In this study, the contents of eight heavy metal(loid)s (As, Pb, Zn, Cd, Cr, Cu, Sb and Tl) in 50 sediment samples from a headwater of Beijiang River were studied to understand their pollution, ecological risk and potential sources. Evaluation indexes including sediment quality guidelines (SDGs), enrichment factor (EF), geo-accumulation index (I_geo), risk assessment code (RAC) and bioavailable metal index (BMI) were used to evaluate the heavy metal(loid)s pollution and ecological risk in the sediments. Pearson’s correlation analysis and principal component analysis were used to identify the sources of heavy metal(loid)s. The results showed that the average concentration of heavy metal(loid)s obviously exceeded the background values, except Cr. Metal(loid)s speciation analysis indicated that Cd, Pb, Cu and Zn were dominated by non-residual fractions, which presented higher bioavailability. The S content in sediments could significantly influence the geochemical fractions of heavy metal(loid)s. As was expected, it had the most adverse biological effect to local aquatic organism, followed by Pb. The EF results demonstrated that As was the most enriched, while Cr showed no enrichment in the sediments. The assessment of I_geo suggested that Cd and As were the most serious threats to the river system, while Cr showed almost no contamination in the sediments. Heavy metal(loid)s in sediments in the mining- and smelting-affected area showed higher bioavailability. According to the results of the above research, the mining activities caused heavier heavy metal(loid)s pollution in the river sediment. Three potential sources of heavy metal(loid)s in sediment were distinguished based on the Pearson’s correlation analysis and PCA, of which Cd, Pb, As, Zn, Sb and Cu were mainly derived from mining activities, Cr was mainly derived from natural sources, Tl was mainly derived from smelting activities.

The Fengfeng mining area is in the transition zone between the North China Plain and the Taihang Mountains, and groundwater is the main source of water supply in the district. Under the combined influence of human activities and natural geological conditions, the quality of different types of groundwater varies greatly, posing a potential threat to the safety of drinking water. In this study, hydrogeochemical processes in different types of groundwater were analyzed using multivariate statistical analysis methods with ion–ratio relationships, and a groundwater quality and health risk assessment model was developed. The research findings show that the main chemical components and TDS in the groundwater have obvious spatial distribution characteristics, i.e., the content of deep karst water (DKW) in the west is significantly lower than that of shallow pore water (SPW) in the east, and the hydrochemical type has changed from HCO₃–Ca to SO₄–Ca. The chemical components of SPW and DKW are mainly derived from silicates and carbonates, accompanied by weathering dissolution of sulphidic minerals, especially SPW. The chemical components of the groundwater was also influenced by the cation exchange reaction and human activities. The quality of the SPW was significantly worse than that of the DKW, and the nitrates in SPW carry a high non-carcinogenic risk, especially to children. The shallow pore water is not suitable for drinking water. This study can provide guidance on the safety of drinking water in the Fengfeng coal mining area and other areas with intensive industrial, mining, and agricultural activities.

The oxidation of sulfide minerals in the presence of oxygen and water, facilitated by microbes, is the principal cause of acid mine drainage (AMD). Static testing for the quantitative assessment of the acidic potential and acid-neutralizing capacity of mineral samples has been thoroughly investigated; the extent of its accuracy remains uncertain. This study involved 329 ore samples from 34 drill holes from abandoned mining sites and conducted laboratory static tests and mineralogical analysis. Static testing and mineralogical characterization identified a significant positive correlation between total sulfur and net acid generation (NAG), confirming that sulfide oxidation is the dominant mechanism for acid production. Furthermore, the strong positive correlation between calcium content and acid-neutralizing capacity (ANC) demonstrates that the buffering capacity stems mainly from carbonate dissolution, with negligible contribution from silicate weathering. The effectiveness of a detailed acid-generating potential discrimination chart was also assessed. Through the examination of acid drainage samples and groundwater from the research area, with their stable isotope and Deuterium excess (D-excess) properties, hydrochemical classifications were established, and sources of acid drainage were evaluated. This comprehensive method pinpoints the main “acid-generating sources” in the abandoned mining sites, elucidating the geochemical origins of acid drainage in the research area. It offers a case study and analytical framework for employing static test findings from abandoned mining sites to evaluate acid-generating potential in those areas.

Dissolved organic matter (DOM) in coal mine drainage (CMD) interacts with potentially toxic elements (PTEs), posing environmental risks across diverse coal-bearing basins in China. CMD from 37 mines were classified hydrogeochemically into three categories and were analyzed by multi-spectroscopy. CMD in Category II (pH = 5.78) confronted with severe PTEs enrichment, with Fe concentration reaching 275.23 mg·L^-1 (917 ×standard) alongside uniquely elevated Tl (502 ×standard). Mn, Al, Hg, Cd, Pb, B, Co, and Mo also exhibited category-specific risks in CMD. DOM was predominantly composed of lignin-derived polyphenols (C3, 59.36 %). Category I showed the highest microbial-derived humic-like fluorescence intensity (C2) and the strongest aromaticity (SUVA₂₅₄ = 0.31 L·(mg·m)^-1), while Category II displayed prominent gallic acid-like components (C1), peak chromophoric DOM (a(350) = 8.18 m^-1), and relatively the highest molecular weight. DOM composition in CMD was controlled by hydrogeochemical and environmental characteristics, such as pH and TDS, exhibiting autochthonous sources and weak humification. Redundancy analysis identified Ba, significantly correlated with DOC, as the primary driver of DOM spectral variation (54.20 % explained). DOM composition in CMD was significantly influenced by coal, with both systems dominated by lignin (53.09 %-55.78 %) and CHO compounds (53.94 %-64.20 %). Predicted transformation pathways for coal-derived molecules entering CMD involved decarboxylation (25.91 %), oxygen addition (25.85 %), and dealkyl group (22.64 %), which mainly occurred in the lignin/CRAM and were dominated by the reduced states, resulting in obvious disappearances of CHOS compounds. XGBoost-SHAP modeling confirmed that the nominal oxidation state of carbon was the key feature predicting molecular reactivity (mean |SHAP| = 1.43), followed by the O/C ratio (1.17). These findings provided molecular-level insights for environmental management in coal mines.

This study aims to address the critical challenge of the formation of acid mine drainage (AMD) in coal mining areas by systematically investigating groundwater recharge pathways and developing targeted source reduction strategies. A range of methods were employed, including field investigations, surveying and mapping, in situ measurements of hydraulically conductive fracture zones (HCFZs), spatial and hydrological analyses, yielding multi-source data. Based on the comprehensive dataset obtained, a novel methodology was developed to identify surface water infiltration pathways. Downhole video monitoring results indicate that the advancements in coal mining technology have gradually increased the heights of HCFZs. Furthermore, mining-induced fissures in hard rock layers were found to extend further vertically and form dense, interconnected networks, leading to higher permeability coefficients compared to those in weak rock layers. Surface water preferentially infiltrates at intersections of HCFZs, coal seams, and topographic features. Notably, groundwater recharge in the goaves of the No. 10 coal seam primarily occurs along the paleo-valley system where natural drainage aligns with mining-induced fissures. This study provides an example of source reduction treatment for AMD in mining areas.