Chronopotentiometry of plutonium in mineral acid media

Abstract

The chronopotentiometric behavior of plutonium(III), plutonium(IV), and plutonium(VI) at a platinum electrode in various mineral acid media has been studied in order to determine the diffusion coefficients of the different plutonium species, the effects of surface oxidation of the platinum electrode, and the possible analytical usefulness of chronopotentiometry for the determination of plutonium. The reduction of plutonium(IV) to plutonium(III) at a platinum wire cathode in perchloric, sulfuric, nitric, and hydrochloric acid solutions has been investigated. The relatively small diffusion coefficient of plutonium(IV) in each of these media plus the spontaneous chemical oxidation of the platinum electrode by plutonium(IV) result in a significant positive error in chronopotentiometry with concentrations of plutonium(IV) below O–O1 M. Chronopotentiograms for the oxidation of plutonium(III) to plutonium(IV) in sulfuric acid show one wave due to oxidation of plutonium(III) followed by a second wave attributable to the formation of a platinum oxide film. Plutonium(III) in sulfuric acid medium, chemically reduces the oxide film. The electro-oxidation of plutonium(III) in perchloric acid medium gives a well-defined chronopotentiogram at either pro-reduced or pre-oxidized electrodes. The chronopotentiometric reduction of plutonium(VI) in a 1 F perchloric acid solition proceeds, in a step-wise fashion, first to plutonium (V) and then to plutonium(III). For the experimental conditions employed, there was no evidence to show that plutonium(V) undergoes significant disproportionation in the perchloric acid medium.