SEPARATION STUDIES OF YTTRIUM(III) AND LANTHANIDE(III) IONS WITH 4-BENZOYL-2.4-DIHYDRO-5-METHYL-2-PHENYL-3H- PYRAZOL-3-THIONE AND TRIOCTYLPHOSPHINE OXIDE USING A ROBOTIC EXTRACTION SYSTEM

We studied the extraction of trivalent Y, La, Pr, Nd, Sm, Eu, Gd, Dy, Er, and Lu from aqueous perchlorate solutions using a mixture of 4-benzoyl-2,4-dihydro-5-methyl-2-phenyl-3H-pyrazol-3-thione (HBMPPT) and trioctylphosphine oxide (TOPO). The metal ion distribution coefficients (D-values) as a function of increasing lanthanide atomic number increased initially, reached a maximum value at Nd, then decreased to a nearly constant value for Gd and the later lanthanides. The D-values vary slightly across the lanthanide series, the maximum difference being a factor of 14 between La and Nd. Analysis of the slopes of plots of log D versus pH, log [HBMPPT], and log [TOPO] indicated that the stoichiometries of the extraction complexes varied across die lanthanide series showing a decrease in the number of HBMPPT (and/or BMPPT) units and an increase in the number of TOPO molecules involved in the major extraction species. This extraction system can provide a good way to separate the trivalent actinides from the trivalent lanthanides.