Assessment of the modified slump test as a measure of the yield stress of high-density thickened tailings

Yield stress values of four thickened (high-density) mineral tailings at varying solids concentrations were determined using three different techniques. The first set of values was measured using the modified slump test approach with an open-ended cylinder having an aspect ratio of 1.2. A second set was derived from measurements obtained from a coaxial cylinder fitted to a Rheolab® MC1 rheometer. The results were graphically compared with those obtained using the miniature vane technique, a popular and well-accepted method of measuring yield stress. Empirical relations developed from the modified slump test appear to predict reasonably accurate yield stress values up to about 200 Pa when compared with the vane and rheometer results. It is concluded that, although the time-dependent nature of the tailings tested may induce errors as much as ±30% for some samples, the modified slump test provides a reliable and simple test for evaluating the yield stress of thickened tailings. The method can therefore be employed as a first approximation of the changing parameters of high-density thickened tailings in the field without necessarily resorting to sophisticated equipment.Key words: high-density thickened tailings, rheology, shear yield stress, slump, torque.