Investigation of indium and other valuable metals leaching from unground waste LCD screens by organic and inorganic acid leaching

Abstract

• Investigation of indium extraction from waste LCD screen. • Variation of the indium amount on different parts of the LCD screens. • Effect of inorganic and organic acid types on the selective indium leaching. • Reaching relatively high indium concentration while minimizing impurities by H 2 SO 4. • Increasing the indium concentration by reusing the leachate. Indium (In) is the indispensable part of liquid crystal display (LCD) screen which is applied as a thin semiconductor layer on the surface mainly in the form of indium tin oxide (ITO), and feasible end-of-life recycling of indium from this electronic devices is technologically challenging. The present study investigates the recovery of indium from spent untreated liquid crystal display (LCD) screen by inorganic and organic leaching. Critical process parameters such as effects of different acids, leaching duration, reusability of acidic solution and both sides of the organic layers on the LCD were studied to optimize the indium leaching from the waste screen. The efficiencies of inorganic acids (nitric and sulfuric) and organic acids (citric, glycolic, L-ascorbic, maleic and DL-tartaric) to leach metals on LCD were investigated in different leaching duration from 3 to 168 h. Extracted metal concentrations and dissolved organics are characterized by inductively coupled plasma with mass spectrometry and total organic carbon analyser, respectively. The results indicate that over 90% extraction of indium and the lowest amount of other impurities can be achieved using 1 M H 2 SO 4 for a leaching period of 48 h. Moreover, similar results could reach with 1 M HNO 3 , while organic acids were less successful under these conditions. Overall, the indium amount could reach up to 69 mg/kg ITO glass for the front and 31 mg/kg ITO glass for the back side glass. However, relatively high amount of organic layer from LCD screen dissolves in nitric acid solution up to 4000 mg TOC /l, which can affect the further stages of a recycling process. Besides, aluminium, zinc and tin were identified as the elements with the highest amount with indium in the leachate. All these elements were found in both, glass and organic layer of the LCD screen. Although metals from LCD screen have limited solubility in organic acids, specifically tartaric acid has a selective extraction behaviour for molybdenum. By reusing the leachate for further leaching processes, the concentration of indium could be increased constantly up to five times, which indicates that it is possible to increase the indium concentration to the industrially processable amount.