Heavy Metal Migration and Potential Environmental Risk Assessment During the Washing Process of MSW Incineration Fly Ash and Molten Slag

Based on the simulated moderate acid rainfall condition, MSW fly ash and molten slags were washed to investigate the effect of alkalinity on the migration and the speciation transformation of heavy metals in the approaching natural environment. All the samples were washed 150 min at 25̊C with the 100ul/min flow speed, then the after-washing samples were placed at air atmosphere for 60 days to get dried after-washing fly ash and molten slag samples. The total concentration of heavy metals in raw fly ash was followed by Zn>Pb>Cu>Cr>Cd>As>Ni, After washing process, the order is still the same, and the content of heavy metals in fly ash were significantly increased due to soluble salt leaching, especially Cr, Cu, Ni, Zn. The potential ecological risk (PEI) analysis, using STI toxicity model, indicated that PEI index of fly ash after washing was 2.3 times than that before washing. Therefore, it will cause greater ecological risk for the open storage of fly ash. When the fly ash was converted into molten slag, the alkalinity in the range between 0.8 and 1.2 was benefical for reducing PEI index of molten slags. The ash molten slag can be directly used as roadbed material due to the good solidification effect of heavy metals.