Is octavalent plutonium really formed during oxidation in alkaline aqueous solutions?

Abstract

Abstract The solution, containing 2 M NaOH and 4.8 mM Pu(VI) mainly in ionic-dispersed phase, becomes dark blue during 2–3 min under ozonation. The absorption spectrum of the solution in the visible range coincides with the well-known absorption spectrum of Pu(VII). The addition in Pu(VII) solution of the aliquot of Pu(VI) solution reduces the absorbance of the solution at any wave length in proportion to dilution. Consequently there is no the influence of Pu(VI) on the absorption spectrum of Pu(VII). Thus, it is become obvious no Pu(VIII) formed in the course of ozonolysis of Pu(VII) alkaline solution. Additionally, crystalline Pu(VII) and Np(VII) compounds were synthesized, their electron absorption spectra were measured and compared with the ones of alkaline solutions. A similar structure of the spectra also indicates a heptavalent oxidation state of neptunium and plutonium in the synthesized crystalline compounds. Thus, the experimental results of this work, along with an analysis of the experimental results of other authors, presented in this work, make it possible to definitely conclude that at present time the highest of the known oxidation states of plutonium oxidation in aqueous solutions is the heptavalent state and all statements about the production of octavalent plutonium in aqueous solutions should be considered as unreasonable.