Investigating the effect of energy input on flotation kinetics in an oscillating grid flotation cell

Abstract

This paper investigates the effect of energy input (or agitation) on the flotation kinetics of quartz in a novel oscillating grid flotation cell. Oscillating grids generate near ideal hydrodynamic environments, characterised by turbulence which is relatively homogeneous and isotropic. The cell consists of a 10 l tank agitated by 19 grids, having a mesh size of 8 mm and grid spacing of 18 mm. Flotation tests were performed on methylated quartz particles ( p 80 = 100 μm) over a range of power intensities (0.015–0.60 W/kg) and using three different bubble sizes, generated by sintered glass discs (0.13, 0.24 and 0.82 mm). The flotation rate constant was found to increases approximately linearly with increasing particle size and to follow an inverse power relationship with the bubble size. These trends are well established in the flotation literature. More significantly, the flotation rate constant was found to increase approximately linearly with increasing power intensity for all particle and bubble sizes used in this study. The majority of theoretical and experimental studies have found energy input to have less of an effect than the proportional/linear dependence observed in this study. In addition, the increase in the flotation rate constant with increasing power intensity was observed to depend on the particle size but to be less dependent on the bubble size. These findings suggest that energy input and bubble size may, respectively play more and less of a role in promoting particle–bubble contacting in turbulent environments than noted in the flotation literature. However, a recent study by Newell and Grano [Newell, R., Grano, S., 2006. Hydrodynamics and scale up in Rushton turbine flotation cells: Part 2. Flotation scale-up for laboratory and pilot cells. International Journal of Mineral Processing, 81, 65–78] in a stirred tank has also noted this linear dependence.