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

Abstract

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 pKa 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−, NO3− and SO42−) and concentrations (0.1, 0.5 and 1.0mol/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, HNO3 and H2SO4 were examined. The results showed that the pKa 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, HNO3 and H2SO4 solutions when the pH was at or below 1.2. Among the three inorganic acids, H2SO4 was the most effective stripping agent. INET-3 can separate heavy RE(III) efficiently, and the separation factors of adjacent heavy RE(III) βEr/Ho, βTm/Er, βYb/Tm and βLu/Yb were 3.25, 2.73, 2.96 and 1.53, respectively, when extracted from a Ho/Er/Tm/Yb/Lu quinary system.