Leaching and Selective Extraction of Indium and Tin from Zinc Flue Dust Using an Oxalic Acid-Based Deep Eutectic Solvent

Deep eutectic solvents have previously been used as cost-effective and readily available alternatives to conventional ionic liquids. Due to their versatile complexation properties, they are potential lixiviants for selective metal processing. In this study, we investigate the leaching behavior of three choline chloride-based deep eutectic solvents to selectively separate indium and tin from an oxide flue dust material. Ethylene glycol, urea, and oxalic acid dihydrate were used as hydrogen bond donors in the eutectic mixtures. The highest leaching yields were observed in the oxalic acid system Oxaline. A two-step precipitation procedure was developed for the leachate solution to separate the target metals indium and tin from the main flue dust components, i.e., iron, zinc, lead, and copper. This ionometallurgical approach was compared to equivalent leaching experiments using aqueous oxalic acid solutions and other deep eutectic solvents.