Water-Soaking Pretreatment for Enhanced Performance and Heavy Metal Immobilization in Alkali-Activated Pyrolysis MSWIFA Materials

This study demonstrates that synergistic pyrolysis and water-soaking pretreatment transforms municipal solid waste incineration fly ash (MSWI FA) into high-performance alkali-activated materials when combined with ground granulated blast furnace slag (GGBS). Pyrolysis reduced chlorine content by 94.3% and increased reactive components by 44.4%, thereby shifting hydration products from Friedel's salt to ettringite (AFt). Subsequent water-soaking eliminated expansion-causing elemental aluminum, liberating activators for enhanced reaction completeness (29% higher cumulative heat release) and enabling a denser matrix with 71.5% harmless pores (<20 nm). The dual-treated FA (T-PFA) achieved exceptional mechanical performance-295.6% higher 56-day compressive strength versus untreated FA at a 1:1 ratio-while reducing porosity by 29.1% relative to pyrolyzed-only FA. Despite 22-38% increased total heavy metal content post-pyrolysis, matrix densification and enhanced C-A-S-H/AFt formation reduced Cr/Cd/Cu/Pb leaching by 11.3-66.7% through strengthened physical encapsulation and chemisorption, with all leachates meeting stringent HJ 1134-2020 thresholds. This integrated approach provides an efficient, environmentally compliant pathway for MSWI FA valorization in low-carbon construction materials.