Solvent extraction of trivalent actinides with di(2-ethylhexyl) phosphoric acid

Abstract We carried out solvent extraction on the trivalent actinides of Am, Cm, Cf, and Fm and the lanthanides (except Pm) using di(2-ethylhexyl)phosphoric acid (HDEHP) in benzene by a batch method. The extraction constants of the HDEHP complexes for these elements were determined systematically under identical conditions. The tetrad effect was clearly observed in the variation of the extraction constants of the lanthanide series. We found that the extraction constant for Fm(III) is much smaller than that for Dy(III), which have similar ionic radii. The extraction constants for Am(III), Cm(III), and Cf(III) are similar to those for corresponding Ln(III) having similar ionic radii. Two possibilities that account for the lower extraction constant of Fm(III) is suggested.