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Rheology of Aqueous Suspension of Sodium/Calcium Montmorillonite

Institute of soils and Water, Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel

* Corresponding author.

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.

This research was supported by grant no. I-743-84 from BARD-The United States-Israel Binational Agricultural Research & Development Fund. Contribution from the ARO, The Volcani Center, Bet Dagan, Israel no. 2138-E, 1987 series.

Received for publication August 24, 1987.

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