Recovery of indium from etching waste by solvent extraction and electrolytic refining

A large amount of an etching waste containing indium is wasted by plants manufacturing liquid crystal displays. In this study, the recovery of indium from the etching waste by solvent extraction and electrolytic refining was investigated. Initially, major impurities, such as aluminum and molybdenum, were removed by dissolution using sodium hydroxide. From the resulting etching cake, solvent extraction of indium was studied for the extractant of PC88A. Indium was extracted efficiently in an acidity range of 0.1 to 0.5 mol/dm3 (MH+). PC88A extracts indium, aluminium, molybdenium, and iron from the HCl medium, but indium could be selectively stripped from the loaded solvent. The conditions for continuous running on a pilot scale using PC88A were obtained. The resulting indium solution was further purified to metal by electrolytic refining so that the final purity of the indium metal was 99.997%.