Extraction of the trivalent transplutonium actinides americium through einsteinium by the sulfur donor Cyanex 301

Abstract

In the extraction of lanthanides by the sulfur donor ligand, Cyanex 301 (HC301, bis(2,4,4-trimethylpentyl)dithiophosphinic acid), a transition in the coordination mode of extracted complexes has been observed between Eu and Gd. The light lanthanides La–Eu tend to be extracted as inner sphere complexes with HC301 directly coordinating the metal whereas the second half of the series Gd–Lu have a tendency to be extracted as outer sphere complexes. Without extended actinide studies, spanning the transplutonium actinides, it was unclear if a similar change in the extraction mechanism occurs in the actinide series. To assess this, solvent extraction studies were completed examining the slope dependence of the actinides and lathanides in the presence of varied nitrate and acid concentrations. Significant variation in the slope dependences was not observed for either the actinides or the lanthanides as pC_H+ varied, however, the nitrate dependence and neodymium spectroscopy data suggest that the formation of outer sphere complexes is suppressed by higher nitrate concentrations. This suppression of outer sphere complexes enhanced the extraction of lanthanides, but not the actinides and suggests that the actinides form inner sphere complexes. Therefore, the HC301 separations chemistry observed thus far suggest differences in the chemistry of the actinides and lanthanides continues to persist deep into the actinide series.