Leaching Behavior and Kinetics of Gallium with Organic Acids: Foundations for E-Waste Recovery and Bioleaching Applications

This study systematically concerns the leaching behavior and dissolution kinetics of gallium (Ga). The objective was to identify sustainable leaching agents by incorporating organic acid reagents. Using a novel approach involving pH-adjusted experiments, the findings elucidated the dissolution behavior, delineating acidolysis and complexolysis. The screening results 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 (SCM) revealed a synergistic mechanism governed by film diffusion and surface chemical reaction control, with chemical reaction control dominating at higher temperatures. One-factor-at-a-time (OFAT) experiments clarified the influence of experimental parameters on Ga leaching yield. In addition, the Box-Behnken design (BBD) was employed to evaluate parameter interactions, confirming the significance of the process parameters, including interaction terms, while characterizing the model in terms of a quadratic expression. 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, emphasizing its promising integration into biogenic production pathways and sustainable closed-loop gallium recovery processes.