Synergistic extraction and separation of yttrium from heavy rare earths using mixture of sec-octylphenoxy acetic acid and bis(2,4,4-trimethylpentyl)phosphinic acid

Synergistic extraction and separation of yttrium (Y) from heavy rare earths (HRE) in chloride medium using mixture of sec-octylphenoxy acetic acid (CA-12, HA) and bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex272, HL) in n-heptane has been investigated. The synergistic enhancement coefficients, Rmax, were obtained for Ho3+ (5.12), Y3+ (5.34), Er3+ (7.04), Tm3+ (7.50), Yb3+ (13.12) and Lu3+ (17.58). The separation factors (SF) between Y3+ and HRE were obtained, and it was found that Er3+ would form the new complex as ErH6A4L5 in the mixture system. A cation exchange mechanism was proposed. The equilibrium constant, formation constant and thermodynamic parameters such as ΔG = −18.48 kJ/mol, ΔH = −1.36 kJ/mol and ΔS = 0.058 kJ/mol were determined. The CA-12 and Cyanex272 mixture system showed higher extraction efficiency, larger separation factors as well as excellent stripping behaviors. The application potential of the mixture system to separate Y from HRE has been discussed.