water for controlled pit filling to mitigate acid mine drainage (AMD) and enhance long-term landscape sustainability. The framework is applied to Pit D2 in the Binungan River watershed, evaluating two scenarios: precipitation-only and river-supplemented filling. Hydrological modelling using HEC-RAS identifies an optimal diversion channel elevation of +4 masl to manage flood risks. Water quality modelling with PHREEQC demonstrates that river supplementation significantly improves water chemistry, reducing Fe concentrations from 211.57 to 0.94 mg/L, sulphate from 459.46 to 28.83 mg/L, and increasing pH from 5.64 to 6.07—approaching regulatory standards. Beyond improving water quality, the study highlights the potential of pit lakes as flood retention systems in high-rainfall areas such as Kalimantan. Given limited regulatory guidance on river use for pit lake filling, this research underscores the importance of considering such approaches within mine closure planning. Future efforts should further integrate pit lake development into early-stage mine design to support sustainable, multi-functional post-mining land use.

Gold cyanidation effluent often contains high levels of cyanide and metals. While removal in synthetic water is well demonstrated, real process water introduces complexities that need further study. Batch tests with process waters from three Peruvian sites evaluated an electrochemical approach for contaminant removal. Cyanide destruction was two orders of magnitude slower in real water, and copper removal varied with water composition. The results underscore the need to understand process water chemistry to create a reliable treatment design framework. Additional research is essential for optimizing cyanide and metal removal in practical applications.

Mining activities are ancient in Portugal, dating back to the Pre-Roman and Roman periods. They played an important role in the Portuguese economy of the 19^th and 20^th centuries associated mainly with polymetallic sulphides in the south, and uranium minerals in the north. In the second half of the twentieth century, almost all the mining activities were suspended and consequently many mine sites were left untreated. The fact that much of Portugal mineralization is associated with sulphide minerals provided great potential for acid mine drainage (AMD) production and an estimate of about 14 % of the Portuguese mines were found to generate acidic waters. São Domingos mine, a deposit of polymetallic sulphides explored mainly for copper, located in Southeast Portugal in the Iberian Pyrite Belt, is an example of a serious problem resulting from the existence of AMD. The inactive open-pit from the mining operations resulted in the creation of a large pit-lake with acid water with pH close to 2 containing high concentrations of sulphate and heavy metals (mainly aluminium, iron, zinc and copper). The contamination is not only confined to the pit-lake since the downstream area is also affected and its impact extends to several water bodies located nearby.

The problems associated to AMD in Portugal and in São Domingos in particular were the driving force that stimulated the studies of our research group for the development of alternative treatment processes based on the use of Sulphate-Reducing Bacteria (SRB), since traditional neutralization do not address the reduction of sulfate, are expensive and result in the formation of high volumes of sludge. Moreover, the use of biologic techniques offers several opportunities, such as the possibility to recover the metals, namely as metal sulphide nanoparticles and nanocomposites with functional applications.

Since the first studies several carbon sources have been tested, mainly waste locally available, such as wine waste that have been very efficient. In addition to the characterization of the consortia and their dynamics, other optimizations were introduced to the bioremediation systems aiming to improve the efficiency of the process and the quality of the effluents for irrigation purposes.

As a result, a pilot plant has been installed on-situ at São Domingos mine. Presently, the characterization and potential use of acidophilic SRB consortia are under investigation and new projects aiming at their utilization and the eventual co-treatment with other waste are envisaged, expecting to bring new challenges and opportunities.

The mine water levels in large parts of the Ruhr region are currently rising to an optimized level, among other things with the aim of reducing the number of dewatering locations. This offers the opportunity to convert the sites to modern submersible pumps wells. These developments also place new demands on numerical modelling. A method was therefore developed to be able to depict the pump management typical for well pumping stations using numerical modelling with the established box model.

Submersible pumps wells are characterized by only a few pumps, each with a comparatively high flow rate. This means that, depending on the water inflow and the void volume available as storage, the water levels rise and fall depending on the number of active pumps. Stationary water levels, such as those maintained by underground pumping systems, will hardly exist in the future. For the planning of pump levels, pump design and water level variations to be applied for, predictions of the expected rise and lowering behaviour under realistic operating conditions are required.

To date, only a few pumping scenarios have been taken into account in the box model. A distinction was made between pumps that keep the water level at a certain level and pumps with a predetermined constant pumping rate. However, in order to model well water management, it is necessary to be able to switch between different pumping rates at short notice and to comply with upper and lower water level limits.

In addition to these internal mine factors, external conditions also influence future pumping management. The most important parameter in planning is the mixed water concentrations that arise in the receiving waters. For this, the pre-loading of the mine water and the discharge quantities must be forecast as accurately as possible. Many mine drainage systems also have seasonally fluctuating inflow rates, which show a climatic connection. The receiving waters also have these seasonal variations, albeit at a different time than the mine water, which increases the risk of limit values in the receiving waters being exceeded, especially in the summer months. By integrating pumping strategies adapted to these conditions in the box model, well-founded forecasts for discharge rates and loads can be made that also take seasonal requirements into account.

Sedimentation pond facilities are integrally associated with the treatment of mine water characterized by Suspended Solid (SS) content. Design criteria for sedimentation ponds are typically determined utilizing Stokes' law with an estimated particle settling velocity or by assuming particle-specific gravity. However, under actual conditions, particle characteristics may vary depending on the location. Finer sediments, such as colloidal clay (<2 µm), frequently deviate from Stokes' law due to inter-particle interactions and agglomerative behaviour. Consequently, additional data, including particle size and settling velocity, are necessary to establish design criteria that accurately represent the specific conditions of each site.

This investigation focuses on settling tests of mine water with existing water quality characteristics. Six water samples from diverse locations were analyzed for physical parameters including pH, Oxidation Reduction Potential (ORP), Total Suspended Solid (TSS), and Iron and Manganese Metals (both total and dissolved). Discrete particle sedimentation tests, jar tests utilizing lime or aluminum sulfate, and floc particle sedimentation tests were conducted for each water sample. Column settling tests with a water level of 100 cm and a sampling port at a depth of 80 cm were employed to assess the settling rate of discrete particles from various sites.

This study has identified that natural gravity settling (without the addition of chemicals) can occur for water with acidic characteristics, with pH values ranging from 3.16 to 4.05. In acidic water, up to 57.4% of SS removal can be achieved within 50 minutes as the zeta potential approaches zero. Conversely, neutral pH water required chemical coagulation, with optimum doses ranging from 20 to 200 mg/L, contingent upon the initial water characteristics. Furthermore, the settling test was conducted subsequent to jar testing, with sampling ports at 20 cm depth intervals and measurements taken at 15-minute intervals over 60 minutes. Iso-removal curves were utilized to determine parameters such as detention time and overflow rate. Additionally, iron and manganese concentrations post-chemical treatment were evaluated.

This research is anticipated to serve as a reference for sedimentation pond design strategies, addressing both dimensional considerations and the selection of chemicals using a non-Stokes' law approach.

The Li Valdeflorez deposit is located in the Cáceres Syncline (Spain). Its northern flank forms a narrow valley between two quartzitic ridges, in the middle of which the Li mineralization is located in an Ordovician psammopelitic sequence (Valhondo unit) with 111.3 Mt @ 0.61 wt% of Li2O, one of the largest Li deposits in Europe.
Underground mining works will be located in the low permeability Valhondo Unit, while the Tailing Mills Facility (TMF), refining plant and auxiliary facilities will be located 1.5km to the southwest on top of El Calerizo Unit, a carbo-dolomitic Carboniferous sequence. Both units are isolated from each other by levels of slates and vulcanites with very low permeability that guarantee the individualization of their hydrogeological behavior.
Underground facilities have been projected using a responsible design, optimized through geotechnical modeling, which includes a crown pillar, in order to avoid mining collapses and protect the Valhondo creek, which drains the area. Will be accessed via two ramps. Auxiliary infrastructures and TMF will be isolated from the substrate using multi-barrier systems. Mine development has been planned to reduce the surrounding rock disturbance and hence to minimize effects on its permeability. Mine water collection and management, and the monitoring program, will prevent waters mixing and infiltration of water from the mine to the aquifers.
The carbo-dolomitic aquifer substrate has been characterized through various geophysics campaigns: SEVs, Electrical Tomography, Magneto-Telluric Tomography, in order to determine the geometry of its superficial zone (0-20 m), and deep zone (up to 300 m). 11 infiltration tests were carried out on the decalcification clays that cover the carbonate outcrops that will constitute the substrate for the auxiliary facilities and the TMF. They show permeability values in the range of K = 10-7 / 10-6 m/s. The deep substrate has been characterized through 4 pumping test, obtaining transmissivities of less than 1 m2 /day. Two additional tests, somewhat further south, indicated higher transmissivities: 16 to 100 m2 /day.
This information, and the results of piezometric and chemical quality campaigns define a conceptual model that shows the heterogeneity of El Calerizo aquifer, where areas with different hydrogeological characteristics coexist, and confirms the marked anisotropy of the medium and a blocks-structure with different hydrogeological conditions. This information is relevant for the location of Surface facilities and the observation boreholes of the Underground Water Control Network, which will allow the performance assessment and evolution of the El Calerizo aquifer.

The presence of water invariably causes a loss of performance of the pit slopes. The water pressure acting within any discontinuities and pore spaces in the rock mass reduces the effective stress, with a consequent reduction in shear strength of the rock mass. Either the slope must be depressurized, designed with a lower factor of safety, or flattened to compensate for the reduced rock mass strength. Where excess water pressures occur below the pit floor, heave may result groundwater pressure is the only geotechnical parameter in pit slope engineering that can readily be modified. It is for this reason that it is necessary to know which sectors of the pit may present stability problems triggered or unleashed by groundwater, that is, where hydrogeology may be a risk to the stability of the open pit slopes.

This paper presents a methodology to estimate the hydrogeological risks associated with slope stability in open-pit operations. The proposed approach integrates geotechnical and hydrogeological data, emphasizing the influence of groundwater flow, pore pressure, and water table fluctuations on slope performance. By combining field measurements, hydrogeological numerical modeling (developed in MINEDW software) and hydrogeological uncertainty analysis and stability analysis (simulated by FLAC3D Software), this methodology provides a comprehensive tool to assess potential risks and inform mitigation strategies. The results aim to enhance slope management practices, minimize failures, and improve safety in open-pit mining environments. The methodology combines different maps that account for (1) Density of existing hydrogeological data in the mine, (2) Deviation between monitored and modelled heads and pore pressures, (3) compliance of pore pressures targets to maintain FoS above defined thresholds, and (4) the sensitivity of FoS to fluctuations in the pore pressures. A hydrogeological risk contour map is generated from these maps for several predictive stages of the mine.

These maps provide a quick and simple way to assess the implications of hydrogeology on slope stability, identifying areas where depressurization processes are necessary, zones where improved hydrogeological characterization and monitoring is needed, and even sectors where the mine planning design needs to be reviewed.

We present an approach to get the most information from static tests. The geochemical characteristics of mining waste and ore are a key factor for the technical and environmental viability of a mine. In this regard, the static geochemical tests usually used are focused in acid-base accounting (ABA) based mainly on carbonates as neutralizer and pyrite as the sulphide. However, this is a partial view. In many cases, the environmental risk of a mining project must also consider other mineral species such as silicates, as they can also provide neutralization capacity and also release metals. Furthermore, metal leaching is sometimes not fully considered in the static tests suite, and is left for long-duration humidity cell or column tests. However, the risk of metal leaching can also be assessed by combining on-site water samples and static leaching tests on drill-cores and old waste dumps.

Mineralogical analysis (XRD) can be used as an initial approximation to calculate a mineralogical neutralization potential (NP) in the sample and check whether the ABA test (EN 15875) may not consider all the available NP, for example, from silicates. Regarding metal leaching, in Spain, the Spanish Geological Mining Institute (IGME) recommends the UNE12457 standard as a leaching test for existing old dumps. This could also be applied to drill-core samples to test for immediate leaching. In addition, the assay of the NAG (Net Acid Generation) test eluates can be used to assess the risk of metal leaching if sulphides are oxidised. Instead of using the Geochemical Abundance Index - GAI (Gard Guide) as an approximation to environmental risk based on rock analysis, we assess the risk based on leaching tests. The reason is that an enrichment in the rock – what the GAI assesses- is not directly related to a risk in metal mobility. Instead, we compare the results of the leaching tests with European or national standards for surface waters, inspired by the IGME methodology.

Our procedure has allowed us to identify whether NP from silicates is likely underestimated in the ABA test and also, based on short-term tests, the metals that pose an environmental risk if the future mine waste is not managed properly.

The results are compared with the existing mine-influenced waters at the site and specific management measures are proposed to the different lithologies of the future mine.

Reprocessing potential and environmental risk of Bielatal tailings material, Altenberg, Germany, were assessed using percussion core samples (7 m depth), analyzed for geochemical, mineralogical composition, particle size, and milieu parameters (pH, Eh, EC). Tin (0.12 wt%) and lithium (0.10 wt%) were valuable elements, while arsenic (0.04 wt%) posed environmental concerns. Tin and lithium were associated with cassiterite and mica phases respectively. Samples were composed of 56% silt, 35% fine sand, and 9% clay, with enrichment of tin, lithium, and arsenic in fine fractions. Weak acidity (pH 6) and low oxidation (Eh 160 mV) suggest minimal acid mine drainage risk.

To combat the climate crisis, more metals are needed to accelerate the pace of replacing fossil-fuel-based technologies with renewable energy sources. Although remining has been researched for several decades, the extent to which it could supplement virgin extraction of critical minerals and metals is currently unknown. Programs under way by the US Geological Survey and the European Union, including the EU’s Critical Raw Materials Act of 2024, will increase our knowledge of remining’s potential.

A review of relevant studies, operations, and planned projects has been conducted to examine remining in four areas: Sampling and geochemical characterization; global, regional, and national estimates of the potential for recovery of valuable minerals; remining examples and technical feasibility; and environmental and health effects. This review provides updated remining estimates and examples in the United States, Europe, Australia, Chile, and China and makes recommendations for better understanding remining’s environmental effects and resource potential.

Remining sources for renewable energy metals (e.g., Co, Ni, REEs, Mn, Li) include legacy and existing mine wastes and associated mine waters, coal mine residues, and byproduct and primary production materials. Current remining operations are largely focusing on gold. Tailings are of greatest interest due to their abundance globally and the fact that they are already crushed and ground, which lowers energy and water use. Pollutant registries in the United States, Europe, and Australia can be used to get a very rough estimate of the amount of renewable energy metals in mine wastes, but reporting improvements are needed to better estimate the metal “reserve” and to determine economic viability. Geochemical characterization methods typically applied at active mines for predicting pollution potential need to be expanded to include methods such as mineral liberation analysis and bench-scale process testing for remined materials.

Of the processing approaches examined for recovery of renewable energy metals from tailings, bioleaching appears to offer the most benefits with the fewest potential downsides. The advantages and challenges of different processing methods will be presented. Best practices specifically designed for remining do not currently exist but are urgently needed to improve resource estimates and avoid adverse effects such as the two tailings dam failures that occurred at remining operations in Romania and South Africa.

Interest in remining is booming due to its potential to increase domestic supply. If properly conducted, remining can also improve circularity and environmental conditions in areas affected by existing and legacy mining activity.

Acidic Mine Waters (AMWs) present a major environmental risk due to their high acidity and transition metal content, which can contaminate water bodies and ecosystems. Traditional treatments, while effective at neutralizing acidity and removing metals, generate hazardous sludge, which creates additional environmental concerns. However, recent advances in sustainable technologies have opened up new opportunities to treat AMW in a more resource-efficient way. By considering AMW as a secondary source of Critical Raw Materials (CRMs), such as Rare Earth Elements (REEs), this approach not only mitigates environmental risks but also addresses the increasing demand for CRMs, essential in high-tech industries.

This study introduces a circular treatment scheme for AMW that integrates selective precipitation and ion exchange to recover valuable REEs, focusing on a sustainable alternative to traditional lime-based treatments. AMW from the Aznalcóllar open-pit mine in Spain was utilized, containing relevant amounts of metals like Al, Fe, Zn (in the order of several mg/L), and a total REEs concentration of 18.6 mg/L. The process began with the removal of Fe and Al through precipitation, followed by the selective removal of Zn as a sulfide. Moreover, a fractionation process was developed to separate heavy and light REEs using two different ion exchange resins, prior to their recovery as oxalates.

The study achieved highly efficient metal removal from the AMW, with Fe and Al being removed more than 99.9% and 90%, respectively. The removal of transition metals (Zn, Cd, Cu) as sulfides also exceeded 99% efficiency. Their removal allowed to maximize REEs uptake in the ion-exchange, with concentration factors for REEs up to 50. The final REE oxalates obtained had purities exceeding 90%, confirming the effectiveness of the combined treatment processes.

This research highlights a promising, sustainable approach for the recovery of valuable REEs from AMW, addressing both environmental hazards and the demand for CRMs. The findings suggest that such a circular treatment strategy could be widely applied to treat mine waters while simultaneously generating economic value from CRM extraction. Moreover, this approach reduces hazardous sludge generation, offering an eco-friendly alternative to conventional mine water treatments, with potential for application in other contaminated water sources worldwide.

Tailings management in iron ore mining rose to prominence following the dam failures in 2015 and 2019 in Brazil, underscoring the urgent need for safer and more sustainable practices. In response to these events, the Global Industry Standard on Tailings Management (GISTM) was introduced to guide the adoption of best practices aimed at ensuring the safety and integrity of tailings disposal structures. Dry stacking has emerged as a viable alternative to conventional tailings dams, as it minimizes water retention within the tailings, thereby reducing hydraulic risks.

This paper presents a detailed protocol for the chemical, mineralogical, and hydrogeochemical modeling—both conceptual and numerical—of iron ore beneficiation waste. The protocol was developed for one of the first dry stacking facilities in Brazil, implemented in response to the 2015 dam failure. The proposed methodology enables continuous assessment of the chemical stability of the waste, integrating hydrochemical analyses and monitoring the reagents used in the beneficiation process. The developed hydrogeochemical model follows a systematic and integrated approach, utilizing the available information about the structure. Its objective is to consolidate data on the factors influencing fluid percolation and movement, considering geotechnical, hydrogeological, and hydrochemical aspects, as well as the physicochemical and mineralogical properties of the materials involved.

Three key conditions were identified within the context of the structure. The first relates to seasonal fluctuations in the water level within the structure, which control the geochemical conditions. Second, the numerical model investigated the degradation of ether-amines—reagents used in the beneficiation process—and how their breakdown may affect the redox environment within the structure. Lastly, an analysis was conducted to evaluate the potential for chemical clogging of the bottom drains of the dry stack.

Successfully conceived and implemented, the protocol has proven to be a valuable tool for the continuous assessment of the chemical stability of these materials. It offers an integrated methodology encompassing the hydrochemical analysis of effluents and industrial waters, as well as the monitoring of organic reagents used in mineral processing. The results indicate that primary iron ore beneficiation practices comply with international standards and best industry practices, reinforcing the commitment to safety and sustainability in mining operations.

The mining activities of Lorraine coalfield (France) caused drawdown of the Lower Triassic sandstone aquifer. This was due to extensive mine drainage and additional water extraction by surrounding industries and communities. The prolonged water table decline over a century led to the drying of wetlands, while regional land development proceeded without recognizing the unsustainable nature of this water depletion. With the cessation of coal mining in the early 2000s and the gradual closure of other water-intensive industries from the 1980s onward, the Lower Triassic sandstone aquifer began to recover. In this paper, the authors provide a detailed description of the coalfield's general conditions, the methodology used for long-term flood risk management in vulnerable built-up areas.

In response to these challenges, GEODERIS and BRGM implemented a 3D hydrodynamic model to assess and predict the long-term influence of groundwater recovery. After a history matching phase based on available geological and piezometric data, predictive simulations were conducted to first estimate future water table levels and then guide the gradual deployment of the pumping network in flood-prone zones. Two climate simulations based on the work of the IPCC were utilized: one representing average rainfall and the other representing intense rainfall. These scenarios were used to estimate the effect of climate change on the extent of vulnerable areas and to inform adaptations for the well field.

Initial findings revealed that the groundwater rebound occurred at varying rates on either side of the Longeville-Hombourg fault, faster in the western part of the basin. Moreover, numerous built-up areas in the western sector are already at risk from the rising water table, with projections extending to the eastern sector by the 2040s–2050s. The predictive simulations were also used to calculate the pumping flows required to manage this risk.

To mitigate the potential influence of rising groundwater, a network of pumping wells is to be implemented to maintain water table levels at a minimum depth of 3 meters in vulnerable areas. In addition, a comprehensive piezometric monitoring network is to be set up to track water table dynamics across the different geological compartments, enabling model refinement and adaptive management of the well field. Given the assumptions underlying the 3D numerical model and the time scale of the concerning phenomenon, the overall strategy adopted is clearly data-driven. This approach aims to improve forecasts and refine geological and hydrogeological interpretations of the coalfield.

Mines and mining companies face two main challenges to translate broad corporate water stewardship goals to meaningful site level investment plans to manage their water projects and to intern link these site level actions to wider water resource goals. Firstly, the level of investment needed to bring mining projects to the desired level of maturity, depending on corporate commitments is challenging given the cost pressures of commodity pricing, the requirements of the project and other priorities competing for investment. Secondly, mining companies are challenged to present their position to their stakeholders in a transparent manner that justifies investment decisions and presents a realistic picture of where they are in terms of what is achievable.

Benchmarking can be considered to address these two challenges as a useful tool to both understand what is achievable versus level of investment and to build trust with stakeholders on the current state of maturity of the company or project portfolio. However, quantitative benchmarking of mine water use within the mining industry has been difficult to achieve given the integrated nature of mines with their environments as opposed to other industry where systems are less integrated. Also, the number of factors affecting mine water benchmarking is substantial, and it is therefore not meaningful to compare all mines with one another. With this in mind, we have developed an innovative methodology to undertake meaningful quantitative benchmarking making use of publicly available information and industry understanding which compares mines of technical similarity in terms of mine water metrics.

This paper will focus on the use of this benchmarking data, the factors to consider in the interpretation of publicly available water data, along with the limitations of such a benchmarking exercise. Relevant examples will be discussed to demonstrate the value of and potential use of the benchmarking outcomes.

This tested quantitative benchmarking methodology has been developed to allow mining companies to use benchmarking in a way that is meaningful to their planning and investment processes, reporting, and stakeholder engagement. It can be used to guide executives in setting company commitments as well as to provide the basis for project level investment decisions to execute projects aligned with those commitments. And finally, it can be used to support building trust with project stakeholders and communities when reporting on progress and making future commitments, satisfying ESG commitments and avoiding claims of greenwashing.

Two pit lakes formed in mine pits in an arid region. To estimate potential future pit lake water quality composition, and given uncertainties and data gaps in the dataset, eight scenarios were modelled for each pit lake using end-member input for the most-sensitive and least-understood input parameters. Key inputs were the hydraulic conductivity of the aquifer, and the acidity of pit wall runoff. In all but one scenario, both pit lakes remained circumneutral, but water quality is unlikely to meet water quality standards in any scenario because arsenic exceeds the agricultural use standard. The estimates were used to prioritize field programs to reduce uncertainty.

Water is an important factor in the stability of large mine slopes. Groundwater pressure on a potential failure surface in a slope reduces the effective stress on that surface, which reduces frictional strength of that surface and the Factor of Safety of the slope by as much as 40%. This effect is normally considered in standard slope stability analyses. However, water pressure acting on the surface of a potential failure mass also exerts a lateral driving force, which in saturated slopes generally exceeds the gravitational driving force, and results in a further reduction of the Factor of Safety of more than 50%. This water-drive is rarely correctly considered in standard slope stability analyses. For slopes that can have positive groundwater pressure within them, ignoring water-drive leads to dangerously under-estimating the likelihood of failure. This paper presents the theoretical basis for including water-drive in slope stability analyses, quantifies the magnitude of the failure risk that is introduced by water drive, and provides stabilization strategies that manage those risks.

With the closure of several dams, tailings disposal in dry stacks has become a management challenge from both geotechnical and environmental perspectives. One key concern is the quality of the effluents generated by these new structures. It is crucial to predict the chemical composition of the drainage that will pass through the bottom drains and eventually be discharged into the environment. Leading global guidelines and best practices for effluent management in mining (e.g., MEND, AMIRA, INAP) recommend conducting predictive studies of chemical concentrations before constructing tailings containment structures, including dry stacks. Additionally, the Global Industry Standard on Tailings Management (GISTM) advises multidisciplinary studies encompassing geochemistry, water quality, hydrology, and geotechnics, among other fields.

In this context, the objective of this study is to assess potential changes in the chemical composition of effluents resulting from the mixing of iron ore tailings with lime. This mixture aims to reduce the moisture content of filtered tailings and improve the geotechnical stability of dry stacks. However, it is essential to evaluate the environmental and hydrogeochemical implications of this strategy.

The study was conducted during the conceptual phase of the project, aligning with best environmental practices. The methodology combined laboratory testing with hydrogeochemical numerical modeling to predict the long-term behavior of the tailings-lime mixture. Laboratory tests included static and kinetic drainage prediction, as well as chemical and mineralogical analyses of pure iron ore tailings and tailings mixed with lime in varying proportions. Hydrogeochemical modeling was performed using the PHREEQC software to simulate the deposition of the material in a dry stack, considering scaling factors, rainwater percolation, hydrogeology, and partial gas pressure. The laboratory results revealed that mixing iron ore tailings with lime generates an alkaline pH, which promotes silicate dissolution and the formation of neoformed minerals through pozzolanic reactions. Additionally, kinetic tests showed that the alkaline conditions favor the release of metals into solution, which would otherwise remain relatively inert under neutral pH.

The numerical modeling indicates that calcium carbonate precipitation may occur under atmospheric exposure, potentially creating low-permeability zones and preferential flow paths within the dry stack structure. These factors should be carefully considered in geotechnical designs. This study highlights key factors related to effluent quality and environmental impacts that must be addressed in projects involving the mixing of iron ore tailings with lime.

Tailings Management Facilities may pose a significant risk to downgradient surface water and groundwater environments. Evaluating the risks these facilities present to water resources is pivotal during mine closure. This paper discusses the use of probabilistic simulation within quantitative analytical models to evaluate these risks, especially in scenarios where limited environmental data may undermine confidence in the predictive outcomes.

The application of probabilistic modelling will be demonstrated through case studies that utilise probabilistic risk assessment to evaluate various closure and remediation strategies for a tailings management facility, as well as to quantify uncertainty levels in risk assessments. The paper will consider the impact of different liner and cover systems and the importance of considering tailings management facility holistically recognising that factors such as closure landform and cover design are as integral to mitigating risk as basal liner design.

Brumadinho and Samarco Mariana tailings storage facilities (TSF) failures in Brazil caused deaths and environmental damage, prompting the Global Industry Standard on Tailings Management (GISTM) in 2020. The International Council on Mining and Metal (ICMM) required members to disclose information on extreme and very high consequence TSFs by 2023 and all TSFs by 2025. This study analyses the integrated knowledge base developed for 56 TSFs across various geographies and commodities, assessing data sufficiency across 25 water topics. Despite generally high compliance, systematic gaps exist globally. The findings are relevant to mining companies, environmental professionals and the ICMM for GISTM compliance.

The Salave Gold Prospect is the largest unexploited and well-known gold deposit on the Iberian Peninsula (measured resources are more than 1 Moz Au at 4.6 g Au/t). It is located in NW Spain, 2 km E of the village of Tapia de Casariego, about 500 m far from the coastline, in the Bay of Biscay. It is an intrusion-related gold deposit, hosted by a Hercynian-age granodiorite (330-287 My), in which gold occurs almost exclusively as refractory and invisible, mainly within the arsenopyrite crystal structure. Although there are appreciable quantities of other metallic sulfides, the main species are pyrite, arsenopyrite, stibnite and molybdenite. This project -currently immerse in the administrative processing phase- is envisioned to be exclusively developed by underground mining. The final product, in order to avoid in situ cyanide employment, is a sulfide concentrate obtained by gravity and flotation.
The flotation tailings obtained in the bench scale and pilot testing (carried out on well mineralized core intervals), are mainly composed by plagioclase, mica, K-feldspar group species and some quartz. They also contain 0.1% of sulfides, mostly arsenopyrite, pyrite and stibnite. Although they will be used in the backfill of the underground workings, it is expected that approximately 2 Mt of these tailings will have to be allocated in an excavated and isolated dam. In order to optimize the long-term behaviour of the tailings deposit, some laboratory studies have been carried out: different mixtures of lime, blast furnace slag, Portland cement and limestone filler were tested to immobilize, from a geochemical point of view, some metal(loid)s and sulfates. The leachability tests were carried out in accordance with European Standards EN-12457:4 (dynamic leaching) and EN-15863 (static leaching).
The mixture formed by 5% of Portland cement, 5% of lime and 1% of limestone filler achieved a reduction in permeability (when compared to the untreated tailings) of more than 90%. The reductions accomplished (after 28 days of setting) in the leachability of As and Sb are 98.37% and 87.23% respectively. For sulfate leachability, the reduction is complete. Although the present work is focused on the behaviour of As, Sb and sulfate, satisfactory results have also been achieved for some of the other metals analysed; Pb is the only one that has shown an erratic behaviour.
Flotation tailings derived from mineral deposits that fit into the intrusion-related gold systems can be expected to behave in a similar way.

In the Iberian Pyritic Belt (IPB), Hg-sulfides, often found in association with massive metal-sulfides, are responsible for generating Hg-rich fluxes of AMD that represents a potential focus related to water quality degradation. This study aims to monitor the spatial and temporal behavior of Hg in the watercourses drained by a huge pile of mining wastes at Caveira Mine (SW Portugal), and to test the most effective technology in retaining Hg.

Water from the watercourses were collected in two consecutive years (2022-2023). Total-Mercury was determined in samples using a mercury analyzer (NIC MA-3000). The sample with highest levels, was selected for laboratory-scale tests to evaluate the effectiveness of some nature-based materials (powders of carbonate rocks, terra rossa, iron oxides, clays, cellulose residues, acacia biochar, activated carbon from coconut shell), to be applied in the upstream sectors of the watercourses, to restore the quality of the hydrographic network.

The Hg levels in the water of consecutive years followed an identical pattern, with major values in areas near the tailings (2022: 16-18µgg^-1, 2023: 26-28µgg^-1), above the reference value, 0.3µgg^-1 (EU Regulation, 2009). The retention capacity of materials in relation to Hg, was determined by analyzing the ionic exchange capacity, kinetic tests (Hg-solution at pH5.5) and simulation of “ponds” containing different proportions of materials vs. mining water. While cellulose, limestone and marble powders were most effective in raising the water pH, increasing from pH1.56 to 6.6 after 7 days of contact, activated carbon showed the greatest retention capacity, retaining 99.99% of Hg after 15 minutes of contact with the synthetic Hg-solution, followed by bentonitic clay and cellulose. Analysis of Hg in the water from the “ponds” test, where mining water was used in its natural state, showed a greater efficiency in reducing the original levels (461µgg¹) for limestone, marble, activated carbon and cellulose (2µgg¹-3µgg¹). The slight difference observed is due to: (1) some materials increased the water pH when in contact, while others did not (e.g. activated carbon) and (2) chemical competition at the adsorption sites of materials between Hg and other elements also present in excess (As-Fe-Cu-Zn-Pb).

The remediation technologies should be applied in areas where the AMD flows, before entering the streams, following two stages (1) pond with a cellulose bottom, limestone or marble powders to increase pH, (2) new pond or reactive barrier with activated carbon to retain the Hg that has not precipitated with Fe-oxides in stage 1.

Acid mine drainage (AMD) derived from the oxidation of sulfide has become a major environmental issue facing the global mining industry. AMD can be highly acidic, rich in sulfates and metals, and poses long-term, large-scale pollution, with its treatment being complex, costly, and challenging. Although various remediation technologies have been proposed, high operational costs associated with large-scale applications warrant further development of low-cost, sustainable AMD treatment technologies.

This study proposes a novel method for preparing multifunctional remediation materials using natural attapulgite and industrial by-product (alkaline residues). These materials were applied to improve the filler in constructed wetlands (CWs), substantially enhancing the performance and stability of the wetland system in treating AMD. Additionally, through in-situ mineralization, this study not only effectively reduced pollution levels but also explored the resource utilization of AMD, contributing positively to the development of sustainable remediation concepts.

Compared to traditional CWs, those filled with the attapulgite-alkaline residue composites demonstrated a 30% improvement in sulfate removal and a 10-70% increase in the removal of metal ions such as iron, manganese, copper, zinc, cadmium, and lead. These metal ions were primarily retained in stable forms within the wetland filler, such as carbonate-, Fe/Mn (oxide) hydroxides-, and sulfides-bound forms. Moreover, the composites mitigated the adverse effects of AMD on wetland plants and microbial communities. Notably, the abundance of sulfate-reducing bacteria (such as Thermodesulfovibrionia and Desulfobacca) were increased, promoting the formation of metal sulfides on the surface of the composites. This allowed the saturated composite to regenerate and continue capturing metal ions. The synergy between adsorption by the composites and microbial sulfate reduction enabled the CW system to maintain long-term, efficient, and stable operation. While AMD is a major pollution source, it is also a potential resource for metals and sulfates. This study utilized sulfates and metal ions from field AMD to generate layered double hydroxides (LDHs) in-situ, effectively promoting the direct fixation of arsenic and antimony in AMD. Additionally, the study revealed the formation mechanism of arsenic- and antimony-loaded LDHs and their competitive effects on LDH surfaces.

Overall, the research demonstrates that integrating low-cost, sustainable materials with advanced treatment strategies can offer a viable pathway for the green and sustainable management of AMD. This approach could have broad applications in the mining industry, especially in regions facing severe environmental impacts from AMD, and could also be extended to other industrial wastewater treatment scenarios.

The significant costs involved in Acid Mine Drainage (AMD) remediation have led to a search for low-cost liming alternatives. The cost-effectiveness of concrete, which has enabled it to be the most dominant construction material, can be tapped into to provide an economic passive treatment for AMD. Laboratory Investigations on the use of pervious concrete (PERVC) have shown that PERVC is an effective treatment method for AMD. However, no pilot studies have been conducted on PERVC.

The aim of the study was to design and evaluate the application of a PERVC permeable barrier system for the remediation of AMD at an abandoned coal mine site. Furthermore, the study aimed to show that PERVC can effectively treat polluted mine water to meet the national limits applicable to wastewater discharge into a water resource. The PERVC pilot plant comprised a gravel pre-treatment zone (PTZ) overlying a PERVC reactive barrier zone. A 2000L precast tank was used as a distribution tank for the AMD. From the gravel PTZ, the AMD seeped below onto a PERVC bed for treatment. Thereafter, the treated AMD went into a collection chamber. The concentrations of Na, Mg, K, Ca, Cr, Mn, Fe, Co, Cd, Pb, Ni, Cu, Zn, and Al were determined using the Avio 200 Inductively Coupled Plasma Optical Emission Spectrometer. The concentration of SO₄ was determined using the Aquakem 250 Discrete Analyser. The temperature (T), pH, electrical conductivity (EC), and total dissolved solids (TDS), were recorded using a Hanna Combo pH/Conductivity/TDS Tester. Pervious concrete samples were analysed using the Pan Analytical X-X’pert PRO X-Ray diffractometer (XRD) and the ZEISS EVO Scanning Electron Microscope to identify mineral phases formed before and after exposure to the AMD.

The results showed that following treatment with PERVC, the pH increased from 2.6 to 12. Al, Fe, Zn, Ni, Co, Cu, and Mn were effectively removed from the mine water with efficiency levels of 98% to 100% within 24h of the experiment. Throughout the two years of monitoring, all pollution indicators showed significantly lower values than the South African limits for pollutant discharge into a water resource. Precipitation of heavy metals with an increase in pH, along with their possible adsorption onto calcium silicate hydrate, are the primary mechanisms for heavy metal removal by PERVC.

The successful demonstration of the PERVC treatment system offers a low-cost technology for polluted mine waters that can be marketed to the mining industry for practical implementation.

Mine closure has become an integral part of mine planning in order to mitigate post-closure financial, social and environmental risks to ensure the sustainable closure of mines. Including mine closure considerations into short and long-term mine planning reduces the end of life of mine closure liabilities. Open cast mining activities will ultimately result in a final mine void which, over time, fills with water and forms a pitlake. Pitlakes are becoming increasingly more acceptable forms of mine closure, provided that long term environmental risks can be mitigated. In addition, pitlakes may negate rehabilitation costs associated with backfilling of the final mine void, potential long term water treatment costs and associated carbon emissions.

The paper discusses case studies for mine closure using pitlakes in coal, diamond, manganese and chrome mines in South Africa.

Asturias was historically the second largest producer of mercury in Spain, following Almadén, and by the end of the 1960s, it accounted for 5% of the world’s mercury production. However, a sharp decline in mercury prices led to the gradual closure of all the mines, with the last one, La Soterraña, ceasing operations in 1974. This intense mining activity has left numerous remains of old mines scattered throughout the region, including mine entrances, dumps, piles, and abandoned installations. In the specific case of mercury mines, most of these sites are classified as ‘orphan mines’ due to their abandonment.

It can be observed that virtually all mercury mineralisations in Asturias exhibit a significant geochemical anomaly for arsenic. This element was also historically exploited as a by-product, resulting in the contamination of the tailings. These mines currently present a considerable environmental concern due to the aforementioned contamination. In this study, geochemical modelling was employed as an effective tool to predict the distribution of species in water, primarily focusing on arsenic, and to identify potential arsenic precipitation phases.

The distribution of these deposits is categorised into four districts: Somiedo, Central Carboniferous Basin, Beleño-Ribadesella, and Picos de Europa. With the exception of the deposits in the latter district, which possess distinctive characteristics, the genesis and characteristics of all the deposits are similar. They are associated with fractures, folds, and thrusts affecting Paleozoic materials and are embedded in carbonate materials.

The combination of geochemical modelling and meteorological analysis provides a deeper understanding of the mechanisms behind arsenic mobilisation, which is crucial for the design of effective decontamination strategies. The processes that govern arsenic distribution and precipitation can be better understood by elucidating these mechanisms by this study, contributing to the development of effective remediation efforts aimed at mitigating the environmental impact of historical mining activities in Asturias. The insights gained from this research are essential for informing future policies and practices in environmental management and mine reclamation

Mining has been a traditional economic activity in the province of Córdoba, in the north of Colombia, representing in average 1.83% GDP of the region and producing over US$4.920 million in annual royalties for the country. Nickel, coal, gold, limestone, clays and building materials are resourced, and there are great expectations to produce copper. It faces, however, critical environmental challenges, particularly in water management, due to inadequate regulatory frameworks and the rise of informal mining activities. This study analyzes environmental licenses issued in Córdoba over the past two years by the regional environmental bodies, focusing on coal and building materials extraction, to assess compliance with national and international standards. The findings reveal significant gaps in Colombia’s regulatory framework, especially in water management, compared to global best practices outlined by organizations such as the International Council on Mining and Metals (ICMM) and the Asia-Pacific Economic Cooperation (APEC).

Key deficiencies include the lack of detailed strategies for water resource monitoring, prevention of acid mine drainage (AMD), and long-term water quality protection. Current closure plans often fail to incorporate site-specific water monitoring, such as tracking pH levels, heavy metal concentrations, and total dissolved solids, which are crucial for early contamination detection. Additionally, the absence of robust financial assurances and climate change adaptation measures further exacerbate the risks of long-term environmental liabilities.

The study highlights the need for Colombia to align its regulatory framework with international standards, emphasizing integrated water management, stakeholder engagement, and post-closure monitoring. Addressing these gaps is essential for ensuring sustainable mining practices, mitigating environmental and social risks, and safeguarding water resources in mining regions like Córdoba. The findings underscore the importance of adopting global best practices to enhance environmental stewardship and achieve long-term ecological rehabilitation in Colombia’s mining sector.

Keywords: Mine closure practices, water management, community engagement, socioeconomic effects, Colombia.

Uncertainty means a lack of knowledge. No matter how much information is available, data are always limited since available information sets are constrained in space and time. In groundwater-related studies, it is often assumed that uncertainty can be compensated by simple parameter uncertainty analysis (sensitivity analysis, stochastic simulations, fuzzy arithmetic). However, in the real world, the total uncertainty of a system is controlled by additional sources, like data, conceptual models, design uncertainty, uncertainty related to the selection of modelling tools, and human behaviour. This presentation intends to address these additional sources of uncertainty by using the theory of system analysis.

Beyond the parametrisation of a groundwater system which is inherently non-unique, it is even more critical to fully understand the system`s key characteristics. A false conceptualisation cannot be compensated with the assessment of parameter uncertainty. However, conceptualisation is sometimes subjective, heavily reliant on previous experience and usually non-unique just like system parametrisation. Therefore, a method is required to manage uncertainty associated with the “lack of knowledge” in conceptualisation and with any other potential sources of uncertainty. The nuclear industry has developed the method of features-events-processes method (FEP catalogues) to manage this kind of conceptual uncertainties, and it is a robust, transparent, comprehensive and clear way to develop base case and alternative scenarios which may form the basis of quantitative predictions. However, this method is not used in mining projects to its fullest potential.

In this presentation, the theory of system analysis will be presented with the theoretical and pragmatic limitations of hydrogeological knowledge. The method of system analysis is applied at several mine sites, especially to assess potential risks in post-closure phases. This approach can be used to list all features, events and process affecting a mine groundwater system and their interaction to assess all potential evolution pathway of a mining activity, and the way to develop most likely (base-case) and a set of alternative scenarios. Also, it will be demonstrated how this approach compares with the traditional approach where conceptualisation relies on one single, deterministic model.

It is shown that system analysis may result in several benefits in mine water management:

• Consideration of all sources of uncertainty with potential effect on the groundwater system.
• Finding optimal project design and ranking alternative scenarios.
• Reduced project risks and preparation for hydrogeological “surprises” and for alternative system evolution pathways.
• Cost benefits.
• Meeting regulatory requirements.

Dissolved organic matter (DOM) has been confirmed to be one of the important factors affecting the migration and transformation of antimony (Sb) in the aquatic environment. Studies have shown that terrestrial organic matter with strong aromaticity in natural water in mining areas may be an important carrier of antimony migration. However, the characteristics of DOM and its impact on the migration and enrichment behavior of Sb are still unclear at the molecular level.

In this study, we combined hydrogeochemistry with optical (Excitation-Emission-Matrix Spectra, EEMs) and molecular characteristics (Fourier transform ion cyclotron resonance mass spectrometry, FT-ICR MS) of DOM to characterize the source and molecular composition of DOM in water environment in the antimony mining area and its influence mechanism on antimony migration and enrichment.

We identified three DOM fluorescent components, a tryptophan protein component (C2) and two terrestrial humus-like components (C1 and C3). The humus-like components in groundwater had a higher degree of unsaturation, while there might be a degradation process of C3 to C1 and C2 in surface water. Antimony in groundwater was positively correlated with non-bioactive compounds that were difficult to degrade, such as unsaturated compounds, polyphenols, and polycyclic aromatic, corresponding to C3 humus-like components. They were mainly composed of compounds containing N and S. In addition, CHON and CHO compounds were more conducive to the enrichment of Sb in groundwater than CHOS. Antimony in surface water was positively correlated with easily photodegradable compounds such as lignin and lipid structures, which was consistent with the changes in the C1 components of photolysis products along the stream. Accordingly, complexation was considered to be an important mechanism for the enrichment of antimony in dissolved organic matter in water environments. Non-biologically active compounds and organic matter photodegradation products were important complexing species. At the same time, there was fluorescence quenching after the protein-like components bind to antimony. In addition, organic matters containing O and N functional groups were easier to combine with antimony than organic matters containing S functional groups.

The results of this study provided new insights into the mechanism by which DOM affects the migration and transformation of Sb in aquatic environments at the molecular level. That will improve the biogeochemical process of antimony, and lay a theoretical foundation for the prevention and control of antimony pollution in mining areas.

As the ' antimony capital of the world ', the continuous mining activities have caused the increase of antimony content in the groundwater environment, which is widely distributed in the environment and can carry out long-distance migration. The toxicity and migration process of antimony are closely related to its valence state in the environment. Sulfate is an important factor affecting the valence state transformation of antimony. It is of great significance to study the influence mechanism of sulfate on the migration and transformation of antimony.

In this study, Xikuangshan in Hunan Province was taken as the research area. The interaction process between atmospheric precipitation and surface water and groundwater was analyzed by sulfur and oxygen isotopes, and the sulfate composition in groundwater system was identified. Combined with the valence state analysis of antimony, the influence of sulfate on the migration and transformation process of antimony was further explored.

Isotope analysis of groundwater in different lithology shows that the contribution rate of rock salt dissolution in limestone aquifer is 37.6%, while that in argillaceous limestone aquifer is 65.53%. When the concentration of sulfate increased, the Sb(III)/Sb(total) increased from 2.39% to 88.63 %, indicating that sulfate could inhibit the conversion of Sb(III) to Sb(V), or in the process of sulfate reduction, sulfide reduced Sb(V) to Sb(III). Compared with surface water in winter and summer, it was found that the fluctuation of antimony valence state in summer was more intense in response to sulfate concentration, indicating that sulfate may have microbial effects on the influence of antimony valence state. When the sulfate concentration is low, the antimony concentration is 206.55μg/L, and the antimony concentration is 161.69μg/L when the sulfate concentration is high, indicating that Sb(V) is easier to migrate than Sb(III). Further study of the effect of sulfate sources on antimony found that Sb(III)/Sb(V) was 91.91 % and 59.28 %, respectively, at high endogenous sulfate concentration and high exogenous sulfate concentration, indicating that endogenous sulfate has a more thorough effect on valence state.

The sulfate reduction process can change the valence state composition of antimony in the water and soil environment. By controlling the exogenous sulfate input of groundwater in the contaminated area, it can drive the conversion of pentavalent antimony to trivalent antimony. This discovery provides new ideas and possibilities for the prevention and control of antimony pollution in groundwater.

The development of waste rock dumps closure projects in Peru is substantially based on physical and chemical criteria, which prioritise the stability of the component, leaving aside other important aspects such as biological, vegetative and landscape adaptation.

Since 2021, Compañía de Minas Buenaventura, owner of the Santa Bárbara mining environmental liability located in the department of Huancavelica - Peru (which was one of the first gold and silver mines exploited by the Spanish conquistadors upon their arrival in America), commissioned Amphos 21 to develop basic and engineering studies for the design of a closure project for three waste rock dumps and an open pit. Thus, the unification of these deposits was proposed under a new geomorphological restoration approach, which allowed a complete change from the regulatory closure approach to one that was more compatible with the natural environment.

The most outstanding feature of this pioneering and innovative project is that it is not necessary to use concrete channels for surface water management; an organic soil cover layer was designed that varies in thickness depending on the slopes generated, accompanied by native high Andean species. This will result in lower post-closure maintenance costs and lower socio-environmental risks associated with these types of components.

The construction of this project demonstrated that we still have many challenges in Peru to introduce innovative models and new criteria to approach the closure of mining environmental liabilities and existing operations. The successful implementation of this project is feeding a new way of approaching closure from the perspective of sustainability, ensuring that the quality of the designs and their execution are durable, sustainable and perfectly integrated into the environmental and social environment. In this case, the articulation with the Buenaventura tourism project and the regional government, make this geomorphological restoration an important point in the company's closure strategy.

Tailing storage facilities (TSF) can have detrimental environmental consequences in their surroundings, in the hydrogeological field this happens particularly when water from the tailings infiltrate into groundwater. Even with the current technologies and evolution on tailing deposition, infiltration is expected to occur in most of the cases, and its detection represent a challenge for the operation as this process is influenced by unsaturated properties and behavior of the soil foundation that are hard to characterize and is not usually under monitoring.

This study addresses the critical challenge of understanding and managing the evolution of infiltration plumes from a specific TSF that has been under study since 2016. By employing geophysical methods, we provide an approach to assess the spatial extent and temporal dynamics of the infiltration from tailings. In this study case geoelectric methods (NanoTEM and electrical resistivity tomography) are utilized to characterize the subsurface identifying anomalies that are indicative of infiltration. These techniques offer considerable advantages over traditional monitoring methods, as they provide high-resolution data without the need for intrusive sampling, and through repeated surveys it is possible to capture the temporal evolution of the infiltration plume, revealing its migration pathways and potential effects on groundwater quality.

Our findings demonstrate the effectiveness of geophysical methods in delineating the spatial extent of the infiltration plume, identifying areas of high contaminant concentration, and assessing the potential for groundwater contamination. Moreover, the temporal analysis of the data provides valuable insights into the rate of contaminant migration and the effectiveness of mitigation measures, or after this analysis new methods or locations to control the increase of the infiltration area could be suggested.

The results of this study have important implications for the management of the TSF. By providing a comprehensive understanding of infiltration dynamics, it is possible to develop more effective strategies for preventing and mitigating groundwater contamination risks. Furthermore, the geophysical methods employed in this research offer a valuable tool for environmental monitoring and assessment.

The Environmental Qualification Resolution contemplates the monitoring of the presence and quality of groundwater downstream of the High Density Thickened Tailings (HDTT) in five monitoring wells, which are compared to process water and tailings water to identify possible infiltrations from the tailings. The monitoring well in the embankment is called MW-1 and it began to be sampled and measured in 2020. During the environmental follow-up monitoring in 2022, unexpected concentrations of certain elements were detected in the water of well MW-1, so additional studies were developed to determine if they corresponded to specific data or a trend.

In this context, geophysics was carried out to determine the origin and destination of a local infiltration in the west abutment of the embankment, specifically, through a canalization structure. Therefore, an engineering solution was implemented which consisted of the installation of a system with auxiliary drains. It was confirmed that the reported soil moisture was coming from the canalization as indicated by geophysics. Nevertheless, the field campaign continued in 2023 along with new geophysical profiles and monitoring piezometers. According to the fieldwork observations, there was a high certainty that the measurement implemented through the drains eliminated the infiltration identify in the west abutment, but it was unsure if it was related to the MW-1 results. It was proposed to perform additional fieldwork in 2024 consisting of the construction of three wells and repeating the previous geophysical profiles.

According to the interpretation of the results, high conductivity horizons were likely associated to fine grain material and/or to infiltrations recognized in the unsaturated zone (UZ). The infiltration in the drainage system in the embankment area that reached the monitoring well MW-1 was controlled in the UZ at least, given that the UZ was found to be dry. However, there might be other infiltration paths that explain the on-going unexpected values on monitoring well MW-1.

The application of an integrated hydrogeological fieldwork campaign design has proven to be helpful to identify sources of infiltrations associated with a HDTT deposit. In this case the campaign consisted in the construction of wells screened at different depths, combined with additional hydrochemistry and isotopical information obtained from the new wells has been helpful to analyzed, complement and validate the previous assumptions.

This study focuses on an abandoned tailings deposit from 1978, located on the suburb of Santiago, Chile, with insufficient mitigation measures. The tailings dam is located on the banks of the Mapocho River, the main river of the city, and less than 60 meters from a residential area, constituting a potential threat to both the environment and public health. The tailing drains directly into Mapocho River, affecting the fluvial ecosystem. Technical reports affirm the deposit partially collapsed in 1987 due to a flood of Mapocho River, releasing approximately 400,000m³ into the river and flood plains. This copper tailing deposit contains potentially toxic elements (PTEs) and exhibits potential acid drainage generation, as stated in technical evaluations. Considering the associated risks, understanding tailings accumulation zones along the river is essential.

The primary aim of this research is to study the downstream dispersion of collapsed tailings material along the river and to assess the geochemical stability of these materials. A photogeomorphological map and DEM of the area were created to identify points of tailings accumulation. Trial pits were excavated at different depths (0.15 to 2m) at several locations downstream, where samples of tailings and sediments were collected. Currently, the work is underway on granulometric measurements, geochemistry, and mineralogy of the samples. Additionally, a hydraulic sediment transport model is being implemented to evaluate areas of erosion and deposition, which will facilitate further investigation of accumulated tailings material.

Preliminary results indicate presence of oxidised tailings remnants in the surrounding area of the collapse. The tailings material displays strata in yellowish-brown, and grey hues, with a grain size predominantly comprising sands. The paste pH results ranged between 1.8-4, indicating the material has the potential to generate acid drainage. The chemical analyses revealed concentrations of Cu and Fe that exceed environmental sediment quality guidelines. Regarding the dispersed material, geomorphological analysis suggested the existence of a tailing accumulation zone on a lateral bar of the river, which was validated through a trial pit where two levels of tailings were recorded, one of them exceeding 1m in thickness at 0.8m depth.

The results indicates that tailings material has been transported and deposited in fluvial bars and floodplains, which are neither monitored nor remediated, thereby posing ecological and agricultural risks downstream. The integration of geological and hydraulic methodologies has proven effective in assessing the transport and fate of the collapsed tailings, offering replicable tools for similar case studies in Chile.

Gold mining in Colombia is a widespread industry, with operations occurring in over 15 departments and nearly 100 municipalities. In the department of Antioquia, gold mining activities are particularly prevalent in the sub-regions of Bajo Cauca and Nordeste, which collectively account for the majority of the department's gold production, making Antioquia the leading gold producer at the national level.

This research was conducted through a collaborative effort between the National University of Colombia and the University of Oviedo in Spain, utilizing materials from the "El Molino" beneficiation plant located in the municipality of Andes in the department of Antioquia. Here, the stark contrast between the gold mining operations and the surrounding agricultural landscape and coffee plantations is evident. Mining activities generate tailings composed of silica-rich crushed rock combined with processing fluids, resulting in the formation of contaminants.

In this study, gold mining sands containing refractory minerals were employed for the manufacture of clinker. The research proposed a comprehensive methodology to optimise the utilisation of these wastes, which included three primary objectives: firstly, to identify the parameters of mining waste that affect clinker manufacture; secondly, to determine the appropriate raw material proportions using Bogue's moduli; and thirdly, to compare the mechanical performance of cement produced from mining waste with that of conventional Portland cement.

The obtained results indicated that thermal pre-treatment is a crucial step in effectively reducing contaminants. However, the particle size required for an efficient reaction of silica requires a significant energy input, even though the energy consumption involved is considerably lower than would be necessary for these wastes to degrade naturally over an extended period of time The study emphasises the necessity of optimising the utilisation of waste materials, not only to enhance the efficiency of clinker production but also to mitigate the environmental impact of mining activities. The conversion of mining waste into valuable raw materials for cement production represents a significant step towards the development of more sustainable and environmentally friendly industrial practices. The results demonstrate the potential of novel approaches to waste management in the mining industry, which could lead to economic and environmental benefits.

Environmental remediation of legacy mining sites in Portugal has been done since 2001 by EDM - Empresa de Desenvolvimento Mineiro, a state-owned company, including radioactive and sulfide polymetallic mines. One of the main focuses of the remediation design projects is the control and treatment of mine water using combined active and passive treatment systems. This paper presents the mine water treatment processes and monitoring that are implemented at Urgeiriça uranium legacy site. The treatment system is divided into two lines, active treatment and passive treatment. The active treatment includes pH neutralization with calcium hydroxide and addition of barium chloride followed by and sedimentation for solid-liquid separation. The secondary passive treatment system, includes several steps such as aeration, sedimentation, filtration in adsorbent media and phytoremediation in aerobic wetlands. Both systems are monitored before, in the intermediate steps and at the end of the treatment, and the water quality control programme includes in situ parameters (pH, electrical conductivity, temperature, redox potential, total dissolved solids and flow rate) and laboratory analysis of chemical and radiological parameters as total uranium, U238, U234, Ra-226, sulphates, chlorides, manganese, calcium and sodium. These elements were identified in previous studies as the best indicators of hydrogeochemical contamination related to the legacy uranium mining sites in Centro Region, Portugal. This paper will present an overview on the evolution of the mine water quality and treated volume since 2001, including a critical assessment on the effects of the implementation of the remediation of two tailings dams, waste rock piles, uranium mill and other affected areas in the Urgeiriça legacy mining site and the resulting water quality improvement, specific removal efficiency rates and compliance with regulatory limits for water discharge. Also, it will present the quantities of used chemical reagents and operation and maintenance costs of mine water treatment and how these processes can be further optimized.

In a small-scale column leaching study, treating pyritic waste rocks with silica (SiO2) proved suitable for preventing Acid Mine Drainage (AMD) formation by chemically passivating pyrite surfaces and maintaining the leachate pH at a circumneutral level. Aligned with the circular economy initiative and to ensure economic feasibility, treating pyritic waste rock to prevent AMD in the future should utilize readily available silica-bearing industrial residues as a potential source of dissolved Si.

However, preventing AMD by silica treatment on pyritic waste rock using industrial waste streams as a source for dissolved Si has yet to garner attention in previous research. Therefore, in this study, we will test several waste stream samples from extractive industries at various pH conditions to find the most optimum conditions to enhance their dissolution to leach out the silica and alkalinity. A batch leaching test will be conducted on several materials, i.e., waste rock containing a substantial amount of reactive silicate minerals (clays and micas), silicate-bearing desulfurized tailing, and siliceous slag. The materials will be tested at various experimental conditions, i.e., different pH levels and redox conditions, and as a mixture. Slag will be added to waste rock in a small proportion to achieve an alkaline pH. The leaching will also be conducted in an acidic pH environment to allow an acid-consuming reaction of the silicate phases, releasing silica and alkalinity.

Batch leaching using milli-Q water at circumneutral pH resulted in a low release of Si from these materials (i.e., 9 mg/L Si from the tailing, 9.6 mg/L Si from air-granulated slag, and 2.5 mg/L Si from water-granulated slag at a liquid-to-solid ratio 2:1) and an overall very low leachability of Si, despite the large surface area of the tested materials. Due to the unsatisfactory yield, we will test the leaching at various pH ranges to maximize the release of alkalinity and silica, promoting the silica precipitation on pyrite to control AMD.

This study contributes to solving environmental issues in mine waste management and AMD prevention using a novel method, i.e., chemical passivation. We will present more detailed results of our experiments, including batch leaching test results (i.e., physical parameters and chemistry of the leachates), solid phase analyses using Scanning Electron Microscopy (SEM), and implications will be discussed.

Carbonate aggregates such as limestone are commonly used in passive mine water treatment systems to neutralize acidity and generate alkalinity to remove metals. The service life of the aggregate is typically limited by the accumulation of metals solids which decreases both permeability and reactivity of the aggregate. These decreases normally occur well before the neutralizing capacity of the aggregate is depleted. Carbonate aggregate treatment effectiveness can be restored at lower cost than replacement through mechanical cleaning of the aggregate to remove the metals solids.

Carbonate aggregate cleaning methods can be divided into three general categories: mixing, pushing, and screening. The mixing and pushing methods utilize equipment to agitate the aggregate within the treatment cell to dislodge solids. The screening methods used specialized equipment to separate metals solids from cleaned aggregate outside the treatment cell.

To determine which carbonate aggregate cleaning method is most effective, five cleaning methods were evaluated by cleaning 16 oxic limestone beds in Pennsylvania, USA. All methods involve mechanically handling the aggregate to dislodge solids which are then carried away by flowing water to a detention pond. Short tern cleaning effectiveness was quantified by determine pre and post cleaning treatment effectiveness, alkalinity generation, porosity, and retention time. The composition of solids dislodged by the cleaning was also analyzed and the cleaning throughput per hour was estimated.

The evaluation found that all methods can effectively remove solids from the surfaces and pore spaces of the aggregate. The primary difference between the effectiveness of the methods was how much of the dislodged solids were removed from the treatment cell. The incomplete removal of solids has important implications for long-term operation as they will eventually require removal and disposal. While cost varied widely based on site characteristics, equipment availability, and local labor rates, in all cases the cost of cleaning aggregate was less than half of the cost of new aggregate.

Improvement of aggregate cleaning methods will lower operational costs for passive treatment systems and allow better prediction of long-term costs. Cleaning and reuse of existing aggregate also has lower environmental impact than removal and disposal of fouled aggregate followed by production, transport, and placement of new aggregate.

This work provided a promising methodology for removing iron ions and recovering copper ions from copper-containing AMD by incorporating the copper ions sulfide precipitation, iron ions biomineralization, and lime neutralization. The experimental results indicated that nearly all copper ions were removed in the sulfide precipitation process and 82.2% of iron ions were removed after biomineralization treatment. Additionally, the consumption of lime slurry was reduced compared to the conventional direct neutralization method. By integrating various techniques, it is possible to improve the removal efficiency of iron ions, reduce the consumption of lime, and recover the copper and sulfur from the AMD.

The contamination of water sources with potentially hazardous elements (PHEs), particularly in areas with active mining activities, represents a considerable risk to the environment and public health. The release of PHEs, including arsenic (As), lead (Pb), and cadmium (Cd), from both active and abandoned mines into surrounding water bodies has resulted in increased pollution levels and posed serious threats to ecosystems and human health. This study explores the potential of waste-derived carbohydrates as a viable and efficient material for passive plate heat exchanger removal from mining-impacted waters, with a preliminary case study involving arsenic.

Hydrochar, a carbonaceous material produced through the hydrothermal carbonisation of biomass, has demonstrated considerable promise due to the functionality-rich surface it exhibits, which facilitates the adsorption of various contaminants. This study examines the potential of hydrochar derived from a diverse range of biodegradable feedstocks, including unused woods, green waste, the organic fraction of municipal solid waste, grape bagasse, and other analogous materials, as a sustainable and effective material for the passive removal of PHEs from mining-influenced waters. The study places particular emphasis on a preliminary case study involving arsenic.

This study undertook a meticulous examination of the ability of hydrochars produced at a pilot scale to capture arsenic in its two prevalent forms, As(III) and As(V). This provided a comprehensive understanding of the material's adsorption capabilities. The adsorption process was subjected to detailed analysis in order to determine the efficiency and capacity of hydrochar in removing arsenic from contaminated water sources.

This preliminary assessment of arsenic behaviour during the adsorption process provides a robust foundation for further research into the effectiveness of hydrochar in conjunction with other PHEs. This places waste-derived hydrochar at the forefront of a versatile, cost-effective, and sustainable solution for both active remediation efforts and long-term passive systems, such as constructed wetlands or permeable reactive barriers, which are essential for mitigating the environmental impact of mining activities. The findings of this study indicate that hydrochar could play a pivotal role in developing innovative and sustainable strategies for water purification and environmental protection.

Large volumes of mine water need to be managed, or treated at great cost. However, many mine waters are suitable for irrigation, a consumptive use of water, and large tracts of rehabilitated land are often in close proximity to these water sources. In addition, off-site environmental impact of mine water irrigation may be expected to be less when irrigating rehabilitated land compared to unmined land, as return flows will report to old pit voids below irrigated fields. Furthermore, productively irrigating with suitable mine water on appropriately rehabilitated land will promote agricultural activity, improve food security and the livelihoods and well-being of surrounding local communities, thereby making an important contribution towards the Just Energy Transition. Guidance is needed on the characteristics of rehabilitated land that will make it irrigable, and not just arable.

Irrigation of rehabilitated land is a relatively new approach to mine water management, and no guidance is available on the requirements for rehabilitated land to be considered irrigable. Such guidelines are presented here.

Primary factors rendering rehabilitated land unsuitable for irrigation include inappropriate topography (surface drainage and erosion risk) micro-relief (subsidence), incorrect use of soil materials, compaction, poor surface infiltration and subsurface drainage, and insufficient rooting depth. Therefore, the focus of the guidelines is on physical properties that include hydrological position in the landscape, slope and micro-relief, and soil physical factors that affect infiltrability, permeability, water holding capacity and internal drainage. Although chemical limitations to crop production are important, these are more easily remedied than physical limitations, and are thus not considered as part of the irrigability assessment criteria. Guidance is given on the successful rehabilitation of open-cast mined land to irrigable standards, the assessment of the irrigation potential of such rehabilitated mine land, and the remediation of sub-optimal areas in such fields, should these be present.

The guidelines will support the rehabilitation of mined land to irrigable standard, assist with selection of areas of rehabilitation for irrigation, and provide guidance for the remediation of areas of rehabilitation that cannot currently be irrigated sustainably and profitably.

The right volume of water, at the right quality, at the right time is essential for sustaining both aquatic and riparian ecosystems. The same can be said of mining operations. However, mining activities can negatively affect water resources by degrading land, altering watercourses, and exposing water to ore and tailings. Surface water in West Africa is an essential resource for both natural systems and local communities affected by mining. To minimise environmental consequences and balance the mine’s water requirements with those of the surrounding environment, a comprehensive understanding of these competing needs was developed during the mine planning stage of this project.

The mining area is located between several watercourses, which transition from fresh water in the upper reaches to estuarine in the lower reaches, incorporating a complex combination of wetland, peat and mangrove habitats. Geochemical modelling undertaken indicated that acid rock drainage can be expected. This paper presents the multi-disciplinary approach adopted for the determination of the Ecological Flow requirements of the surrounding watercourses both in terms of water quantity and quality. A web of interdependencies between the individual specialist fields and the mine planning team was developed prior to project commencement. Roles and interdependencies were defined in an optimised, integrated approach. The focus was on the development of a dynamic, daily time-step model, in GoldSim, which integrated the mine water balance, salt balance, streamflow and in-stream water quality for the mine and the associated catchment. The model included a stochastic rainfall generator to enable probabilistic estimates of streamflow and mine water make, calibrated against flow and water quality data from the local environment and a similar local mining operation. The model was utilised as an interfacing tool between mine planning and the Ecological Flow teams, assessing mining scenarios and mitigation of environmental effects.

A holistic assessment facilitated the development of a balanced mine design that is expected to effectively mitigate the environmental effect on water resources to an acceptable level. Ecological Flow requirements for both water quantity and quality are therefore likely to be met. Concomitantly, the design supports the mine’s operational- and financial imperatives.

This study underscores the value of a detailed and integrated hydrological model in mine planning and the management of environmental effects on water resources. With a multi-disciplinary team, ongoing engagement and a co-operative relationship between the engineering and environmental teams, it is possible to achieve outcomes that satisfy both mining and environmental objectives.

Hydrogeological studies are essential during the exploration phase of mining operations to ensure sustainable water management, especially in the case of phosphate mining in Morocco, where the risks extend beyond water scarcity for mining operations to the management of significant volumes of water that at least partially or completely submerge phosphate layers, notably in the Beni Amir deposit, where high evaporation exacerbates water shortages.

By integrating geological, hydrogeological, and geophysical data into both two-dimensional and three-dimensional models, the study introduces a new approach for identifying both submerged and dry phosphate layers. This advancement addresses a critical knowledge gap regarding hydrogeological conditions in sedimentary rock mining regions, offering a novel tool for assessing and managing groundwater-related challenges. This modeling effort is particularly groundbreaking given the lack of research on hydrogeological processes in North African phosphate deposits, especially in complex mining environments.

The study followed a multi-step process. First, geological and hydrogeological data were collected and analyzed to develop a hydro-stratigraphic conceptual model, which detailed the interaction between phosphate layers and the water table. This model was based on data from 692 boreholes across the study area. A delineation map was then created to identify the saturated zones, where phosphate layers are submerged, as well as the dry areas. The findings showed that approximately 73% of the Beni Amir deposit is at least partially submerged by the aquifer, while the remaining 27% constitutes dry zones. These results guided the placement of geophysical profiles and surveys to refine the initial results and characterize water-bearing geological formations. This geophysical assessment helped determine hydrogeological parameters and quantify water content using a combination of Electrical Resistivity Tomography (ERT) and Magnetic Resonance Sounding (MRS).

The combined ERT and MRS results identified multiple aquifers within distinct geological formations. The Lutetian and Danian-Thanetian formations exhibited higher water content and permeability, while the Maastrichtian formations showed moderate permeability with variable water content. The Senonian formations were highly heterogeneous. Strong correlations between MRS and ERT results were validated by piezometric levels. MRS estimates of permeability and transmissivity also demonstrated minimal uncertainty (1.74%) compared to pumping well data, indicating high accuracy.

This comprehensive understanding of groundwater dynamics at the mine site is crucial for developing effective strategies to mitigate water-related hazards, ensuring the safety of mining operations, and protecting valuable water resources.

Large Open Pit mines in Chile currently operate below the natural groundwater level, leading the operations to deal with big challenges related to groundwater, as could be obtaining field data measurements and perform hydraulic test, or controlling the seepage that flows into the pit slopes, among other relevant issues. These challenges are usually investigated by different consultants to help the mining operation, sometimes with different scopes, as could be regional groundwater modeling for environmental studies, or mine-scale models for slope stability analysis.

The continuity and duration of studies for specific hydrogeological topics is always different and depends on the scopes, but some tasks and works are repeated year after year, like data gathering, or modelling processes for Five Year Plan evaluation. Sometimes in these processes the consultants leading those works are changed for different reasons, as could be economic reasons. When this happens and a new consult starts from zero, there is a knowledge that is lost, and a new learning curve starts. In this case after five years working as hydrogeological consultants for one of these Large Open Pit mines, different lessons have been learned and are presented in this paper.

One of the main lessons is that critical data review must be performed every time, even for repeated tasks when the same data is received from the mine staff, it must be reviewed carefully because it could have different values for old data, indicating inconsistencies that should be raised before starting to work with it. Another relevant matter that helps both mine operation and consultant companies is the constant Peer Review processes, that allow to highlight improvement opportunities to the work that has been done, and from a third-party eye, issues and new ideas for field work, conceptual model and numerical model are obtained to achieve robust hydrogeological study.

Finally, this knowledge obtained after five years of constant work with the mine staff leads to a better understanding of the hydrogeological conditions in the study area and allows us to help the client with additional topics like the knowledge sharing for new staff or new consultants. It also generates a high standard hydrogeology area inside the mining company that can deal with technical issues and uncertainty for the future of the mine site.

Irrigation has been proposed as a cost-effective, long-term option for managing mining-influenced waters in the Witwatersrand Goldfields. However, there are concerns about the suitability of these waters for crop production as well as the safety of the produce for consumption. To address these concerns, A glasshouse pot trial was established where crops were irrigated with untreated and HDS-treated mine water from the Eastern, Central and Western Basins of the Witwatersrand Goldfields. The findings of this study indicate that crops that are safe to consume can successfully be produced with treated mine waters from the Witwatersrand Goldfields. Furthermore, the findings suggest that untreated mine waters from these goldfields can be utilized for irrigation if soils are strategically limed.

Critical elements, especially rare earth elements (REEs), are essential in various applications, including clean energy, medical, communication, and defense technologies. Waste associated with coal mining operations, such as coal-based acid mine drainage (AMD), has recently enticed great interest as a potential unconventional source of REE.

We investigated the distribution, modes of occurrence, and relative extractability of REE from AMD-based materials at Tab Simco, an abandoned coal mining operation in the Illinois Basin, U.S.A. We collected aqueous and solid samples and analyzed the concentrations of REEs in: (1) size fractionated (0.01, 0.22, and 0.45 μm) AMD samples; (2) Fe(III)- and Al-bearing colloids; and (3) AMD-based sediments accumulated in a bioreactor constructed to treat the AMD.

In AMD, the REEs are partitioned between the truly dissolved fraction (<0.01 μm) and the suspended solid fraction (>0.01 μm), which carry a significant fraction of REE. The suspended colloidal and particulate fractions included detrital REE-bearing minerals (e.g., clay minerals, monazite, apatite, and zircon) from the weathering coal mining waste and newly formed Fe(III)-phases. During AMD treatment in the bioreactor, dissolved Fe(II) is effectively removed from AMD through oxidation and precipitation of Fe(III)-phases, onto which REE can adsorb or co-precipitate. Concurrently, the detrital minerals dominated by silicates are sequestered in the AMD-based sediments accumulating in the bioreactor. The overall REE content of AMD suspended fraction, with an average value of 40 mg/kg in total REE, is orders of magnitude higher than that of AMD dissolved fraction. Bulk AMD sediments accumulating in the bioreactor have total REE contents varied from ~20 mg/kg in Fe(III)-rich sediments up to 250 mg/kg in silicate-rich sediments. A consistent positive correlation occurred between REE and Al contents, indicating that detrital fraction was an essential carrier of residual REE.

The preferential enrichments of REE-bearing phases in the silicate-rich particulate fractions, which can contain up to 300 mg/kg of REEs (corresponding to 0.04% REO), make an attractive target for REE extraction. Therefore, if current technologies, which primarily target extraction of REE from AMD, can be extended to include the silicate-rich particulate fractions, it could contribute to improved economic feasibility of the REE extraction operation at abandoned coal mines.

Valuable metals are strategically important for the global economy, as they play a crucial role in industries such as renewable energy and modern technology. However, their availability is becoming increasingly limited, making it essential to develop new technologies for their efficient recovery and reintegration into the supply chain. Within this context, the Horizon Europe Resilex project introduces an innovative circular treatment process to recover metals like zinc (Zn), copper (Cu), and cobalt (Co) from acid mine drainage, while also producing sulfuric acid from mining waste.

The technology comprises seven bench-scale units, forming a circular process to treat acid wastewater and mining wastes from Tharsis mines in the Iberian Pyrite Belt. The first unit, treating 25 L/h, employs physico-chemical treatment to remove iron (Fe) and aluminium (Al) from acid wastewater. A 20-L anaerobic membrane bioreactor (AnMBR) follows, producing hydrogen sulfide (H₂S) from sulfates (SO₄) and organic waste. This H₂S is used to precipitate Zn and Cu as metal sulfides. In the next stage, Co is captured via ion-exchange resins. Simultaneously, solid mining waste undergoes thermal valorisation at high temperatures to produce sulfuric acid, which is used for resin regeneration. A ceramic nanofiltration membrane recovers sulfuric acid from the resin regeneration eluent. Finally, an evapocrystalliser extracts bieberite (CoSO₄·7H₂O) from the concentrated nanofiltration membrane stream, completing the circular process.

The system is currently in the operational and optimisation phase. During the physico-chemical treatment, acid wastewater with a pH of 2.5 and containing Fe (2 g/L), Al (30 mg/L), SO₄ (5.5 g/L), Cu (50 mg/L), Zn (260 mg/L), and Co (5.6 mg/L) is neutralised with NaOH, removing over 99% of Fe and 70% of Al at pH 4.5. Cheese whey has been identified as the most effective substrate for the H₂S production in the AnMBR, enabling 90% removal of Cu and Zn as sulfides, yielding up to 6.4 g CuS and 34.7 g ZnS recovery per 100 L of feed water. The ion-exchange resins concentrate Co up to 3 g/L and 1.8 g of bieberite can be recovered per 100 L, while the thermal valorisation unit can produce sulfuric acid up to 50% purity.

These circular economy-based treatment lines valorise acid effluents and mining waste, maximising metal and sulfate recovery. This strategy has the potential to make mining operations worldwide more sustainable, turning waste into valuable resources.

The growing demand for critical raw materials (CRMs) for a climate-neutral economy has intensified challenges in waste generation and management. Traditional mine waste characterization, focused on environmental risk assessment within a linear economy framework ("take-make-dispose"), contrasts with the circular economy approach ("make-use-return"), which aims to minimize waste and recover valuable materials. However, unlocking the potential of mine waste requires robust, multi-scale characterization techniques. In this study, we review multi-scale characterization protocols to assess mine waste streams in support of a circular economy. In particular, we highlight the use of hyperspectral imaging as a key monitoring technique, enabling the semi-quantitative assessment of hydrogeochemical parameters and metals in mine water, identification of mineral associations in waste rock, and mapping of metal concentrations in tailings. Although challenges remain regarding sensor sensitivity, cost, and large-scale integration, addressing limitations and improving on standardization of such advanced monitoring tools can enhance mine waste management by improving environmental risk monitoring and enabling resource recovery.

Mining activities generate substantial volumes of mine effluents with high concentrations of ammonia nitrogen (NH₃-N), posing severe environmental challenges. Ammonia is toxic to aquatic organisms and contributes to eutrophication, negatively affecting water quality. As regulatory agencies impose increasingly stringent limits on ammonia concentrations, effective treatment of mining effluents has become critical. This study addresses the urgent need for advanced treatment solutions to manage ammonia nitrogen and ensure compliance with environmental standards.

This research investigates the application of ozone microbubbles, an advanced oxidation process (AOP), for treating ammonia nitrogen in mining wastewater. Ozone microbubbles enhance oxidation rates by increasing the gas-liquid interface area, thereby improving contact between ozone and contaminants. A series of experiments were conducted, including precipitation methods like Friedel's salt, to evaluate treatment efficacy and reduce chloride concentrations in effluents post-ozonation. The study involved testing both synthetic and real effluents from Canadian mines to assess the effectiveness of ozone microbubbles under varying salinity conditions typical of mining environments.

Results indicated that ozone microbubbles achieved over 99% removal efficiency for ammonia nitrogen across all tested conditions, with treatment times ranging from 60 to 150 min. Notably, the presence of thiocyanates (SCN⁻) majorly increased treatment time, as they oxidize more readily than NH₃-N. Additionally, chloride concentrations were reduced by 30% after ozonation using the Friedel's salt precipitation method. Salinity, including chlorides and sulfates, had minimal influence on the removal efficiency of ammonia nitrogen, representing a positive outcome despite the elevated salinity levels. Furthermore, no chlorinated byproducts were detected during ozonation with saline effluents, likely due to operational conditions, as chlorates form at elevated temperatures, while tests were conducted at approximately 20 °C.

These findings highlight the potential of ozone microbubble technology as a viable solution for treating ammonia nitrogen in mining wastewater, particularly in cold climates where conventional methods often limited performance efficiency. The relevant reduction of chloride levels enhances the overall treatment process, aligning with regulatory standards and promoting sustainable water management practices in the mining industry. Continued optimization and further research into the integration of ozone microbubble technology could advance more effective and environmentally friendly mining operations.

AMD are a major environmental issue, but they can also contain valuable metals. A typical treatment of AMD involves neutralization and metal precipitation through liming, generating sludge primarily composed of metal oxyhydroxides and gypsum. Depending on the composition of the AMD, this sludge may contain substantial concentrations of valuable metals. This is an example of how human activity can create artificial accumulation of metals, forming over time an “anthropogenic ore deposit”.

In this study, we focus on the recovery of Cu, Zn, and the treatment of Cd from sludge produced during AMD liming, while addressing the challenges of residual contaminants. The sludge used originated from a former mining site in France. The 75,000 m³ of sludge accumulated over 150 years of AMD treatment contains around 1.3% Cu and 5.1% Zn.

This process begins with selective acid leaching, achieving dissolution of over 80% of Zn and Cu, and more than 98% of Cd. Key parameters, such as acid concentration and solid-to-liquid ratio, were optimized to maximize Cu, Zn and Cd dissolution while minimizing the concentration of unwanted elements in solution like Fe and Al. After leaching, selective precipitation recovered 97% of Cu as copper sulfide and 84% of Zn as zinc hydroxide, with some Zn co-precipitating with Cu and minor amounts remaining in the residues.

A preliminary economic assessment, based on metal yields and current market prices, indicated that the process is economically viable, with positive margins after accounting for reagent costs. However, unresolved challenges remain, including the lack of valorization options for the remaining sludge matrix—primarily gypsum and iron oxides—and incomplete depollution, as Zn concentrations in the treated residue (>0.5%) still exceed regulatory limits. Moreover, regulatory hurdles related to waste management and environmental compliance must be addressed for large-scale implementation. This process offers a promising solution for metal recovery from AMD sludge. The positive financial margins generated could contribute to the rehabilitation of the contaminated site, potentially financing techniques such as surface covering or phytostabilization. Addressing both environmental and economic challenges could thus transform a long-term liability into a sustainable opportunity.

Mining of PT Freeport Indonesia’s Grasberg open pit required filling the Wanagon Valley and constructing an Overburden Stockpile (OBS) in this major drainage system. OBS material placement began in the late 1990s and incorporates a coarse drain zone constructed at the base of the valley fill and designed to convey flows exceeding 3.2 cubic meter per second. The Wanagon OBS is more than 3,300 m long, varies from 250 to 1,200 m in width, has a slope height of 1,000 m with fill depths that vary from 1 to 400 m, and a volume of approximately 430 million cubic meters. As the open pit operations have ended, closure of the Wanagon OBS is continuing. A primary factor critical to the overall project success is in understanding the pore pressure conditions within the OBS to help ensure designs meet acceptance criteria, to optimize construction requirements, to provide inputs for stability assessments, and to support operational and long-term safety.

Estimating pore pressures distributions within stockpiles is controlled by the complex distribution of hydraulic properties linked to the OBS construction methodology and sequence and poses a significant challenge in industry. A novel approach has been developed by CNI to model the Wanagon OBS hydraulic system to provide accurate and efficient interpretations of pore pressures at an appropriate scale for stability analysis using an unstructured FEFLOW mesh. The new methodology and advanced tools provide the capability to efficiently create an unstructured 3D FEFLOW model and facilitates assigning complex material property distributions to match the OBS construction sequence. A seamless integration between FEFLOW and geotechnical stability models allows for direct transfer of pore pressure distributions into the mechanical stability model eliminating the need for interpolation between the models.

With this new approach the resolution of the pore pressure model was enhanced and an excellent calibration to hydraulic monitoring data within the OBS was achieved. In addition, using this unstructured approach resulted in an increase in the numerical stability of the pore pressure model with more efficient time stepping, convergence properties, and mass balance behavior.

The hydro models have been used to identify areas of hydrogeological/geotechnical concern, provide guidance for monitoring targets, and inform/optimize design geometries and material requirements for stability. Using this new approach improves analysis efficiency and risk assessments, development of appropriate Trigger Action Response Plans (TARP), and implementing monitoring systems in support of the Wanagon OBS closure project.

Neves Corvo is a world-class underground copper-zinc mine located in the south of Portugal. The mine has been operated since 1988 by Somincor. The pyritic tailings produced by the operation have a very high acid generation potential and have been placed, since mine startup, subaqueously in the Barragem Cerro do Lobo tailings storage facility (TSF), a large tailings pond created by a rockfill dam across a natural river valley. Due to the finite capacity of the existing impoundment, alternatives for provision of sufficient storage capacity were studied by Somincor. Surface disposal of thickened tailings was identified as the preferred option, which was considered a novel approach at the time given the high reactivity of the tailings and the arid climate at Neves Corvo. In 2010, the TSF was converted from a sub-aqueous to a thickened tailings deposition facility, without requiring any future raises of the main and perimeter rockfill embankments. The design included disposal of tailings with run-of-mine waste rock, which is potentially acid generating, in a co-disposal system. The waste rock is used for construction of peripheral berms and covers.

Monitoring data collected since late 2010 include records of produced /thickened tailings densities, yield stress, particle size distribution, and specific gravity. Settlement, deposition slopes and piezometric levels in the paste and underlying subaqueous deposit are also routinely monitored. The environmental component of the monitoring program, which is the focus of this paper, includes the determination of ponded water quality as well as compositional profiling of the paste and underlying slurry tailings with depth through acid base accounting (ABA), net acid generation (NAG) testing, chemical composition, paste pH and conductivity, and short-term leach testing.

The concentration profiles demonstrate that oxidation is limited to approximately the upper 2 meters of the paste deposit. The waste rock dikes enhance oxidation, likely through promoting horizontal drainage and depression of the water table in their vicinity. Oxidation when paste is exposed is more prominent than when a cover is present while oxidation is also more pronounced at higher elevations in the facility. Metal leaching trends are consistent with geochemical principles, with lower pH typically resulting in enhanced leachability.

The ongoing monitoring of the tailings mass and operational experience at Neves Corvo indicate that surficial deposition of high-sulfide tailings in an arid climate represents a feasible alternative that enhances operational flexibility, facilitates concurrent reclamation and permits co-disposal.

Since 1979, an active treatment system has been operating at Legacy Mine X, located in the Tohoku area of Japan, to prevent water contamination in the surrounding region. Although effective, this system relies on energy-intensive processes that generate major CO₂ emissions and incur high operational costs. In 2021, a pilot-scale bioreactor passive treatment system was introduced to treat manganese and zinc, achieving a 98% removal efficiency. However, the environmental impacts, particularly CO₂ emissions and operational costs of scaling up the passive treatment system have not yet been fully evaluated.

This study employs life cycle assessment (LCA) to compare the environmental and economic aspects of the current active treatment system with scenarios for a full-scale passive treatment system, based on the existing pilot-scale setup and assuming the treatment of 4046 m³ of mine drainage water per day. The assessment focuses on CO₂ emissions using a midpoint evaluation method, with the functional unit expressed as kilograms of CO₂ equivalent per year during the operational period. Operational costs are integrated into the LCA for economic comparison. The system boundaries encompass all components of the treatment plants, including energy use, water sampling, sample handling, transportation, and labor. Proposals for reducing CO₂ emissions in the passive treatment system by utilizing various energy sources are also included. The cost for the active treatment system was calculated based on annual mine drainage treatment costs and mine drainage volume

The passive treatment system is estimated to emit 154,078 kg of CO₂ equivalent per year, with an operational cost of 20 million JPY (Japanese yen) annually. In contrast, the active treatment system generates approximately 10 times more CO₂ emissions annually, with a total cost of around 147 million JPY (METI, 2010). The unit processing cost per m³-waste water was 99.5 JPY/m³ for active treatment, compared to 13.5 JPY/m³ for passive treatment. However, switching to solar energy could reduce these emissions to 16,210 kg of CO₂ equivalent annually, while lowering energy costs by 9 million JPY per year.

The results suggest that scaling up the passive treatment system to full operational capacity at Legacy Mine X would substantially reduce both operational costs and CO₂ emissions. These findings could serve as a model for implementing more sustainable remediation strategies at other legacy mine sites.

Evapotranspiration (ET) covers are an industry-standard tool for mine waste leachate mitigation in arid and semi-arid climates. A new ET cover was designed, field-tested, and optimized with computer modeling for the tailings storage facility (TSF) at the Zangazeur Copper-Molybdenum Complex (ZCMC) in Kapan, Armenia. Collected field data from ET cover test cells, soil characteristics, and climate data were combined to create a variably saturated groundwater flow model which simulated the effectiveness of the new cover for over 10 years. The model was validated to the field-observed measurements of moisture. A minimum thickness of cover that would prevent breakthrough was recommended.

The Almadén Mining District (AMD) is an area of concern due to the significant contamination generated by mining activities that have impacted regional ecosystems. Inadequate mine closure practices have contributed to the worsening of this issue. In this context, it has been confirmed that the local population consumes crayfish (Procambarus clarkii), a species known for bioaccumulating heavy metals, making it a valuable bioindicator for the aquatic ecosystem. Despite studies conducted on the impact of contaminants on the health of the local population, the potential of this crustacean species as a bioindicator in the area has not been thoroughly explored, nor has its consumption's effect on consumer health been evaluated. Therefore, the objective of this study is to assess the non-carcinogenic human health risk associated with the consumption of Procambarus clarkii in the AMD.

Muscle and hepatopancreas samples from crayfish were analyzed using Energy Dispersive X-ray Fluorescence (ED-XRF) to identify Potentially Toxic Elements (PTEs) such as As, Hg, Cd, Pb, Cu, Zn, and Sb. Total mercury concentration (HgT) was determined through Zeeman-corrected atomic absorption spectrometry. A probabilistic human health risk assessment was conducted using Bayesian models, which allowed for the estimation of non-carcinogenic risk in terms of the Hazard Quotient (HQ), using data on PTEs concentrations and surveys applied to the local population.

Results showed HgT concentrations of up to 3.4 mg kg⁻¹ in abdominal muscle, exceeding the European Union's allowed limit for human consumption of 0.5 mg kg⁻¹. Additionally, high concentrations of other PTEs were found, particularly As and Cd, which showed significant accumulation in the hepatopancreas.

These findings are expected to be relevant in understanding the environmental impact of mining activities on aquatic ecology and their potential repercussions on local populations through the bioaccumulation of PTEs in this species and their subsequent incorporation into the food chain. Additionally, this study may serve as a reference for future research, as the crayfish species used here is considered a valuable bioindicator, and the analysis was carried out in the Almadén Mining District, recognized as one of the most significant mercury mining regions globally.

Climate change poses one of the biggest global challenges of the century. To mitigate its effects, Germany and the European Union aim to achieve climate-neutrality by 2045 and 2050, respectively. This goal necessitates a drastic reduction in CO₂ emissions from mining rehabilitation activities, including mine water treatment.

The Lausitz and Central German Mining Administration Company (LMBV) manages rehabilitation of former East German lignite mining areas. As a first step towards CO₂ emission reduction, a carbon footprint assessment of LMBV's mine water neutralization was conducted, focussing on limestone and its products.

Neutralization of mining-affected waters releases CO₂ at every stage:

(1) Extraction, treatment and transportation of lime products,

(2) Thermal separation of CO₂ from limestone in the production of quicklime,

(3) Release of the CO₂ component from carbonate neutralizing during dissolution in water,

(4) Application of neutralizing agents (e. g. plant operation, fuel use).

LMBV’s main treatment technologies are in lake neutralization in post-mining lakes by mobile water treatment vessels and stationary plants as well as stationary plants for treatment of acidic groundwater, river water and seepage water.

During the assessment, CO₂ released at each stage of the neutralization process has been quantified specifically for each type of lime and its application. From 2015 to 2022, LMBV utilized 280,000 t of lime-based neutralization agents, with 77% for in lake neutralization and 23% for other water treatment plants. This resulted in 188,000 t of CO₂ emission, 63% from in lake treatment and 37% from conventional water treatment plants. Further key findings are:

• Quicklime and hydrated lime production is particularly CO₂-intensive (compared to limestone powder and chalk) with approx. 95% of total CO₂ emissions attributable to the burning process.
• Transportation and application of lime products contribute minimally to overall CO₂ emissions compared to the production and chemical dissolution in the treated water.
• In-lake technologies are more favorable in terms of CO₂ emissions than conventional water treatment plants.
• The carbon footprint of many water treatment sub-steps depends on the carbon footprint of electricity generation.

Based on this assessment, strategies are now being developed to reduce the carbon footprint of the LMBV's water treatment measures.

This study utilized ten sampling locations from nickel mine wastewater. The primary pollutants identified were Fe, Mg, Ca, and Al, with the highest concentrations observed at screening stations and processing facilities. Wastewater from Mobile Equipment Maintenance areas exhibited elevated levels of Mg, Ca, Fe, and Na, while mining sites was augmented with Al and Ni. Analyses of particle size and zeta potential revealed larger particles with higher zeta potentials during the dry season, in contrast to smaller, colloidal particles prevalent in the wet season. This investigation contributes to the development of efficacious treatment strategies for nickel mine wastewater in Indonesia.

Cyanide has been used extensively in gold heap leach facilities (HLFs) to extract gold. Although liners, compacted clay layers, and leachate detection and collection systems for HLFs are installed to capture gold-cyanide pregnant leach solution (PLS), deformities and perforations occur and have the potential to propagate into point-sources of environmental contamination. This paper presents a case study for predicting an environmental release of cyanide from an HLF and determining the necessary response plan.

The study commenced with an evaluation of the leak history and PLS application schedule to determine where the leak (or leaks) may occur. Once leak location(s) were estimated, the transport and fate of PLS which passed under the HDPE liner into the Low Conductivity Clay Layer (LCCL) and substrate was evaluated.

To replicate the flow conditions within and below the HLP, a two-dimensional, finite-element, variably saturated seepage modeling program (SEEP/W) was utilized. The model considered the loading rate of the HLF (the change in height over time), the leaching history, and the location of the leaks. Geotechnical and hydrogeologic testing was performed on LCCL material, heap material, and the substrate under the LCCL and aquifer tests were performed in the saturated zone downgradient of the HLF for additional model properties. During transient model runs, an opening in the HDPE liner simulated the leak, and model parameters were calibrated from rates observed in HLF leak detection points. After calibration, fate and transport of the PLS was simulated.

Initial results of the model indicated the low conductivity and capillary action of the LCCL prevented PLS release into the substrate. However, the rate of observed leakage increased, and the model was adjusted accordingly. The new results showed PLS migration into the substrate but the driving force for this migration is temporary due to the short leaching time of the HLF. Over time, capillary forces within the substrate slowed PLS propagation.

The results of the model showed the PLS did not reach an environmental receptor (a groundwater well downgradient of the HLF) after 30 years of post-heap closure. This model was incorporated into the response for regulators, who accepted a management plan based on leachate collection from detection sumps and a stand-by monitoring approach. Additionally, model results demonstrate changes in fluid transfer dynamics as PLS flows through unsaturated porous media into saturated media.

Mine water management infrastructure is commonly designed to pass or retain a runoff event resulting from a low-frequency, high-magnitude rainfall event. The annual exceedance probability, or recurrence interval of these events are estimated based on a series of historical annual maxima for the duration of interest (e.g., 24-hours). It is well established globally that relatively small increases (+0.5°C) in temperature cause statistically significant changes in temperature extremes and intensification of heavy precipitation from historical reference periods. These projected changes in high-magnitude precipitation events will have direct consequences for the design and operation of mine water management infrastructure and should be considered in technical evaluations where infrastructure is expected to operate within the same tolerances in the future.

While the scientific principles underlying the linkage between increased air temperature, air mass moisture capacity and precipitation intensity are well established, the translation of these relationships under a changing climate to future design rainfall estimates is not well defined. To address this gap, technical guidance was developed to assist practitioners when developing scalars that consider the projected effects of climate change on rainfall magnitude. Key considerations are: the risk associated with potential failure of a structure to operate within design criteria, the intended design life for existing or new infrastructure, and the appropriate emissions scenario.

The guidance is intended to be applicable globally, and worked examples are provided to illustrate the scalar development process under various data availability scenarios. Based on case studies completed to date, derived rainfall scalars were comparable across multiple analysis methods, including use of gridded reanalysis products, publicly available guidance, and the Clausius-Clapeyron equation. There is evidence for deviation from the simplified relationship between precipitable water and air temperature in moisture limited (i.e., arid) areas (lower scalars), and areas where convective cells drive higher moisture content, and therefore higher localized rainfall amounts.

This guidance will assist practitioners in developing rainfall exceedance probabilities that account for projected future climate change. It provides a way to clearly link the infrastructure risk profile, design life, infrastructure update cycles and mine life planning to emissions scenarios, and the derived scalars recommended for use in design work. This workflow allows for clear communication to stakeholders of the magnitude of potential changes in rainfall intensity, as well as their effect on mine planning/budgeting, and effective lifespan of the infrastructure in question.

Fluoride in mine drainage poses substantial environmental risks, often exceeding South Korea’s regulatory discharge limit of 3.0 mg/L. This study assessed treatment processes combining precipitation and adsorption for fluoride and toxic metals from the Samwon mine drainage. To treat aluminum, manganese, and fluoride, experiments involving injection of calcium hydroxide and reaction with slag-limestone mixture were conducted. Subsequently, to treat remnant fluoride, experiments involving precipitation/adsorption using aluminum sulfate and lanthanum chloride as well as adsorption using Al-rich coal mine drainage sludge and domestic water purification sludge were conducted. The results demonstrated substantial fluoride reduction, with adsorption kinetics following a pseudo-second-order model.

The treatment of water in mining operations is a critical aspect of environmental sustainability. As the demand for minerals and metals continues to grow, the need for effective water treatment solutions has never been more pressing. The discharge of untreated or poorly treated water can have devastating consequences for local ecosystems and communities.

A Swedish metal mine is replacing its existing water treatment system to meet more stringent treatment objectives. This upgrade is necessary to ensure that the mine's water treatment process is able to effectively remove contaminants and meet the required standards. To achieve this, the mine has adopted a collaborative approach, involving a consultant and a technologies supplier from the outset of the project. This approach allows for a comprehensive understanding of the mine's specific needs and the development of a tailored solution that optimizes water treatment.

Through this project, several key findings have emerged. The selection of adequate chemistry, using multiple precipitation mechanisms, is crucial to reduce sludge formation, increase performance and reduce chemical consumption. Additionally, a comprehensive approach to water treatment, taking into account the specific requirements of the mine and the local environment, is essential for effective water management. By prioritizing water treatment and management, mining companies can reduce their environmental impact, improve their social license to operate, and create economic benefits.

The approach taken by this Swedish metal mine provides a model for other mining companies to follow, and highlights the importance of innovation and collaboration in addressing the complex challenges of water treatment in mining operations. As the demand for minerals and metals continues to grow, the need for effective water treatment solutions will only increase. By adopting a proactive and collaborative approach to water treatment, mining companies can ensure that their operations are sustainable, efficient and environmentally responsible.

Two metalliferous mine drainages from El Triunfo 1 (ET) and Santa Teresita (ST) mines in the Ancash region of Peru were selected to assess the feasibility of (semi-)active treatment methods, including the efficiency of As coprecipitation with Fe in inflows. Elevated concentrations of Al, Fe, Mn, and Zn at both mine drainages were reduced to target levels at pH 10. Additionally, the As concentration of 1.69 mg/L at the ET mine was reduced by approximately 93%, reaching 0.124 mg/L at pH 10, suggesting that coprecipitation and adsorption by Fe in the mine drainage played a substantial role in As removal.

An understanding of geochemical reactions and environmental factors that control water quality is required for management and mitigation of environmental effects from acid mine drainage (AMD). This paper describes water-quality modeling tools that were developed to aid in the evaluation of key hydrogeochemical processes and their relative importance in controlling concentrations of dissolved metals and associated constituents in AMD and the effluents from treatment systems.

The mining industry faces environmental and reputational risks due to the toxicity of mine wastewater, which can have devastating consequences for ecosystems and local communities. In gold mining operations, contaminants such as cyanide species, ammonia, and metals can generate a toxic effluent that is harmful to aquatic life. A Canadian gold mine operating in a very cold climate faced recurring toxicity issues, despite implementation of metals removal in its mining effluent, and was pressed by local regulations to address the issue.

A rigorous process of discovery was undertaken to understand the source of the toxicity and identify a suitable solution, taking into account local constraints such as climate and limited footprint. This case study highlights the approach to resolve the toxicity issues, from theoretical to laboratory validation, and then followed by piloting confirmation to lead to the full-scale application. Cyanide species were targeted as the major source of toxicity as well as ammonia, both of which can be treated by enhanced biological degradation through a moving bed bioreactor (MBBR). The biological degradation was implemented in addition to metals removal, in order to completely address all the sources of toxicity.

The study demonstrates the effectiveness of the combined MBBR and metals removal solution in reducing acute toxicity to aquatic life, with five years of data on the full-scale application supporting the findings. The MBBR process successfully degraded cyanide species and ammonia, while the removal of metals, such as copper, upstream of the biological process was crucial to address the toxicity of these metals to the biomass responsible for degrading the cyanide and ammonia. The case study provides valuable insights for the mining sector, showcasing the challenges that were overcome and the innovative solutions for the industrial sector implemented to address the toxicity issues.

The complexity of toxicity in mine water is challenging, and this study demonstrates the importance of understanding the water quality in its entirety to implement the best solution. By considering the interplay of various contaminants and factors, mining operations can develop targeted and effective treatment strategies to mitigate toxicity and protect the environment. This approach is crucial for ensuring the long-term sustainability of mining operations and minimizing their environmental footprint.

Recovery of metals from acidic pit lakes in copper-rich deposits has the potential to generate a circular economy, improve water quality, provide a domestic supply of critical materials, and demonstrate corporate investment in Environmental-Social-Governance goals. The European Union lists several constituents found in acidic pit lakes as Critical Raw Materials (CRM; e.g., antimony, cobalt, manganese, vanadium) and Strategic Raw Materials (SRM; e.g., copper, nickel). Additional metals (e.g., zinc) can have high market value. Metal recovery from pit lakes in the Iberian Pyrite Belt (IPB), Spain, has been previously investigated but not advanced. Recent investigations into zinc and copper recovery from two acidic pit lakes in the United States plus resource supply chain risks in Europe may renew interests in metal recovery from IPB pit lakes.

A screening-level economic evaluation required dissolved concentrations of metals, lake volume, and market values of metals. Surface water concentrations (2008) from thirteen, acidic (pH<5), IPB pit lakes were assumed to represent average water column concentrations. The surface of each lake was assumed to be circular allowing the volume of each lake to be estimated using the geometry of a cone. These assumptions have several limitations (e.g., concentrations at depth are typically higher than surface concentrations, particularly in meromictic lakes) that can be refined after screening. Where concentration data are missing, a novel, artificial intelligence (AI) program, called the “Pit Lake Decision Support Tool” (PLDST), can help identify additional lakes for consideration.

Three pit lakes (Corta Atalaya, San Telmo, and Aznalcollar) were found to store between € 2.2 and €10.6 million in combined cobalt, copper, nickel and zinc (Table 1). Further refinement will combine volume vs depth measurements with recent concentration vs depth data to revise values as a function of depth. Often pit lakes are connected to large “mine aquifers,” or underground networks of flooded mine tunnels storing additional metal-rich water, which will be included in revised resource assessments. The PLDST will then be used to estimate the cost and return-on-investment associated with various metal recovery methods including sulfide precipitation, electrowinning, solvent extraction-electrowinning, and copper cementation.

This study raises awareness within mining companies and government agencies of the potential value of CRM stored in European pit lakes. The screening method is simple and identifies high-value pit lakes for advanced resource investigation. The PLDST can identify new potential resources, rapidly estimate costs of different metal recovery methods, and project returns to inform a business case.

Rising prices as a consequence of running short natural resources, continuously increasing demand and a strong dependence upon third party countries led the European Commission to the publication of a list with 34 critical elements, most of them being metals.

With this background, the research project IAW33 was established at the THGA Bochum in 2022, that is founded by the RAG foundation for three years. The aim of the project is the first screening and evaluation of mine water sludges of all active pumping sites in the former coal areas of the Ruhr and the Saar region and the former mine in Ibbenbueren (NRW) for their production potential of critical metals. The sludges were collected with the help of precipitation reactors for low and highly mineralized mine waters. Besides that, two available settlement lagoons were also sampled and analyzed via ICP-MS for all critical metallic and several further economically valuable elements (55 in total).

The results show, that the sludges of some active pumping sites in the Ruhr area exhibit increased concentrations of critical alkaline earth elements, such as strontium, barium and magnesium. Nevertheless, the former mining site in Ibbenbueren (northern part of NRW) shows the most promising results with respect to critical and economically valuable metals. Three samples were taken at one of the four settlement lagoons. After drying, these samples showed just total metal concentrations of nearly 20%, but high rates of nickel, titan, cobalt and rare earth elements. Relating to 1.000 kg of dried sludge, several hundred grams of these metals are contained in it. That means that with a total area of 236.000 m² of all settlement sites, about 32 tons of cobalt, 47 tons of nickel, 38 tons of titan and 10 tons of rare earth elements are present within every meter depth of sludge. Recently ongoing experiments (October 2024) shall enhance the concentrations of these elements with the help of a graded precipitation with the adjustment of different pH levels.

As a conclusion may be drawn, that the former mining site in Ibbenbueren shows the most promising option for a re-mining of the deposited sludges. The recovery of these elements may help to reduce the costs of the mine water treatment at this site and may also reduce the need of large settlement areas. Furthermore it is possible that it contributes on a small scale to the reduction of dependencies upon third party countries.

In the state of Santa Catarina, Brazil, coal mining began in the late 19th century and, for decades, occurred without environmental care. The coal in the region has a high sulfur and ash content. To meet the standards of the local thermoelectric plant, the coal needs to be processed to remove pyrite and associated rocks, generating 50%–70% waste. It is estimated that more than 320 million tons of coal waste have already been deposited on the surface. The result is a legacy of immense waste with a high pyrite concentration (12%), representing a major environmental problem in Brazilian mining: there is contamination of soil, surface water and groundwater of three river basins by acid mine drainage (AMD). Although legislation and actions to ameliorate environmental damage have advanced substantially since the 1990s, some areas remain affected. Models indicate that AMD may continue to be generated for more than 500 years, requiring effluent treatment and long-term monitoring of the areas. However, in the 1980s, coal waste was reprocessed to concentrate pyrite for the production of sulfuric acid. This practice was discontinued and it is considered one of the major setbacks in the sector, as it went from a clear circular economy to a linear economy (coal to thermoelectric power).

This study assessed the environmental, economic and social benefits that the use of pyrite would have brought to the southern region of Santa Catarina if pyrite concentration had continued. It used quantitative coal waste production data and pyrite was subjected to gravimetric separation tests performed in the laboratory. The processing products were characterised in terms of the sulfur content (pyritic, organic, sulfate and total) and acid generation potential.

The results showed that pyrite recovery would provide the following advantages: reduce the mass of waste by approximately 10%, and decrease the net acid generation potential and lime consumption in active AMD treatment systems by 60%–70%. In addition, there might have been easier decommissioning of the areas and a better supply of sulfuric acid on the Brazilian market. Finally, the results are discussed in terms of the Brazil’s energy matrix, in which coal has lost strength. At present, the decommissioning of this sector is in progress.

In conclusion, if the region had been seen both as a coal and a sulfide deposit, this transition would have been smoother and would have left less of a legacy of pollution for future generations.

The objective of this study is to analyze the failure mechanisms of the Tailing Storage Facility (TSF) Brunita in NE Spain. The dam collapsed on October 20, 1972, resulting in substantial environmental damage and economic consequences. The forensic analysis employed geological, geotechnical, and geophysical criteria to determine the causes of the flow failure.

Despite extensive research on the dam by various experts, none have confirmed the failure process through numerical modeling. Hence, numerical simulations using the GeoStudio Core software package were conducted in four stages: (1) steady-state infiltration analysis to establish reference conditions prior to heavy rainfall, (2) transient infiltration analysis to account for additional water from heavy rainfall, (3) calculation of safety factors and potential failure surfaces using limit equilibrium methods, and (4) stress-strain analysis to estimate displacements and deformations in potentially unstable zones under variable saturation conditions.

The results indicated that heavy rainfall of 119 L/m² in one week substantially increased pore water pressures, leading to a drastic reduction in shear strength and TSF stability. The failure was primarily triggered by internal erosion (piping) and loss of suction in the tailings. The increased pore water pressure weakened the structural integrity of the dam, making it susceptible to failure under the added stress of the heavy rainfall. The findings demonstrate that the dam needs to remain in unsaturated conditions to ensure its stability. This study underlines the fundamental role of effective drainage systems in maintaining the stability of tailings storage facilities under extreme weather conditions. Proper drainage systems can help manage water infiltration and prevent the build-up of pore water pressure, which is crucial for the long-term stability of such structures. Additionally, the study highlights the importance of continuous monitoring and maintenance of tailings storage facilities to detect and mitigate potential failure mechanisms before they lead to catastrophic events.

In conclusion, the forensic analysis and numerical simulations provided valuable insights into the failure mechanisms of the TSF Brunita. The study emphasizes the need for robust design and maintenance practices to ensure the safety and stability of tailings storage facilities, particularly in regions prone to heavy rainfall. By understanding the factors that contributed to the failure, future incidents can be prevented, thereby protecting both the environment and the communities living near such facilities.

Based on two real scale trials carried out in an abandoned mercury mine waste dump, a solution to prevent and reduce the contamination of water with arsenic (As) and mercury (Hg) is proposed. First, the waste surface is covered with a layer of fly ash preventing 90% of the water to be contaminated. Second, the leachate is treated in filtering channels with fly ash and steel slags to reduce the As concentration in four stages with reduction of 60% in each stage. The results demonstrate the feasibility and usefulness of the proposed solution.

Acid mine drainage (AMD) is widely recognized as one of the most significant environmental challenges in the mining industry. AMD is characterized by higher concentrations of metals and sulfate and an acidic pH.

Several techniques are commonly employed to treat AMD, including raising the pH by adding alkaline materials, precipitating dissolved metals by introducing sulfide reagents, and using biological processes.

Superabsorbent polymers (SAPs), known for their high water absorption and retention capacity, offer a promising alternative for treating mining effluents due to their unique properties. In this study, synthetic metal solutions were used to assess the effectiveness of SAPs in effluent treatment.

Investigation results demonstrate the effectiveness of SAPs in sequestering heavy metal ions. The sequestration capacity of metals is influenced by pH, the ionic radius of the element, and the availability of binding sites in the SAPs.

To better understand the relationship between metal ion absorption rates and these chemical factors, an equation has been proposed that considers both ionic radii and the concentrations of the elements analyzed. This equation provides highly accurate predictions of the metallic ion absorption rate. However, further validation using data not included in the equation's development is required to generalize its applicability.

Mine waters exhibit variable compositions with a range of pH and dissolved solutes. Waters with pH less than six are referred to as acid mine drainage (AMD), and waters with pH greater than six are classified as saline drainage (SD) or neutral mine drainage (NMD) depending on the concentration of dissolved solutes. Plumlee et al., (1999) developed a set of trace elements that when compared with pH, enabled definition of mine waters into twelve categories and later developed this into a geo-environmental model using mine sites from a limited geography within North America. This study uses a wider international sample-set of surface water drainage from mines to assess whether this model has global applicability.

Hydrochemical data from thirty-eight mines located on four continents were plotted onto the Plumlee model to assess the boundaries of each field. Early geology-based classification schemes (e.g. Cox and Singer, 1986) have evolved into mineral deposit models that classify deposits using geologic, geophysical and geochemical characteristics that consider the overall ‘geodynamic’ context of ore deposits (Gessner et al., 2018).

The results of this study correlate well with the fields set out in the original Ficklin diagrams from the 1990s. This approach helps move towards more refined mine water quality predictions early on in a project development and allows easy revision of the model throughout the project life cycle. These models can be used as an improved predictive tool by researchers including consultants, mining professionals, regulators and other stakeholders.

This study investigated the release of potentially toxic elements (PTEs) from the Gold One Tailings Dam Complex (TDC) in Randfontein, South Africa. The Gold One TDC generally comprised a PTE-leached upper oxidized zone and PTE-enriched lower oxidized, transition and reduced zones. Acid-base accounting determined that TD materials were largely acid-generating. According to sequential extraction procedures, Co and Pb yielded the highest potentially bioavailable concentrations, compared to Cu, Ni and Zn. The results suggest that Co and Pb may pose increased threat to the health of the environment and wildlife.

Since the initiation of the Global Industry Standard on Tailings Management (GISTM), the adoption by mining companies of advanced monitoring technologies has expanded. These systems utilize continuous, near-real-time data from diverse sensors, integrating geotechnical, hydrological, and environmental measurements. Enhanced by real-time data fusion and advanced statistical analysis, the technology enables the detection of subtle structural deviations, improving the accuracy of quantitative risk assessments, and reducing false positives. Dynamic, tailored response plans are activated based on detected anomalies and forward-looking statistical trend analysis, enabling swift, informed decision-making. This approach enhances safety and proactive risk management for tailings storage facilities and promotes regulatory compliance, operational efficiency, and sustainability.

Catoca mine is an open-pit diamond mine belonging to Sociedade Mineira do Catoca in Angola that began in 1995. It has a large active tailings storage facility (TSF) and two smaller deactivated TSFs. Catoca aims to comply with Global Industry Standard on Tailings Management (GISTM) and has installed a comprehensive monitoring and fully automated control network infrastructure that is connected to a database and dashboard viewed by operators and managers. This interactive database can be accessed anywhere in the world. The enhanced monitoring network can be used in analysing the causes of TSF failures and providing early warnings for prevention of failures.

Potential alternatives to acid mine drainage (AMD) treatment, in abandoned mines in Iberian Pyrite Belt were using industrial byproducts. Repurposing these waste materials, could decrease environmental impacts and promote a circular economy.

The paper industry produces alkaline residues by the kraft process. These solid residues are rich in lime and recalcitrant organic compounds are commonly disposed of in landfills. Nevertheless, high alkalinity and calcium concentrations suggest the residues could be used to neutralize AMD. Organic matter in the residue could facilitate metal attenuation and settling. Likewise, biochar has emerged as another organic material of interest for AMD remediation due to its adsorptive properties. Biochar is produced through the oxygen-limited thermal combustion of biomass residues from agriculture, (vineyard olive orchards), forestry and sewage sludge.

Bench-scale experiments were conducted simulating ponds to investigate the potential for paper sludge or biochar to neutralize and attenuate metals in AMD. Various material-to-AMD ratios (1:50, 1:100, and 1:200) were investigated over 10-day tests. For each ratio, oxic/anoxic and different stability conditions were tested. The pH and electrical conductivity of the effluent were measured daily, and on the 10^th day, the final effluent and solids were analyzed using ICP-OES.

The best results came from conditions simulating stable, open ponds. The paper sludge increased the pH from 1.64 to 6.23 at 1:50 proportion, 3.30 at 1:100, and 2.20 at 1:200. Attenuation of Fe was 100%, 99.3%, and 62.3% at the 1:50, 1:100, and 1:200 proportions, respectively. However, the biochar tests did not result in substantial Fe removal, as the pH remained low for the same AMD: materials ratios as above.

Kinetic tests were also conducted while maintaining a pH of 5 to evaluate the retention of metals by each material. Biochar had adsorption rates of 98% for Cu, 18% for Mn, 21% for Zn, and 18% for Hg over 24 hours.

Based on the bench-scale results, a geochemical model of potential treatment of the AMD was created using these waste materials. The simulation included a downflow pond, using paper sludge as the bottom layer material to raise the water pH and precipitate Fe, followed by a reactive barrier made of biochar for the retention of Cu and other metals. The modeling indicates sequential changes in the chemistry of the treated AMD as a function of the specified AMD: materials ratios and reaction times and may be useful to indicate potential size of a field-scale treatment.

Herein, acid mine drainage (AMD), a highly acid and biorecalcitrant wastewater matrix, was used as a valuable secondary source for valuable mineral recovery. Specifically, AMD is amongst the main issues of environmental concern in South Africa and countries with strong mining industries, being also responsible for water scarcity and socioeconomic pressures. As such, research has focused on its sustainable treatment, including its beneficiation (minerals recovery) and valorisation (water reclamation). For this reason, real AMD was collected from an active coal mine in South Africa and was used for the selective recovery of ferric oxide (Fe(III)). By doing so, the pH of the AMD was slightly corrected, and its dissolved metals loading was also reduced.

Along with Fe(III), aluminium (Al) and sulfate (SO^-2₄)were also recovered and this material was then used for the production of iron chloride (FeCl₃) an important coagulant that is currently used by water and wastewater industries throughout the world. The produced FeCl₃ also included Al and SO^-2₄ in its matrix, which could further improve its efficiency as a coagulant.

For this reason, batch experimental studies were carried out to identify the effectiveness of the AMD-synthesized FeCl₃ for water and wastewater treatment applications. The efficiency in contaminants removal from real river water as well as from wastewater in the South African setting was identified and compared to the one of commercially available FeCl₃ coagulant. Preliminary results suggest that the efficiency of the AMD-synthesized FeCl₃ in contaminants removal from those aqueous matrices is on par or even better than the one achieved when using commercially available FeCl₃ coagulant. As such, the beneficiation of AMD can present a novel and sustainable avenue for the production of ferric salt coagulant in South Africa and further afield.

The demand for critical raw materials (CRMs) is rising due to their essential role in industries like electronics and renewable energy. Current reliance on ore mining to source these materials raises concerns about sustainability. This study addresses these challenges by investigating CRM extraction from a notable waste stream – mining-influenced water (MIW) – as a sustainable alternative to traditional methods.

In this study, the recovery potential of 19 CRMs from MIW using ion exchange (IX) technology was assessed. The novelty of the study lies in the selection/evaluation of ten different IX resins, including aminomethylphosphonic, carboxylic, phosphonic, polyamine, sulfonic, and chelating acid resins. The focus was on extracting high-value CRMs while minimizing iron (Fe) extraction, as previous studies indicated that Fe in solution hindered other CRM extraction. This study aimed to better understand the differences in selectivity, affinity, breakthrough behaviour, and desorption characteristics between CRMs. Equilibrium experiments (spanning 72 hours) were conducted along with continuous-flow column studies at varying bed volumes (BV) (6 - 15 BV/hour). Modified competitive isotherm models were applied to evaluate the data obtained.

Key findings revealed that sulfonic acid resin exhibited the highest overall capacity for CRM recovery while minimizing Fe adsorption. Chelating resins, although lower in capacity, demonstrated greater affinity for specific lanthanides. The selectivity order for the chosen sulfonic resin was: Tm > Lu > Tb > Ho > Eu > Yb > Er > Pr > Sm > Dy > Gd > La > Nd > Y > Ce >> Mg >> Fe. The presence of magnesium (Mg), thorium (Th) and uranium (U) had minimal influence on other CRM adsorption, while Fe showed competitive behaviour. Breakthrough and desorption studies indicated that Fe formed an outer layer over an inner lanthanide layer, which was released first during elution. Selective desorption was possible based on the eluant used, with chelating agents offering better CRM separation.

Approximately $35 USD per 1000 L of MIW was extracted through selective CRM recovery in this study. These findings suggest that substantial value can be obtained from MIW. Prioritizing and implementing practices like this could reduce the environmental effect of CRM sourcing while supporting the development of a circular economy.

Understanding hydrodynamics in stratified underground mines is critical for effective mine water management. In Tyrol’s Georgi-Unterbau mine, density stratification in a subvertical shaft between levels 20 and 40 enabled the study of flow and tracer dispersion using four solid tracers and a fluorescent dye introduced at varying depths. An inclined rise connected to the shaft required adding table salt as a tracer, disrupting the delicate density layering with a 0.1–0.2 K difference. While flow paths and velocities were measured, the stratification breakdown caused by the injected brine highlighted the sensitivity of such systems. This study underscores the challenges of external interventions and provides insights for managing stratified mine water.

The needs of today's mines require the use of waste rocks for the construction of components, i.e. tailings dams, so having a good system to monitor and predict the geochemical behaviour of the components where these materials have been used is essential, especially regarding the acid rock drainage and metal leaching. The application of this methodology strengthens the use of geochemistry to add value to operations and reduce closure costs in mining projects.

The use of cells in the field for more than six years has allowed the evaluation of acid rock drainage and metal leaching, both of isolated materials and of combinations between different lithologies, which has allowed defining the ranges of acceptable chemical and mineralogical compositions for construction materials; as well as the optimal combinations of rocks. The installation of oxygen, temperature, electrical conductivity and water content sensors has allowed these parameters to be monitored inside the component for a period of more than three years. Using the above results, together with data on drainage flow rates and water quality, a reactive transport model has been calibrated under unsaturated conditions and with multiphase flow (water and air) in non-isothermal conditions, to predict the long-term behaviour of the materials used in the construction and to assess the future drainage water quality of the component.

The good correlation between the field cell tests and the evaluated behaviour of the different materials inside the component, demonstrate the value of these field tests to determine the compositions of those materials that can or cannot be used in the construction of certain mining components. Furthermore, the information generated by the sensors, especially those of water content and temperature, has proven to be of great value in understanding the flow of water inside the component and the generation of acid drainage associated with the oxidation of pyrite (exothermic reaction), allowing to corroborate the compositional ranges of the materials used in the construction.

The use of this methodology, in line with the mine planning, allows for better use of waste rock instead of considering it as a liability, minimising the volume of rock sent to the waste dump and, therefore, minimising its handling and the costs associated with mine closure. Likewise, the establishment of long-term geochemical monitoring and control programmes is of great help in optimising the use of these materials and planning mine closure activities.

The primary objective of the study was to develop and implement a coupled groundwater-surface water flow and solute transport modelling workflow to evaluate the influence of mine water rebound from an abandoned underground coal mine on the overlying aquifers and nearby streams. This workflow is crucial as it enhances the accuracy of simulations, improves risk assessments, informs environmental management strategies, and supports sustainable development.

The developed workflow relies on the industry standard groundwater modelling code MODFLOW 6 (MF6) and the FloPy Python library and is able to represent groundwater-surface water interactions dynamically in space and time both for flow and solute transport. This comprehensive approach ensures accurate simulation of complex hydrological and hydrogeological processes. The modelling workflow aims to identify contaminant migration pathways and potential receptors of mine water discharge, by estimating increases of concentration for four key chemical species: chloride, sulfate, total iron, and ammoniacal nitrogen.

The modelling results indicate that important areas of the aquifer and nearby streams could potentially be affected by discharge from the abandoned mine, under the considered assumptions associated with a worst-case scenario. The model also suggests substantial groundwater-surface water interaction, where contaminants migrate from the aquifer into the stream and vice versa depending on the location and time of the year, with relatively fast travel times in the streams.

The ability to model groundwater-surface water interactions dynamically provides a more accurate representation of real-world hydrological and hydrogeological processes, enhancing the reliability of risk assessments, more effectively informing environmental management strategies, and supporting the development of effective remediation plans. In particular, it has been observed that coupled modelling allows to present solute transport results in easy-to-understand figures and animations, which promote understanding and engagement of the different stakeholders. By engaging stakeholders through clear visualizations and predictions, it fosters informed decision-making, ultimately contributing to the preservation of natural resources and the promotion of a sustainable future. The additional effort involved in the development of the coupled approach is marginal when compared to traditional modelling approaches, making it a valuable tool for environmental scientists and policymakers.