Formation of the self-assembled magnesium oxychloride cement in the alkali-activated geopolymerized municipal solid waste incineration fly ashes and exploration of interactive mechanisms.

The disposal of municipal solid waste incineration fly ashes (MSWI-FA) is complicated by soluble chlorides, which increase the risk of heavy metals (HMs) leaching toxicity and hinder the further use of remediated MSWI-FA. In this study, the self-assembly potentiality of magnesium oxychloride cement (MOC) in geopolymerization was explored and utilized to enhance the solidification/stabilization (S/S) of the MSWI-FA. The MOC-self-assembled geopolymerization kinetics can be suitably described by the JMAK model. The employment of caustic calcined magnesia (CC-MgO) increased the residue moieties of Zn, Pb, Cu, Cd, and the total Cr to 93.28 %, 87.97 %, 86.10 %, 87.21 %, and 92.47 %, respectively, and significantly reduced the releasing concentration of free Cl in the matrix. Both 5 Mg(OH)•MgCl•8HO (phase-5) and CaAlSiO•4HO (M-A-S-H) were formed in the CC-MgO-participated geopolymerized samples. The CC-MgO reacted with Cl ions dissolved from MSWI-FA in the alkali-activated condition to form phase-5, which released surplus OH ions. The CC-MgO also substituted the role of CaOHCl to react with geopolymer gels to generate M-A-S-H. In addition to the convincing support of MOC self-assembly between CC-MgO and MSWI-FA without MgCl, this study provides a significant reaction theory basis for the employment of CC-MgO in enhancing S/S of the geopolymerized MSWI-FA.