Interfacial Reactions of Uranium Related to Geology and Biology

The increasing input of uranium into bio-sphere by mining and milling an dindustrial processes like production of cement, using fossile fuels, and fertilizers has led to the realization of the importance of environmental chemistry of uranium. Detailed knowledge of the nature of uranium complexes formed on the interfaces of relevant geo- and bio-systems is an essential prerequisite to describe the migration behavior in the environment. Our investigations are focused on surface complexation of uranium on phyllite and its mineral constituents like chlorite, muscovite, albite and quartz. Weathering of iron containing chlorite forms ferrihydrite as a secondary phase on the mineral surface. Results showed that the formed ferrihydrite is dominating the surface complexation. Furthermmore, the changing of uranium speciation on the surface layer will be discussed in dependence on different weathering conditions, the presence of humic acids, and the formation of biofilms on the surface. Bacteria are ubiquitous in nature and can influence the uranium transport by mobilization or immobilization. Formation of biofilms can immobilize uranium by increasing the sorption. On the other hand the formation of bio-colloids can promote the uranium transport. In dependence on the living mechanism, bacteria have different structure of the outer cell membrane and can express a wide variety of complexing ligands with various functionalities. Results about binding of uranium on cell surfaces of selected bacterial strains will be presented. For uranium speciation determination various laser spectroscopic methods and X-ray absorption spectroscopy were used. For localization of uranium on the surfaces sensitive microscopic techniques were helpful.