Heavy metal stabilization via copyrolysis of comodified vermiculite with municipal sludge/aged refuse: Comprehensive analysis of hazards and characteristics of multiple coexisting heavy metals

Mg²⁺ impregnation, intercalation-exfoliation, and thermal activation methods were employed to create various types of modified vermiculite (MV), with their combination creating linked-modified vermiculite (LMV). Copyrolysis of MV with municipal sludge (MS)/aged refuse (AF) in a fluidized bed improved heavy metal (HM) stability compared to copyrolysis of original vermiculite, with LMV demonstrating superior performance compared to other types of MV. The HM retention rate, potential ecological risk assessment, and form distribution analysis supported the efficacy of the approach. Doping of MS with AF was not beneficial to reducing the hazards posed by HMs. New calculation models for HM hazard assessment were developed that integrated HM concentration and form. Without additives or when only original vermiculite was added, increased pyrolysis temperature facilitated the reduction of hazards posed by HMs, indicating that HM form greatly influenced the effectiveness of the pyrolysis reaction. The characteristics of the reaction with multiple coexisting HMs and vermiculite at different pyrolysis temperatures were investigated via simulations, and the effect of interactions between HMs was explored. HMs mainly exhibited repulsive interactions, and adsorption became more unfavorable with increasing pyrolysis temperature as the repulsive force increased. The Cr, Cu, and Zn atoms in compounds formed covalent bonds with the O atoms of LMV, in contrast to the ionic bonds formed by the Pb and Cd atoms in some compounds, which may explain the differences in their reactivities with LMV.