Efficient extraction and separation of indium from waste indium–tin oxide (ITO) targets by enhanced ammonium bisulfate leaching

In this paper, a closed-loop hydrometallurgical process was proposed for indium recovery from waste indium–tin oxide (ITO) targets. Both high indium recovery and recirculation of leaching reagent have been achieved. This process included ammonium bisulfate leaching, selective precipitation of tin by adding ammonia, indium hydroxide precipitation and roasting to prepare indium oxide product. Moreover, a shrinking core model was implemented to depict indium leaching process with an activation energy of 52.64 kJ/mol calculated, which showed that the rate was controlled by the surface chemical reaction. And the reaction orders were determined as 0.60, 0.34 and −0.69 with respect to initial ammonium bisulfate concentration, oxygen partial pressure and particle size, respectively. Since the tin was more sensitive to temperature, acidity and oxygen, the leaching solution finally contained 14.31 g/L indium and 0.05 g/L tin. Subsequently, the application of two-step precipitation realized selective precipitation of tin for purifying solution and preparation of precursor. Indium oxide product was obtained by calcination of the precursor at 600 °C for 1 h. Finally, the supernatant after indium precipitation was concentrated, evaporated and thermally decomposed, and then returned to the leaching process. This study provided a feasible process for high-value use of waste ITO targets.