Mineralogical, Geochemical and Geotechnical Study of BCV 2017 Bentonite—The Initial State and the State following Thermal Treatment at 200 °C

Bentonites are considered to be the most suitable materials for multibarrier system of high-level radioactive waste repositories. Since BCV bentonite has been proved an ideal representative Czech Ca-Mg bentonites in this respect, it included Radioactive Waste Repository Authority (SÚRAO) buffer and backfill R&D programme. Detailed knowledge processes material induced by thermal loading provides invaluable assistance regarding evolution under repository conditions. Samples both original 2017 same thermally treated at 200 °C were characterised means chemical analysis, powder X-ray diffraction, infrared spectroscopy, cation exchange capacity, specific surface area (BET) measurements, determination swell index, liquid limit, swelling pressure water retention curves. The smectite comprises montmorillonite with a significant degree Fe3+ substitution octahedral sheet. Two main transformation observed following heating over 27 months, first which comprised dehydration subsequent reduction 001 basal distance from 14.5 Å (the 2017) 9.8 Å, thus indicating absence molecules interlayer space. second concerned partial dehydroxylation goethite. With exception space, PXRD FTIR study revealed crystallochemical stability selected experimental geotechnical tests indicated no major changes mechanical properties bentonite, as demonstrated similar values. However, variation index gradual increase limit wetting time lower hydration rate. curves consistently showed capacity samples, incomplete re-hydration exposed air humidity difference its behaviour compared water.