A Comparative Study on Pollution Assessment and Migration Paths of Slag Heaps from Coal Gangue and Pyrite in the Mountainous Areas of Southeast China

This study focuses on the pollution assessment, potential ecological risks, influencing factors, and migration pathways of trace elements from slag heaps of coal gangue and pyrite to farmland in the mountainous areas of southeast China. Based on the pollution index and correlation analysis of trace elements, Cd, As, Pb, and Zn were identified as characteristic pollutants. In the solid waste, surrounding soil, and farmland soil, the mean concentrations of Cd, As, Pb, and Zn of pyrite slag heaps were generally 9.7–86.7 times higher than those of coal gangue dumps. In contrast, higher levels of As were found in coal gangue surrounding soil, while higher Cd and As concentrations existed in coal gangue-affected farmland soil. Mantel test results revealed significant statistical correlations between characteristic pollutants and environmental factors (geographic location, weather, and climate), particularly for pyrite slag heaps. The potential migration pathways from solid waste to the surroundings (soil and water) and then to farmland soil were finally revealed using partial least squares path modeling. This study demonstrated that the pyrite slag heaps were more heavily polluted than the coal gangue dumps. The pyrite slag heap was more susceptible to environmental factors, which could rapidly transfer trace elements to farmland soil via the surrounding soil and water. Therefore, this study offers a statistical framework to infer plausible trace element migration trends via multi-medium monitoring data. It also delivers comparative analytical references for risk assessment of two distinct types of slag heaps.