Rheological behaviour of lateritic smectite ore slurries

The characterisation and rheology of several nickel laterite smectite ores and pure minerals are compared to assess the effect of mineralogy and particle size on the viscosity of high pulp density slurries. A vane viscometer was used to determine the “optimum pulp density” (OPD) that gave a yield stress of 100 Pa which is considered to be optimal for pumping slurries into autoclaves in the HPAL process. In general, slurries containing finer particles were more viscous and smectite slurries exhibited poor rheological behaviour as compared to slurries of goethite < kaolin < talc < hematite < maghemite < magnesite. Blending the smectite ores with a fraction of the pure minerals improved the rheological behaviour of the pulp and can increase the optimum pulp density of the smectite blend by over 5% w/w.When the physical properties of the smectite ore and slurry were examined, a very good linear correlation was obtained between the optimum pulp density and the settling density which provides a simple measure of predicting rheological behaviour of slurries. The variation in the viscosity of the nickel laterite ores depends largely on their mineralogy and particle size distribution. The mean particle size and P80 values of various smectite ores containing the same mineral phases were also found to have a reasonably good linear correlation with OPD in saline water, but the correlation of ore surface area with OPD was a poorer fit.

Research highlights
► Rheology of smectite ore and some pure minerals were found to be in the order of smectite < goethite < kaoline < talc < hematite < maghemite < magnesite.
► Blending of pure minerals such as goethite, hematite, maghemite, kaoline, talc and magnesite reduced the viscosity of the smectite ore slurries.
► Addition of coarse particle improved the rheological characteristics of smectite ore slurry.
► The optimum pulp densities at 100 Pa yield stress (from vane measurement) and the maximum settled densities of various smectitic laterite ores were found to be linearly correlated.