The development of a cavern model for mechanical flotation cells

Certain fine particle and high solid concentration mineral slurries used in the froth flotation process have been shown to exhibit non-Newtonian rheologies, including a yield stress. The mixing characteristics of these fluids are often problematic as a cavern of yielded fluid forms around the impeller whilst the rest of the fluid remains stagnant and therefore unmixed. This paper aims to develop a semi-empirical model to calculate the height of caverns forming in non-Newtonian mineral slurries in a mechanical flotation cell.Cavern shapes in a pilot-scale Batequip flotation cell were numerically determined for a range of mineral slurries using an experimentally validated Computational Fluid Dynamics (CFD) model. Development of the cavern height model was based on the assumption that the cavern boundary was formed where the shear stress imposed on the slurry equaled the fluid yield stress and also that the flow along the cell walls could be represented by an annular wall jet. It was found that the cavern height was directly proportional to the product of the slurry density and the square of the impeller tip speed, and inversely proportional to the slurry yield stress.