Effects of bentonite concentration and solution pH on the rheological properties and long-term stabilities of bentonite suspensions

Abstract The influences of bentonite concentration and solution pH on the rheological properties and long-term stabilities of bentonite suspensions were studied in this research. Rheological properties were measured at bentonite concentrations of 5, 7, and 9 wt.%. It was found that the viscosity and shear stress increased with increasing bentonite concentration and storage time. The initial shear stress of the 9 wt.% bentonite suspension grew larger with increasing storage time than did the yield stress value obtained from Herschel–Bulkley model fitting. The result showed that a significant yield value was required to break the particle network due to the large cohesion force between the particles. Rheological properties and zeta potentials were measured with various amounts of a 1 M HCl solution added to a 5 wt.% bentonite suspension. The amount of HCl solution added had a significant impact on the zeta potential of the bentonite suspension. The absolute value of the zeta potential decreased as the added amount of HCl solution increased. Therefore, particle aggregation was facilitated due to a decrease in the stability of the suspension. Comparing the shear stress obtained from the upward flow curve at a shear rate of 3.4 1/s with the yield stress obtained from the downward flow curve fitted with the Herschel–Bulkley model or Bingham model, as a function of the added amount of HCl solution, showed that the difference between the two values was large in acidic media with high HCl content, but insignificant in neutral or basic media. In addition, the large shear stress phenomenon at a shear rate of 3.4 1/s diminished with increasing storage time, which was due to the change in the pH of the suspension from acidic through neutral, to basic with increasing storage time.