Selective Extraction of Sc(III) over Y(III) and Fe(III) with a Deep Eutectic Solvent Composed of N-Lauroylsarcosine and Tri-n-octylphosphine Oxide

Demand for scandium (Sc) has been increasing in recent years. However, there are almost no ores containing Sc, and the supply is insufficient because the separation and recovery of Sc as a byproduct from oxide minerals such as ilmenite ore, bauxite, and laterite are difficult. In this study, extraction and separation of Sc3+ from acidic chloride or acidic nitrate solutions containing transition metals such as Fe3+, Co2+, Ni2+, Zn2+, and Pd2+ were studied using N-lauroylsarcosine (NLS) and tri-n-octylphosphine oxide (TOPO), which together create a "deep eutectic solvent" (DES). Owing to the respective selectivity of NLS and TOPO by different extractive interactions between metal ions and the two extractants in toluene, Sc3+ was effectively and selectively separated even from Fe3+ in the aqueous ammonium nitrate solution, the mutual separation of which is difficult with NLS alone. The mutual separation of Sc3+ and Fe3+ in acidic chloride solution is in general very difficult, while the mutual separation of these metals from acidic nitrate solution is successful. This is due to either anions forming complexes with Sc3+ in the aqueous phase (chloride) or not (nitrate). The potential use of the combination of the NLS with TOPO for selective recovery of Sc3+ from Fe3+ in a refining process is demonstrated.