Selective Extraction of Scandium from Transition Metals by Synergistic Extraction with 2-Thenoyltrifluoroacetone and Tri-<i>n</i>-octylphosphine Oxide

There has been an increasing demand for scandium (Sc). However the supply is insufficient because the separation and recovery of Sc as a byproduct from ores is difficult. In this study, extraction and separation of Sc³⁺ from a sulfuric acid solution containing transition metals such as Al³⁺, Fe³⁺, Mn²⁺, Co²⁺, Ni²⁺ and Zn²⁺ was investigated using a β-diketone, HTTA and a neutral extractant, TOPO. Due to the synergistic effect with the two extractants, Sc³⁺ was effectively and selectively separated even from Fe³⁺, the separation of which is difficult with HTTA alone. The extraction mechanism was examined and it was revealed that Sc³⁺ is extracted with three HTTA and one TOPO molecules. Scandium was readily stripped from the extracting phase by 1 M sulfuric acid. The potential use of the combination of the β-diketone with TOPO for the recovery of Sc³⁺ in a refining process was demonstrated.