Treatment method of acid wastewater in closed pit coal mine: a case study of Pingmoshan Closed Pit Coal Mine in Daozhen County of Guizhou Province

A case study of Pingmoshan Closed Pit Coal Mine in Daozhen County of Guizhou Province, to explore the practical technology suitable for the treatment of acid wastewater（ADM） from closed pit coal mine in karst mountainous area, and to provide reference for the acid wastewater treatment project from closed pit coal mine in karst mountainous area. The relationship of surface water and groundwater recharge, drainage and discharge as well as the quantity and quality of acid wastewater in the mining area are comprehensively analyzed. The method of combining active treatment and passive treatment is adopted to carry out comprehensive treatment through sewage diversion project, acid wastewater purification and upgrading project, constructed wetland purification project, reclamation project and auxiliary project. After the completion of the project, the water samples at the end of the treatment area are tested and analyzed. The results show that the pH value of the water at the end of the treatment area is 6.42, the concentration of sulfate ion（SO4²⁻） is 248 mg/L, the concentration of iron ion（Fe） is 5.42 mg/L, and the concentration of manganese ion（Mn） is 3.28 mg/L. The concentration of suspended matter is 46.64 mg/L, and the results show that the 5 important monitoring indicators pH value, sulfate ion, iron ion, manganese ion and suspended matter concentration are all lower than the emission standard of Coal Industry Pollutant Discharge Standard（GB 20426—2006）, and the treatment effect is relatively significant. While effectively improving the ecological environment of the mining area, the cultivated land area is increased by 4 800 m², the vegetation restoration area is increased by 918 m², and the basin protection length is 9.8 km. The research results can provide a technically feasible and economically reasonable treatment model for acid wastewater treatment of abandoned closed pit coal mine in karst mountainous areas.