Leaching of indium from waste LCD screens by oxalic acid in temperature-controlled aciduric stirred reactor

Abstract

Recovery of rare metal indium from waste LCD screens is important since its content is about 500 times of the original ore. Oxalic acid has excellent ability to leach indium from waste LCD screens, and how to achieve reactor scale operation is critical to promote indium recovery. In this study, a temperature-controlled aciduric stirred reactor (TCASR) was constructed to investigate the effects of operational conditions on the leaching efficiency of indium at reactor scale. Results showed that complete leaching was achieved in 10 min under the conditions of 0.2 mol/L oxalic acid, 300 g/L of ITO glass powder dosage, 90℃ and 500 rpm of stirring speed. Compared with the previous study, the consumption of oxalic acid decreased 3/5, ITO glass powder dosage increased by 6 times and reaction time decreased 7/9. Meanwhile, the duration of indium ion concentration was maintained for 20 min instead of decreasing immediately after reaching the peak, which was conducive to actual application. The process kinetics model illustrated that temperature played the most important role in affecting the reaction rate. The potential reason of longer indium ion concentration maintaining duration was preliminarily speculated as a faster leaching of indium than calcium result in less coprecipitation caused by calcium oxalate. Therefore, the TCASR is applicable for leaching of indium from waste LCD screens by oxalic acid due to the higher leaching efficiency, less reagents consumption and stronger processing ability.