Effects of pH and exposure time to alkaline solutions on the mineralogy of the Opalinus Clay from the lower sandy facies of Mont Terri site

The Opalinus Clay is a claystone considered as potential host rock for deep geological disposal of radioactive wastes in Switzerland and Gemany. During the operational phase repository, an increase underground water pH , from 7.5 to value high 13.5 expected, due release alkaline plumes concrete degradation, resulting possible changes mineralogy rock. While clay mineral dissolution known occur affect hydro-mechanical properties rock, other minerals present claystone, i.e., quartz calcite, can also take place. This study focuses on identification such dissolutions by considering NaOH Ca ( OH ) 2 KOH solutions at different pHs (8.5, 11.5 13.5). A low = 8.5 was investigated consider gradual progressive infiltration plumes. Series samples lower sandy facies Mont Terri site were immersed these six months one year. It found that occurred significantly higher than 11.5, but 8.5. longer exposure time, more significant dissolution. Calcite observed after year Thus, seemed be governed while calcite depend both time value, carbonation phenomenon. generally attention has been paid effect alkalinity minerals, this paper meticulously studies initially proportions investigating wide range . will undoubtedly hydraulic mechanical claystone. Thereby, it paramount importance phenomenon order ensure long-term safety nuclear waste disposal. Furthermore, early stage (low late (high ). • exhibits large variability mineralogy. Quartz mainly depends solutions. Carbonation limits