(Session 3)Submitted for Flotation '11, Cape Town, South Africa, November 2011Effect of energy input on detachment of particles from bubblesin a turbulent flow.

摘要

The flotation process is widely used to separate valuable minerals from waste material in theminerals industry. It is well known that recovery decreases with increasing particle size, and areason often given is that large particles detach from bubbles in the turbulent shear flow inducedby the impeller in mechanical flotation cells. The energy produced by the impeller is transferredto the liquid in the cell and dissipates throughout the tank. In the impeller region, the turbulenceis non-isotropic, but in a very short distance, it becomes isotropic, with the typical cascade ofeddies from large to micro scale length scales.The aim of this study is to observe the behaviour of particle-laden bubbles in the turbulent shearflow near a rotating impeller in a flotation cell. An agitated vessel was constructed in whichbubbles could be introduced beneath the impeller. Bubbles were generated in a liquid-fluidisedbed in a special chamber beneath the cell, in which the fluidising liquid contained flotationcollector that enabled the particles in the bed to adhere to the bubbles. When the bubbles enteredthe impeller zone, some particles were observed to detach, while others remained attached to thebubble and rose out of the vessel as a flotation product. The fractional detachment of particleswas related to the mechanical energy dissipation rate in the region of the impeller. A standardRushton turbine was used. The results are compared with theoretical predictions of Schulze(1977, 1982).