Experimental and mechanism study on enhanced leaching of indium from waste indium tin oxide targets

In this paper, an innovative approach was proposed to leach indium from waste indium-tin oxide targets (WITOT) by variable speed stirring (VSS). A discrete element method-volume of fluid (DEM-VOF) model was used to study the mixing state of multiphase flow. In the VSS mixing system, the blade tip tail vortex was constantly growing and breaking. The resulting shear force enhanced the efficient mixing of multiphase flows. Therefore, the leaching rate of indium in the VSS system reached 89.65 %, which was enhanced by 16.39 % in contrast with the uniform speed stirring (USS) leaching system. The leaching reaction of indium within 30 min was controlled by chemical reaction with an activation energy of 53.28 kJ/mol. The reaction orders of hydrochloric acid concentration and particle diameter were 1.20 and -1.21, respectively. The reaction was controlled by diffusion in the time range of 30-120 min with an activation energy of 11.11 kJ/mol. The reaction orders of hydrochloric acid concentration and particle diameter were 0.95 and -1.62, respectively. The duration of the low RSD value increased by 77.78 % in the VSS mixing system compared to the USS mixing system. The WITOT particles were distributed more uniformly in the VSS system, that promoted effective contact between hydrochloric acid and WITOT, thereby enhancing the efficiency of indium leaching. These results will provide an excellent theoretical basis for the recovery of indium from secondary indium resource.