Separation of trivalent rare earths from chloride medium using solvent extraction with heptylaminomethyl phosphonic acid 2-ethylhexyl ester (HEHHAP)

Abstract

A novel extractant heptylaminomethyl phosphonic acid 2-ethylhexyl ester (HEHHAP, abbreviated as H2L2) was synthesized for the extraction and separation of trivalent rare earths (REs: La ~ Lu, plus Y) from chloride medium. The results showed that the extraction of heavy REs by HEHHAP was higher than that of light one as in the order: La < Gd < Ho < Y < Er < Tm < Yb < Lu. The extraction reaction was a cation exchange process and the extracted complexes were determined to be REClH2L4. The extraction process was an endothermic reaction and the thermodynamic parameters were calculated. Moreover, the separation factors between heavy REs and yttrium in HEHHAP, i.e. βEr/Y, βTm/Y, βYb/Y and βLu/Y, were determined to be 2.18, 9.36, 14.9 and 24.3, respectively, which was higher than those of HEHEHP and D2EHPA, indicating that HEHHAP was more efficient to separate yttrium from heavy REs. The extraction capacities of Yb (III) and Lu (III) were calculated to be 12.76 g/L and 15.43 g/L, respectively. HCl was founded to be the best stripping agent as compared with H2SO4 and HNO3.