Actinide/Lanthanide interaction studies with a typical bacterial isolate from Mont Terri Opalinus Clay a potential host rock for nuclear waste disposal

The Opalinus clay layer of the Mont Terri Underground Rock Laboratory (Switzerland) is one potential host rock tested for nuclear waste disposal [1]. It is well known that bacteria indigenous to such subterranean environments can affect the speciation and hence the mobility of actinides [2]. The unknown interactions between U(VI), Cm(III)/Eu(III) and Pu with Sporomusa sp. MT-2.99 cells was explored. This bacterium was recently isolated from Mont Terri Opalinus clay core samples by our group. Strong An/Ln interactions of this clay isolate within a broad pH range (2-8) were detected. Thermodynamic stability constants of bacterial U(VI)/Cm(III)/Eu(III) surface species were determined and will be discussed. The biosorption process of U(VI)/Cm(III)/Eu(III) can be described as a pH-dependent binding on phosphoryl and carboxyl sites of the cell membrane. For Pu a complex interaction mechanism was identified. Besides biosorption strong abiotic and biotic plutonium reduction processes were observed. The information obtained in our study is of great importance for predicting the safety of a planned nuclear waste repository.

Acknowledgements. The authors thank the BMWi for financial support (contract no.: 02E10618 and 02E10971) and the BGR for providing the clay samples.

References
[1] M. Thury, P. Bossart (1999). The Mont Terri Rock Laboratory, a new international research project in a Mesozoic shale formation, in Switzerland. Eng. Geol. 52,347-359.
[2] J.R. Lloyd, G.M. Gadd (2011). The Geomicrobiology of Radionuclides. Geomicrobiol. J. 28, 383-386.