Fundamental insights into gallium leaching for sustainable electronic waste recovery

This study systematically concerns the leaching behavior and dissolution kinetics of gallium (Ga) with the objective of identifying sustainable leaching agents by incorporating organic acid reagents. A novel approach involving pH-adjusted experiments was utilized, elucidating the dissolution behavior and delineating acidolysis and complexolysis. The findings demonstrated the efficacy of oxalic acid (10 mM), which extracted 1105.2 ± 61.4 mg/L of Ga at pH 1.2. Dissolution kinetics based on the shrinking core model revealed a synergistic mechanism governed by film diffusion and surface chemical reaction control, with the latter dominating at higher temperatures. One-factor-at-a-time experiments clarified the influence of experimental parameters on Ga leaching yield, while the Box-Behnken design was employed to evaluate parameter interactions, confirming the significance of process parameters and interaction terms. Under optimized conditions—710.55 mM acid concentration, a reaction temperature of 84.5◦C, and a solid loading of 50 g/L—37% of Ga was effectively extracted within 3.2 hours. These findings underscore the selectivity and operational compatibility of oxalic acid compared to conventional leaching agents, highlighting its promising integration into biogenic production pathways and sustainable closed-loop gallium recovery processes.