Behaviour of Plutonium Interacting with Bentonite and Sulfate-Reducing Anaerobic Bacteria

Abstract

The interactions between sulfate reducing anaerobic bacteria and plutonium, with or without bentonite present, were investigated using distribution coefficients {Kd (mlig)} as an index of the radionuclide behaviour. Plutonium Kds for living bacteria varied within a large range, from 1,804 to 112,952, depending on the pH, while the Kds ranged from 1,180 to 5,931 for dead bacteria. In general, living bacteria had higher plutonium Kds than dead bacteria. Furthermore, the higher Kd values of 39,677 to 106,915 for living bacteria were obtained for a pH range between 6.83 and 8.25, while no visible pH effect was observed for dead bacteria. These Kd values were obtained using tracers for both 236 Pu and 239 pu, which can check the experimental procedures and mass balance.Another comparison was conducted for plutonium Kd values of mixtures of living bacteria with bentonite and sterilized bacteria with bentonite. The range of Kd values for the non-sterilized bacteria with bentonite were 1,194 to 83,648 while Kd values for the sterilized bacteria with bentonite were from 624 to 17,236. Again, the Kd values for the living bacteria with bentonite were higher than those of sterilized bacteria with bentonite. In other words, the presence of living anaerobic bacteria with bentonite increased, by roughly 50 times, the Kd values of 239 pu when compared to the mixture of dead bacteria with bentonite. The plutonium Kd values for bentonite alone, both non-sterilized and sterilized, were within a constant range of around 10,000 even though some of the data are not yet available.The bentonite used for this experiment was a product of Japan and the sulfate reducing anaerobic bacteria was previously used for the treatment of a pulp and paper wastewater. The results indicate that the effects of anaerobic bacteria within the engineered barrier system (in this case bentonite) will play a significant role in the behaviour of plutonium in geologic repositories.

The potential of subterranean microbes in facilitating actinide migration at the Grimsel Test Site and Waste Isolation Pilot Plant

“…at pH 5.0, consistent with studies of growing cultures of halophiles at pHs 6 and 8 in which only 2.5 to 9% of the Pu was associated with biomass [6]. Kudo et al [28] examined the uptake of Pu (10 −17 M) by sulfate-reducing bacteria and found that living cells sorbed more than dead cells. This study shows that the near-and far-field repository environments investigated harbor viable microbial populations capable of actinide uptake.…”

Chemical Speciation and Association of Plutonium with Bacteria, Kaolinite Clay, and Their Mixture

“…Therefore, insoluble plutonium hydroxides are precipitated on the bacterial surfaces, and/or Pu 4+ is sorbed by the functional groups thereon. Kudo et al (37) reported that the distribution coefficient (Kd) of Pu for a mixture of bacteria and bentonite, a backfill material for isolating radioactive wastes, was nearly the same as that of bacteria alone, whether the bacteria were sterilized (killed) or not. However, they did not measure the chemical states of Pu throughout the sorption experiments.…”

Probability of Production of Mobile Plutonium in Environments of Soil and Sediment

“…The Kd values were measured under the following four conditions: sterilized bacteria in distilled water, non-sterilized bacteria in distilled water, a mixture of sterilized bacteria and bentonite in distilled water, and a mixture of non-sterilized bacteria and bentonite in distilled water. We used non-sterilized bentonite for the bacteria interaction, because there were no great differences in Kd values between sterilized and non-sterilized bentonite [18].…”