Yield and flow measurement of fine and coarse binary particulate mineral slurries

The presence of coarse particulate components in tailings streams poses significant challenges to the mineral processing industry. Suspensions with fast-settling coarse fractions make traditional rheological measurements tedious and inaccurate. These measurements are critical to the design and operation of mixing, dewatering, pumping and tailings equipment and operations. A methodology for predicting the gel point, close packing fraction and shear rheology of particulate slurries containing a binary mixture of fine and coarse material is presented. The model has validity subject to the constraint that the particle size of the coarse material is sufficiently distinct from that of the fine material. The model enables calculation of the gel point and close packing fraction of the mixture based on the gel points and close packing fractions of the pure fine and coarse materials in the suspension. The model predicts that the gel point (and close packing fraction) of the fine material increases with increasing coarse fraction until a maximum value is attained before decreasing to the gel point (or close packing fraction) of the coarse material. This relationship provides a subsequent basis for a yield stress model to accurately predict the yielding behaviour of binary mixtures of fine and coarse material. The model is useful in determining whether a sample exhibits yield stress behaviour through knowledge of the gel point and close packing fraction of the constitutive fine and coarse components. The model is exemplified using particulate mixtures containing coagulated aluminium oxide, calcium carbonate and coarse sand.