Abstract
Metal sulfide oxidation in abandoned exposed stone coal mines leads to the generation of Acid Mine Drainage (AMD), characterized with high uranium concentration, which is a major concern for local public health. This work employs an approach of geochemical analysis and modelling to determined the mode of occurrence of uranium. Additionally, potential environmental risks were evaluated.
The results revealed that the primary source of uranium pollutants in the surrounding environmental media was attributed to the weathering of mine waste. Concentrations of harmful elements (e.g., U, Fe, sulfate) and acidity in water rapidly decreased to background levels with increasing distance from the mine. The geochemical distribution characteristics of sediments and water exhibit notable similarities. The species of uranium underwent a transformation as uranium in mine waste rocks migrated to environmental media. In acidic pit water, uranium primarily existed as uranyl sulfate, gradually transitioning downstream to complexes dominated by hydrophosphate and carbonate. This transition was accompanied by the coprecipitation of significant amounts of uranium with phosphate and iron hydroxides. Results from the geoaccumulation index (Igeo) and risk assessment codes (RAC) indicated that uranium in unweathered coal waste rocks and newly formed pit sediments posed a high environmental risk, with a bioavailable fraction reaching up to 26.44% and 48.0%, respectively. This research holds significant importance in devising remediation and management strategies for abandoned coal mines to mitigate the impact of uranium release and mobility on the surrounding ecological environment.