CaO-activated municipal solid waste incineration fly ash and ground granulated blast furnace slag for heavy metal immobilization

Municipal solid waste incineration fly ash (MSWIFA) contains high concentrations of heavy metals, requiring effective solidification technologies to ensure safe disposal. Alkali-activated cementitious materials offer a promising environmentally-friendly solution. In this study, a one-part alkali-activated slag–fly ash composite cementitious (OPACCM) material was developed using calcium oxide (CaO) as a solid actvator. By combining ground granulated blast furnace slag (GGBFS) with MSWIFA, the material simultaneously enhances mechanical properties and heavy metal immobilization. The optimized composition (20 % MSWIFA, 80 % GGBFS, 10 % CaO) achieved a compressive strength of 51.0 MPa at 28 days and immobilized more than 90 % of Pb, Cr, Cu, and Zn. The CaO activation mechanism simultaneously streamlines material processing while effectively immobilizing chloride ions through Friedel's salt formation and enhancing C-(A)-S-H gel densification, ultimately reducing harmful porosity to below 10 %. Structural analysis confirmed the development of stable hydrotalcite and aluminosilicate gel networks that efficiently adsorb heavy metal ions. Laboratory tests demonstrated that the material meets construction strength standards while effectively treating MSWIFA, exhibiting superior environmental compatibility compared to conventional cement systems. This research presents a high-performance and sustainable strategy for recycling solid waste and managing hazardous municipal residues.