Abstract

Three parameters are generally used to describe gas dispersion in a flotation machine: superficial gas (air) velocity, gas holdup and bubble size. Techniques and sensors to measure local values of these parameters in industrial flotation machines have been developed. Models proposed to predict one of these gas dispersion parameters from measured values of the other two have proven unreliable. Bubble terminal velocity is an important variable in these models as its calculation is the initial step in the determination of the bubble swarm velocity. Numerous equations have been proposed to calculate bubble terminal velocity and their testing is the objective of this work. Measurements using a high speed camera have demonstrated that bubble shape and velocity are interrelated, and that bubble shape is affected by water viscosity and by the frother type and concentration in use. By adding a polymer to vary water viscosity, to produce changes in shape and velocity of single bubbles generated by controlled injection of air through a capillary, equations for bubble terminal velocity are being tested. The results demonstrated that only equations considering parameters describing bubble shape are able to predict terminal velocity with reasonable accuracy.