Multi-stage Activation of Fly Ash for Al(OH)3 Extraction: Process Optimization and Mechanistic Insights
Selective recovery of aluminum compounds from fly ash is a key route for its high-value utilization. This study developed a multi-stage activation process for extracting Al(OH)3 from fly ash, comprising mechanical activation, calcination activation, chemical separation, and carbonation precipitation. Fly ash was mixed with carbide slag and CaF2, then calcined; the resulting clinker was leached with Na2CO3 solution to extract Al. The CaO generated from high-temperature calcination of carbide slag facilitated the separation of Si and Al. After solid-liquid separation, CO2 was introduced into the Al-rich leachate to precipitate Al(OH)3. The process promoted the formation of Ca12Al14O32F2 and inert Ca2SiO4, achieving efficient Si-Al separation during calcination. Under optimal conditions (mechanical activation for 60 min, 4% CaF2, calcination at 1000°C for 2 h, leaching with 40 g/L Na2CO3), the Al extraction rate reached 91.8%, and the product purity was 98.9%. The alumina extraction residue exhibited porous and highly reactive characteristics, suitable for producing flame-retardant materials or high-value silicon-based products (e.g., white carbon black, molecular sieve adsorbents). The process offers a promising industrial route for fly ash valorization, with potential integration with cement production lines for synergistic CO2 capture and utilization.