Rheology of sodium and calcium bentonite–water dispersions: Effect of electrolytes and aging time

Bentonitic clays are largely composed of the mineral montmorillonite. Today, bentonites are used in different branches of industry, such as in drilling fluids, dyes, Pharmaceuticals, paper, cement, nanocomposites, polymer composites and ceramics. Bentonite dispersions are widely used in industrial processes because of their exceptional rheological behavior. In this work, the rheological behavior of three types of bentonites with different Na+/Ca+ 2 ratios was investigated. The bentonite dispersions showed Newtonian, Bingham plastic and shear thinning behaviors depending on the solid concentration and bentonite type. Although, all bentonite dispersion exhibited a thixotropic behavior, the Na-bentonite showed a greater degree of thixotropy which was two order of magnitudes greater than that of Ca-bentonite. The rheological behavior of bentonite suspensions developed significantly in the first 24 h of preparation. The addition of electrolytes in a concentration range of 0.02–0.2 M reduced the apparent viscosity of the bentonite suspensions and changed its rheological behavior from shear thinning to Newtonian and shear thickening. The divalent cation salts experienced more reduction in the apparent viscosity and yield stress of suspension than the monovalent cation salts.

Research Highlights
► Bentonite was found to exhibit non-Newtonian behavior starting from 4.0 wt %.
► The transition in rheological behavior depends on the ratio in the bentonite.
► Increasing the ratio in bentonite increased the degree of thixotropy.
► The apparent viscosity of the bentonite suspension increases with aging time.
► The presence of electrolytes led to a decrease in the viscosity of all bentonites.