Studies on the synergistic extraction of rare earths with a combination of 2‐ethylhexylphosphonic acid mono‐2‐ethylhexyl ester and trialkylphosphine oxide

The synergistic extraction of rare earths (La, Nd, Gd, Y and Yb) with a mixture of 2‐ethylhexyl 2‐ethylhexylphosphonate (EHEHPA) (HA) and trialkylphosphine oxide (Cyanex 923) (B) from a hydrochloride medium was investigated. The mixed system significantly enhances the extraction efficiency for lighter lanthanides and the synergistic enhancement coefficients for La (4.52), Nd (3.35), Gd (2.08), Y (1.31) and Yb (1.08) decrease with decreasing ionic radius of the rare earths. The extraction equilibrium of La, Nd and Gd indicate that La and Nd were extracted as MA3·B, whereas Gd was extracted as Gd(OH)A2(HA)2·B. The equilibrium constants, thermodynamic functions such as ΔG, ΔH and ΔS and formation constants of the extracted species were determined. The stripping properties were also studied.