On the transfer mechanism of uranium (VI) and plutonium (IV) nitrate in the system nitric acid-water/tributylphosphate-dodecane

Using the single-drop method as experimental technique, the initial transfer rates of uranium(IV) and plutonium(IV) have been determined between aqueous nitrate or nitric acid and TBP dissolved in dodecane. The results of kinetic measurements have been interpreted in terms of chemical interface reactions. As soon as the metal enters the interface either in ionic or neutral form it is an interfacial complex which adds TBP molecules by degrees from the organic phase as well as nitrate anions from the aqueous phase. No evidence exists of a distinct sequence in the addition of the ligands; that means that the TBP reacts not only with the neutral metal compound but also with the ionic species. The interfacial complexes cannot be distinguished according to the phase they came from. Equilibrium is obtained by a dual transformation of the interfacial complexes either to the organic or to the aqueous phase and not by two reactions running independently in opposite directions.