Distribution coefficient and redox behaviour of uranium in Authie Bay (northern France)

Abstract

Some mechanistic aspects associated with uranium release/immobilization and sedimentation in Authie Bay are presented in the present work. For this purpose, U contents in estuarine oxic waters, porewaters and sediment solids are determined. These analytical data allow us to appraise the partitioning of this metal between the liquid phase and the particulate matter/sedimentary material by calculating its distribution coefficient. Our findings further reveal that the distribution coefficient varies significantly with depth probably in response to the microbial activities in these sediments. This is confirmed by our studies on the geochemical behaviour of Fe and Mn in Authie Bay sediments. Finally, studies on the thermodynamic characteristics of sedimentary U in Authie Bay are undertaken in order to select possible U water–mineral equilibria that could involve in this environment, and to help define conditions of sedimentary U bioreduction.

Keywords:

• Uranium
• Iron
• Manganese
• Early diagenesis
• Redox potential
• Partition coefficient
• Thermodynamic calculation

Acknowledgements

This work was supported by the Region Nord Pas-de-Calais (CPER Authie) and the PNETOX program. Many thanks to Jean-François Barthe (LCAM, ELICO) for the core samplings.