Speciation, Techniques and Facilities for Radioactive Materials at Synchrotron Light Sources

We discuss the sources of radionuclides in the environment and summarise the level of radioactive contaminations world-wide. We delineate how X-ray absorption spectroscopy (XAS) can be used in molecular-level environmental radionuclide research and demonstrate the technique’s application on the following three research topics related to contaminations from uranium mining: 1. The structure of a recently discovered aqueous species, Ca2UO2(CO3)3(aq.) was studied by EXAFS and compared to the model systems [UO2(CO3)3](aq.) and Ca2UO2(CO3)3 · 10H2O. 2. EXAFS were used to study the aqueous complexes of U(VI) with a model substance, 3,4-dihydroxybenzoic acid (protocatechuic acid; PCS), and 2-hydroxyphenol (catechol; BCT). PCS is produced in flooded uranium mines by hydrothermal and microbial degradation of lignin, an initial wood degradation product. By comparing the results of the PCS complexation with those for BCT, it was established that the U(VI) is bound at low pH to the carboxylic group and at high pH to the hydroxy group(s). 3. A sulphate-reducing bacterial strain of the species Desulfomicrobium baculatum metabolises U(VI). The uranium oxidation state after metabolisation was determined by X-ray absorption near-edge fine structure (XANES) spectroscopy.