Water soluble NOM are of environmental importance in the evaluation of safety scenarios concerning geological disposal of nuclear waste and contaminated legacies, as they are generally polyelectrolytes decorated with functional groups capable of forming complexes with metal cations, including radionuclides. Thus they can potentially serve as vehicles for colloid mediated transport of radionuclides over large distances[ii]. Early structural studies of the interaction between actinide cations and NOM (specifically humic acid, HA) were performed at the Research Centre Rossendorf during the time when Heino Nitsche was director. These investigations involved characterisation of the coordination structure of [Ann+HAx](n-x)+ complexes using An L3 edge EXAFS and comparison to reference complexes. Results revealed the primary interaction to be cation binding via HA carboxylate functional groupse.g. [iii]. Later studies of such complexes from the ligand point of view using C 1s NEXAFS and scanning transmission x-ray microscopy (STXM), in conjunction with quantum chemical calculations to support interpretation of observed spectral trends, support these findingse.g. [iv]. Aging of actinide loaded HA colloids leads to their densification, which has implications for their mobility. F.J. Stevenson, Humus Chemistry: Genesis, Composition, Reactions, Wiley, New York (1994) [ii] N.D. Bryan, L. Abrahamsen, N. Evans, P. Warwick, G. Buckau, L. Weng, W.H. Van Riemsdijk, Applied Geochemistry 27(2), 378–389 (2012) [iii] M.A. Denecke, T. Reich, S. Pompe, M. Bubner, K. H. Heise, H. Nitsche, P. G. Allen, J. J. Bucher, N. M. Edelstein, D. K. Shuh, K. R. Czerwinski, Radiochim. Acta 82, 103-8 (1998). [iv] M. Plaschke, J. Rothe, M. K. Armbruster, M. A. Denecke, A. Naberb, H. Geckeis, J. Synchrotron Rad. 17, 158–165 (2010).

X-ray spectroscopy characterisation of radionuclide-NOM interaction

249th National Meeting (2015)

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