Sorption of trivalent plutonium onto UO2and the effect of the solid phase on the Pu oxidation state

Summary A problem with plutonium in sorption studies is its tendency to occur in a mix of oxidation states. This work was a study of the sorption of plutonium on the solid phase UO2— in a perchlorate medium as a function of pH — where plutonium is kept in its trivalent oxidation state. Experiments also showed that uranium(IV) oxide can reduce Pu(IV) to Pu(III) in an acidic solution and maintain it in that state. It was observed at the same time that the chemically inert solid phases TiO2and ThO2possibly increase the rate of disproportionation of Pu(IV) at a pH of about 0.5. In accordance with previous studies MnO2was found to have an oxidizing effect, converting Pu(IV) into Pu(VI). A comparison is made between the sorption of Th(IV), Pu(III) and Co(II) on UO2and TiO2, and Pu(VI) on TiO2.