Extractant (2-ethylhexyl)(2,4,4′-trimethylpentyl)phosphinic acid (USTB-1): Synthesis and its extraction and separation behaviors for rare earths from chloride media

By combining the structures of P227 and Cyanex 272, a nonsymmetric dialkylphosphinic acid USTB-1 was synthesized. Its structure was confirmed by 31P NMR, 1H NMR, MS and IR. Its pKa and purity were determined through potentiometric titration method. Its extraction and separation performance for RE(III) were studied. The purity of USTB-1 was 97.6%. Its pKa was 5.73, which was very close to that of P227 and Cyanex 272. Its solubility in deionized water was 34.7 mg/L. Its extraction ability was equal to that of P227 and Cyanex 272. It can reach extraction equilibrium as fast as Cyanex 272. Its complex with Lu(III) has larger solubility in n-octane than that of Cyanex 272, which indicated that USTB-1 has higher extraction capacity than Cyanex 272. The Lu(III) loaded in USTB-1 solution can be stripped by HCl as easily as the Lu(III) loaded in P227 and Cyanex 272 solutions. USTB-1 has good separation performance for RE(III), especially for heavy RE(III). Its average separation factor of adjacent heavy RE(III) from Ho to Lu was 2.21, superior to Cyanex 272 (βN+1/N‾ from Ho to Lu: 2.08).