Rheology of concentrated slurries of particles of natural size distribution produced by grinding

Abstract

The rheological properties of concentrated slurries of natural size distributions of ground coal and quartz were determined in a cup-and-bob viscometer in the laminar flow region, using a ridged bob and cup. Organic liquids of the same density as the solids were used to prevent settling of the solid. It was found that slurries had a true yield stress, followed by a transition to a Bingham plastic character (with a higher extrapolated Bingham yield stress) for shear rates above 40 s −1. Empirical equations were developed to describe the results as a function of the Rosin—Rammler characteristic size and distribution modulii of the particle size distributions, for solid concentration of 30 to 60 vol.%. The two most significant parameters were volume per cent solids and size modulus, with the distribution modulus m having a minor effect between m = 0.4 to m = 0.9. Results from both coal and quartz were fitted by the same equations for plastic viscosity and yield stresses when these were expressed relative to the viscosity of the carrier liquid. Existing theories of slurry rheology do not appear to be adequate to explain the results.