Liquid crystal displays (LCDs) are becoming of common use as a replacement for the old cathode ray tube monitors. The new technologies largely rely on the use of critical raw materials, such as indium. This element makes up the transparent conductive coatings in the thin film displays. Considering the high demand of indium for electric and electronic equipment and the limited size of the reserves, the importance of indium recycling is increasing. Waste electric and electronic equipment (WEEE) represents a valuable source for secondary production of indium, as its concentration in WEEE is often higher than in the ores where it is present in association with zinc and extracted as a by-product. In the last years the focus of the research has been pointed out to find technologies addressed to the extraction and recovery of indium from WEEE. In the present paper we describe the results of indium recovery from waste LCD panels using sulphuric acid leaching followed by zinc cementation. The problem of the low concentration of indium in the leach solution has been overcome by applying an innovative technology: cross-current leaching. This methodology is based on two leaching steps using the same leach solution to solubilise indium from different stocks of LCDs. Overall, we found that indium was recovered from waste LCDs with an efficiency of about 90 %, with important consequences from an economic and environmental perspective.
