Characteristics of variably saturated granular bentonite after long-term storage at near-field relevant temperatures
| Autor: | Michael Plötze, Martin Valter |
|---|---|
| Rok vydání: | 2013 |
| Předmět: |
Chemistry
Mineralogy 020101 civil engineering 02 engineering and technology Thermal treatment 010502 geochemistry & geophysics 01 natural sciences 0201 civil engineering Adsorption Chemical engineering Hydraulic conductivity Geochemistry and Petrology Specific surface area Bentonite medicine Cation-exchange capacity Swelling medicine.symptom Clay minerals 0105 earth and related environmental sciences |
| Zdroj: | Clay Minerals. 48:343-361 |
| ISSN: | 1471-8030 0009-8558 |
| DOI: | 10.1180/claymin.2013.048.2.14 |
| Popis: | Bentonite is a potential material for use in the engineered barrier of radioactive waste repositories because of its low hydraulic permeability, self-sealing capability and retention capacity. It is expected that bentonite would react at the elevated temperatures accompanying the radioactive decay in the nuclear waste. The presented study was started in order to improve understanding of the coupled influence of temperature and (pore) water on the physicochemical and mineralogical properties of bentonite during thermal treatment under near-field relevant conditions. Granular Na-bentonite MX-80 was differently saturated (Sr= 1–0.05) and stored at different temperatures (50–150°C) in a closed system. Upon dismantling after different periods of time (3 to 18 months), mineralogical characteristics, cation exchange capacity and content of leachable cations, as well as physicochemical properties such as surface area and water adsorption were investigated.The results showed a high mineralogical stability. A slight conversion from the sodium to an earth alkali form of the bentonite was observed. However, considerable changes in the physicochemical properties of the bentonite were observed, particularly by treatment above the critical temperature of 120°C. The cation exchange capacity decreased during heating at 150°C by approximately. 10%. The specific surface area dropped by more than 50%. The water uptake capacity under free swelling conditions showed a slight tendency to lower values especially for samples heated for more than 12 months. The water vapour adsorption ability in contrast drops by 25% already within three months at T = 120°C. These changes are mostly related to the variations in the interlayer cation composition and to smectite aggregation processes. The observed alterations are rather subtle. However, temperatures ⩾ 120°C had a remarkable negative influence on different properties of MX-80. |
| Databáze: | OpenAIRE |
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