A detailed knowledge of the molecular reactions of radionuclides at the aqueous-mineral interface is required for a reliable assessment of their dissemination in the environment. Among numerous spectroscopic approaches, in situ vibrational spectroscopy has been developed to a powerful tool for the study of surface complexes of heavy metal ions on solid phases. In particular from vibrational data, molecular information can be derived which might be complementary to those obtained from other widely applied techniques, such as X-ray absorption spectroscopy. In this study, a survey of very recent results obtained from sorption reactions of radionuclides, namely U(VI) on iron(hydr)oxides and Se(VI) on metal oxides is given.A significantly different surface complexation of U(VI) was found for two different iron bearing mineral phases, that is ferrihydrite and maghemite. As in situ IR spectroscopy allows the investigation of sorption and desorption processes in real time under environmentally relevant conditions, the type of surface complexation can be identified by the extent of reversibility of the sorption reactions. Moreover, the evaluation of the formation of ternary U(VI)carbonato surface complexes provides further details of the sorption processes.The selenate anion (SeVIO42-) preferentially shows relatively weak interactions (physisorption) with mineral phases in the circumneutral pH range. However, the electrostatic interactions of this ion with the mineral surfaces, referred to as outer-sphere complexation, might base on different types of surface complexes as shown by vibrational data from surface complexes on different minerals. With respect to the high selectivity of vibrational spectra to molecule symmetry, the results from Se(VI) sorption experiments on different mineral phases clearly demonstrate two different types of outer sphere complexes.

Surface speciation of dissolved radionuclides on mineral phases derived from vibrational spectroscopic data

248th National Meeting (2014)

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