Rheology of Aqueous Suspension of Sodium/Calcium Montmorillonite

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Abstract
The rheological characteristics of montmorillonite suspension as a function of exchangeable sodium percentage (ESP), (when the complementary cation is Ca2+), Na‐polymetaphosphate adsorption by clay, and suspension pH were studied in aqueous media at a clay concentration of 25 g kg−1 and temperature of 25 °C. The differential viscosity (the derivative of shear stress with respect to the shear rate at a given shear rate), the extent of deviation from Newtonian flow, and the extrapolated shear stress values all increased with ESP at the range between 20 and 60%, but the values remained constant at 60 < ESP < 100. The rheology of Na‐montmorillonite suspension changed from non‐Newtonian to Newtonian as the Na‐polymetaphosphate (NaPO3)13 concentration in suspension increased. The rheology of montmorillonite suspension was pH‐independent when the clay was saturated with Ca ions, but pH‐dependent when the clay was saturated with Na ions. The differential viscosity increased as the pH decreased. At pH 10.0, Na‐montmorillonite suspension showed a Newtonian behavior, whereas at pH 7.0 non‐Newtonian behavior was observed. The power law coefficients and the extrapolated shear stress values indicate that the particle‐particle linkages increase by introducing Na ions to the exchangeable complex in the range 10 < ESP < 60. The edge surfaces were associated with the formation of linkage between clay platelets and were responsible for the pseudoplastic characteristics of the suspension.
Funding Information
  • BARD-The United States-Israel Binational Agricultural Research & Development Fund (I-743-84)

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