New model of municipal solid waste incineration fly ash treatment and its comprehensive benefits

Municipal solid waste incineration fly ash (MSWI FA), characterized by high concentrations of chlorides, heavy metals, and dioxins, presents significant environmental challenges. This study developed a synergistic washing-hydrothermal oxidation process for safe resource recovery. Optimized three-stage countercurrent washing (L/S ratio of 4 mL/g, 750 rpm, 25 °C, 20 min) yielded 79.86% chloride removal efficiency, meeting the 2% residual chloride threshold. Subsequent hydrothermal treatment (300 °C, 90 min, pH 7.0, L/S ratio of 4 mL/g) enhanced residual metal fractions (Cu: +36.32%, Zn: +40.61%, Cd: +38.81%) versus washed ash, with leached concentrations complying with GB 8978-1996. Dioxin toxicity equivalence was reduced by 99.7% (1.87 μg-TEQ/kg to 5.4 ng-TEQ/kg), far below the 50 ng-TEQ/kg regulatory limit. Life cycle assessment confirmed superior environmental performance over landfilling, particularly in heavy metal emissions and human toxicity mitigation. Risk analysis validated effective leached metal toxicity reduction. Carbon accounting bounded by the resource-based production of ceramic pellets from treated fly ash demonstrates a double offset: substitution of carbon-intensive building materials with enhanced carbon sequestration for net life-cycle carbon reductions. Economic projections indicate USD 363 million revenue potential by 2030. Thus, the synergistic washing-hydrothermal oxidation process developed herein enables efficient dechlorination, heavy metal stabilization, and deep dioxin degradation in MSWI FA. This integrated approach delivers significant environmental, carbon-reduction, and economic benefits, enabling viable fly ash resource utilization.