Plutonium in higher oxidation states in alkaline media

Abstract

Experimental chemical and electrochemical properties of plutonium in strong alkaline solution are described. Using different chemical and electrochemical methods to determine plutonium oxidation state speciation, we suggest that during oxidation of Pu(VI) in alkaline media Pu(VIII) is produced in a mixture with Pu(VII). Probable values of molar extinction coefficient of Pu(VIII) at 635 nm, and Pu(VII) at 500–550 nm, were estimated as ∼2600 ± 400 and ∼100 M −1 cm −1, respectively. The yield of presumed Pu(VIII) in the experimental solution was estimated to be ∼(15 ± 5)%. From electrochemical calculations we estimate that the values of the reduction potential of Pu(VIII)/Pu(VII) and Pu(VII)/Pu(VI) pairs in 2 M NaOH are greater than 0.90 V, and 0.68 ± 0.05 V (vs. NHE), respectively. The possible presence of other unknown oxidations (such as Pu(VII) peroxo-compounds) that might give similar results are discussed. For uncontestable proof of existence of Pu(VIII) in alkaline solutions, advanced spectroscopic techniques should be employed.