VALENCE CONTROL AND SOLVENT-EXTRACTION OF AMERICIUM IN THE PRESENCE OF AMMONIUM PHOSPHOTUNGSTATE

Fundamental investigations on valence control and solvent extraction o f americium were carried out to develop a method for americium separat ion from reprocessing solution. In order to adjust americium valency f rom III to IV and VI, (NH4)(10)P2W17O61 synthesized was used as comple xant stabilizing Am(IV). Oxidation behavior of americium was investiga ted as a function of (NH4)(10)P2W17O61 to americium ratio. Using 0.1M (NH4)(2)S2O8 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)(2)S2 O8 could be reduced to 1/15 compared to the previously reported method in which no complexant was used. Americium(IV) was also prepared by r eacting O-3 and AgNO3 but no Am(VI) was obtained even at low (NH4)(10) P2W17O61 to americium ratio. Americium(VI) could be extracted by tri-n -butyl phosphate stably without influence of (NH4)(10)P2W17O61. The di stribution coefficient of Am(VI) was 4 between 100% tri-n-butyl phosph ate and 1M nitric acid, and separation factor from Nd(III) was 50. Wit h regard to the americium separation method which implemented valence control follow-ed by extraction, adding (NH4)(10)P2W17O61 led to minim ization of waste volume and improvement of extraction efficiency.