Water-uptake capacity of bentonites

• Published in: Clays and clay minerals Vol. 58; no. 1; pp. 37 - 43
• Main Authors: Kaufhold, Stephan, Dohrmann, Reiner, Klinkenberg, M
• Format: Journal Article
• Language: English
• Published: Cham Clay Minerals Society 01.02.2010; The Clay Minerals Society; Springer International Publishing
• Subjects: adsorption; Bentonite; Biogeosciences; cation exchange capacity; chemical properties; clastic rocks; clay mineralogy; Earth and Environmental Science; Earth Sciences; Earth, ocean, space; Enslin-Neff; Exact sciences and technology; experimental studies; Geochemistry; Medicinal Chemistry; Mineralogy; Nanoscale Science and Technology; rock, sediment, soil; sed rocks, sediments; Sedimentary petrology; sedimentary rocks; Silicates; Soil Science & Conservation; Swelling Capacity; water vapor; Water-Vapor Adsorption; Bentonite; Water-vapor Adsorption; Swelling Capacity; Enslin-Neff; adsorption; cations; cation exchange capacity; porosity; bentonite; swelling; specific surface; sedimentary rocks; percolation; corrections; correlation; water vapor; humidity; populations; theory; clastic rocks
• ISSN: 0009-8604; 1552-8367
• DOI: 10.1346/CCMN.2010.0580103

The present study compares the water-vapor adsorption capacity of bentonites (natural cation population) with the Enslin-Neff method. Water-vapor adsorption at 50% r.h. (relative humidity) or 70% r.h. is known to depend heavily on the amount of permanent charge and on the type of exchangeable cation. At approximately 80% r.h. Na+- and Ca2+/Mg2+-dominated bentonites take up equal amounts of water. Comparing the water-uptake capacity at 80% r.h. with the cation exchange capacity (CEC) revealed a close correlation between these two variables. Appreciable scatter apparent from this plot, however, suggests that additional factors influence the water-uptake capacity. Water adsorption at external surfaces was considered to be one of these factors and was, in fact, implicated by N2-adsorption data. The ratio of external/internal water ranged from 0 to 1, which suggests that water-adsorption values cannot be applied in the calculation of the internal surface area without correction for external water. The Enslin-Neff water-uptake capacity, on the other hand, is unaffected by microstructural features (e.g. specific surface area and porosity). The amount of exchangeable Na+ is the most important factor. However, the relationship between the Na+ content and the Enslin value is not linear but may be explained by percolation theory.