SEM-EDX study of bentonite alteration under the influence of cement alkaline solutions

Daniel E. González-Santamaría, Ana Justel, Raúl Fernández, Ana Isabel Ruiz, Alexandra Stavropoulou, Juan Diego Rodríguez-Blanco, Jaime Cuevas
2021 Applied Clay Science  
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
more » ... exploration and analysed using an energy-dispersive Xray 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.
doi:10.1016/j.clay.2021.106223 fatcat:we6shiyvu5cpbgojwmz73v4y44