Macro- and micro-scale studies on U(VI) immobilization in hardened cement paste |
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Authors: | E Wieland N Macé R Dähn D Kunz J Tits |
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Institution: | (1) Laboratory for Waste Management, Nuclear Energy and Safety Research Department, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland;(2) Present address: CEA Saclay, DEN/DANS/DPC/SECR, 91191 Gif-sur-Yvette Cedex, France |
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Abstract: | Wet chemistry and synchrotron-based (micro-)spectroscopic investigations have been carried out to determine the uptake and
speciation of U(VI) in hardened cement paste (HCP). The wet chemistry experiments included kinetic studies and the determination
of the sorption isotherm. The latter measurements allowed conditions for linear sorption to be distinguished from those where
precipitation occurred. Micro-X-ray fluorescence and X-ray absorption spectroscopy (μ-XRF/XAS) were used to determine the
elemental distribution and the coordination environment of U(VI) in an intact HCP sample at the atomic level. The sample was
prepared by in-diffusion of U(VI) into HCP over 9 months. Micro-XRF maps revealed a heterogeneous distribution of U(VI) in
a ten micron thick layer on the surface of the HCP disk. Micro-XAS measurements on a U(VI) hot spot showed that the coordination
environment of U(VI) is similar to that in U(VI) doped HCP and in C-S-H sorption samples. To the best of our knowledge this
is the first synchrotron-based micro-spectroscopic study on the speciation of diffusing uranyl ions with micro-scale spatial
resolution. |
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