Synergistic solvent extraction of heavy rare earths from chloride media using mixture of HEHHAP and Cyanex272

Abstract The synergistic extraction of heavy rare earths from chloride medium was investigated using the mixture of heptylaminomethylphosphonic acid mono-(2-ethyl-hexyl) ester (HEHHAP, HA) and bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex272, HB) in heptane. The extraction efficiency of heavy rare earths and the separation factors between adjacent lanthanides with the HEHHAP-Cyanex272 mixture are both better than those for the sole HEHHAP or Cyanex272 system. The separation factors between adjacent heavy rare earths are also higher than those for other synergistic systems. The rare earth extraction is a cation exchange process deduced by both slope analysis method and constant molar method. The extracted complexes are determined to be LnH2Cl2A2B (Ln = Yb, Lu). The loaded metal ions can be easily stripped by HCl or H2SO4. The stripping efficiency is over 90% when the concentration of HCl was more than 1 mol/L. The synergistic extraction of heavy rare earths with the mixed HEHHAP-Cyanex272 system is an endothermic reaction. The negative values of ΔG indicates that the extraction reaction of Ln(III) is spontaneous and favorable.