SOLVENT-EXTRACTION CHARACTERISTICS FOR MUTUAL SEPARATION OF RARE-EARTHS OF CYANEX-272 AND TR-83

Equilibrium distribution in the solvent extraction of 12 kinds of rare earths from hydrochloric acid solutions with 2 kinds of commercial phosphorus-based acidic extractants, Cyanex 272 and TR-83, were investigated at 303 K using IP solvent, a commercial diluent of iso-paraffins, as a diluent in order to examine the separation factors between adjacent elements by these extractants. It was found that rare earths are extracted with these extractants according to the cation-exchange reaction releasing three hydrogen ions per unit metal ion as observed in the extraction with other acidic extractants. The plots of the apparent extraction equilibrium constants for each metal against atomic number exhibited the ''tetrad effect'' as reported in the extraction with PC-88A and D2EHPA. The separation factor between La and Ce by Cyanex 272 was much greater than other extractants. Those between Nd and Sm, and Gd and Dy were also great with this extractant. In the case of TR-83, it was great for Sm/Nd and Yb/Er.