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.