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-trimethylpentyl)octylphosphine oxide (CYANEX 925) in xylene as an extractant by tracer techniques. The results demonstrate that these trivalent metal ions are extracted as M(SCN)3·3CYANEX 925. The equilibrium constants of the extracted complexes have been deduced by non-linear regression analysis. 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 metal ions have been calculated and compared with commercially important extraction systems like tributylphosphate (TBP), trioctylphosphine oxide (TOPO), octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) and di-2-ethylhexyl phosphoric acid (DEHPA). The possibilities for separating yttrium from trivalent lanthanoids has also been discussed. (author)