Solidification of municipal solid waste incineration fly ash and immobilization of heavy metals using waste glass in alkaline activation system

Hazardous heavy metals in Municipal Solid Waste Incineration (MSWI) fly ash are a threat to the environment and ecosystems. The objective of the work is to investigate the solidification of MSWI fly ash and the immobilization of the heavy metals through alkaline activation reaction with waste glass as an additive. Compressive strength measurement, X-ray diffraction (XRD), ²⁹Si nuclear magnetic resonance spectroscopy (²⁹Si NMR) and scanning electron microscope (SEM) were performed to evaluate the solidification effect and characterize the microstructure of alkali-activated MSWI fly ash-based mortars. The leaching test, back-scattered electron microscopy (BSE) and X-ray photoelectron spectroscopy (XPS) were conducted to determine the heavy metals' immobilization effect and their immobilization forms. It was found that waste glass addition effectively reinforced the solidification of MSWI fly ash and immobilized the heavy metals. With 40% addition of waste glass, the compressive strength reached a maximum of 3.55 MPa. The immobilization efficiency of Cr increased with the addition of waste glass, while that of Cu, Pb, Zn and Cd is dependent on the eluant final pH, which decreased with the decrease of eluant final pH. The main immobilization forms include physical encapsulation, the formation of alkaline environment and the generation of silicate compounds.