# End-of-Life Liquid Crystal Display Recovery: Toward a Zero-Waste Approach
## 3 Results and Discussion  
Figure 2 shows the entire developed process, including all necessary phases for end-of-life LCD use. As described in the previous paragraph, improvement of the process included the addition of a grinding step to obtain a particle size smaller than 1 mm. This mechanical treatment, which substitutes high-impact washing reported in the literature, allowed the removal of organic compounds. In this regard, Figure 3 shows the liquid crystal presence in the panel scraps with size around 10 mm (highlighted by iridescence in Figure 3a) and the complete absence at the end of grinding (Figure 3b). The second block includes an extraction carried out by a 1-2 M sulfuric acid solution, with a solid concentration of 20%, at 60-80 \({}^{\circ}\)C for about 20 min, under stirring. 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. Wastewater recirculation can be repeated up to three times without a significant decrease in efficiency. The extraction treatment produced two output flows, the solid scraps and a leaching solution, to send to further recovery. 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). Microstructural investigation identified two different morphologies within the same sample. It was possible to recognize agglomerates of small particles (10-20 \(\upmu\)m) and single particles (0.5-1 mm). This description is common for both samples before and after treatments. Elemental analysis, performed on both morphologies (on three different points of each sample), showed a higher indium concentration before leaching (2.2%, wt%) than after the treatment (0.5%, wt%), without differences between single particles and agglomerates. The following recovery step included a preliminary pH adjustment up to 2.5-3 by sodium hydroxide at 60 \({}^{\circ}\)C under stirring. When the operative conditions were fixed, zinc powder was added at a concentration around 3 g/L (0.005 kg of Zn/kg of treated panel and 30 kg of Zn/kg of recovered indium), and the reaction was carried out for 20 minutes. The treatment produced indium, in the form of metal, with an efficiency higher than 90%. Among the extracted metals, aluminum represented the main impurity in the product, despite its low extraction yield [16]. Nevertheless, its presence is not critical since the literature describes different applications of alloys with indium and aluminum content [38; 39]. Concerning tin, the other ITO component, a recovery lower than 10% of the waste content was observed [16]. However, this element was not chosen as the process target because of both its low concentration [13] and market price compared to indium (290 \(\upepsilon\)/kg of indium vs 18 \(\upepsilon\)/kg of tin) [40; 41]. Additional production of mortar, classified as compressive strength CS II and CS III (suitable for general works or as a plaster for indoor/outdoor), allows overcoming the process' criticality connected to leaching solid waste, around 99% of the entire amount [42]. The best selected conditions for mortar production include a two-step washing of the leaching solid waste, as already discussed in [23], at room temperature for 20 min with a solid:liquid ratio of 1:3 by weight. Both the produced mortars included a quantity of solid waste (glass cullet) around 40%, mixed with additional components, as reported in Table 1. Considering implementing the process in a real-world context, and the related pending patent, the agent's ratio can be slightly adjusted based on the required compressive strength.