Combination of multi-scale and multi-edge X-ray spectroscopy for investigating the products obtained from the interaction between kaolinite and metallic iron in anoxic conditions at 90 °C
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In the context of radioactive waste repository in geological formation, kaolinite-metallic iron interaction in chlorine solution was conducted in batch experiments, under anoxic conditions at 90 °C during 9 months. After a mineralogical characterization at a global scale, products were analyzed at the micrometer and nanometer scales by X-ray absorption spectroscopic techniques (XAS and STXM). Absorption at Al, Si and Fe edges was investigated to have a complete overview of the distribution and status of constituting elements. Whereas Si K-edge results do not evidence significant evolution of silicon status, investigations at Al K-edge and Fe L-edges demonstrate variations at aggregate and particle scales of IVAl:VIAl and Fe2+:Fe3+ ratios. Spectroscopic data evidence the systematic crystallization of Fe-serpentines onto the remaining particles of kaolinite and the absence of pure species (kaolinite or Fe-serpentines). Combination of spatially resolved spectroscopic analyses and TEM-EDXS elemental distribution aims to calculate unit cell formulae of Fe-serpentines layers and abundance of each species in mixed particles. For most of the investigated particles, results reveal that the variations of particles composition are directly linked to the relative contributions of kaolinite and Fe-berthierine in mixed particles. However, for some particles, microscale investigations evidence crystallization of two other Fe-serpentines species, devoid of aluminum, cronstedtite and greenalite.
KeywordsX-ray absorption spectroscopy XAS STXM Phyllosilicate Berthierine Iron
This work was financially supported by Andra (Agence nationale pour la gestion des déchets radioactifs—French national radioactive waste management agency). The STXM data were collected at the Canadian Light Source, which is supported by the Natural Sciences and Engineering Research Council of Canada, the National Research Council Canada, the Canadian Institutes of Health Research, the Province of Saskatchewan, Western Economic Diversification Canada, and the University of Saskatchewan. We also thank SOLEIL facility for financial and technical supports. This work could not have been done without the collaboration of LUCIA beamline staff Nicolas Tercera, Anne-Marie Flank and Pierre Lagarde. We also thank Valérie Briois from SAMBA beamline for collecting data at Fe K-edge on her “home beamtime”. We gratefully thank Jaafar Ghanbaja for TEM investigations. A special thanks goes to Yves Moëlo who provided berthierine sample and to Markus Plaschke who kindly shared Fe–L edges data on reference samples so that we could operate validation tests on the fitting procedure of Fe–L spectra.
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