Numerical modelling of non-Newtonian slurry in a mechanical flotation cell

Abstract

Certain mineral slurries used in the minerals processing industry have been shown to exhibit non-Newtonian rheologies, particularly with finer particle sizes and at higher solid concentrations. Research has also shown that a cavern containing yielded fluid surrounded by stagnant fluid form around the impeller during the agitation of non-Newtonian fluids exhibiting yield stresses, and this is therefore hypothesised to occur inside mechanical flotation cells which may adversely affect fluid hydrodynamics. A single phase non-Newtonian fluids was modelled using CFD, using the Herschel–Bulkley non-Newtonian model with constants derived from experimentally determined Bindura nickel ore slurry, known to be rheologically complex due to the presence of fibrous mineral types, such as serpentine. The modelling methodology was first validated against published experimental results in a stirred tank, and results were experimentally validated using piezoelectric pressure transducers to measure the magnitude of pressure fluctuations due to the fluid velocity in order to define the cavern boundary. Both experimental and numerical findings show that a cavern forms around the stator, with its size depending on slurry yield stress. It was also found that the shear–stress transport (SST) k – ω turbulence model predicted the cavern boundary most accurately.