# Europium, Yttrium, and Indium Recovery from Electronic Wastes
## 4 Conclusions  
The recovery of rare earths from WEEE is feasible by the hydrometallurgical route, using for this purpose processes such as: acid leaching, solvent extraction, and precipitation. It should be noted that the WEEE from which it is desired to extract the rare earths must be pulverized in order to release the elements of interest.  
In the case of europium and yttrium dissolution from the CTRs, the best leaching agent turned out to be HNO\({}_{3}\) at 250 g/L of concentration. Leaching tests demonstrated that leaching times longer than 24 h allow higher recoveries, because there is a longer contact time between the nitric acid and the components of the coating powder that may be dissolved. Similarly, higher amounts of other metals such as zinc make it necessary to increase the leaching time to dissolve rare earths. In addition, when pulp density increases, the solution is saturated with the formed europium and yttrium nitrates. On the other hand, the reduction of the acid/powder ratio can also negatively influence rare earths dissolution, since there is less formation of soluble products, and therefore lower recoveries.  
The solvent extraction stage was carried out with DEHPA at a concentration of 0.5 mol/L with a contact time of 5 min and using \(n\)-heptane as a diluent. Subsequently, a purification step of the organic phase was carried out with HNO\({}_{3}\) of 120 g/L concentration to extract the europium. Finally, the re-extraction of yttrium was carried out in the aqueous phase using HCl of 300 g/L concentration. The yttrium precipitation was carried out with four times the stoichiometric amount of oxalic acid, and the solid obtained was calcined at 600 \({}^{\circ}\)C for 2 h to obtain yttrium oxide of 68% purity.  
Figure 10: Process flow diagram for indium oxide recovery from LCD panels.  
For the extraction of indium from the LCD screens, H\({}_{2}\)SO\({}_{4}\) leaching agent was used at a concentration of 90 g/L at 20% solids for 4 h. The extraction by solvents was carried out with the DEHPA extractant at a concentration of 0.50 mol/L with diesel as the diluent. The contact time was 10 min, and the aqueous phase-organic phase ratio was 1. For the re-extraction, H\({}_{2}\)SO\({}_{4}\) was used at a concentration of 10 mol/L with a contact time of 5 min. Finally, when the solution evaporated, the precipitated indium was obtained in the form of sulfate, which was calcined at 700 \({}^{\circ}\)C for 2 h to obtain indium oxide.  
The following are available online at [[http://www.mdpi.com/2075-4701/8/10/777/s1](http://www.mdpi.com/2075-4701/8/10/777/s1)]([http://www.mdpi.com/2075-4701/8/10/777/s1](http://www.mdpi.com/2075-4701/8/10/777/s1)), Figure S1: CRT powder SEM image, Figure S2: Yttrium oxide SEM image, Figure S3: Yttrium oxide chemical characterization with SEM, Figure S4: Yttrium oxide diffractogram obtained after calcination, Figure S5: Indium oxide diffractogram obtained after calcination, Table S1: Yttrium oxide characterization.  
Conceptualization, E.T.; Data curation, S.G.; Formal analysis, S.G.; Investigation, C.R. and E.V.; Methodology, C.R. and E.V.; Project administration, E.T.; Writing--original draft, S.G.; Writing--review & editing, S.G.  
This research was funded by the Project PIS 039 12 of the Escuela Politecnica Nacional, which was executed in the Department of Extractive Metallurgy.  
The authors address their thanks to the Escuela Politecnica Nacional for the support in the development of the present research.  
The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.