Influence of Inorganic Permeants upon the Permeability of Bentonite

A total of 16 inorganic aqueous solutions were utilized as permeants to determine their effects upon the permeability of both contaminant resistant (polymerized) bentonite and untreated bentonite. It was found that, of the aqueous solutions tested, those with potassium (K⁺) cations or chloride (Cl⁻) anions or both induced the largest permeability increases with increasing electrolyte concentration. Conversely, solutions with sodium (Na⁺) cations or carbonate (CO⁻₃) anions had the least impact upon the permeability of bentonite. It was also observed that doubly charged cations (+2) have a greater initial effect on the permeability than do singly charged cations (+1). Furthermore, a “saturation limit” was in evidence for +2 cations, indicating that beyond certain concentrations the further addition of the soluble salts had only limited additional impact upon the permeability.

For selected bentonite-contaminant combinations, slurry cracking pattern tests were conducted. A correlation between the permeability changes and the results of the cracking pattern tests was demonstrated.

Based upon the findings of this study, it is concluded that the character of the solute anions, as well as the primary cations, affect the permeability of bentonite clays. Further, the Gouy-Chapman model of diffuse double layer was found to be generally consistent with the test data.