Solidification of heavy metal in municipal solid waste incineration fly ash and performance evolution of alkali-activated foam concrete

The heavy metals in municipal solid waste incineration fly ash (MSWIFA) limit its large-scale application. To improve the utilization ratio of MSWIFA, a slag-MSWIFA-fly ash alkali-activated foam concrete (ASFC) was prepared in this study. The influence of MSWIFA content on the performances of ASFC and the solidification effect of heavy metals in MSWIFA by alkali-activated materials were studied. The results show that the performance of ASFC was directly related to the pore structure, which was affected by the fluidity and setting time of the paste, as well as the quantity and type of hydration products. When the MSWIFA substitution rate was 25-50 %, the fluidity of the paste was better, the pore diameter decreased, and the number of closed pores increased. The compressive strength of ASFC at 28 d was 1.72-2.01 MPa, and the thermal conductivity was 0.1305-0.1340 W/(m center dot k). The leaching concentrations of the six heavy metal elements in the 28 d hardened paste of ASFC were all lower than 0.04 mg/L, and the solidification efficiencies of Pb and Zn, the two heavy meta elements with higher concentrations in MSWIFA, were both greater than 90 %. This study provides a technical and theoretical reference for applying MSWIFA in alkali-activated foam concrete.