The Effect of Bubble Size on Fine Particle Flotation

Abstract

Expressions for the probability of collision (P_c) and adhesion (P_a) have been derived for fine particle flotation by calculating the trajectory of particles as they flow past a bubble in streamline How. Three different flow regimes have been considered in the present work, i.e., Stokes, potential and intermediate. For the intermediate flow conditions in which most flotation operations are carried out, the particle trajectories have been determined using an empirical stream function derived in the present work. For the case of a very hydrophobic coal sample, the values of the probability of collection (P) determined experimentally have been found to be in close agreement with the theoretically predicted P_c values over a range of bubble and particle sizes The expression for P_a has been derived by determining the time it takes for a particle to slide along the surface of a bubble after collision. It has been assumed that the bubble-particte adhesion occurs when the sliding time is equal to or exceeds the induction time, which varies with the particle hydrophobicity. P_a is shown to be a function of particle size, bubble size and induction time. The values of P_a predicted in the present work are in good agreement with the results of microflotation tests conducted on a coal sample.