Aquatic chemistry of actinides

Selected research examples

Simple organic acids are released into groundwater by the microbial degradation of natural organic matter or organic contaminants. These organic ligands from strong complexes with actinides like uranium, thereby inhibiting retardation processes like the sorption to clay minerals or the precipitation as minerals. The molecular structure of such complexes has been elucidated by applying iterative transformation factor analysis and Monte-Carlo simulations to EXAFS spectra. These structural data are important information to predict the complexation behaviour and hence the mobility of actinides in groundwater.

A. Rossberg, A. C. Scheinost, Analytical and Bioanalytical Chemistry 383, 56-66 (2005). A. Rossberg et al., Radiochimica Acta 88, 593-597 (2000). A. Rossberg, T. Reich, G. Bernhard, Analytical and Bioanalytical Chemistry 376, 631-638 (2003). A. Rossberg, A. C. Scheinost, Physica Acta T115, 912-914 (2005).    

Aquifers are commonly oxygen depleted due to microbial metabolism and slow oxygen diffusion from the atmosphere. To be able to simulate these conditions, we have developed a spectro-electrochemical cell, which allows us to observe structural changes of aqueous actinide complexes at different reduction potentials. The figures above show the significant structural reconfiguration during uranyl reduction in chloride, sulfate and carbonate-rich waters, which are typical for the saline, pyritic and carbonaceous  geologic formations of nuclear waste storage sites.