Previous studies of dispersant–aqueous kaolin dispersions have indicated clearly that the concentration of the dispersant determines the type of rheological behavior. Those studies focused on the use of dispersant concentrations below the limit of saturation, ignoring what might have happened at concentrations above that limit, and the practical uses to which such information might be put. The present study examined the influence of sodium hexametaphosphate dispersant on the viscous and viscoelastic properties of aqueous kaolin dispersions when its concentration was greater than the saturation limit. A concentric-cylinders geometry sensor system (with a narrow gap between the cylinders) was used to test the rheological behavior of Na hexametaphosphate-aqueous kaolin dispersions. Aqueous kaolin dispersions were viscoplastic, thixotropic, and viscoelastic fluids. The analysis of frequency sweep tests in the linear viscoelastic limit and steady-flow curves led to the conclusion that an increase in the dispersant concentration above the limit of saturation gave way to ‘solid-like’ dispersions.

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