Understanding the release, migration, and risk of heavy metals in coal gangue: An approach by combining experimental and computational investigations

The lack of understanding on the environmental fate and implications of heavy metals in coal gangue (CG) has restrained its utilization. Conventional extraction methods provide empirical measures of heavy metal speciation, lacking a detailed description of bound strength, which limits long-term risk assessment. In this study, the releasing and migrating behavior of six heavy metals (Cd, As, Pb, Ni, Cu, and Cr) were investigated through an approach by combining experimental and computational investigations. The corresponding mechanisms and risks were understood and discussed on a molecular level. The results suggested that CG is primarily a natural kaolinite α-quartz and anatase mineral. The sequence extraction results showed that heavy metals in CG are mainly distributed in stable silicate and iron manganese oxide-bound states. The toxicity characteristic leaching procedure test advised Cu, Cr, Ni, and Pb had a high toxic level and thus required long-term monitoring and controlling. A quantum chemical calculation demonstrated that the heavy metals were more likely to be embedded in silicate minerals with high binding energy than those binding on the anatase surface. The findings of this research provide a promising approach to comprehensively evaluate the stability mechanism and potential long-term risks of heavy metals in solid waste.