Solvent Extraction of Scandium(III) by an Aqueous Biphasic System with a Nonfluorinated Functionalized Ionic Liquid

The use of ionic liquids (ILs) as solvents for extraction of metals is a promising development in separation science and technology; yet, the viscosities of ionic liquids (ILs) can be so high that long reaction times are required to reach the equilibrium state. An aqueous biphasic system (ABS) consisting of the nonfluorinated carboxyl-functionalized phosphonium IL [P444C1COOH]Cl and a 16 wt % NaCl solution is described. The IL-rich phase of the aqueous biphasic system has a very low viscosity, in comparison to the pure IL [P444C1COOH]Cl. This system has excellent extraction properties for scandium. Different extraction parameters were investigated, including contact time and metal loading. The influence of the pH on the solubility of the IL cation in the water-rich phase was determined via quantitative 1H NMR. The stripping of scandium with oxalic acid from the IL phase was also investigated. A plausible extraction mechanism is proposed where three IL cations are deprotonated to form zwitterionic compound...