Influence of adsorbed sulfate on the engineering properties of kaolinite and bentonite

Abstract

The effect of sulfate adsorption ( from 0.5$ N Na_2SO_4 $soln)on the Atterberg limits, free-swell index, and consolidation characteristics of kaolinite and bentonite is reported. The amts. of sulfate adsorbed by kaolinite and bentonite were 5.21 meq/100 g and 8.33 meq/100 g. Kaolinite gave a less flocculated fabric because of decrease in pos. charge and the consequent redn. in pos. edge-neg. face contacts. The Atterberg limits and free-swell index were unaffected by the change in fabric. Odometer data showed that anion adsorption led to lower equil. void ratio, less compressibility, and slower rate of consolidation. The coeff. of permeability was not significantly affected. The equil. void ratio at $0.0625 kg/cm^2$, the compressibility index, and the coeff. of consolidation at the pressure of 1 kg/cm^2 for sulfate-adsorbed kaolinite were 1.03, 0.136, and $2.4 \times 10-2 cm^2/s$, whereas corresponding values for untreated kaolinite were 1.29, 0.16, and $9.0 \times 10-2 cm^2/s$, resp. In contrast, adsorption of sulfate by bentonite led to an increase in flocculation, equil. void ratio, compressibility index, and coeff. of consolidation. The liq. limit was increased from 495 to 630\%, and the free-swell index from $30.0 to 41.5 cm^3/g$. The coeff. of permeability was unaffected by sulfate adsorption.