Effects of Aluminum Dosage on Gel Formation and Heavy Metal Immobilization in Alkali-Activated Municipal Solid Waste Incineration Fly Ash

This work attempts to investigate the effects of aluminum dosage on the immobilization of heavy metals in alkali-activated municipal solid waste incineration fly ash-based pastes to manage hazardous threats in it. A variable proportion of metakaolin is used to achieve different aluminum dosages in the synthesized pastes. Structure, composition, morphology, and mechanical property of the prepared pastes are studied by employing X-ray diffraction, Si-29 NMR, scanning electron microscopy, and compressive strength measurements. The results showed that a 5% metakaolin-composed paste exhibited the highest compressive strength (10.94 MPa). The addition of the aluminum dosage-converted soluble chloride salt into Friedel's salt, subsequently, improved the immobilization of heavy metals. The toxic characteristic leaching procedure test showed that a small amount of aluminum can improve immobilization dominantly because of the effective encapsulation ability of the pastes. The molecular modeling and simulation analysis illustrated that because of the presence of Na+ in it, sodium-alumino-silicate- hydrate (N-A-S-H) gel possesses the most stable molecular orientation.