Electrochemical and spectroelectrochemical behaviour of Np(VI) ions in nitric acid solutions

Abstract

SummaryElectrochemical and spectroelectrochemical has been used to investigate the behaviour of neptunium (VI) in 1 ∼ 8 M HNO3solutions. The electrochemical reactions of Np(VI) ions were found to occurquasi-reversibly. The formal redox potentials (E°) for Np(VI)/Np(V) couples were determined to be +0.906, +0.908, +0.909, +0.902, +0.896, +0.895, +0.888, and +0.884 V (vs. Ag/AgCl) for Np(VI) ions in 1, 2, 3, 4, 5, 6, 7, 8 M HNO3solutions, respectively. The reduction processes of Np(VI) ions were followed spectroelectrochemically by using an optical transparent thin layer electrode cell. It was found that the absorption spectra measured at the applied potentials from +1.10 to +0.60 VversusAg/AgCl reference electrode redox couple for Np(VI) in HNO3solution have clear isosbestic points. These results indicate that the only reduction product of Np(VI) is Np(V), which is of considerable stability in HNO3solutions.