On-line version ISSN 2411-9717
J. S. Afr. Inst. Min. Metall. vol.108 n.4 Johannesburg Apr. 2008
N. MangesanaI; R.S. ChikukuI; A.N. MainzaI; I. GovenderI; A.P. van der WesthuizenI; M. NarashimaII
ICentre for Minerals Research, University of Cape Town, South Africa
IIJulius Kruttschnitt Mineral Research Centre, University of Queensland, Australia
The effect of high solids concentration and coarse particle sizes (d50 ranges 90-300 μm) on the viscosity of a suspension of water and silica sand was investigated. The experiments were designed to include conditions that have been tested by other authors and those encountered in the operation of tumbling mills.
The rheological data was measured using a tube rheometer with operating pseudo shear rates of up to 1500 s-1. The rheograms obtained depicted dilatant behaviour. The Otswald-de Waele, Bingham, Herschel-Buckley and Casson models were fitted to the experimental data. The Herschel-Buckely model, which approximates the yield point and gives an indication of the shear thinning or shear thickening behaviour of the suspension, was found to provide the best description of the flow curves for all slurries. The Herschel-Buckely model was then used to determine the apparent viscosity of all the tests.
The apparent viscosity and yield stress increased with solids concentration and particle size at the different pseudo shear rates. The increase in slurry viscosity with solids concentration was attributed to increased frequency of particle-particle interactions. The increase in slurry viscosity with particle size was attributed to increased inertial effects. At low shear rates the sand slurry exhibited shear thinning behaviour for all solids concentrations. At higher shear rates above 1000 s-1 the high solids concentration suspensions exhibited a transition from shear thinning to a shear thickening behaviour.
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Paper written on project work carried out in partial fulfillment of Bsc (Chem. Eng.)-N. Mangesana degree and Bsc (Honours in Chem. Eng.)-R.S. Chikuku degree