Characterization of heavy metals in coal gangue-reclaimed soils from a coal mining area

Coal gangue is practically used as a filling material for soil reclamation in the coal mining subsidence areas. Due to the toxic elements enriched in coal gangue, the reclaimed soils potentially pose great environmental concerns. In this study, we investigated the distribution and mobility of six heavy metals (As, Cr, Cu, Mn, Pb and Zn) in coal gangue-reclaimed soils (n = 26) from a typical coal mining area of Huainan Coalfield, China. The concentrations of Cu, Pb and Zn in the reclaimed soils were enriched by a factor of 1.51, 1.48 and 2.05 compared to the original agricultural soils, indicating potential migration of these heavy metals from coal gangue to soils. The soils of the finest particle grain size fraction (< 74 mu m) had the highest concentrations of these heavy metals. The sequential extraction procedure results demonstrated that major portions of As, Cr and Pb existed in the residual fractions, whereas Mn was dominated in the reducible fraction and Cu, Zn in the oxidizable fractions. The results of risk assessment code and individual contamination factor revealed that Mn had a medium risk to the local ecology and the other heavy metals had lower potential risks. This study has a great implication to understand the behavior of heavy metals in soils and to implement various remedial options for soil pollution.