Indium, a strategic key metal, is mainly recovered from zinc leaching residue. However, a challenging problem in the treatment of zinc leaching residue is how to efficiently and cleanly treat the poorly soluble phase, the indium-bearing zinc ferrite (IBZF). Here, we propose a novel strategy for the selective extraction of indium, zinc and iron from IBZF. By introducing water to regulate the coordination environment of a choline chloride-anhydrous oxalic acid based deep eutectic solvent (ChCl-Oxa based DES), efficient leaching and deep separation of indium, zinc and iron were achieved. Water, acting as both co-solvent and diluent, played a critical role in the whole process. The addition of a little water reduces the viscosity of the DES, thereby improving the leaching of indium, zinc and iron. Under specific leaching conditions (leaching temperature of 90 °C, liquid/solid ratio of 20:1 ml/g, molar ratio of ChCl:Oxa = 1:1, molar ratio of DES:H2O = 1:3 and reaction time of 3.5 h), the leaching efficiencies of indium, zinc and iron were 96.27 %, 95.55 % and 96.33 %, respectively. The subsequent addition of large amounts of water dilutes and dissociates the structure of the DES, facilitating the stepwise precipitation and deep separation of metal ions. The precipitation efficiency of zinc and iron reached 93.06 % and 98.07 %, respectively. Residual indium ions in the solution were effectively adsorbed by activated carbon, with a recovery efficiency of 75.7 % after five cycles of adsorption. The solution separated from the metal ions was well regenerated by evaporation and addition of Oxa. Our work represents a novel approach for the recycling and clean utilization of zinc leaching residue. And the regulation of the coordination environment of metal ions in DES is proved to have great potential in metal recycling.
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