Synergistic recovery for Al and Ga within high-alumina fly ash by carbochlorination using the response surface method

The synergistic extraction of critical elements (Al, Ga) from high-alumina fly ash has gained prominence in addressing resource scarcity and mitigating environmental impacts. This study introduces an efficient carbochlorination approach to overcome the drawbacks of conventional acid/alkali methods, including excessive energy demand and secondary pollution. Response surface method was employed to optimize Al and Ga recovery, identifying optimal parameters: a temperature of 1000℃, a time of 60 min, and a carbon content of 40 wt%, a gas flow rate of 13 L·min^-1, and an oxygen content of 10 vol%. Under these conditions, 80.10 % Al and 73.52 % Ga were chlorinated. The quadratic model demonstrate superior performance in predicting both Al and Ga carbochlorination efficiencies (p < 0.0001). Phase characterization revealed that Ga, existing as isomorphic substitutions in aluminosilicate structures, participated in cooperative chlorination reactions with the aluminosilicate matrix. The Al-bearing phase decomposition facilitated Ga release during the phase transformation. This work elucidates the mechanistic for Al-Ga co-recovery from high-alumina fly ash and provides critical insights into the industrial implementation of high-alumina fly ash resource recovery.