Abstract
End-of-life liquid crystal displays (LCD) represent a possible source of secondary raw materials, mainly glass and an optoelectronic film composed of indium (90%) and tin (10%) oxides. A strong interest for indium, classified as critical raw material, pushed research towards the development of high-efficiency recycling processes. Nevertheless, a deepened study of the technological innovation highlighted that only a small number of treatments included use of whole waste. Furthermore, these processes often need high temperatures, long times, and raw materials that have a significant environmental impact. In this context, this article shows an approach developed in accordance with the “zero waste” principles for whole, end-of-life LCD panel recycling. This process includes preliminary grinding, followed by cross-current acid leaching and indium recovery by zinc cementation, with efficiencies greater than 90%. A recirculation system further increases sustainability of the process. To enhance all waste fractions, glass cullets from leaching are used for concrete production, avoiding their disposal in landfill sites. Considering the achieved efficiencies, combined the simple design suitable for real-scale application (as confirmed by the related patent pending), this process represents an excellent example of implementing circular economy pillars.
Highlights
Management of end-of-life liquid crystal displays (LCDs), classified as waste from electrical and electronic equipment (WEEE), in the category of screens, monitors, and equipment containing screens having a surface greater than 100 cm2, represents a critical issue for modern society because significant quantities of waste are reaching worldwide collection centres, often illegally [1,2,3,4,5]
To implement the cross-current design, the solution from the first leaching step was used for the following indium extraction, after refreshing about 10% of the volume to ensure an acidic pH
The solid was observed by scanning electron microscopy (SEM), equipped with EDS EDAX detecting unit (PHILIPS ELECTRONICS N.V., Eindhoven, The Netherlands, 1992), to know the indium content before (Figure 4a,b) and after cross-current acid leaching (Figure 4c,d)
Summary
Management of end-of-life liquid crystal displays (LCDs), classified as waste from electrical and electronic equipment (WEEE), in the category of screens, monitors, and equipment containing screens having a surface greater than 100 cm , represents a critical issue for modern society because significant quantities of waste are reaching worldwide collection centres, often illegally [1,2,3,4,5]. The reason is there are several applications of LCD technology (e.g., PC monitors, televisions, notebooks, etc.) combined with short lifespans, between three and eight years [6,7] This end-of-life equipment is dismantled to separate possible hazardous components, (e.g., brominated flame retardants and backlight fluorescent lamp systems that contain mercury), which varies on the basis of the specific brand and generation [8,9,10,11]. The panel’s composition includes different fractions with a high recovery potential, including the glass and an indium and tin oxide (ITO) film, composed of 90% of indium oxide and 10% of tin oxide This material shows characteristics of transparency to visible light, electric conduction, and thermal reflection [13,14].
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