Publisher © Czech Geological Survey, ISSN: 2336-5757 (online), 0514-8057 (print)
Changes of selected physico-chemical properties of bentonites under the heat and saline treatment
Abstract
Changes of selected physico-chemical properties of bentonites under the heat and saline treatment were examined considering their possible use as an engineered barrier (buffer, backfill) in the nuclear waste repository. Four sets of samples were used in the experiment. Each set contained nine samples (Rokle bulk and MX 80). The samples were treated for two months for 6-8 hours a day, one set at 40 °C, second at 60 °C, third at 90 °C and the last set at 120 °C. Saline environment was simulated by 30 wt. % NaCl solution. After two months the cation exchange capacity (CEC) of monovalent and divalent cations and swell indexes (SI) were determined. Structural changes in the bentonite were identified using X-ray diffraction (oriented and glycolated samples). A significant decrease in CEC and SI values was observed after heat treatment. Samples in high saline environment showed more rapid decrease of CEC and SI (even at the lowest temperature, 40 °C). The three main transformation processes (illitization, beidellitization and kaolinization) changing the significant amount of smectites in the bentonite were identified.
