From waste to resource: Fly ash regeneration salt recycling based on chlor-alkali production

As municipal solid waste incineration (MSWI) continues to expand worldwide, fly ash, an inevitable by-product laden with persistent dioxins, bioavailable heavy metals, and high chloride concentrations, is classified as hazardous waste (HW18). Though substantial progress has been made in the disposal of fly ash, unresolved issues regarding its resource utilization now constitute a critical barrier to supporting sustainable industrialization. To solve this, the study proposed a waste-to-resource route using fly ash regeneration salts (FARS) as a feedstock to partially replace industrial salt (IS) in ion-exchange membrane (IEM) chlor-alkali production. A two-stage purification process was targeted, designed, and optimized to effectively remove characteristic impurities such as Ba^2 + , Ni²⁺, and Fe, supporting scale-up operations. Bench-scale results identified a 20% FARS blending ratio as the optimal benchmark for electrolysis performance, with current efficiency > 98%. An industrial-scale trial further demonstrated the engineering applicability of FARS blending, realizing stable 60-d operation under the total available FARS's supply in a 160,000 t/a chlor-alkali production. This industrial application also achieved steady current efficiency and voltage, controlled leaching toxicity in salt sludge, and standard-compliant product quality. Besides, benefiting from this waste-to-resource utilization, the system effectively reduced environmental burdens by 5.20% and life-cycle costs by 17.01% compared to the conventional IS-based route. The work consequently delivers a feasible engineered route for the high-value recycling of hazardous fly ash, offering a practical solution to boost circular economy implementation and drive sustainable development across waste management and chemical manufacturing.