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.