Synergistic Extraction of Rare-Earth Metals and Separation of Scandium Using 2-Thenoyltrifluoroacetone and Tri-<i>n</i>-octylphosphine Oxide in an Ionic Liquid System

The synergistic extraction of rare-earth metals by a β-diketone and an organophosphine oxide is described. A combination of 2-thenoyltrifluoroacetone (HTTA) and tri-n-octyl phosphine oxide (TOPO) was found to be effective in synergistically extracting rare-earth metals into an ionic liquid (IL). The synergistic effect was strongly influenced by the diluent in which the extractants were dissolved. Extraction efficiencies for all the rare-earth metal ions were enhanced by synergy when a conventional organic solvent was used (n-dodecane). However, the synergistic effect in the IL preferentially improved the scandium extraction, leading to higher selectivity for Sc than for other rare-earth metals. Slope analysis was used to assess each extraction system, and the IL itself was found to be directly involved in the complex formation of the metal extraction system.