Hydrothermal alteration of “La Serrata” bentonite (Almeria, Spain) by alkaline solutions

Bentonite and concrete are considered as backfilling and sealing materials in a deep geologic repository of high-level radioactive waste (HLRW). The pH of the pore waters leached during concrete degradation is >11 for a long period of time. Under these alkaline conditions, bentonite is susceptible to dissolution–precipitation reactions. The aim of this work is to study mineralogical changes in bentonite in contact with synthetic pore waters of cements. The temperature effect has been taken into account in order to consider the thermal impact of radioactive decay. ntonite used comes from “La Serrata de Nı́jar” (Almerı́a, Spain) and is mainly composed of montmorillonite. Bentonite was submitted to alkaline solutions at 35, 60 and 90 °C up to 365 days. Alkaline solutions were similar to the pore waters leached in the first stage of cement degradation. olite crystallization and the increase of magnesium in a non-exchangeable form in the smectitic clay fraction are the main mineralogical changes detected in the bentonite. Both processes are enhanced with the duration time and temperature of reaction.