Study on the distribution characteristics and ecological risk of heavy metal elements in coal gangue taken from 25 mining areas of China

The long-term, high-yield production of coal has resulted in the large-scale accumulation of coal gangue on the ground surface, which causes serious environmental problems. Therefore, clean and environmental treatment of coal gangue is urgently needed. In this study, the inductively coupled plasma mass spectrometer and atomic fluorescence spectrometer were used to test the background values of ten heavy metals in coal gangue taken from 25 coal mines across China; the average content, distribution characteristics, and genesis of heavy metals in these coal gangue were investigated, and the ecological risk of heavy metals in coal gangue in different regions and different geological ages was analyzed and tested. The results show that the average contents of Hg, Pb, Cd, Cr, As, Cu, Zn, Mn, Se, and Be in the coal gangue are 0.081, 17.444, 0.234, 63.329, 2.658, 43.697, 59.290, 427.460, 1.205, and 1.819 mg/kg, respectively; the enrichment sequence of heavy metal elements of coal gangue in geographical areas and geological ages are ordered as follows: South China region > North China region > Northeast China region > Northwest China region, P-2 > C-2-P-1 > K-1 > J(1-2) > E-N. The results also show that Hg has a strong pollution risk, Cd has a moderate pollution risk, and the remaining eight heavy metals have minor pollution risks, and the overall ecological risk indices (RI) of heavy metals in different geographical areas are ordered as (RI) over bar (South China) > (RI) over bar (North China) > (RI) over bar (Northeast China) > (RI) over bar (Northwest China). Moreover, the hydrothermal process occurring in unique sedimentary environments during the formation period is a key factor for the regional heavy metal enrichment in coal gangue.