JOURNAL PAPER

The effect of particle sizes and solids concentration on the rheology of silica sand based suspensions

N. Mangesana^I; R.S. Chikuku^I; A.N. Mainza^I; I. Govender^I; A.P. van der Westhuizen^I; M. Narashima^II

^ICentre for Minerals Research, University of Cape Town, South Africa
^IIJulius Kruttschnitt Mineral Research Centre, University of Queensland, Australia

SYNOPSIS

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.

“Full text available only in PDF format”

References

CHENG, D. C-H. Viscosity-concentration equations and flow curves for suspensions. Chemistry and Industry, vol. 17, 1980. pp. 403-406.         [ Links ]

CLARKE, B. Rheology of coarse settling suspensions. Trans. Inst. Chem. Engrs. vol. 45, 1967. pp. 251-256.         [ Links ]

DE BRUIJN, H. Discussions Faraday Soc. vol. 11, 1951. 86 pp.         [ Links ]

FERREIRA, J.M.F. and OLHERO, S.M. Influence of particle size distribution on rheology and particle packing of silica-based suspensions. Powder Technology, vol. 139, 2003. pp. 69-75.         [ Links ]

KAHN, R. The report on Paterson and Cooke rheometer. 2005.         [ Links ]

KAWATRA, S.K. and EISELE, T.C. Rheological Effects in grinding circuits. Int. J. Miner. Process, vol. 22, 1988. pp. 251-259.         [ Links ]

KLIMPEL, R.R. Influence of material breakage properties and associated slurry rheology on breakage rates in wet grinding of coal/ores in tumbling media mills. In M.J. 1984.         [ Links ]

MORREL, S. and STEPHENSON, I. Slurry discharge capacity of autogenous and semi-autogenous mills and the effect of grate design. Int. Jou. Miner. Proc, vol. 46, 1995. pp. 52-72.         [ Links ]

RUTGERS, R. Relative viscosity and concentration. Rheologica Acta, vol. 2, 1962. pp. 305-348.         [ Links ]

SHI, F. Slurry rheology and its effects on grinding. Phd Thesis. Julius Kruttschnitt Mineral Research Centre, University of Queensland. 1994.         [ Links ]

THOMAS, D.G. Transport characteristic of suspension: VIII. A note on the viscosity of Newtonian Suspensions of uniform spherical particles. J. Colloid. Sci., vol. 20, 1965. pp. 267-277        [ Links ]

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