Membrane Behavior of Kaolin–Bentonite Mixtures

Abstract

The semipermeable membrane behavior of clay effectively reduces solute flux and therefore can be beneficial in clays used as barriers in chemical containment applications. Except for geosynthetic clay liners (GCLs), the membrane behavior of bentonite-amended soils has been evaluated only at a relatively low bentonite content (BC) (≤20%). Kaolin–bentonite mixtures with a BC ranging from 0% to 37.5% were tested for membrane behavior using closed-system (no-flow) boundary conditions. The membrane efficiency coefficient ω was derived from the measured chemico-osmotic pressure differences induced across the specimens under a concentration difference of 20-mM KCl. The ω of the kaolin–bentonite mixtures increased from 0 to 0.197 with increasing BC. The trend of ω with increasing BC could be described in three stages: initial stage, transitional stage, and residual stage. The results indicated the occurrence of a threshold BC above which additional bentonite had limited effect in terms of membrane behavior. The threshold BC in this study was 28.6% for the given test conditions.