Seed-induced Hydrothermal Synthesis of Tobermorite from Municipal Solid Waste Incinerator Fly Ash

Resource recovery of municipal solid waste (MSW) incinerator fly ash is widely concerned. Tobermorite, an important but rare naturally mineral, could not be directly hydrothermal synthesized from it owing to its high content of Ca but low concentration of Si and Al. The selected external silicon-aluminum additives including coal fly ash (CFA), bentonite, kaolin and diatomite were solely or combined added. With the addition of 30% mass composite additive in which the ratio of quality for CFA and diatomite is 1:1, tobermorite could be synthesized most effectively in 48h at 150°C, mainly attributing to the proper element proportion adjusted by additives. Tobermorite seed added could not only promote the large formation of tobermorite, but also inhibit the production of hibschite and kaotoite. Since Ca/(Si + Al) = 1.20 and Al/(Si + Al) = 0.20, addition of 30% mass of composite additive and 3% mass of tobermorite seed would be the recommended technological parameter.