Preparation of lightweight ceramsite from municipal solid waste incineration ash and tuff: Constrained uniform mixture design, thermodynamic simulation and formation mechanism

Municipal solid waste incineration (MSWI) ash (fly ash and bottom ash) contains considerable heavy metals and dioxins, which must be disposed of. Inspired by "zero solid waste" MSWI plant, fly ash and bottom ash were co- thermal treated into a low-aluminum-silicon lightweight ceramsite with the assistance of tuff. The formula of 34.09% bottom ash, 23.02% fly ash and 42.89% tuff was attained by the constrained uniform mixture design, and the resulting ceramsite fulfilled the specifications required for Lytag commercial lightweight aggregate. Thermodynamic simulation, SEM-EDS, FTIR and XRD were conducted to reveal the roasting mechanism of low- aluminum-silicon lightweight ceramsite with four stages. The leaching toxicity of ceramsite was less than limited values of hazardous waste leaching standard, especially for Pb. Heavy metals (Cr, Ni, Cu, Zn, Cd and Pb) primarily engaged in Ca-bearing minerals, leading to the formation of hybrid minerals and the impregnation of amorphous phases ([SiO4]/[AlO4] polymers). Therefore, lightweight ceramsite preparation from fly ash and bottom ash achieves the goal of "zero solid waste" MSWI plant.