Sorption, redox reactions and (nano-)particle formation of uranium and other early actinides at mineral-water interfaces: Lessons (to be) learned from synchrotron methods

The early actinides U, Np and Pu exhibit two to four different oxidation states within the oxic to anoxic regime of typical environmental systems, responsible for their rich and complex biogeochemistry. Due to their high surface area and catalytic activity, clay and iron oxide minerals play a crucial role in controlling the mobility of these radiotoxic elements in the environment. Understanding the underlying (geo-)chemical processes and reactions is of paramount importance for many applications from the design of nuclear waste repositories to the development of efficient remediation strategies for contaminated sites. The electronic and molecular structures of actinides, and their temporal evolution, can be studied in situ by a range of synchrotron methods, including high resolution absorption and emission spectroscopies (XES, RIXS, XANES, EXAFS), high resolution powder and single crystal X-ray diffraction and scattering (PDF) analysis, and surface sensitive techniques (CTR, RAXR). We recently upgraded The Rossendorf Beamline at ESRF to be able to apply all of these techniques to actinide samples. In this talk, I will present the different techniques and what we recently have learned about the geochemistry of uranium, neptunium and plutonium at the strongly dynamic surface of clay and Fe oxide minerals, including sorption, redox reactions, and formation of actinide Eigencolloids and of solid solutions.