Combined stabilization of Cd and Pb in MSWI fly ash by NaH2PO4 and water-soluble thiourea formaldehyde (WTF) resin enabling co-sintering for ceramsite production.

Municipal solid waste incineration fly ash (MSWI-FA) poses significant environmental risks due to high chlorine content and leachable heavy metals. This study presents an integrated approach combining water washing dechlorination, chemical stabilization, and co-sintering to convert MSWI-FA into lightweight ceramsites. Optimal washing conditions (liquid-to-solid ratio of 10 mL/g, 30 min) reduced the chlorine content from 7.27% to 1.51%, meeting the feed standard for high-temperature sintering. A composite reagent comprising NaH2PO4 and water-soluble thiourea-formaldehyde (WTF) resin at a 1:1 ratio was used to stabilize cadmium (Cd) and lead (Pb). At an 8% dosage, the stabilization efficiencies reached 91.74% for Cd and 89.01% for Pb, with leaching concentrations reduced below regulatory limits. The stabilized FA was then co-sintered with wood ash and coal gangue to produce ceramsites with densities ranging from 700 to 900 kg/m3, complying with the Chinese standard GB/T 17,431.1-2010. High-temperature sintering further converted Cd and Pb into stable residual fractions (accounting for over 85% of the total), and their leaching concentrations remained far below permissible levels. This integrated strategy demonstrates a viable pathway for the safe disposal and resource utilization of MSWI fly ash, offering both environmental and economic benefits.