Mechanochemical treatment with red mud added for heavy metals solidification in municipal solid waste incineration fly ash

The effective stabilization of heavy metals municipal solid waste incineration fly ash (FA) is very important for the disposal of FA, due to that heavy metals leaching from FA will induce environmental risks to a content. In this study, Red mud (RM) was used as an additive for the stabilization of heavy metals in FA during the mechanochemical process. The results demonstrated that the addition of RM significantly reduce the leaching of Pb, Cr and Zn from FA. In the conditions of 30 wt% of red mud, 0.1 g L−1 of solid-to-liquid ratio and 24 h of ball-milling time, the leaching concentration of Pb, Cr and Zn decreased by 99%, 81.18% and 100%, respectively. Meanwhile, the residue fraction of Pb, Cr and Zn increased, part of the reducible Cr is changed into acid-soluble fraction of Cr due to oxidation. Moreover, FA was broken into small particles and then agglomerated into larger ones after mechanochemical treatment. The main reasons accounting for the solidification of heavy metals were ascribed to the precipitation and sealing by the fine particles, capture by new phases, dissolution and elution of soluble salt. RM play a key role in forming new phases (include hydrocalumite, andradite and aluminosilicate minerals) which in favor of solidification of heavy metals. This work provides a good method for the effective heavy metals stabilization in FA and presents a new sight into the reuse of RM.