Reduction of uranium (VI) to uranium (IV) by hydrazine in an aqueous nitric acid-30% tri-n-butyl phosphate (TBP) volume emulsion

Tetravalent uranium which has been stabilized with hydrazine is widely used in the extraction technology of regenerating irradiated nuclear fuel as an agent for reduction of plutonium (IV) to plutonium (III). However, it is well known that in two-phase extraction systems of the type aqueous nitric acid solutions of U(IV)-TBP solutions in inert diluents, the U(IV) is insufficiently stable and is oxidized to U(VI) as a result of reaction with nitrous acid which accumulates in the organic phase. The results of kinetic experiments at various concentration of nitric acid, uranyl nitrate, and hydrazine and at various temperatures show that the order of the reduction of U(VI) to U(IV) in the two-phase extraction system emulsion 30% TBP by volume solution in n-paraffins-aqueous nitric acid is zero with respect to uranium and is unity with respect to hydrazine. Typical kinetic curves for the U(VI)-time dependence are given. The kinetic dependences were analyzed in the time range for about 50% completion of reaction.