Phosphorus migration and stabilization in a full-scale MSW CFB incinerator: Implications for targeted recovery and hazardous ash management

The complex transformation of phosphorus (P) during municipal solid waste (MSW) incineration fundamentally dictates its partitioning and subsequent recovery potential. However, its in-situ behavior in circulating fluidized bed (CFB) incinerators remains poorly understood. In this study, the spatial migration and mineralogical stabilization of P in a full-scale MSW CFB incinerator were systematically investigated. The elevated phosphorus concentration observed in the circulating ash (CA, 11.1 mg g⁻¹) may be attributed to conditions within the circulating loop, including the particle-rich hydrodynamic environment, particularly in the cyclone separator, where enhanced gas–solid slip velocities and high local solids concentrations create favorable conditions for volatile P capture. Conversely, the bottom ash (BA) and fabric filter ash (FFA) retain significantly lower P contents (1.70 and 5.35 mg g⁻¹, respectively) due to profound mass and sorbent dilution effects. Micro-scale characterization reveals the co-localization of P with Ca/Mg in high-temperature ash residues (>850 °C), which may originate from calcium phosphates in the feedstock. Subsequently, residual volatile P undergoes heterogeneous condensation in the mid-temperature convective pass (400–600 °C). Environmental assessments indicate that the heavy metal leaching concentrations of CA are below Chinese regulatory landfill limits (GB 16889–2024), supporting a targeted partial bypass discharge strategy to minimize hazardous terminal FFA generation at the source. Meanwhile, the severe heavy metal leaching risk of downstream FFA necessitates thermochemical detoxification. These insights propose a targeted ash management strategy and highlight the imperative of future agronomic bioavailability validation for the recovered phosphate products.