# Europium, Yttrium, and Indium Recovery from Electronic Wastes
## 3 Results and Discussion
### Indium Recovery from LCDs
Finally, it can be observed that the extraction of Fe\({}^{2+}\) and Al\({}^{3+}\) decreases at pH = 1.7, since there is a hydrolysis of the Fe\({}^{2+}\) and Al\({}^{3+}\) ions, which makes extraction difficult [30]. From Figure 7a,b, it is determined that the best extractant is di-(2-ethylhexyl) phosphoric acid (DEHPA) with diesel as the diluent, since with the employment of TBP, indium recoveries are lower than those obtained with DEHPA. In addition, iron and aluminum don't affect indium extraction, although they diffuse to the organic phase. In the case of iron, a 46% recovery in the organic phase was obtained. This finding is similar to the results obtained by [PERSON] et al. [26], since they found that 1 M of Cyanex 923 is the extractant that is required for indium extraction with a 47% iron removal. Unlike the group of [PERSON] et al., the selected extractant in this research for indium recovery was DEHPA, which is suitable as well for rare earths extraction. Figure 8 shows how the extraction of indium, iron, and aluminum with DEHPA at different concentrations occur. As it can be seen in Figure 8a, the recovery of indium is high when the concentration of DEHPA varies from 0.25 mol/L to 1.00 mol/L, regardless of whether diesel or \(n\)-hexane is used as the diluent. In the case of iron, when the concentration of the extractant is increased to 1.00 mol/L with diesel, the recovery is 50%. When \(n\)-hexane is used, the recovery of iron did not undergo any variation when increasing the concentration of DEHPA. Finally, in the case of aluminum, it is observed that when the concentration of the extractant increased the recovery of aluminum in the organic phase, it also increased with both diluents. Thus, for the solvent extraction stage, it is recommended to use DEHPA as an extractant with a concentration of 0.25 mol/L with diesel as a diluent, because it is less expensive than \(n\)-hexane. Figure 7: (a) Recovery of In, Fe, and Al with DEHPA (1.0 M, pH = 1.7) with \(n\)-hexane and diesel as diluents; (b) Recovery of In, Fe and Al with tributyl phosphate (TBP) (1.0 M, pH = 1.7) with \(n\)-hexane and diesel as diluents. For the re-extraction stage, the organic phase was diluted to allow a better diffusion of the indium to the aqueous phase constituted by the concentrated H\({}_{2}\)SO\({}_{4}\) solution. Figure 9 shows the results of re-extraction at different H\({}_{2}\)SO\({}_{4}\) concentrations. The ratio between the aqueous phase and organic phase was six, and the contact time between both phases was 5 min. An increase in the recovery of all of the metals is observed when increasing the H\({}_{2}\)SO\({}_{4}\) concentration from 6 mol/L to 10 mol/L. Therefore, a concentration of 8 mol/L of H\({}_{2}\)SO\({}_{4}\) was chosen to obtain a recovery of 95% of indium, diminishing the re-extractions of iron and aluminium to 37% and 6%, respectively. Afterwards, the solution was evaporated in order to precipitate the indium sulfate. The precipitated solid was subjected to calcination for 2 h at 700 \({}^{\circ}\)C to obtain indium oxide (see Figure S5). In Figure 10, a process flow diagram is shown for indium oxide recovery from LCD panels. Similar to other research studies, this process incorporates the solvent extraction step, which is essential for indium separation from LCD impurities such as iron and aluminum. In contrast with other works [26], this process combines a solvent extraction step and a precipitation for the recovery of indium oxide, which is a salt of great commercial value. Figure 8: (**a**) Recovery of In, Fe, and Al with DEHPA and diesel; (**b**) Recovery of In, Fe, and Al with DEHPA and _n_-hexane. Figure 9: Influence of the concentration of H\({}_{2}\)SO\({}_{4}\) on the re-extraction of indium.