Chemical speciation, distribution, and leaching behaviors of heavy metals in alkali-activated converter steel slag-based stabilization/solidification of MSWI FA

The safe disposal of hazardous heavy metals in municipal solid waste incineration fly ash (MSWI FA) has become an urgent problem for society. This work aimed to investigate the chemical speciation, distribution, and leaching behavior of Zn and Pb in alkali-activated converter steel slag-based stabilization/solidification of MSWI FA. Compared with untreated MSWI FA, leaching of Pb and Zn in the solidified body were greatly reduced. Pb and Zn on the surface of untreated MSWI FA existed in the form of PbCl2, PbCO3, PbSO4, ZnO and ZnCl2, equivalent to the exchangeable and carbonates state in sequential extraction process. Leaching behaviors of Pb and Zn were closely related to the proportion of the exchangeable and carbonates states. The chemical speciation of Pb and Zn were converted into more stable and insoluble precipitate. C-(A)-S-H in the solidified body modified by steel slag showed higher degree of polymerization and crosslinking than alkali-activated MSWI FA matrix, reducing the migration activity of Pb and Zn. Due to the incorporation of steel slag, Friedel’ salt was generated and contributed to the stabilization of chlorine.