Hydrogeochemical genesis and resource utilization of mine water in ecologically vulnerable coal-rich regions

The coal mining areas spanning the Inner Mongolia-Shaanxi border represent both a quintessential ecologically vulnerable zone and a critically important coal production base in China. However, large-scale, high-intensity coal mining has generated vast amounts of mine water. Currently, investigating the hydrogeochemical genesis of mine water and advancing its resource utilization have become critical issues for the green transition of coal industry. This study systematically collected mine water samples from multiple active large-scale coal mines in the region. The hydrogeochemical characteristics and formation mechanisms of the mine water were revealed through laboratory testing and data analysis, and technical pathways for the classified utilization of mine water were proposed based on water quality characteristics. The results indicate that the mine water in the study area is generally weakly alkaline, with an average TDS value of 2 053.57 mg/L. The dominant cations are Na⁺ and Ca²⁺, while the dominant anions are SO₄²⁻ and HCO₃⁻. The hydrochemical types are primarily SO₄-Na, HCO₃-Na and HCO₃-Ca. The chemical composition of the mine water is jointly controlled by silicate weathering and dissolution, evaporative concentration, and cation exchange. The main exceeding indicators in the mine water include TDS, Na⁺, SO₄²⁻, total hardness (TH), Cl⁻,and F⁻. Among these, TDS and Na⁺ have the highest exceeding rates(65%), followed by SO₄²⁻(45%). Furthermore, the integrated weighted water quality index was employed to evaluate mine water quality: Class Ⅰ and Class Ⅱ water each accounted for 25%, Class Ⅲ for 10%, and Class Ⅳ and Class Ⅴ accounted for 5% and 35%, respectively. Class Ⅰ mine water meets the quality requirements for ecological and agricultural irrigation use, whereas water of other classes is unsuitable for direct utilization and requires targeted treatment measures based on its specific hydrochemical characteristics to prevent soil salinization and vegetation degradation.