Effect of zeolite contents on mineral evolution and heavy metal solidification in alkali-activated MSWI fly ash specimens

Abstract

Municipal solid waste incineration fly ash (MSWIFA) with a high heavy metal concentration must be consolidated before disposal in a landfill. Alkali-activated technique contributes significantly to boosting the degree of heavy metal solidification and usage ratio on MSWIFA material. In this work, zeolite, a new additional siliceous material, was employed to improve the properties of a pure alkali-activated MSWIFA (FZ0) matrix. When compared to other FZ specimens with varying zeolite concentrations (0–50 wt%), the compressive strength of alkali-activated MSWIFA with 40 wt% zeolite substitution (FZ40) after 3, 7, 14 d curing was the highest. The compressive strength of partial FZ specimens reduced somewhat after 28 d of curing due to dry shrinkage. According to magic angle spinning nuclear magnetic resonance (MAS NMR) data, the predominant amorphous products in FZ specimens were C-(A)-S-H. Based on X-ray diffraction (XRD) data, new minerals (tobermorite, tilleyite, and calcite) were discovered and quantified in the FZ matrix. Fourier transform infrared spectroscopy (FT-IR) findings revealed partial Na2SO4 in FZ0 specimens. Notably, the leaching concentrations of Pb, Zn, Cu, Cr, Ni, and Cd in FZ0 and other FZ specimens that met Chinese criteria were significantly lower than in the original MSWIFA. Meanwhile, additional FZ specimens showed superior solidification tendencies on Pb, Zn, Cr, and Cd than FZ0 specimens. The inclusion of zeolite may increase the solidification efficiency of heavy metals in the MSWIFA matrix and has a promising application.