Rheological Behavior of Na-Montmorillonite Suspensions at Low Electrolyte Concentration

Abstract

Abstract--The prevailing concept that positive-edge to negative-face attraction accounts for the rheological behavior of montmoriUonite suspensions at low electrolyte concentration was investigated. In one experiment, Mg 2+ released from Na-montmorillonite was measured at several NaC1 concentrations; in a second experiment, the viscosity, n, and the extrapolated shear stress, 0, were measured at several clay concentrations, pHs, and NaC! concentrations; and in a third experiment, the absorbance, A, was measured at two wavelengths (450 and 760 nm) at different clay and electrolyte concentrations. The released Mg 2+ decreased with increasing NaC1 concentration until it became zero at a NaC1 concentration between 0.01 and 0.02 M, depending on pH. Thereafter, it increased with increasing NaC1 concentration. Both 0 and n were highly correlated with the amount of released Mg 2+. Also, A remained constant until the NaC1 concentration corresponded to that at the minimum of 0. Thereafter, it increased and became linearly related to 0. These results suggest: (1) positive-edge to negative-face interaction cannot solely account for the rheological properties of montmorillonite at low electrolyte concentration, and (2) the release of octahedral Mg 2+ from montmorillonite affects 0, because it reduces the negative charge on the particles and, thereby, the repulsive force between them.

Rheology of Na-Rich Montmorillonite Suspension as Affected by Electrolyte Concentration and Shear Rate

“…In accordance with Rand et aL (1980), Brandenburg and Lagaly (1988) and Chen et al (1990), the flow behavior of a Na-rich montmorillonite suspension changed significantly in the presence of NaC1 (Figure 1). At a concentration of 10 mEq L -1, the viscosity was lower than that obtained for the clay suspension without free electrolyte for any shear rate (Figures 1 and 2).…”

“…At low electrolyte concentration in clay suspension, the extended diffuse double layer allows more freedom of movement under stress, whereas at higher electrolyte concentration the attractive forces between clay platelets dominate, and the yield stress and plastic viscosity increase again. Contrary to van Olphen's (1977) hypothesis, Chen et al (1990) suggested that Mg 2+ in octahedral coordination is involved in modifying the rheological properties; Mg 2 § is released from the clay structure by hydrolysis of the clay at low electrolyte concentrations.…”

“…The electrolyte concentration has been observed to have a unique influence on the rheological properties of Na-rich montmorillonite suspensions. A minimum in yield stress and plastic viscosity has been observed in the presence of electrolytes in suspension at low concentration (van Olphen, 1977;Rand et al, 1980;Nitawaki et al, 1981;Chen et al, 1990). Various explanations for this minimum have been suggested.…”

“…The influence of electrolyte concentration on the suspension rheology of some clays has been studied under various conditions (Heath and Tadros, 1982;Rand and Melton, 1977;Rand et al, 1980;Chen et al, 1990;Brandenburg and Lagaly, 1988;Akae and Low, 1988;Nitawaki et al, 1981). The electrolyte concentration has been observed to have a unique influence on the rheological properties of Na-rich montmorillonite suspensions.…”

Analytical Investigations of Disintegrated Granite Surface from the Un-finished Obelisk in Aswan

“…On the other hand, the presence of diff erent types of clay minerals (tosudite, illite, montmorillonite and kaolinite) owing to the feldspar alteration processes which can lead to precipitation of various types of aluminous and alumino-silicate compounds (Guven et al, 1982;Barros, 2000). Th ese types of silicates are composed either residually or primarily and lead to the argillization of granitic rocks producing several types of clay minerals (Zalba, 1982) according to the dominant environmental conditions especially pH values (Dontsova and Bigham, 2005;Chen, 1990) that play an important role both in controlling many chemical reactions and substances solubility (Ollier, 1975). Kaolinite usually develop in an acidic environment or in a neutral environment where intense leaching processes prevail; montmorillonite forms in the presence of certain alkalis and alkaline earths and illite which is the dominant clay mineral in marine sediments (Murray, 1953).…”