Coupled Effects of Thermal and Geochemical Perturbations on the Mineral Stability of Boom Clay and Opalinus Clay: a Batch Experiment at 90°C

Within the frame of the TIMODAZ project (WP 3.2), laboratory batch experiment is performed to study the combined heat and geochemical effects on the mineral stability of Boom Clay and Opalinus Clay. The major scope is to identify and assess the significance of thermally induced modifications of minerals in the two candidate clay host rocks. The solutions with variable pH and chemistry are mixed with Boom Clay and Opalinus Clay in order to simulate the non-disturbed in-situ as well as geochemically disturbed pore water composition coupled with the heat effects. The results indicate no or very limited mineralogical changes in the both rock types for a set of heat and geochemical conditions within the experimental time frame. Low reactivity of clays is attributed to the presence of carbonates, which effectively buffer the pH disturbances in the system. Altogether, this study points to a good buffering capacity of both clays and highlights the role of matrix to effectively prevent minerals from the reaction with the applied solutions.