THE TURBULENT ENVIRONMENT IN A LABORATORY-SCALE FROTH FLOTATION
TANK
Angus James Morrison, Pablo Brito-Parada and Jan Cilliers
Department of Earth Science and Engineering, Royal School of Mines, Imperial London
ABSTRACT
The hydrodynamic environment in a froth flotation tank can be divided into several regions: the settling
region, from which gangue is removed as tails; the shear region, in which bubbles are sheared down to size
and dispersed; the mixing region, in which bubble-particle interactions occur; the quiescent region, in
which separation occurs as laden bubbles rise to the surface and gangue sinks under its own weight; and
the froth region, in which further separation occurs, and the product is removed as overflow.
The turbulent environment in a flotation tank affects its performance in different ways, depending on
where the turbulence occurs. In the shear and mixing regions, turbulence promotes the recovery of valuable
minerals by increasing the likelihood of bubble-particle interactions, whereas in the quiescent and froth
regions, it reduces this recovery by increasing the likelihood of laden bubbles bursting and of valuable
particles detaching from rising bubbles. Turbulence in the quiescent and froth regions also reduces the
product grade by increasing the likelihood of gangue being entrained in the froth, and by reducing the
stability of the froth. Thus the optimal design and operation of a flotation tank entails maximising the
turbulence in some regions, and minimising it in others.
In this work, we characterise the turbulent environment in a continuously-operated, laboratory-scale
flotation tank, operated under various conditions. We do so using a system of piezoelectric transducers
inserted into the tank at various depths and radial distances from the impeller and baffles, coupled with a
torque transducer fitted to the shaft of its Rushton impeller. The turbulence distribution in the tank is then
correlated with the performance of the tank under those conditions to elucidate its effect thereon. Finally, a
series of retrofittable, mechanical modifications are made to the tank to optimise its performance by
adjusting this turbulence distribution.
KEYWORDS
Froth flotation, Turbulence, Froth stability, Flow modification