PhD Project title Numericalmodelling of non-Newtonian slurry in a mechanical flotation cell
(Supervisors: Prof D Deglon, Dr C Meyer) Graduated: 2009
Certain slurries used in minerals processing are known to exhibit non-Newtonian rheology, particularly at finer particle sizes and higher solid concentrations. It is also known that a cavern containing yielded fluid surrounded by stagnant fluid forms around the impeller during the agitation of non-Newtonian fluids exhibiting yield stresses. In this PhD project, commenced in 2007, such a cavern was hypothesised to occur inside mechanical flotation cells, with possible adverse effects on fluid hydrodynamics.
Computational Fluid Dynamics (CFD) was used to model single-phase non-Newtonian fluids, using the Herschel–Bulkley non-Newtonian rheology model with constants derived experimentally from Bindura nickel ore and kaolin slurries - both known to exhibit problematic rheology. The modelling methodology was validated against published experimental results in a stirred tank, and the results were validated experimentally using piezoelectric pressure transducers to define the cavern boundary. Both experimental and numerical findings showed that a cavern formed around the stator. The slurry yield stress and Bingham viscosity were found to have an increasing exponential relationship with the solid concentration. The increase in solid concentration caused damping of turbulence inside the cavern. This is known to reduce the rate of bubble-particle interactions, as well as bubble break-up, thus adversely affecting the flotation process.
Peer-reviewed journal publications
Bakker, C.W., Meyer, C.J. and Deglon, D.A. (2010), “The development of a cavern model for mechanical flotation cells,” Minerals Engineering 23(11-13), pp 968-972.
Bakker, C.W., Meyer, C.J. and Deglon, D.A. (2009), “Numerical modelling of non-Newtonian slurry in a mechanical flotation cell”, Progress in Computational Fluid Dynamics 9(6/7), pp 308-315
Oral conference presentations
Bakker, C., Deglon, D.A. and Meyer, C. (2009), “CFD modelling of cavern formation in a mechanical flotation cell”, SAIMM (Western Cape Branch) Conference, Cape Town, 6-7 August 2009