High efficiency selective recovery of Al from high-alumina fly ash by multistage activation and carbonation on-site application scale

A method of calcination activation-chemical separation-carbonization precipitation was developed for selective recovery of Al from high-alumina fly ash (HAFA). Specifically, calcium carbide slag, CaF₂ and HAFA were used for mechanical mixing and calcination, and then, Al was leached with sodium carbonate solution, followed by the use of CaO to separation and removal of Si, the next step of filtration to remove the residue to obtain, and finally, the precipitation recovery of Al was realized by the passage of CO₂ into the solution. Consequently, the formation of soluble calcium aluminate (C₁₂A₇) and insoluble dicalcium silicate (C₂S) is promoted, effectively achieving the separation of silicon and aluminum during the calcination process. Desiliconization and carbonation of the leaching solution yielded aluminum hydroxide with a conversion rate of 96.67 % and a purity of 98.40 %. Pilot-scale experiments achieve an overall aluminum extraction rate of over 80 % and an aluminum purity of 98 %. In addition, the process absorbs 0.564 tons of CO₂ per ton of Al(OH)₃ produced. This study highlights the feasibility of large-scale collaborative carbon sequestration and efficient HAFA resource treatment.