Solvent extraction and separation of heavy rare earths from chloride media using nonsymmetric (2,3-dimethylbutyl)(2,4,4′-trimethylpentyl)phosphinic acid

Nonsymmetric (2,3-dimethylbutyl)(2,4,4′-trimethylpentyl)phosphinic acid (INET-3) may be a superior extractant for extraction and separation of heavy rare earths (REs), as its extraction ability falls between that of P507 and Cyanex 272. Its purity and pK a were determined using potentiometric titration methods. The extraction mechanism and extraction equilibrium constants of INET-3 for heavy REs from chloride media were studied. The effects of the anion types (Cl − , NO 3 − and SO 4 2   − ) and concentrations (0.1, 0.5 and 1.0   mol/L) on RE(III) extraction were investigated. The extraction capacity and separation factors of INET-3 for heavy REs were determined. The stripping behaviours of heavy RE complexes with INET-3 by HCl , HNO 3 and H 2 SO 4 were examined. The results showed that the pK a of INET-3 was 5.45. The extraction capacity of INET-3 was approximately twice that of Cyanex 272 and only one-third that of P507. Loaded heavy RE(III) extracted by INET-3 was completely stripped out by HCl, HNO 3 and H 2 SO 4 solutions when the pH was at or below 1.2. Among the three inorganic acids , H 2 SO 4 was the most effective stripping agent. INET-3 can separate heavy RE(III) efficiently, and the separation factors of adjacent heavy RE(III) β Er/Ho , β Tm/Er , β Yb/Tm and β Lu/Yb were 3.25, 2.73, 2.96 and 1.53, respectively, when extracted from a Ho/Er/Tm/Yb/Lu quinary system.