Surface processes of Np species on selected mineral oxides - From sorption to precipitation. Vibrational spectroscopic investigations.
Chimie ParisTech, France
Mineral oxyhydroxides play a decisive role during the reactive transport of dissolved contaminants in the environment. The capability of rocks and soils to retard aqueous heavy metal ions is determined by surface reactions at solid-liquid interfaces. They range from sorption processes to formation of new mineral phases with possible intermediate stages, such as oligomerization, colloid formation, clustering or precipitation. In the present work, the speciation of uranium(VI) and neptunium(V) at environmentally relevant mineral – water interfaces of oxides of alumina, iron, silica, and titania has been comprehensively investigated by the application of complementary spectroscopic techniques. Attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopy is a very useful tool for the in situ and time-resolved identification of molecule species sorbed on mineral phases on a molecular level. By the application of X-ray absorption spectroscopy, detailed information about prevailing redox states of the actinyl ions and interatomic distances between single U and Np atoms and surface functionalities of the surface complexes can be obtained.
The results obtained in this work contribute to a better understanding of the geochemical interactions of actinides, in particular U(VI) and Np(V), in the geo- and biosphere. Consequently, more reliable predictions of actinides migration, which are essential for the safety assessment of nuclear waste repositories can be performed.
Fig. 1.: Multi-spectroscopic study of Np(V) sorption onto hematite (left) and gibbsite (right). In the absence of atmospherically derived bicarbonate the formation of a single inner-sphere sorption complex is predicted. In case of gibbsite in the presence of atmospherically derived carbonate a ternary inner-sphere Np(V) carbonate complex is derived from comprehensive ATR FT-IR and EXAFS spectral analysis.
- K. Müller, A. Gröschel, A. Rossberg, F. Bok, C. Franzen, H. Foerstendorf, In situ spectroscopic identification of neptunium(V) inner-sphere complexes on the hematite-water interface, in revision at Environmental Science and Technology (2014)
- K. Schmeide, S. Gürtler, K. Müller, R. Steudtner, C. Joseph, F. Bok, V. Brendler, Interaction of U(VI) with Äspö diorite: A batch and in situ ATR FT-IR sorption study, Applied Geochemistry 49 (2014) 116-125.
- K. Gückel, A. Rossberg, K. Müller, V. Brendler, G. Bernhard, G. Foerstendorf, H., Spectroscopic identification of binary and ternary surface complexes of Np(V) on gibbsite, Environmental Science and Technology 47 (2013) 14418–14425.
- K. Müller, H. Foerstendorf, V. Brendler, A. Rossberg, K. Stolze, A. Gröschel, The surface reactions of U(VI) on γ-Al2O3. In situ spectroscopic evaluation of the transition from sorption complexation to surface precipitation, Chemical Geology 357 (2013) 75-84.
- K. Müller, H. Foerstendorf, T. Meusel, V. Brendler, M. J. Comarmond, G. Lefèvre, T. E. Payne, Sorption of U(VI) at the TiO2 – water interface: An in situ vibrational spectroscopic study, Geochimica Cosmochimica Acta 76 (2012) 191-205.
- M. J. Comarmond, T. E. Payne, J. J. Harrison, S. Thiruvoth, H. K. Wong, K. Müller, H. Foerstendorf, Uranium sorption on various forms of titanium dioxide – influence of surface area, surface charge and impurities, Environmental Science and Technology 45 (2011) 5536-5542.
Conference contributions (Oral presentations):
- K. Müller, J. Berger, A. Gröschel, In-situ vibrational spectroscopic identification of actinide(V/VI) sorption complexes at the mineral oxide-water interface, Invited at Spring 2014 National ACS meeting (16.-20.03.2014, Dallas, USA).
- K. Müller, Actinyl(V/VI) complexes at water-mineral interfaces investigated by vibrational spectroscopy and complementary techniques, Umeå University, Department of Chemistry, Schweden (02/2014)
- K. Müller, J. Berger, M. Cordiez, A. Gröschel, H. Foerstendorf, Vibrational Spectroscopic Study of Np(V) Sorption on Mineral Oxides, Goldschmidt Conference 2013 (25-30/08/2013, Florence, Italy). Mineralogical Magazine 77(5) (2013) 1806.
- K. Müller, A. Gröschel, Identification of Np(V) sorption complexes at the hematite-water interface studied by in-situ ATR FT-IR spectroscopy, Actinides 2013 (9th International Conference on the Chemistry and Physics of the Actinide Elements, 21.-26.07.2013, Karlsruhe, Germany).
- K. Müller, H. Foerstendorf, A. Rossberg, K. Stolze, K. Gückel, Comparative study of the U(VI) complexation onto γ-Al2O3 by ATR FT-IR and EXAFS spectroscopy, Goldschmidt Conference 2011 (14-19/08/2011, Prague, Czech Republic). Mineralogical Magazine, 75(3) (2011) 1513.