Sorption processes of Np on alumosilicates. Vibrational spectroscopic investigations.
Final Report Abstract
The migration behavior of actinides and other radioactive contaminants in the environment is controlled by prominent molecular phenomena such as hydrolysis and complexation reactions in aqueous solutions as well as the diffusion and sorption onto minerals present along groundwater flow paths. These reactions significantly influence the mobility and bioavailability of the metal ions in the environment, in particular at liquid-solid interfaces. Hence, for the assessment of migration processes the knowledge of the mechanisms occurring at interfaces is crucial. In the present study, the speciation of uranium(VI) and neptunium(V) at environmentally relevant mineral – water interfaces of oxides of titania, alumina, silica, zinc, and alumosilicates has been investigated by the application of attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopy. Moreover, the distribution of the hydrolysis products in micromolar aqueous solutions of U(VI) and Np(V/VI) at ambient and inert gas atmosphere has been characterized for the first time by a combination of ATR FT-IR spectroscopy, near infrared (NIR) absorption spectroscopy, and speciation modeling applying updated thermodynamic databases. The results of the actinyl hydrolysis reactions at a submillimolar concentration level and at pH values up to 8.5 reveal discrepancies between the predicted speciation from modeling and the spectroscopic findings. Consequently, the spectroscopic findings will help to verify the thermodynamic data sets and improve the quality of the thermodynamic data bases which represent the general basis for the risk assessment of radionuclide dispersion in the environment. The application of the ATR technique provided an insight into the molecular reactions of actinyl ions occurring at the solid-water interface. The formation of actinyl complexes on metal oxides was monitored under environmentally relevant conditions. For U(VI) different surface species were identified on TiO2 and Al2O3 as a function of surface coverage. In contrast, the formation of only one stable Np(V) complex was found for a number of different mineral oxide phases. The multiplicity of IR spectroscopic experiments carried out within this study yields a profound collection of spectroscopic data which will be used as references for future investigations of more complex sorption systems in aqueous solution. Furthermore, from a methodological point of view, this study comprehensively extends the application of ATR FT-IR spectroscopic experiments to a wide range in the field of radioecology. The results obtained in this work contribute to a better understanding of the geochemical interactions of actinides, in particular U(VI) and Np(V/VI), in the environment. Consequently, more reliable predictions of actinides migration which are essential for the safety assessment of nuclear waste repositories can be performed.
Publications
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(2007) "Hydrolysis of U(VI). An infrared spectroscopic verification of uranyl species." Migration 2007 - 11th Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, Munich, Germany
Müller, K. and Foerstendorf, H.
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(2007) "Infrared spectroscopic identification of aqueous uranium(VI) species." 17th Annual V.M. Goldschmidt Conference 2007, Cologne, Germany. Abstract: Geochim. Cosmochim. Acta 71, A694
Müller, K.; Foerstendorf, H. and Bernhard, G.
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(2007) "Speciation of Np(V) in aqueous solution investigated by FT-IR spectroscopy." Migration 2007 - 11th Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, Munich, Germany
Müller, K., Foerstendorf, H. and Bernhard, G.
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(2007) "Stoichiometry and structure of uranyl(VI) hydroxo dimer and trimer complexes in aqueous solution." Inorg. Chem. 46, 10819-10826
Tsushima, S., Rossberg, A., Ikeda, A., Müller, K. and Scheinost, A. C.
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(2008) "Aqueous uranium(VI) hydrolysis species characterized by ATR FT-IR." Inorg. Chem. 47, 10127-10134
Müller, K., Brendler, V. and Foerstendorf, H.
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(2008) "Infrared spectroscopic comparison of the aqueous species of uranium(VI) and neptunium(VI)." NRC7 – 7th International Conference on Nuclear and Radiochemistry, Budapest, Hungary
Müller, K., Foerstendorf, H. and Brendler, V.
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(2008) "Infrared spectroscopic identification of aqueous neptunium species." V Ibero-American Congress of Environmental Physics and Chemistry 2008, Mar del Plata, Argentina
Müller, K.; Foerstendorf; H. and Brendler, V.
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(2008) "U(VI) sorption onto environmental relevant minerals: vibrational spectroscopy and complementary tools." Unidad de Actividad Quimica, Comisión Nacional de Energía Atómica, San Martin, Argentina
Müller, K.; Foerstendorf, H.; Křepelová, A.; Baumann, N. and Brendler, V.
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(2009) "Direct spectroscopic characterization of aqueous actinyl(VI) species: A comparative study of Np and U." J. Phys. Chem. A 113, 6626-6632
Müller, K., Foerstendorf, H., Tsushima, S., Brendler, V. and Bernhard, G.
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(2009) "Sorption of Np(V) onto TiO2, SiO2, and ZnO: An in situ ATR FT-IR spectroscopic study." Environ. Sci. Technol. 43, 7665-7670
Müller, K., Foerstendorf, H., Brendler, V. and Bernhard, G.
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(2009) "Spectroscopic comparison of aqueous Np(VI) and U(VI) species." 19th Annual V.M. Goldschmidt Conference 2009, Davos, Switzerland. Abstract: Geochim. Cosmochim. Acta 73, A914
Müller, K.; Foerstendorf, H.; Tsushima, S.; Brendler, V. and Bernhard, G.
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(2009) “Photoeffects on U(VI) sorption onto TiO2 studied by in situ ATR FT-IR spectroscopy.” 12th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere 2009, Kennewick, Washington, U.S.A
Müller, K., Meusel, T., Steudtner, R., Foerstendorf, H., Brendler, V., and Bernhard, G.
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(2009) “Sorption of Np(V) onto metal oxide surfaces: An in situ ATR FT-IR spectroscopic study.” 12th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere 2009, Kennewick, Washington, U.S.A
Müller, K., Foerstendorf, H., Brendler, V., and Bernhard, G.
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“Sorption of U(VI) onto TiO2. A vibrational spectroscopic analysis of the sorption processes.” 12th International Conference on the Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere 2009, Kennewick, Washington, U.S.A
Foerstendorf, H., Müller, K., Meusel, T., Brendler, V., Comarmond, J., Payne, T., and Lefèvre, G.
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(2010) “The sorption processes of Np(V) and U(VI) onto metal oxide phases. The formation of sorption complexes and mechanistic aspects studied by in situ ATR FT-IR spectroscopy.” RadChem 2010, 16th Radiochemical Conference, Marianske Lazne, Czech Republic
Foerstendorf, H.; Heim, K.; Müller, K.
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(2010) “Uranium sorption on various forms of TiO2 – Influence of surface area, surface charge and impurities.” RadChem 2010, 16th Radiochemical Conference, Marianske Lazne, Czech Republic
Comarmond, M. J.; Payne, T. E.; Harrison, J.; Thiruvoth, S.; Müller, K.
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“The sorption of uranium(VI) and neptunium(V) onto surfaces of selected metal oxides and alumosilicates studied by in situ vibrational spectroscopy” Ph.D. Thesis, Dresden University of Technology, Dresden
Müller, K.
