Extraction of Trivalent Europium by Bis(Trifluoromethane Sulfonimide) Betaine in Ionic Liquid Beyond Upper Critical Transition Temperature

Herein the study of homogeneous-phase solvent extraction with an ionic liquid ([Hbet][Tf2N]) toward europium (III) from a nitrate system is reported. [Hbet][Tf2N], which forms a homogeneous phase with water above the upper critical solution temperature (UCST), was synthesized via a displacement reaction between (carboxymethyl)trimethylammonium chloride and Li[Tf2N]. The dependence of the distribution ratio (D) on key variables, including initial pH, nitrate concentration, contact time, initial Eu3+ concentration, and temperature, was systematically investigated. The upper critical transition temperature was determined as 333 K, beyond which the homogeneous-phase solvent extraction started. The saturated extraction capacity reached 552.92 mg Eu3+ per liter of [Hbet][Tf2N]. The extraction mechanism was revealed using a slope method. The stripping study was conducted by using HCl of 1.0 mol/L as stripping agent. Thermodynamic parameters (∆H°,∆S°, and ∆G°) were determined from temperature-dependent data. Multi-stage countercurrent extraction was carried out to simulate the industrial process. Above the UCST, the homogeneous ionic-liquid/aqueous system provides enhanced interfacial contact, which promotes the extraction of Eu3+.