Vietti, AJ & Dunn, F 2006, 'Another Dimension to Slump', in R Jewell, S Lawson & P Newman (eds), Proceedings of the Ninth International Seminar on Paste and Thickened Tailings
, Australian Centre for Geomechanics, Perth, pp. 25-36.
Estimating the rheological properties of a paste using convenient methods such as the slump technique are
common practice within the industry. However, the universality of comparing slump heights to estimate the
flow properties for different paste products has been questioned (Clayton et al., 2003; Paterson, 2002). The
dispute relates to the fact that two paste products may in fact exhibit similar slump heights, but may not share
the same shear yield strength since their densities may be different. This discrepancy is catered for by the
method of Pashias et al. (1996) in which the shear yield stress can be conveniently calculated from the slurry
density and the slump height.
However, certain paste rheological behaviours are observed which appear puzzling and which cannot be
explained on the basis of particle size and slurry density alone. The chemical conditions of pastes
(particularly those containing clay minerals) have profound effects on the colloidal interactions of the
suspended solids and hence on the rheological behaviour of pastes (Vietti, 2004; Dunn, 2005).
This paper demonstrates that different slump heights may be observed for a kimberlite paste containing
smectite at one material density, but varying paste chemical conditions.
Brindley, G.W. and Brown, G. (1980) Crystal structure of clay minerals and their X-ray identification, Brindley, G.W. and Brown, G.
(eds.), Mineralogical Society, London.
Clayton, S., Grice, T.G. and Boger, D.V. (2003) Analysis of the slump test for on-site yield stress measurement of mineral
suspensions, International Journal of Mineral Processing, Volume 70, pp. 3-21.
Dunn, F. (2005) A study of the relationship between various slurry material characteristics and the flow behaviour of co-disposed
kimberlite tailings upon deposition, MSc thesis, University of the Witwatersrand, Johannesburg.
Fourie, A.B. (2002) Materials characterisation, Paste and thickened tailings – a guide, Jewell, R.J., et al. (eds), Australian Centre for
Geomechanics, pp. 35-47.
Klein, C. (2002) Mineral Science (22nd edition), John Wiley & Sons, New York.
Pashias, D.V., Boger, N.P., Summers, K.J. and Glenister, D.J. (1996) A fifty cent rheometer for yield stress measurement, J.
Rheology, Vol. 40, No. 6, pp. 1179-1189.
Paterson, A. (2002) Is slump a valid measure of the rheological properties of high concentration paste slurries? Proceedings 15th
International Conference of Slurry Handling and Pipeline Transport, Banff, Canada.
Richards, L.A. (ed.) (1969) Diagnosis and improvement of saline and alkali soils, US Dept. Agriculture Handbook No. 60.
Yield stress vs % solids
50 55 60 65 70 75
pH 8.6 - Vane
pH 8.6 - Slump
pH 6.2 - Vane
pH 6.3 - Slump
pH 11.5 - Vane
pH 11.5 - Slump
rheology And thicKening
Svarovsky, L. (ed) (1981) Solid-liquid separation (2nd edition), Butterworths, London.
Tessier, D. (1990) Behaviour and microstructure of clay minerals. Soil colloids and their associations in aggregates, M. F. De Boodt
et al., (eds.), Plenum Press, New York, pp. 387 – 415.
Tuller, M. and Or, D. (2003) Hydraulic functions for swelling soils: Pore scale considerations, Journal of Hydrology, pp. 50 – 71.
Van Olphen, H. (1977) Clay colloid chemistry, John Wiley & Sons, New York.
Vietti, A.J. (2004) Know your chemistry – Suspension and compaction behaviour of paste, International Seminar on Paste and
Thickened Tailings, Paste 2004, 31 March – 2 April 2004, Cape Town, South Africa.