Preparation and Resource Utilization of Lightweight Ceramsite from High-Chlorine Medical–Municipal Co-Incineration Ash and Tuff

Abstract Purpose Medical–municipal co-incineration fly ash is hazardous because of its high chlorine and Pb/Cd contents. This study converted it into lightweight ceramsite together with bottom ash and tuff and tracked the chlorine and heavy-metal behavior during washing and sintering. Methods The fly ash was dechlorinated by three-stage countercurrent water washing and then sintered with bottom ash and tuff. Single-factor experiments and Box–Behnken response-surface design optimized the formulation and firing schedule. XRD, SEM–EDS, Tessier extraction, and leaching tests characterized the product. Results The optimal formulation was 20% fly ash with a bottom ash-to-tuff ratio of 40:60, preheated at 500°C for 20 min and sintered at 1100°C for 10 min. The 900-grade ceramsite showed a particle strength of 2014 N and a bulk density of 890 kg/m³. Washing removed 96.2% of the chlorine, and 82.2% of the chlorine entering the sintering stage was released to the flue gas. Preliminary balances indicated that 70–85% of Pb, Cd, and Zn remained in the ceramsite. Conclusion The proposed route provides a technically feasible basis for resource recovery of high-chlorine co-incineration fly ash, provided that flue-gas deacidification is implemented and heavy-metal retention is verified by standard sampling.