Abstract:In order to respond to the construction of "waste-free city" in Baotou city and the requirements of mine environmental improvement, typical industrial solid waste (fly ash) is planned to be landfilled for ecological remediation of the mine. However, it is unknown whether the long-term environmental behavior of fly ash landfill will cause pollution to the mine soil and groundwater, the long-term environmental behavior of heavy metals after fly ash was landfilled in mine pit was studied by the indoor simulation method of freeze-thaw cycles-dry-wet, Hydrus-1D model and solute transport model prediction.The results showed that：After 5 years of landfill，the contents of heavy metals Cd, Pb, Cr and Cu decreased by 0.4, 3.23, 16.67 and 12.93 mg/kg respectively, while the contents of Pb, Cr, Cu and Cd in mine soil increased by 9.27, 8.3, 3.3 and 0.04 mg/kg, respectively. At the same time, the speciation analysis showed that Cd and Cr in fly ash are mainly organic-matter bound, Pb is mainly in the residual, and the heavy metal forms changed from Fe-Mn oxides-bound and organic matter- bound to solube-exchangeable and carbonate-bound, which indicated that the heavy metal forms are transformed from stable state to easy migration state. The simulation results showed that five years after the fly ash is landfilled in the mine pit, the heavy metal elements have a tendency to migrate and transform to the surrounding environment. Therefore, in the process of landfill, an anti-seepage layer is laid at the bottom of the mine pit. The four heavy metals (Cr, Cd, Cu, and Pb) did not pose the risk of heavy metal migration to the mine pit soil and groundwater environment, its content is far lower than the screening value in the “Soil Risk Control Standard for Construction Land with Soil Environmental Quality” (GB 36600—2018) and the pollutants in the groundwater in the affected area are lower than the Class IV groundwater standard. Under this condition, the fly ash meets the landfill standard and can be landfilled.This study can provide scientific basis and reference for the application of solid waste in ecological utilization engineering of mines.