Colloidal stability of bentonite clay considering surface charge properties as a function of pH and ionic strength

Surface charge properties of bentonite colloids were investigated to study their colloidal stability in a solution as a function of the pH and ionic strength. Potentiometric titrations and zeta potential measurements for the bentonite colloids depending upon the pH and ionic strength were performed to investigate the surface charge properties. It was observed from the potentiometric titrations that a zero net proton adsorption occurred at about pH 8.2 (pHPNZPC ∼ 8.2). Surface charges of the bentonite colloids mainly carrying structural negative charges revealed a very small dependency on the pH. The same behavior was also observed in the zeta potential measurements. The zeta potential measurements for the bentonite colloid showed that the bentonite colloids were stable at lower ionic strengths of 0.01 and 0.001 M NaClO4 but unstable at a higher ionic strength of 0.1 M NaClO4 within the whole pH range studied. Therefore, it can be concluded that bentonite colloids would be stable in most of the considered fresh groundwater conditions, i.e., pH from 6 to 10 and an ionic strength from 0.001 to 0.01 M, and then they can be mobilized along a flowing groundwater.