La(III) and Ce(III) Extraction using Thermomorphic Ionic Liquid
Juliette SIRIEIX PLENET2, Styliani PAPADOPOULOU1, Antonio DE SOUZA BRAGA2, Anne-Laure ROLLET2, Isabelle BILLARD3, Clément COUSIN2, Guillaume MERIGUET2
1Chimie ParisTech, CNRS, Institut de Recherche de Chimie Paris, PSL University, Paris, France
2 Sorbonne Université, CNRS, Laboratoire PHENIX, Paris, France
3Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, Grenoble INP, LEPMI, Grenoble, France
Keywords: Homogeneous liquid-liquid extraction, separation, Rare Earth
Rare Earth elements (REEs) suffer from high demand as critical materials in modern green and other advanced technologies. Their recycling thus appears essential for a sustainable economy. Currently, the main processes used towards this end are based on hydrometallurgy which involves liquid-liquid extractions using volatile organic solvents. Ionic liquids (ILs) represent a valuable alternative to organic solvents in extraction processes. Interestingly, it has been shown that the use of ILs can remarkably enhance the extraction rate of REE ions from leaching solutions.[1] However ILs present high viscosities which slow down the mass transfer during extraction. As a potential solution to this problem a special type of extraction, Homogeneous liquid-liquid extraction (HLLE), was developed. HLLE is based on the use of thermomorphic ILs i.e. ionic liquids that show temperature-dependent miscibility with water.[2-3] When changing the temperature, a reversible transition from a biphasic mixture to a homogeneous phase is achieved, the interface disappears and there is no diffusion barrier for extraction.[3]
This study is focused on a thermomorphic IL: 2-hydroxyethyl-trimethylammonium bis-(trifluoromethanesulfonyl)imide [Choline][TFSI] for La(III) and Ce(III) extraction in the presence of betaine extractant. [Choline][TFSI] displays thermomorphic behavior with an upper critical solution temperature (UCST).[2] We have determined the ternary phase diagram of the IL-water-betaine extractant mixtures via NMR in order to have a clear idea of the miscibility of the three participating components of the system, playing a crucial role on the HLLE process. The influence of the mass of the extractant, added initially in the aqueous phase, on the efficiency of the metal ion extraction was determined. Results demonstrated that by increasing the quantity of betaine in the system (up to a certain amount), the extraction efficiency E% increases, reaching values as high as 95% for Ce(III) and 93% for La(III). We also aim at reaching a better understanding of the extraction processes of REEs in ILs by determinating of the extraction mechanism.
References:
[1] I. Billard. Handbook on the physics and chemistry of rare earths. 2013. 43, 213-273
[2] T. Vander Hoogerstraete, B. Onghena and K. Binnemans, J. Phys. Chem. Lett. 2013, 4, 1659-1663
[3] B. Onghena, T. Opsomer and K. Binnemans, Chemical Communications, 2015, 51, 15932-15935