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

Abstract

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.

KEYWORDS:

• solvent extraction
• americium
• rare-earth elements
• separation process
• valence control
• ammonium peroxodisulfate
• silver nitcate
• ozone
• TBP
• ammonium phospho-tungstate