YIELD STRESS OF LATERITE SUSPENSIONS

The yield stresses of aqueous laterite suspensions as functions of solids concentration and suspension pH, or ζ potential, were measured using the direct vane method. In addition, capillary rheometer shear stress-shear rate data were taken for the most concentrated test suspension, and these were used to estimate the yield stress by various extrapolations, and to compare them with the directly measured value using the vane geometry. Detailed characterizations of all test suspensions were carried out. The yield stress was found to depend strongly on suspension pH, attaining a minimum at the isoelectric point occurring at high pH. It was found to follow approximately a straight-line relationship with the square of the ζ potential, and its dependence on solids concentration is described by a two-parameter nonlinear relationship which gives the appropriate behavior in both the dilute limit and the concentrated limit near maximum packing.In situ particle size measurements by sedimentation suggest that the degree of flocculation is high under acidic conditions. The capillary rheometer data reflect strongly non-Newtonian, shear thinning behavior. © 1991 Academic Press, Inc. All rights reserved.