Research and prospect of gallium recovery technology in zinc smelting

Gallium is an important dispersive metal with widespread applications in high-tech fields such as semiconductor materials, optoelectronics, and radio technology. Recently, the market demand for gallium metal has grown, given the continuous progress of science and technology. Gallium is primarily recovered as a by-product of aluminum and zinc metallurgy, accounting for approximately 90% and 10% of the total gallium production. The relatively low production share derived from zinc metallurgy is because of the high recovery difficulty. In this study, various technological routes for gallium extraction from zinc metallurgy are summarized with detailed analyses based on technological and economic perspectives. During closed blast furnace zinc smelting, >95% of Ga is enriched in water-quenched slag with an average mass fraction of 0.025%–0.031%. Several methods for extracting Ga from the slag are proposed, including reduction evaporation, chlorination volatilization, sulfuric acid leaching, caustic fusion–leaching, reduction smelting–electrolysis, and reduction smelting–slagging . However, these methods are difficult to obtain industrial applications due to long flow, low recovery, high cost, or severe pollution. During the conventional roasting–leaching–purification–electrowinning process, >93.5% of Ga remains in the leaching residue, closely associated with a ZnFe₂O₄ phase. Next, the reduction volatilization or hot acid leaching is employed to treat the residue. Only 10% of Ga volatilizes into the crude zinc oxide dust, whereas the other Ga remains in the kiln slag, causing huge Ga loss. Ga and Fe are dissolved into the solution through hot acid leaching, and the Ga and Fe separation is a large technological problem. Compared to roasting–leaching, pressure leaching is considered more suitable for treating the Ga-rich zinc concentrate due to the absence of a roasting procedure. Ga can be leached directly into the solution with a high reaction temperature and strong oxidization atmosphere. Before Fe removal, Ga is successfully enriched in the refining residue, with an average mass grade of >0.25%, through preneutralization and zinc powder replacement. Next, the Ga-enriching residue can be further treated by H₂SO₄ leaching and subsequent solvent extraction. Finally, Ga with 99% purity is produced using neutralization–sedimentation, alkaline dissolution, and electrowinning. The total recovery for Ga production from zinc concentrate to gallium product is >70%. Based on this technological route, an annual production of 15 t Ga is established in the Danxia smelter. In this research, the gallium distribution behavior among the multiphase during various procedures such as roasting, leaching, replacement, and sedimentation is clarified carefully, and a reasonable technological route for enriching Ga from zinc metallurgy is proposed. Moreover, the methods for separation and enrichment of Ga from the leaching solution are summarized. The development of solvent extraction, emulsion film, and resin adsorption should be the key progress for green and efficient Ga recovery from zinc metallurgy.