Manufacture of alkali-activated cementitious materials using municipal solid waste incineration (MSWI) ash: Immobilization of heavy metals in MSWI fly ash by MSWI bottom ash

Based on the purpose of safe solid waste recycling, this work proposed a new method of co-treatment of municipal solid waste incineration fly ash (MSWIFA) and municipal solid waste incineration bottom ash (MSWIBA). The alkali-activated binder was synthesized from MSWIFA and MSIWBA by Ca/Si ratio design. The results showed that the maximum compressive strength of the samples at 56 d reached 8.8 MPa. A low concentration of alkali (6% Na₂O dosage) favors the development of compressive strength when more MSWIFA is used in the binder system. The C-S-H gel is the main gel product in this case. In contrast, a high concentration of alkali (8% Na₂O dosage) is required in the MSWIBA-based binder system. And C-(A)-S-H gels and N-A-S-H gels coexist under this condition. The results of leaching tests showed that after 56 d of curing, the reaction products limited the migration and leaching of potentially toxic elements from MSWIFA by physical encapsulation or chemical bonding. The immobilization efficiency of heavy metals such as Cd, Cr, Cu, Ni, Pb and Zn were above 98%, and their leaching concentrations were below the limits of the relevant Chinese standards.