Two alternative process routes for recovering pure indium from waste liquid crystal display panels

Abstract

Recovering indium from liquid crystal display (LCD) screen waste is important from a sustainability point of view for several reasons: the environmentally hazardous metals are not landfilled, the recovery process involves lower CO2 emissions than primary production, and supply from secondary sources matches the continuously increasing demand of indium. In this study, two alternative process routes for recycling the critical metal, indium, from LCD panel waste were studied and compared using laboratory and bench-scale experiments. The first process was a conventional hydrometallurgical process that involves manual dismantling, hammer mill crushing of the glass, cross-current sulfuric acid leaching of the metals, and liquid-liquid extraction separation of indium. Using this process, over 99% pure indium solution can be produced with a recovery yield of over 70%. The second process is novel because it includes (manual) scraping of the indium tin oxide (ITO) layer from the glass panels, followed by sulfuric acid leaching of the metals. The yield of indium was over 80%, and the purity of the resulting solution was over 99%. The solutions obtained from either of the suggested processes were sufficiently pure for cementing indium in high purity. The novel process appears much more straightforward and economically more feasible because the polarizing filter need not be removed and the liquid-liquid extraction purification step is excluded. Moreover, less amount of leaching acid is required.