Oxidation of Pu(III) by Nitric Acid in Tri-n-Butyl Phosphate Solutions. Part II. Chemical Methods for the Suppression of Oxidation to Improve Plutonium Separation in Contactor Operation

A systematic method has been used to screen a number of potential stabilizers (holding reductants) for Pu(III) in tri-n-butyl phosphate/diluent solutions used in irradiated fuel reprocessing systems. The conditions assumed were similar to those used in solvent extraction contactor operations. Of the reagents tested, oximes as a group appeared to be very effective. Acetaldoxime, in particular, was selected for extensive tests and was used as a Pu(III) stabilizer, in both the aqueous and organic phases, in contactor runs for plutonium partition from thorium and uranium. In the best results, the plutonium loss to the thorium/uranium stream was 2.8 × 10⁻⁵ g/ℓ or 0.0046%; without using acetaldoxime, the loss was 12%. Rates of plutonium reduction in 1.5 M nitric acid have been compared for a number of reducing agents under identical conditions. Some derivatives of hydroxylamine were found to be much more effective than hydroxylamine itself.