The bioassociation of actinides, especially at the very low actinide concentrations typically encountered in the environment, is often the key and most important interaction between actinide species and microorganisms.   This association is often the first step in the bioreduction of multivalent actinides which is a critical step in their immobilization under subsurface conditions.  An understanding of this interaction is needed to help define the actinide source term for salt-based nuclear repository concepts and account for potential migration pathways in deep subsurfaces where high ionic strength brine systems predominate.   <br/>The bioassociation of microorganisms that predominate in high ionic strength brines/groundwaters was investigated for the An(III, IV, V and VI) oxidation states using a combination of redox-invariant analogs and redox-stabilized multivalent actinides.  This was done across a wide range of pH and correlated with the changes in the aqueous speciation.  For halophilic bacteria, reversible sorption was often observed that could be modeled with a surface complexation model that was coupled to Pitzer speciation models.  This was however somewhat difficult to de-couple from precipitative processes and colloid formation at pH &gt;8.  Considerably lower sorption and a higher degree of irreversibility were noted for the archaea.  These are believed to reflect the differences in cell structure and mechanisms of the interaction itself.  Progress in all these areas will be reported as this is part of an ongoing and long-term investigation to understand the key effects of microbial processes on actinide speciation and mobility. <br/>

Bioassociation of actinides towards halophilic bacteria and archaea

251st National Meeting (2016)

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