Effect of ion type and concentration on rheological properties of natural sodium bentonite dispersions at low shear rates

Abstract

Understanding the behavior of bentonite dispersions is of remarkable importance in many industrial and engineering applications. Dispersion behavior depends on interparticle interactions. These mechanisms are influenced by the volumetric content of solid particles, ionic concentration in suspending fluid, ion valence, and pH. In this research, natural sodium bentonite dispersions were analyzed. Tests were performed in dispersions prepared with different volumes of particles in solutions of sodium chloride, calcium chloride, and magnesium sulphate with different concentrations. The rheology of dispersions was analyzed by fitting three rheological models, namely the power law, Bingham plastic, and Herschel-Bulkley models. Changes in shear stress and model parameters with ionic strength were analyzed. The observed behavior was interpreted in terms of particle-particle association and was later confirmed by computing the Derjaguin, Landau, Verwey and Oberbeek (DLVO) interparticle interaction energy. Finally, electroviscous effects were analyzed by computing the importance of the electroviscous parameter considering Einstein's equation and the Dougherty-Krieger equation. The electroviscous parameter was found to decrease with the increase in ionic concentration. The influence of ion type had a negligible effect on the electroviscous parameter.