EXTRACTION BEHAVIOR OF TRIVALENT LANTHANOIDS AND YTTRIUM WITH BIS(2,4,4-TRIMETHYLPENTYL)OCTYLPHOSPHINE OXIDE

The extraction behavior of yttrium and trivalent lanthanoids has been investigated from thiocyanate solutions using bis(2,4,4-trimethylpenty l)octylphosphine oxide (CYANEX 925) in xylene as an extractant by trac er techniques. The results demonstrate that these trivalent metal ions are extracted as M(SCN)(3) . 3CYANEX 925. The equilibrium constants o f the extracted complexes have been deduced by non-linear regression a nalysis. The extraction behavior of trivalent lanthanoids and yttrium was found to be ambiguous since the distribution ratios of these metal ions are non-monotonic function of atomic number (La < Y < Pm < Tm < Ho < Eu < Yb < Lu). The separation factors between these trivalent met al ions have been calculated and compared with commercially important extraction systems like tributylphosphate (TBP), trioctylphosphine oxi de (TOPO), tyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (C MPO) and di-2-ethylhexyl phosphoric acid (DEHPA). The possibilities fo r separating yttrium from trivalent lanthanoids has also been discusse d.