Chemical speciation and association of plutonium with bacteria, kaolinite clay, and their mixture

Onuki, Toshihiko; Yoshida, Takahiro*; Ozaki, Takuo; Kozai, Naofumi   ; Sakamoto, Fuminori  ; Nankawa, Takuya ; Suzuki, Yoshinori*; Francis, A. J.

We investigated the interactions of Pu(VI) with Bacillus subtilis, kaolinite clay, and a mixture of the two to determine and delineate the role of the microbes in regulating the environmental mobility of Pu. The amount of Pu sorbed by B. subtilis increased with time, but had not reached equilibrium in 48 h, whereas equilibrium was attained in kaolinite within 8 h. After 48 h, the oxidation state of Pu in the solutions exposed to B. subtilis and the mixture had changed to Pu(V), whereas the oxidation state of Pu associated with B. subtilis and the mixture was Pu(IV). In contrast, there was no change in the oxidation state of Pu in the solution or on kaolinite after exposure to Pu(VI). SEM-EDS analysis indicated that most of the Pu in the mixture was associated with B. subtilis. These results suggest that Pu(IV) is preferably sorbed to bacterial cells in the mixture, and that Pu(VI) is reduced to Pu(V) and Pu(IV).