MUTUAL SEPARATION OF RARE-EARTH ELEMENTS BY EXTRACTION CHROMATOGRAPHYUSING BIS(1,1,3,3-TETRAMETHYLBUTYL)PHOSPHINIC ACID AS A STATIONARY-PHASE

The extraction behavior of rare earth elements was systematically inve stigated,by using bis(1,1,3,3-tetramethylbutyl)phosphinic acid (HMBP) in HNO3 medium. The extraction mechanism was evaluated through a log-l og plot analysis, and the overall extraction equilibrium constant K wa s calculated for each rare earth element(III). The degree of mutual se paration of adjacent pair of rare earth elements was discussed from th e value of separation factor S.F.(z+1/z) and explained by thermodynami c function-the relative free energy change of adjacent rare earth elem ents(III) Delta(Delta G degrees)(z+1/z). The separation of scandium fr om lanthanoids and yttrium was achieved by a single HMBP extraction an d the mutual separation of lanthanum. cerium and praseodymium was achi eved by HMBP-extraction chromatography.