Resourcing of municipal solid waste incineration fly ash for roof tile manufacturing and the mechanism underlying heavy metal immobilization

Large amounts of energy and chemical reagents are required if municipal solid waste incineration (MSWI) fly ash is to be treated harmlessly. The development of MSWI fly ash as a resource has emerged as a critical focus in research on the sustainable treatment of industrial solid waste. Here, we examined the feasibility of using MSWI fly ash as a safe, low-cost precursor in roof tile production. Our as-obtained roof tiles exhibited a considerably high flexural strength (>30.99 MPa) and a low water absorption (<0.51%). During preparation, shale, fine sand, red clay, and MSWI fly ash were mixed at weight ratios of 60%, 20%, 10%, and 10%, respectively, and pressed into tile blanks. These tile blanks were sintered at 1150 °C for 30 min to produce high-quality roof tiles. The presence of Cl in the roof tiles led to a slight volatilization of heavy metals in their chloride forms; nevertheless, most heavy metals were effectively retained within the tiles. The metals leached from the roof tiles were much lower than the limits specified by GB5085.3-2007. The metals were well-immobilized in the roof tiles through encapsulation within amorphous aluminosilicates and fixation in spinel crystals. Moreover, for every ton of MSWI fly ash added during roof tile production, an average of 973.29 kgCO 2 emissions may be avoided. This study successfully prepared roof tiles with enhanced flexural strength using MSWI fly ash as a raw material, without modifying the manufacturer’s existing tile production processes. The research examined the heavy metal leaching toxicity and the immobilization mechanism of heavy metals in these roof tiles, and evaluated the carbon emission reduction potential associated with using MSWI fly ash as a feedstock. This work not only tackles the problem of MSWI fly ash disposal but also facilitates its high-value utilization, thereby advancing the development of “waste-free cities”. • The incorporation of MSWI fly ash can remarkably enhance the mechanical properties of roof tiles. • Heavy metals in roof tile are strongly immobilized through the encapsulation within amorphous aluminosilicates and the fixation in spinel crystal. • The re-utilization of MSWI fly ash in roof tile production significantly reduces CO 2 emissions.