Tailored ternary hydrophobic deep eutectic solvents for synergistic separation of yttrium from heavy rare earth elements

Abstract

Clean, efficient and economical separation of yttrium (Y) from heavy rare earth elements (HREEs) has always attracted attention. Herein, a strategy for the separation of Y from HREEs based on ternary hydrophobic deep eutectic solvent (HDES) extraction has been first reported. A total of 44 HDESs were prepared with four carboxylic acids as hydrogen bond donors (HBDs), bis(2-ethylhexyl) amine (BEA) as the hydrogen bond acceptor (HBA) and 1-decanol (DL) as the third component. The prepared HDESs have the advantages of simple preparation, no purification requirement, low viscosity, low water solubility and low toxicity. Performances of the HDESs for the separation of Y from HREEs were systematically evaluated. The synergistic effects of each component in the HDESs improve the extraction and separation performances of Y from the HREEs without saponification and organic solvents. Among them, the DL : oleic acid (OA) : BEA-based HDES with OA as the HBD has good extraction ability, higher saturation loading capacity and better phase separation stability. The separation factors of the DL : OA : BEA (9 : 1 : 5) HDES for HREEs (Dy–Lu) and Y in the industrial Y-enriched solution are Dy/Y ≥ 3.05, Ho/Y ≥ 3.37, Er/Y ≥ 4.29, Tm/Y ≥ 6.00, Yb/Y ≥ 10.8, and Lu/Y ≥ 11.2, respectively. The loaded HDES can be easily stripped and remains stable during multiple regeneration cycles. The HDES has shown excellent extraction and separation performance for HREEs (Dy–Lu) and Y, and potential for application in sustainable rare earth separation.