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SEM-EDX study of bentonite alteration under the influence of cement alkaline solutions
Abstract Bentonite is a key barrier for the isolation of high-level radioactive waste within Deep Geological Repository. However, bentonite may be altered by contact with cementitious materials and their alkaline pore fluids. This study offers an extensive morphological and semi-quantitative characterization of the bentonite surface exposed to three types of alkaline pore fluids released by different cement-based materials. The bentonite surfaces were studied using a thorough scanning electron microscopy exploration and analysed using an energy-dispersive X-ray detector (SEM-EDX). In addition, statistical, element mappings, X-ray diffraction and infrared spectroscopy analyses were performed. The aim was to have a picture of the morphological and chemical alterations of bentonite at very early stages in accordance with the integrated approach necessary to address bentonite stability in the long-term. As a consequence of the reactivity, two types of morphologies stood out in the matrix of bentonite: platelets and coatings-like crusts characterized by their high Mg and Ca content. These alterations presented a different scope depending on the type of alkaline pore solution involved and suggested the precipitation of authigenic magnesium silicate hydrates (M-S-H) and/or trioctahedral clay minerals and Ca‑carbonates. The knowledge of the performance of bentonite subjected to these alkaline solutions can help in the evaluation of the most suitable cement-based materials to be used next to bentonite.
Graphical abstract Display Omitted
Highlights Large SEM study reveals distinctive morphologies after alkaline exposure of bentonite. Depending on the alkaline solution used different shapes were found on the surfaces. Morphologies and chemical composition could be related using a statistical approach. Crust-like morphologies match to carbonates formation while platelets link to M-S-H.
SEM-EDX study of bentonite alteration under the influence of cement alkaline solutions
Abstract Bentonite is a key barrier for the isolation of high-level radioactive waste within Deep Geological Repository. However, bentonite may be altered by contact with cementitious materials and their alkaline pore fluids. This study offers an extensive morphological and semi-quantitative characterization of the bentonite surface exposed to three types of alkaline pore fluids released by different cement-based materials. The bentonite surfaces were studied using a thorough scanning electron microscopy exploration and analysed using an energy-dispersive X-ray detector (SEM-EDX). In addition, statistical, element mappings, X-ray diffraction and infrared spectroscopy analyses were performed. The aim was to have a picture of the morphological and chemical alterations of bentonite at very early stages in accordance with the integrated approach necessary to address bentonite stability in the long-term. As a consequence of the reactivity, two types of morphologies stood out in the matrix of bentonite: platelets and coatings-like crusts characterized by their high Mg and Ca content. These alterations presented a different scope depending on the type of alkaline pore solution involved and suggested the precipitation of authigenic magnesium silicate hydrates (M-S-H) and/or trioctahedral clay minerals and Ca‑carbonates. The knowledge of the performance of bentonite subjected to these alkaline solutions can help in the evaluation of the most suitable cement-based materials to be used next to bentonite.
Graphical abstract Display Omitted
Highlights Large SEM study reveals distinctive morphologies after alkaline exposure of bentonite. Depending on the alkaline solution used different shapes were found on the surfaces. Morphologies and chemical composition could be related using a statistical approach. Crust-like morphologies match to carbonates formation while platelets link to M-S-H.
SEM-EDX study of bentonite alteration under the influence of cement alkaline solutions
González-Santamaría, Daniel E. (author) / Justel, Ana (author) / Fernández, Raúl (author) / Ruiz, Ana Isabel (author) / Stavropoulou, Alexandra (author) / Rodríguez-Blanco, Juan Diego (author) / Cuevas, Jaime (author)
Applied Clay Science ; 212
2021-07-19
Article (Journal)
Electronic Resource
English
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