Résumé
The development of water immiscible room temperature ionic liquids (RTILs) naturally suggested their use for biphasic extraction as an alternative to molecular organic solvents most notably for their low vapor pressure . However, although liquid-liquid extraction processes using RTILs often reach high efficiency and selectivity, the difficult de-extraction of metallic species is to date as a major technical lock. In this context, in situ electrodeposition in the ionic liquid phase after liquid-liquid extraction could allow species recovery in their metallic form. In this work, we studied the possibility to recover indium by coupling liquid-liquid extraction followed by in situ electrodeposition in the ionic liquid phase. Indium was classified in June 2010 as a critical raw material by the European Commission, due to its high relative economic importance and to high relative supply risk . We first investigated the electrodeposition of In in 1-butyl-1-ethylpiperidinium bis(trifluoromethylsulfonyl)imide (BEPipNTf2) in ambient atmosphere, after its synthesis and its purification . This RTIL, characterized by a wide electrochemical window, a low viscosity and an ultra-low hygroscopic character presents good properties for liquid-liquid extraction and consecutive electrodeposition. Then, based on the works of F. Kubota et al. [4] who showed that In(III) can be quantitatively and selectively extracted in an ionic liquid using trimethylphosphine oxide (TOPO) as extractant, we studied the electrochemical behavior of In(III)-TOPO complex. Voltammetric studies revealed that TOPO is non electroactive and that the In-TOPO complex can be reduced within the electrochemical window of the ionic liquid. The influence of the extractant on the electrodeposition of metallic indium was studied and it appears that indium can be quantitatively electrodeposited in the presence of TOPO. Finally, the feasibility of In electrodeposition in ambient atmosphere after liquid-liquid extraction was then demonstrated.