Valence Control and Solvent Extraction of Americium in the Presence of Ammonium Phosphotungstate.

Fundamental investigations on valence control and solvent extraction of americium were carried out to develop a method for americium separation from reprocessing solution. In order to adjust americium valency from III to IV and VI, (NH4)10P2W 17O61 synthesized was used as complexant stabilizing Am(IV). Oxidation behavior of americium was investigated as a function of (NH4)10P2W 17O61 americium ratio. Using 0.1M (NH4)2S2O8 and 0.01M AgNO3 as oxidation reagent, Am(IV) was obtained quantitatively at the ratio of 15. On decreasing the ratio to 0.6, 92% of americium was adjusted to Am(VI). The concentration of (NH4)2S2O8 could be reduced to 1/15 compared to the previously reported method in which no complexant was used. Americium(IV) was also prepared by reacting O3 and AgNO3 but no Am(VI) was obtained even at low (NH4)10P2W 17O61 to americium ratio.Americium(VI) could be extracted by tri-n-butyl phosphate stably without influence of (NH4)10P2W 17O61. The distribution coefficient of Am(VI) was 4 between 100% tri-n-butyl phosphate and 1 M nitric acid, and separation factor from Nd(III) was 50.With regard to the americium separation method which implemented valence control followed by extraction, adding (NH4)10P2W 17O61 led to minimization of waste volume and improvement of extraction efficiency.