Evolution of Sulfate Attack and Heavy Metal Properties of Sintered Modified Incineration Fly Ash Mortar

Incineration fly ash is a hazardous waste, and thermal treatment achieves its harmless treatment and resource utilization in cement. However, the long-term environmental safety of heavy metals in cement with incineration fly ash has not received much attention. Therefore, the heavy metal safety and mortar performance of cement with incineration fly ash with different sintering modifications in the sulfate environment were evaluated. Results indicated that the mortar mass initially increased and then decreased during sulfate attack. The mass growth of U-IFA (unsintered incineration fly ash) mortar reached 2.81% at 210 cycles, whereas D-IFA (directly sintered incineration fly ash) mortar and C-IFA mortar showed reductions after 120 cycles. C-IFA (cosintered sulphoaluminate cement raw materials and incineration fly ash) mortar exhibited the earliest spalling, compressive strength reduced by more than 22%, which was significantly worse than that of U-IFA and D-IFA. The surface heavy metal concentrations decreased markedly. Under weakly acidic conditions, the leaching of D-IFA mortar and C-IFA mortar increased by 2363.93% and 783.33%, respectively, but remained below the limits. The proportion of labile fractions of Pb and Cr increased, but the overall risk level remained low to medium. The sulfate resistance of C-IFA mortar was weaker than that of U-IFA and D-IFA. Sulfate attack accelerated mortar deterioration and weakened the immobilization of heavy metals; long-term environmental safety assessments of cement with hazardous wastes should be strengthened under complex service conditions.