# Europium, Yttrium, and Indium Recovery from Electronic Wastes
## 3 Results and Discussion  
### Europium and Yttrium Recovery from Cathode Ray Tubes  
From the analysis of crystalline phases performed by X-ray diffraction (XRD), it was found that the main constituent compounds of the coating powder were: zinc sulfide (ZnS) and yttrium oxysulfide (Y\({}_{2}\)O\({}_{2}\)S). During characterization, no europium compounds were found, which was probably due to europium being an activant or dopant of yttrium oxysulfide, but not a differentiable compound. The determination of the elemental chemical composition was carried out by the X-ray analyzer in the scanning electron microscopy (SEM). It should be mentioned that with this analysis, semiquantitative chemical results are obtained, with a limit of detection of 1% (see Figure S1). The results of the elemental chemical composition of the coating powder are shown in Table 1.  
It was found that zinc is the element that is present in the greatest percentage, followed by sulfur. These results corroborate with the results of the analysis by XRD, in which the zinc sulfide is one of the components of the powder. In the case of rare earths, yttrium has a percentage of 8.5%, coming from the yttrium oxysulfide determined in XRD, whereas europium has a percentage of around 1.5%. In addition, there is a 2.6% of niobium that can arouse interest in their recovery. In order to extract the rare earths from the CRTs, the powder was used for the extraction of europium and yttrium by acid leaching and solvent extraction. Figure 1 shows the different leaching agents that are used for this purpose. As it can be seen in Figure 1a, the best leaching agent for complex europium and yttrium turned out to be the HNO\({}_{3}\), which was used at a concentration of 200 g/L. \begin{table}
\begin{tabular}{c c} \hline \hline
**Metal** & **Composition (\%)** \\ \hline Eu & 1.5 \\ Y & 8.5 \\ Zn & 24.2 \\ Al & 9.3 \\ Ti & 1.3 \\ Nb & 2.6 \\ Pb & 7.1 \\ Na & 11.9 \\ S & 13.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Elemental chemical composition of coating powder with an X-ray analyzer in SEM. For the leaching carried out with hydrochloric acid, values of recovery were approximately 2% for europium and 7% for yttrium, while with sulfuric acid those values increased to 5% for both metals. Finally, different results are observed in nitric acid leaching tests, in which the increase in recovery is considerable, since approximate values of 48% were reached for both europium and yttrium. In order to determine the optimal concentration of nitric acid, the concentrations were varied from 100 g/L to 350 g/L. The highest recovery of rare earths in solution was obtained when the concentration of HNO\({}_{3}\) was 250 g/L. It should be noted that all of the tests were carried out for 24 h at 10% of solids. It is important to notice that other research studies have demonstrated that sulfuric acid or hydrochloric acid are suitable as well for yttrium dissolution [27]. However, in this case, only nitric acid resulted to be the best leaching agent for rare earths recovery. Based on these results, tests were carried out to study the influence of leaching time on the recovery of europium and yttrium. In Figure 2a, europium and yttrium recoveries are shown at different leaching times. As the leaching time was increased, higher europium and yttrium recoveries were obtained, reaching the maximum recoveries of both metals at 72 h of agitation. Finally, it can be seen that the curve tends to have an asymptotic shape, so at higher values of leaching time, the stabilization of the curve would be expected in practically constant recovery values. To complement the study of the leaching process, the influence of pulp density was assessed. In Figure 2b, the europium and yttrium recoveries are shown for leaching tests with different percentages of solids at 250 g/L of HNO\({}_{3}\) for 48 h of stirring. In the case of europium, the recovery decreases from 95% to values of 14% and 4% for a pulp density of 20% and 30%, respectively.