Behavior of Sb and As in the hydrogeochemistry of adjacent karst underground river systems and the responses of such systems to mining activities

Through the investigation of Qinglong mining area and adjacent karst underground river system, mining activities and water-rock interactions are found to control the hydrogeochemical evolution of karst underground water. Along the flow direction of the karst underground river, the hydro-chemical type is converted from HCO₃-Ca type to SO₄-Ca type. The concentrations of Sb and As also gradually decrease. Using PHREEQC to calculate the SI shows that: in the karst underground river system, both gypsum and fluorite are unsaturated, indicating a high degree of water-rock interaction. LogPCO₂ is negatively correlated with pH, indicating that the karst underground river systems are both open systems. The dissolution of carbonate minerals and the alternate adsorption of ions are the main water-rock interactions that lead to the rapid decline of Sb and As concentrations. This research also applies principal component analysis to identify the types of pollution in adjacent karst underground river systems. The results show that the LongBaiwei underground river was mainly affected by coal mining activities, and Fe was more prominent; the ShuiYa underground river was more significantly affected by the leachate from the antimony tailings yard. This study provides a scientific basis for the evolution of the water environment as well as strategies for pollution prevention and control in typical karst underground river systems owing to the influence of mining activities.