Effects of Site Karst Water on Fresh Coal Gangue at Baizhuang Coalfield, China—Leaching Characteristic

Abstract

In mining areas where gangue is used for infill mining, Ordovician limestone karst water is affected by discarded gangue, and the water quality changes significantly. In this study, the effects of gangue on water quality change under different immersion solution conditions were evaluated by Zhai Zhen Coal Mine, Hongqi Coal Mine Ordovician Limestone Karst Water, and Baizhuang Coal Mine. The results showed that the cations in each group of immersion solutions had similar trends, and the Na+ concentration fluctuations were greater in karst water immersion solutions with higher initial sodium ion concentrations, while the fluctuations of calcium and magnesium ions were more obvious in the early stage of immersion, and the fluctuations were gradually slowed down in the later stage. The anions in the immersion solution also have a similar fluctuation trend, but only in the early stage of immersion. By comparing the changes of the three indexes (pH, TDS, and ORP) in the immersion solution, it was found that highly mineralized karst water had a good buffering effect on the changes in the basic water quality index, while the ultrapure water quality index with low salinity had the greatest change. The 100% stacked columnar plot between the main water chemical ion changes shows the relative scale relationship of the water chemical components in the immersion solution at each period, and the water chemical components change significantly in the early immersion period (0–7 d), and then enter the fluctuation changes period, and the ion changes in the fluctuation changes period are mainly Na+ and SO42− ions. This study provides a theoretical basis for exploring the changes of gangue to the quality of karst water in Ordovician limestone and also provides theoretical guidance for the study of groundwater pollution mechanisms in closed coal mines.