Thermal–Physical Pretreatment and Extraction of Indium from LCD Waste Stream

Abstract

Liquid Crystal Display (LCD) waste from various sources, such as TVs, desktop monitors, and computer notebooks, is increasing and has become an environmental issue, requiring legalized disposal and practical recycling technologies to address it. LCD screens generally contain Indium–Tin–Oxide (ITO), which are critical and valuable metals worth recovering. The aim of this research is to optimize the thermal–physical pretreatment of LCD screens after dismantling to effectively recover indium via leaching and solvent extraction at an acceptable recovery rate. A comparative study was conducted on the recovery of indium from LCD waste from TVs and a mixed waste stream, where the latter source represents the total proportion of LCD waste accumulation. This comparison aimed to identify key factors for effective recovery from TV and mixed waste streams, containing lower and higher amounts of indium, respectively. The recovery process consisted of waste pretreatment, leaching, and solvent extraction. In the first pretreatment, ethanol immersion was found to be the most practical for polarizing film removal for both streams in comparison with manual peeling, water immersion, surface heating, and calcination. Comminution in the second pretreatment aimed to increase the surface area for the subsequent chemical reaction. For both streams, HCl leaching allowed effective indium recovery of >99.9% at the optimal conditions of 5 M HCl with 10% H2O2 addition and an S/L ratio of 500 g/L under ultrasonication for 1 h. Subsequent purification via solvent extraction was conducted to exclude iron as the key impurity. In solvent extraction, D2EHPA concentration, pH, and the organic-to-aqueous ratio (O:A) was investigated. Optimal solvent extraction was achieved using 0.25 M D2EHPA at pH 1 and an O/A ratio of 1:5 for 5 min, while ascorbic acid was added to eliminate undesirable iron. Although both waste streams achieved >99.9% leaching efficiency, they exhibited different extraction behaviors after scrubbing and stripping. The TV waste stream achieved 74.32% solvent extraction efficiency. The higher indium recovery of 84.34% via solvent extraction through the stripping of the mixed stream might be due to the higher initial indium concentration reacting with D2EHPA. This led to the overall recovery of the two waste streams as 70.22% and 80.24% for TV and mixed waste streams, respectively, possibly due to higher amounts of indium in the initial waste stream. The findings of this study serve as research and practical guidance for indium recovery and EOL–LCD recycling.