Separation and cyclic enrichment of valuable elements (Ga, Ge, In) from Zn vacuum smelting slag by stepwise leaching with sulfuric and acetic acid

Zinc vacuum smelting slag contains valuable metals, including gallium (Ga), germanium (Ge), and indium (In). However, their highly dispersed distribution presents significant challenges for efficient recovery. This study developed a sustainable stepwise leaching strategy, combining sulfuric acid (H 2 SO 4 ) leaching with acetic acid (HAc) leaching, for the efficient recovery of Ga, Ge, and In from refractory zinc vacuum smelting slag. The complex occurrence states of Ga, Ge, and In in the slag and their transformation behaviors during leaching behaviors were systematically investigated. During H 2 SO 4 leaching, zinc (Zn) recovery reached up to 96.3% under optimal conditions, while the valuable metals (Ga, Ge, and In) became enriched in the H 2 SO 4 post-leach residues. The enrichment mechanism of Ga, Ge, and In in the post-leach residues was elucidated and found to involve hydrolysis and replacement processes. Subsequently, the H 2 SO 4 post-leach residues were treated with HAc to recover Ga, Ge, and In, achieving recoveries of 83.3%, 91.2%, and 91.4%, respectively. Through a cyclic leaching process (five cycles), the concentrations of Ga, Ge, and In in solution were increased to 0.72 g/L, 5.14 g/L, and 2.71 g/L, respectively. This green and efficient process offers a technically feasible and environmentally benign strategy for recovering valuable metals from secondary resources, thereby promoting resource circularity and waste valorization in the zinc industry.