Separation of oxidised americium from trivalent transplutonium elements and lanthanides by solvent extraction

Abstract

Trace amounts of americium, contained in 0·05 M nitric acid and preheated with 0·05 M ammonium persulphate, remained in the aqueous phase, presumably as the pentavalant species, AMO 2 +, when contacted with the solvent mixture, thenoyltrifluoroacetone (HTTA) and tri- n-octylphosphine oxide (TOPO) in cyclohexane. However, synergism occurred in the solvent extraction of the trivalent actinides and lanthanides with this mixture, the extraction coefficients for these elements approaching 10 2. Occasional spurious results occurred in the solvent extraction of oxidised americium caused by initial failure to oxidise americium solutions quantitatively to the higher valence state and/or partial reduction of the oxidised species back to Am(III). These inconsistencies were eliminated by suitable pretreatment of glassware and solvents and the use of the more stable potassium persulphate as oxidant. The small extraction of the oxidised americium showed little dependence on the diluent, the concentration of HTTA or TOPO, and the persulphate concentration. This contrasted with the marked dependence of the extraction of curium(III) on each of these parameters. The extraction coefficient of this metal ion decreased by a factor greater than 10 2 for various diluents from cyclohexane to chloroform. Tracer studies showed that the composition of the extracting species for curium is Cm(TTA) 2 x (TOPO) 2, where x is NO 3 − or HS 2O 8 −. It was not possible to obtain quantitative extraction of hexavalent americium by this solvent mixture or the organophosphoric reagent, di-(2-ethylhexyl) phosphoric acid in cyclohexane.