Acid Mine Drainage Research Articles

Infiltration Characteristics of Surface Water in Coal Seam Mining Beneath Gullies and Corresponding Preventive Measures

Infiltration Characteristics of Surface Water in Coal Seam Mining Beneath Gullies and Corresponding Preventive Measures

Prediction of Floor Failure Depth Based on Dividing Deep and Shallow Mining for Risk Assessment of Mine Water Inrush

Understanding and predicting floor failure depth is crucial for both mitigating mine water inrush hazards and safeguarding groundwater resources. Mining activities can significantly disturb the geological strata, leading to shifts and damage that may result in floor cracks. These disruptions can extend to confined aquifers, thereby increasing the risk of water inrushes. Such events not only pose a threat to the safety of mining operations but also jeopardize the sustainability of surrounding groundwater systems. Therefore, accurately predicting floor failure depth to take effective coal seam floor management measures is the key to reducing the impact of coal seam mining on water resources. Seventy-eight sets of data on coal seam floor failure depth in China were collected, and the main controlling factors were considered: mining depth (D1), working face inclination length (D2), coal seam inclination (D3), and mining thickness (D4). Firstly, the distance evaluation function based on Euclidean distance was constructed as the clustering effectiveness index, and the optimal cluster number K = 3 was determined. The collected data were clustered into three categories using the K-means clustering algorithm. It was found that the clustering results were positively correlated with the size of D1, indicating that D1 played a dominant role in the clustering. The D1 dividing points of the three types of samples were between 407.7~414.9 m and 750~900 m. On this basis, the grey correlation analysis method was used to analyze the order of the influence weights of the main controlling factors of coal seam floor failure depth. For the first group, the order was D2 > D1 > D3 > D4, while, in the other two, it was D1 > D2 > D3 > D4. D1 emerged as the most influential factor, surpassing D2. Therefore, D1 between 407.7 and 414.9 m could be used as the boundary, the first group could be classified as shallow mining, and the second and third groups could be classified as deep mining. Based on this boundary, CatBoost prediction models for the depth of coal seam floor failure in deep and shallow parts were constructed and the prediction results of the model test set were compared with the calculation results of the empirical formula. These models exhibited superior accuracy with a lower mean squared error (MSE) and mean absolute error (MAE) and a higher R-squared (R2) compared to the empirical formula. This study helps to enhance the understanding of coal seam floor behavior, guide floor management, and protect groundwater resources by defining deep and shallow mining to accurately predict floor failure depth.

Groundwater in Katowice - center of a large urban and deep coal mining area in Poland

The paper presents the groundwater resources of Katowice and the results of studies conducted to identify prospective areas in aquifers with sufficient water resources for the location of public water intakes. The city of Katowice is the capital of Upper Silesia, the largest urban-industrial area in Poland, the region with a highly developed hard coal mining and many other different industries covering almost the entire scope of the economy. Due to long term drainage of mines causing the depletion and deterioration of groundwater and surface water resources, the main municipal water intakes have been located outside Katowice. Most of the pumped mine water is discharged into surface waters, causing significant salinity of water and disallow its use for municipal or industrial purposes in Katowice. The water collection and supply system is very extensive and covers a significant part of the Silesian agglomeration which is why Katowice is supplied with water from surface water intakes located outside the city. According to older published materials, such as the Hydrogeological map of Poland, there were no aquifers in the city that could have been used to supply the city with drinking water, however recent studies have shown that groundwater in the Quaternary aquifers in the western part of the city can be used to supply the city with public water. Less productive, Quaternary aquifers in north-eastern parts of the city may constitute the basis for drinking water supply in emergency situations, when surface intakes cannot be used, such as toxic, radiological or viral contamination or damage to the water supply network eg. as a result of an earthquake or warfare.

Sustainable remediation of acid mine drainage (AMD)- and crude oil-contaminated sites through wastewater-enhanced Pseudomonas aeruginosa ATCC 15442 treatment

The increasing rate of soil contamination poses a major challenge to the sustainability of the ecosystem. Acid mine drainage (AMD) and crude oil are among the major soil contaminants contributing to the degradation of soil organic matter. This study aims to evaluate the application of Pseudomonas aeruginosa ATCC 15442 (PA-15442) and wastewater for the treatment of AMD- and crude oil-contaminated soils. A microcosm containing 1 kg each of AMD- and crude oil-contaminated soils was inoculated with PA-15442, and brewery and domestic wastewater were added for the bioaugmentation study. The result of the 28-day study conducted under mesophilic conditions showed an average TPH and metal removal efficiency of 58.84% and 52.75%, corresponding to 51.07, 47.29, 59.32, 58.98, and 47.1% for the individual metals (Fe, Al, Cu, Zn, and Mn), respectively, and 49% for the average sulfate removal after the treatment period. This study has shown that bioaugmentation of contaminated soils with the strain of PA-15442, and the addition of wastewater could be an environmentally friendly and sustainable approach for the remediation of AMD- and petroleum-contaminated soils.Graphical

Biogenic Sulfide-Mediated Iron Reduction at Low pH

Acid mine drainage (AMD) pollutes natural waters, but some impacted systems show natural attenuation. We sought to identify the biogeochemical mechanisms responsible for the natural attenuation of AMD. We hypothesized that biogenic sulfide-mediated iron reduction is one mechanism and tested this in an experimental model system. We found sulfate reduction occurred under acidic conditions and identified a suite of sulfate-reducing bacteria (SRB) belonging to the groups Desulfotomaculum, Desulfobacter, Desulfovibrio, and Desulfobulbus. Iron reduction was not detected in microcosms when iron-reducing bacteria or SRB were selectively inhibited. SRB also did not reduce iron enzymatically. Rather, the biogenic sulfide produced by SRB was found to be responsible for the reduction of iron at low pH. Addition of organic substrates and nutrients stimulated iron reduction and increased the pH. X-ray diffraction and an electron microprobe analysis revealed that the polycrystalline, black precipitate from SRB bioactive samples exhibited a greater diversity of iron chalcogenide minerals with reduced iron oxidation states, and minerals incorporating multiple metals compared to abiotic controls. The implication of this study is that iron reduction mediated by biogenic sulfide may be more significant than previously thought in acidic environments. This study not only describes an additional mechanism by which SRB attenuate AMD, which has practical implications for AMD-impacted sites, but also provides a link between the biogeochemical cycling of iron and sulfur.

Dynamic leaching behaviors of heavy metals from recycled coal gangue aggregate under loading conditions during solid backfill mining

In solid backfill coal mining, recycled coal gangue aggregate (RCGA) is subject to the combined effects of overlying strata stress and leaching by mine water in the goaf. This process causes heavy metals to be leached and released from RCGA, which can lead to groundwater contamination. In this study, the release patterns of heavy metals in RCGA under the coupled effects of stress, solution pH, and solution flow rate were investigated, and the interactions between RCGA and the surrounding environment were explored. The findings indicate that: (1) The combined action of effective stress and mine water promotes the leaching of heavy metals. Specifically, the leaching of Pb, Zn, and Mn of RCGA is primarily influenced by the pH value of the leaching solution, while the leaching of Cu and Cr of RCGA is more closely related to the stress level; (2) Acidic environments accelerate the release of carbonate-bound fraction (CAR) in elements, facilitating the transformation of Fe/Mn oxide-bound fraction (XXI) into soluble forms; (3) The leaching ratios (Lr) of heavy metals follow the order: LrZn > LrPb > LrMn > LrCu > LrCr. This research provides guidance for the safe application of RCGA in solid backfill coal mining.

Production of low-sulphur tailings by hydrocycloning

Acid mine drainage (AMD) is an environmental problem in gold mines containing sulphur minerals. The potential for acid drainage in tailings facilities must be considered when studying their dry closure. Therefore, controlling the sulphur content in the final layer of tailings deposition has the potential to prevent AMD after closure. In this context, the rougher flotation tailings were hydrocycloning in a pilot plant in a gold mining company to assess the potential for generating modified tailings with low-sulphur content. A total of 10 samples were composited over one hour of pilot plant operation. The hydrocyclone overflow showed an average reduction of 36.2% in sulphur content and an average metallurgical recovery of 20.0%. The underflow had an average increase in sulphur content of 16.8% and 80.0% metallurgical recovery. These results demonstrated the possibility of generating modified tailings with reduced sulphur content through hydrocycloning.

Scalable mesoporous biochars from bagasse waste for Cu (II) removal: Process optimisation, kinetics and techno-economic analysis

As the world faces the brink of climatological disaster, it is crucial to utilize all available resources to facilitate environmental remediation, especially by accommodating waste streams. Lignocellulosic waste residues can be transformed into mesoporous biochar structures with substantial pore capacity. While biochars are considered a method of carbon dioxide removal (CDR), they are in fact an environmental double-edged sword that can be used to extract metal ions from water bodies. Biochars possess high chemical affinities through chemisorption pathways that are tuneable to specific pH conditions. This work demonstrates how biochars can be enhanced to maximise their surface area and porosity for the removal of Cu (II) in solution. It was found that bagasse derived mesoporous biochars operate preferentially at high pH (basic conditions), with the 1.18 mKOH/mSCB material reaching 97.85% Cu (II) removal in 5 min. This result is in stark contrast with the majority of biochar adsorbents that are only effective at low pH (acidic conditions). As a result, the biochars produced in this work can be directly applied to ancestral landfill sites and carbonate-rich mine waters which are highly basic by nature, preventing further metal infiltration and reverse sullied water supplies. Furthermore, to assess the value in the use of biochars produced and applied in this way, a techno-economic assessment was carried out to determine the true cost of biochar synthesis, with possible routes for revenue post-Cu being removed from the biochar.

Geological factors in the sustainable management of mine water heating, cooling and thermal storage resources in the UK

Re-use of the UK's coal mine water heating, cooling and thermal storage resource is increasing in scale and the number of schemes. The upward trajectory requires 3D planning, regulation and licensing to manage sustainable deployment. We review geological factors controlling thermal and flow processes in the anthropogenically-altered subsurface, critical for resource management with multiple users of the same space. Potential interactions of mine water geothermal schemes with the wider environment are also summarized, leading towards concepts of 3D mine water thermal blocks, protection zones, or management strategies integrating heating, cooling and storage demands. Factors such as the magnitude, extent and timescale of thermal processes to underpin management approaches are poorly quantified by data measured at-scale under varying pumping rates and thermal loads. We demonstrate early insights of how two infrastructures, the UK Geoenergy Observatory in Glasgow and the Coal Authority's Mine Water Heat Living Lab in Gateshead, can measure and monitor heat-flow processes in real world settings to provide an evidence base. For example, a thermal storage test at Glasgow showed rapid temperature changes in the rock and mine workings at the re-injection borehole and indicated an influence of lithologically-controlled transmissivity and thermal conductivity on temperature dissipation and recovery.

A Quantitative Particle-Based Approach for the Geometallurgical Assessment of Tailings Deposits

Tailings generated during ore processing may host significant residual contents of valuable commodities, including critical metals. The particle properties of the tailings, such as mineralogy, particle size, and the surface liberation of ore minerals, strongly control processing behaviour. This study explores a novel combination of methods for incorporating particle data, derived from automated mineralogy, into geometallurgical models of tailings deposits to better understand their reprocessing potential and the economic feasibility of re-mining. This was achieved through binning of different particle types, geostatistical modelling of particle bin frequencies, and bootstrap resampling to reconstruct particle populations. The spatial distributions of processing-relevant particle properties throughout the tailings deposit were predicted with corresponding uncertainties. There are clear systematic trends in the spatial distributions of different particle types, resulting from the sedimentary-style deposition of the tailings. For instance, the tailings nearer the dam walls comprise coarser, silicate-rich particles, while fine-grained and well-liberated sulphide mineral particles are more abundant in the centre of the tailings deposit. As a result, robust models could be developed for the spatial distributions of particle size and mineralogy, which strongly control the sorting of particles during deposition, and other related properties, such as sulphide mineral grain sizes. Finally, a bulk sulphide flotation process was simulated and acid mine drainage potential estimated using the interpolated particle data. Around 58% of the sulphide minerals present could be recoverable by flotation, with the recoverable sulphide portion decreasing towards the centre of the TSF due to the fine-grained nature of the sulphide minerals. The acid mine drainage potential of the tailings is estimated to be moderate to high, indicating that the carbonate minerals present are not sufficient to neutralise the high acid-generating potential of the sulphide minerals. Overall, this study demonstrates how particle-based geometallurgical models can be developed and utilised for practical applications, with the aim of improving the accuracy of resource and reserve estimations of tailings deposits and the sustainable and responsible management of anthropogenic resources. The methodology proposed here can be easily transferred to other tailings deposits.

Insights into catalytic co-pyrolysis of spent coffee grounds and high density polyethylene (HDPE) using acid mine drainage (AMD) treated sludge based catalyst: Analysis of kinetics, mechanism and thermodynamic properties

The present study aims to investigate the catalytic effect of acid mine drainage (AMD) treated sludge based catalyst on the co-pyrolysis of spent coffee grounds and HDPE. The sludge was generated during the treatment of AMD using eggshell and hydrogen peroxide. Theromogravimetric analysis of pyrolysis of spent coffee grounds (SC), HDPE (High density polyethylene), blend of spent coffee grounds and HDPE (SC+HDPE) in the ratio of 1:1, and blended feedstock with sludge derived catalyst (SC+HDPE_AMDC) (1:1 wt. ratio) was conducted at various heating rates of 10 °C/min, 20 °C/min, 30 °C/min and 40 °C/min respectively. Iso-conversional models such as Ozawa Flynn Wall (OFW), Kissinger Akahira Sunose (KAS), Friedman, and Starink were utilized for the determination of activation energy (Ea) of the process. The results showed that using AMD treated sludge based catalyst to the pyrolysis process, enhances its overall efficacy by lowering the activation energy (Ea) (OFW- Ea: 209.11 to 177.14 KJ/mol, KAS-Ea: 208.30 to 173.06 KJ/mol, Friedman- Ea:210.54 to 176.28 KJ/mol, and Starink- Ea:208.60 to 173.44 KJ/mol). Criado's z-master plot (CZMP) method was utilized to analyze the mechanism of the reaction. The pre-exponential factor and thermodynamic parameters were also evaluated. It is concluded that the incorporation of sludge based catalyst (AMDC) lowered enthalpy and randomness of system. Catalytic co-pyrolysis requires less energy, making it more environmental friendly choice for the sustainable processing of biomass and plastics. The present investigation will aid in the design, optimization and scalability.

Geochemical characterization of waste rock dump and its potential to predict acid mine drainage

Acid Mine Drainage (AMD) is an environmental phenomenon that is being experienced by mining companies in Ghana. High levels of heavy metals have been reported in mining areas especially in Obuasi over the years; however, as to whether these heavy metals are being released from the mine wastes (waste rocks) is of concern. Therefore, this paper evaluates the potential of the abandoned Anyankyirem waste rock dump located in Obuasi to cause AMD. Twenty rock samples were collected from various locations of the dump site and their elemental and physicochemical compositions were examined. XRD analysis was conducted to assess the mineralogy of the samples. Acid Base Accounting (ABA) test was used to ascertain the AMD potential of the dump. The ABA test comprises calculating the Acid Neutralization Capacity (ANC) and Maximum Potential Acidity (MPA) of the various samples. The MPA and ANC values were used to compute the rock samples' Net Neutralization Potential (NNP). A column leaching test was carried out. Leachates were collected over a period of 20 weeks. From the column leaching experiment, the rate of weathering of calcium carbonate throughout the 20-week leaching experiment was 3.6 %. Leachates from the column test showed a circumneutral pH (7.1–8.0). The sulphate concentrations from the leachates decreased over the entire period from 96.60 to 3.70 mg/L. Iron recorded the highest concentration of 7783.65 mg kg-1 and the lowest of 0.645 mg kg-1 was recorded in Bi. From ABA test and the column leaching test results, Anyankyirem waste rock dump is not acid generating and therefore can serve as buffer for high pyrite waste rocks. However, significant levels of some heavy metals (As, Fe, Zn, Cr, Mn and Se) were recorded in the leachates even though the leachates’ pH were circumneutral. The results suggest that not only acidic conditions can leach out heavy metals.

Mobility and fractionation of rare earth elements during black shale weathering: Implications from acid rock drainage and sequential extraction study

Black shale is a type of sedimentary rocks that are enriched in rare earth elements (REEs). It is of both economic importance and environmental significance to understand REE mobility during black shale weathering. The present study approaches to this by analysing REEs in acid rock drainage (ARD) from black shale weathering system, fresh and weathered black shales, soils derived from black shales, and sequential extractants from black shales at Dongping town in Hunan province (China). Results showed that REEs had variable high concentrations in ARD as shown by total REE + Y (∑REY) concentrations from 162 to 4074 (μg/L). REEs in ARD displayed hat-shape NASC-normalized patterns with significant enrichments of middle REEs (MREE) relative to light REEs (LREE) and heavy REEs (HREE), and had significant negative Ce (Ce/Ce⁎ = 0.6) and positive Y (Y/Y⁎ = 1.5) anomalies. MREE enrichment in ARD could be evaluated using MREE/MREE⁎ values, which varied from 1.43 to 1.81 with a mean of 1.65, distinctly higher than those of whole rocks (around 1.0). 1 M HCl extraction results suggested that REEs were integratedly mobilized during shale weathering, while six-step extraction studies identified that REEs in ARD resulted from exchangeable and Fe-oxide fractions with MREE and HREE enrichment in shales respectively. MREE in exchangeable and HREE in Fe-oxide fractions were preferentially released during weathering, as illustrated by plots of MREE/MREE⁎ against HREE/LREE ratios of ARD and six-step extractants. Therefore, geochemical processes for REE mobility during black shale weathering included integrated mobilization and preferential release. Integrated REE mobilization resulted from the dissolution of REE-bearing minerals and oxidation of sulfides. Preferential REE release resulted from acid fluids produced by sulfide oxidation during weathering. Thus, a new model was proposed for interpreting geochemical processes of REE mobility during black shale weathering, and for understanding REE distribution in ARD from natural and anthropogenic systems.

Photochemical Origins of Iron Flocculation in Acid Mine Drainage.

Acid mine drainage (AMD) raises a global environmental concern impacting the iron cycle. Although the formation of Fe(III) minerals in AMD-impacted waters has previously been reported to be regulated by biological processes, the role of abiotic processes remains largely unknown. This study first reported that a photochemical reaction coupled with O2 significantly accelerated the formation of Fe(III) flocculates (i.e., schwertmannite) in the AMD, as evidenced by the comparison of samples from contaminated sites across different natural conditions at latitudes 24-29° N. Combined with experimental and modeling results, it is further discovered that the intramolecular oxidation of photogenerated Fe(II) with a five-coordinative pyramidal configuration (i.e., [(H2O)5Fe]2+) by O2 was the key in enhancing the photooxidation of Fe(II) in the simulated AMD. The in situ attenuated total reflectance-Fourier transform infrared spectrometry (ATR-FTIR), UV-vis spectroscopy, solvent substitution, and quantum yield analyses indicated that, acting as a precursor for flocculation, [(H2O)5Fe]2+ likely originated from both the dissolved and colloidal forms of Fe(III) through homogeneous and surface ligand-to-metal charge transfers. Density functional theory calculations and X-ray absorption spectroscopy results further suggested that the specific oxidation pathways of Fe(II) produced the highly reactive iron species and triggered the hydrolysis and formation of transient dihydroxo dimers. The proposed new pathways of Fe cycle are crucial in controlling the mobility of heavy metal anions in acidic waters and enhance the understanding of complicated iron biochemistry that is related to the fate of contaminants and nutrients.

Oxidative weathering of pyrite in acidic environments: Data-driven experimental evaluation coupled with Raman hyperspectral imaging

This study deals with the identification of the factors that affect pyrite oxidation in acid mine drainage conditions. For this scope, weathering experiments have been carried at laboratory scale based on the design of experiments methodology to evaluate the effect of factors such as major ion concentrations, crystal size, and humic acids presence over the amount of elemental sulfur produced due to the involved weathering reactions. In particular, metal and anionic concentrations in solution were quantified by inductively coupled plasma-atomic emission spectroscopy and ion-chromatography techniques, respectively, whereas the amount of elemental sulfur was quantified with a high-performance liquid chromatography with diode-array detection technique after proper extraction procedure. A partial least squares regression was calculated to establish a quantitative relationship between the considered factors and the amount of elemental sulfur. After evaluation of the model, ferric iron, crystal size and the presence of humic acids were identified as the relevant factors for pyrite oxidation under acidic conditions. In addition, the surface of the samples was characterized by Raman imaging spectroscopy and subsequently analyzed by explorative hyperspectral analysis methods to assess the spatial distribution of the elemental sulfur as the main weathering product, resulting in a homogenous distribution.

Hydrochemical Characteristics, Controlling Factors and Groundwater Sources of Zaozigou Gold Mine

The Zaozigou gold deposit is recognized as one of the largest and most significant independent gold deposits in northwest China, representing a colossal orogenic gold-antimony deposit. It is imperative to delve into the hydrochemical characteristics and controlling factors within the mining area to unveil the groundwater circulation evolution process and enhance water resource management. In 2018, a comprehensive collection of 50 groups of groundwater samples was conducted, alongside 17 groups of surface water and underground mine water samples in 2023. Compositional descriptive analysis, correlation analysis, Piper three-plot, Gibbs map, ion ratio method, hydrogeochemical simulation and PCA methods were employed to reveal the chemical characteristics and evolution process of groundwater in the Zaozigou gold mine. Furthermore, employing water isotopes theory allowed for the identification of recharge sources and circulation conditions within the Zaozigou Gold Mine. The findings indicated a transition from HCO3-Na·Ca type polluted water in 2018 to primarily the SO4-Ca·Mg type and HCO3·SO4-Na·Ca·Mg type groundwater hydrochemistry types by 2023. The hydrochemical characteristics of the study area are closely related to the mining depth and time. The chemical characteristics are influenced by various factors such as rock weathering, mineral dissolution, cation exchange processes, atmospheric precipitation as well as human activities related to pollution from industrial mining activities.

Alkali-activated materials containing mine tailings and zeolite for seepage water treatment in a closed nickel mine

AbstractIn the present study, alkali-activated materials were assessed as adsorbents for mine water treatment. The composition of alkali-activated materials, involving mixtures of metakaolin, blast-furnace slag, mine tailings, and zeolite, was optimized based on their leaching behavior and adsorption performance. The most effective adsorbent contained solely blast furnace slag as an aluminosilicate precursor and was selected for a pilot-scale study at a closed nickel mine in Finland. In the pilot, seepage water from a gangue area with an influent flow rate of 0.5 m3/d was treated using a permeable reactive barrier set-up containing 10 kg of slag-based adsorbent prepared by a granulation-alkali activation process. During a one-week experiment, the adsorbent granules were capable of effectively uptaking Ni, Fe, and Mn from the seepage water; the removal percentages of Ni, Fe, and Mn were 82.4%, 81.6%, and 82.5%, respectively. The results indicated the feasibility of blast furnace slag-based adsorbents for toxic element removal in a potentially sustainable approach.

Characteristics of roof rock failure during coal seam mining and prediction techniques for mine water inflow in exposed karst areas

Characteristics of roof rock failure during coal seam mining and prediction techniques for mine water inflow in exposed karst areas

Development of a Hydrometallurgical Process for the Extraction of Cobalt, Manganese, and Nickel from Acid Mine Drainage Treatment By-Product

Critical minerals (CMs) are pivotal in modern industries, such as telecommunications, defense, medicine, and aerospace, contributing significantly to regional and global economic growth. However, the reliance on external sources for 26 out of 50 identified CMs raises concerns about supply chain vulnerabilities. To address this, the research focused on developing a hydrometallurgical process for extracting cobalt, manganese, and nickel from acid mine drainage (AMD) treatment by-products, emphasizing the need to diversify CM supply chains within the United States (US). A solution composed of an REE solvent extraction raffinate loaded with cobalt, manganese, nickel, and various impurity metals was utilized as a feedstock in this study. The developed hydrometallurgical process involved initial sodium hydroxide precipitation to remove impurities like aluminum and iron from an SX raffinate solution generated during the extraction of rare earth elements (REEs). Precipitation stages were performed in a pH region ranging from 2 to 12 to identify the optimum pH values, achieving a tradeoff between recovery and impurity removal. A subsequent precipitation process at pH 5–10 yielded a product rich in CMs, such as manganese, cobalt, and nickel. Further separation steps involved nitric acid washing, resulting in a Mn product with a purity of 47.9% by weight and a solution with extractable concentrations of cobalt and nickel. Stagewise precipitation with sodium sulfide subsequently produced three solid products: cobalt and nickel product at pH 1–5, manganese product at pH 5–10, and magnesium at pH 10–12. The study also explored other separation approaches, including solvent extraction, to enhance the separation of nickel from cobalt. Overall, the developed hydrometallurgical process generated the following products with varying degrees of purities: cobalt (9.92 wt.%), nickel (14 wt.%), manganese (47.9 wt.%), and magnesium (27.49 wt.%). This research aimed to contribute to the sustainable extraction of CMs from secondary sources, reducing the US’ reliance on imports and promoting a more resilient supply chain for these crucial elements.

Characterizing and tracing the heavy metals' spatial distribution in karst surface river affected by acid mine drainage

A series of pollution problems have been caused by the drainage of closed coal mines. This study focuses on the XZ River in Guizhou Province, employing a comprehensive approach involving hydrochemical analysis, mathematical statistics, and one-dimensional water quality modeling to investigate the spatial evolution and source apportionment of heavy metals in karst surface rivers affected by AMD. The average pH, EC, and Eh values of groundwater and surface water in the XZ river basin were 6.27, 331 <i>μ</i>s/cm, 230 mV and 3.86, 1671.57 <i>μ</i>s/cm, 412.71 mV, respectively, indicating severe pollution of surface water by AMD. The study reveals that groundwater in the XZ River Basin is predominantly of the HCO<sub>3</sub>-Ca-Mg type, shifting to HCO<sub>3</sub>-SO<sub>4</sub>-Ca-Mg type with the influx of acid mine wastewater. Utilizing statistical methods for source apportionment analysis indicated that downstream concentrations of Fe, Mn, Zn, Cu, As, and Sr most likely originate from tributaries. Further analysis through one-dimensional water quality simulation confirmed that downstream concentrations of Fe, Mn, Zn, Cu, As, and Sr are attributed to tributaries. This suggests that XZ River is affected by pollution from different coal mines, primarily from coal mine M4, followed by coal mine M1.