# Europium, Yttrium, and Indium Recovery from Electronic Wastes
## 3 Results and Discussion
### Europium and Yttrium Recovery from Cathode Ray Tubes
On the other hand, yttrium recoveries decrease from 86% to 25% and 8% for pulp densities of 20% and 30%, respectively. Figure 1: **(a) Recovery of europium and yttrium with different leaching agents after 24 h of stirring and 10% of solids; (b) Recovery of europium and yttrium at different concentrations of HNO\({}_{3}\) (10% of solids and 24 h of agitation). **  
Figure 2: **(a) Recovery of europium and yttrium with HNO\({}_{3}\) at 250 g/L and 10% of solids; (b) Recovery of europium and yttrium at different percentages of solids with HNO\({}_{3}\) at 250 g/L for 48 h of agitation. **  
Once the leaching conditions were optimized, the solvent extraction stage was carried out in order to separate the europium and yttrium in the organic phase of the aqueous phase, considering that europium is a light rare earth and yttrium is a heavy rare earth. This classification is according to the atomic masses of the rare earths. In the case of yttrium, there is a phenomenon called lanthanide contraction, which consists in the atomic radius contraction, making this element a heavy rare earth [16]. The \(n\)-heptane was used as the organic diluent, and the following substances were used as extractants: di-(2-ethylhexyl) phosphoric acid (DEHPA), tributyl phosphate (TBP), and trioctyl ammonium chloride (Aliquat 336). The ratio between the aqueous phase and the organic phase was 1:1, whereas the contact time between both phases during all of the tests was 10 min. Figure 3 shows the recovery of europium and yttrium in the organic phase. Figure 3a shows that there is a high preference for yttrium with the three extractants used, with DEHPA being the one that showed the greatest separation factor (8.67) and recovery (90%). In addition, for europium recovery, a separation factor of 0.24 was achieved with DEHPA as the extractant, whereas a separation factor of 0.01 was obtained with TBP. Therefore, any of the tested extractants are suitable for europium recovery from the aqueous solution. On the other hand, when observing Figure 3b, an increase in the DEHPA concentration increases the recovery of both elements in the organic phase. For a concentration of 0.5 M, europium recovery was 3% and 80% for yttrium, while for a concentration 1.5 M, it was 40 and 97%, respectively. The last results are not what is desired, since the aim is to separate both elements in the two phases. For both of the analyzed cases, a concentration of 1 M of DEHPA allowed the balance between a greater extraction of yttrium and a lower co-extraction of europium in the organic phase. A lower concentration of DEHPA implies a lower extraction of europium, while with a higher concentration, there are high extractions of both metals in the organic phase. In addition, although zinc and iron are dissolved in the aqueous solution, they do not affect yttrium extraction at all when DEHPA was used as an extractant. For the entire set of solvent extraction assays, elements such as Zn or Al were not detected in the organic phase after samples analysis via atomic absorbtion. Consequently, the interferences of these elements were considered negligible in this process. This result is in accordance with other works that found DEHPA to be the best substance for yttrium recovery [26]. The results shown in Figure 3a,b suggest that DEHPA is the best extractant for yttrium recovery from the aqueous phase, due to the high recovery (90%) and high separation factors (8.67) that this substance presents (see Appendix A, Tables A1-A3). Figure 4a shows the purification step of the organic phase (Scrubbing) with HNO\({}_{3}\) in order to remove the co-extracted europium. For this, the organic phase was put in contact with an aqueous phase corresponding to solutions of nitric acid at different concentrations. Figure 3: (**a**) Recovery of europium and yttrium in the organic phase with different extractant agents (extractants concentration in \(n\)-heptane: 1 M); (**b**) Recovery of europium and yttrium at different concentrations of di-(2-ethylhexyl) phosphoric acid (DEHPA).