Multi-stage Activation of Fly Ash for Al(OH)3 Extraction: Process Optimization and Mechanistic Insights

• • Achieved 91.8% Al extraction rate from fly ash under optimal conditions: mechanical activation (ball milling for 60 min), 4% CaF2 addition, calcination at 1000°C for 2 h, and leaching with 40 g/L Na2CO3 solution. • • Produced Al(OH)3 with 98.9% purity, meeting industrial-grade standards, via CaO desilication and CO2 carbonation of the Al-rich leachate. • • Reduced sintering temperature by 300–400°C compared to conventional limestone sintering (from 1300–1400°C to 1000°C), significantly lowering energy consumption. • • The process enables efficient Si-Al separation through formation of Ca12Al14O32F2 and inert Ca2SiO4, and the residue is suitable for producing flame retardants or high-value silicon-based materials.