Ion concentration caused by an external solution into the porewater of compacted bentonite |
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| Institution: | 1. School of Engineering, University of Guelph, Guelph, Ontario N1G 2W1, Canada;2. Ontario Ministry of Transportation, 301 St. Paul Street, St. Catharines, Ontario L2R 7R4, Canada;1. Key Laboratory of Geotechnical and Underground Engineering of the Ministry of Education, Tongji University, Shanghai 200092, People''s Republic of China;2. United Research Center for Urban Environment and Sustainable Development, The Ministry of Education, Shanghai 200092, People''s Republic of China;3. Laboratoire Navier, Ecole des PontsParisTech, France |
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| Abstract: | The concentrations caused by the external solution into the porewater were studied with compacted bentonite (MX-80), from which easily dissolving components had been removed in order to ensure that the ions in the porewater came from the external solution. The dry densities of the samples varied from 700 to 1700 kg/m3 and NaCl solutions of 0.1–3 M were used as the external solution for saturation. The concentrations in the porewater were determined by the direct analysis of the squeezed porewaters and by dispersing the sample in deionized water.At high concentrations, the Donnan model can predict the concentrations in the porewater rather well. At low concentrations, where the ion exclusion is stronger, the measured concentrations are clearly higher than the modelled values. One possible explanation for this discrepancy is the microstructure of the bentonite, and an attempt to couple the effects of the microstructure and the Donnan model was made. It was assumed that there are two pore types, interlamellar pores in the montmorillonite stacks and large pores in the gel between the stacks. The dimensions of the microstructure were obtained from SAXS and BET(N2) measurements. In this case, the fitting is much better, which supports the assumption of different pore types in bentonite. |
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