Enhancement of Zn adsorption on coal fly ash-based geopolymer with steel slag incorporation: leaching behavior and performance insights

Industrial solid wastes like coal fly ash (CFA) and steel slag pose environmental challenges, while the remediation of heavy metal-contaminated water remains a global priority. This study investigates the impact of incorporating steel slag during the synthesis of CFA-based geopolymers (CFAG) on the leaching characteristics of inherent heavy metals in CFA and the Zn adsorption performance of CFAG. Leaching experiments show geopolymerization effectively immobilizes heavy metals including Fe, Cr, As, Cd, and Ti in CFA while having little effect on Mn, V, and Ni. The incorporation of 10wt% steel slag into CFAG further enhances the stability of As but slightly elevates the release of Fe, Ti, Cu, V, and Cd. Column experiments demonstrate steel slag doped-CFAG (SCG) achieves over a 50% improvement in Zn adsorption performance compared to CFAG. Furthermore, hydrochemical analysis, X-ray absorption spectroscopy, and sequential desorption experiments reveal Zn is removed from solution by SCG primarily through surface complexation and precipitation as ZnSiO₄, which have suitable stability and resistance to desorption. These findings suggest doping steel slag into CFAG is a viable strategy to enhance Zn removal in contaminated water, decrease remediation costs, and effectively consume CFA and steel slag. Nevertheless, potential trade-offs concerning heavy metal leaching should be carefully evaluated to balance the performance and environmental impacts of SCG.