Leaching behavior and environmental risk assessment of toxic metals in municipal solid waste incineration fly ash exposed to mature landfill leachate environment.

Solidification/stabilization pretreatment + landfill disposal in municipal solid waste (MSW) landfill sites is a widely accepted MSW incineration (MSWI) fly ash (FA) management strategy in China. However, in reality, the stability of FA disposed in MSW landfill sites may be affected by the organic landfill leachate environment. The purpose of this study was to explore the mobility and environmental risks of six toxic metals (M, Pb/Zn/Cu/Cd/Cr/Ni), from raw and solidified/stabilized FA, by simulating a leaching environment with mature landfill leachate (MLL). The leaching of M mainly occurred in the early leaching stage, and their leaching behavior was controlled by the diffusion of surface M in the FA matrix. The destructive effect of dissolved organic matter (DOM) on the local precipitation-dissolution equilibrium of FA-leachate interface, the formation of non-adsorptive DOM-M complex (easy to migrate), and the competitive effect of DOM on the binding sites of M on the surface of the FA matrix may play an important role in increasing the leaching level of most M. By contrast, the potential of solidified FA in reducing the environmental risk level of leached M was better than that of stabilized FA. However, the immobilization capability of solidification/stabilization pretreatment on various types of M in FA should be judged according to their practical disposal environment. Compared to MLL leaching tests, Acetic Acid Buffer Solution Method (HJ/T300-2007) can effectively strengthen the exposure environment and provide a reliable reference level of environmental risk for MSWI FA disposed in MSW landfill sites.