Clays and Clay Minerals, Vol. 58, No. 3, 351–363, 2010.
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Authors
Mazzieri, Francesco
Emidio, Gemmina Di
Van Impe, Peter O.
Issue Date
2010
Type
Article
Language
Keywords
Periodicals , Geology , Chemico-osmotic Efficiency , Contaminant-resistant , Diffusion , Hydraulic Conductivity , Membrane , ‘Multiswellable’ Bentonite , Propylene Carbonate , Swelling
Alternative Title
Diffusion Of Calcium Chloride In A Modified Bentonite: Impact On Osmotic Efficiency And Hydraulic Conductivity
Abstract
Chemically modified bentonites are being developed with the aim of preserving low hydraulic conductivity in the presence of potentially aggressive permeants in pollutant-containment applications. ‘Multiswellable’ bentonite (MSB) has been obtained by treating standard sodium bentonite with propylene carbonate. Research on the engineering properties of MSB has focused mainly on permeability and chemical compatibility. Solute diffusion and membrane behavior inMSB have not yet been investigated. A combined chemico-osmotic/diffusion test was performed on a MSB specimen using a 5 mM CaCl2 solution. Permeability with distilled water and with the 5 mM CaCl2 solution was measured prior to and after the chemico-osmotic/diffusion tests. The material exhibited time-dependent membrane behavior with a peak osmotic efficiency value (o) of 0.172 that gradually shifted to zero upon breakthrough of calcium ions. Effective diffusion coefficients of calcium and chloride ions were in the range commonly described for untreated bentonite at similar porosities. After the chemico-osmotic/diffusion stage and permeation with 5 mM CaCl2, the hydraulic conductivity of MSB increased from 1.1610-11 m/s to 7.0 610-11 m/s. The MSB was apparently converted into a calcium-exchanged bentonite at the end of the test. Prehydration and subsequent permeation might have contributed to elution of the organic additive from the clay. Further investigation is recommended to clarify the effect of prehydration on the hydraulic performance of MSB in the presence of potentially aggressive permeants.
Description
gsccm58306-maz.pdf -- 392KB
Citation
Clays and Clay Minerals, Vol. 58, No. 3, 351–363, 2010.
Publisher
The Clay Minerals Society
License
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