THE EFFECT OF AIR FLOW RATE ON THE KINETICS OF FLOTATION

Bubble size distribution and flotation rate were investigated as a function of air flow rate (AFR) and methyl-isobutyl carbinol (MIBC) concentration, in a batch flotation cell designed for the quick removal of the froth phase. This cell design permits unambiguous determination of the flotation rate of material from the slurry to the froth. Average bubble size decreased as MIBC concentration increased and decreased slightly as AFR increased. The total bubble surface area was found to increase as either AFR or MIBC concentration increased. The flotation rate constant of different size classes of silica and galena increased as AFR increased and reached a maximum at an intermediate AFR. Further increases of the AFR caused a decrease of the flotation rate constant. This effect was explained by and correlated with the increase of average bubble size, which decreases bubble-particle collision efficiency.;The effect of AFR on flotation selectivity in the slurry was investigated. AFR was found to have little effect on selectivity, except at very low and very high AFRs, for which selectivity is slightly decreased. The effect of AFR in the froth phase was also investigated, in a two mineral system. Selectivity was found to increase as either AFR increased or froth thickness decreased. These findings, in conflict with known industrial behaviour, can be accounted for by the design of the experimental cell, which preludes hydraulic entrainment, and the batch nature of the work.;The effect of AFR and froth thickness on the flotation of a zinc ore in a small scale continuous cell was also investigated. Sphalerite recovery proved to be nearly independent of AFR and froth thickness. Non-sulphide recovery was closely correlated with water recovery, and was found to be independent of particle size. The behaviour of pyrite was intermediate between that of sphalerite and non-sulphides. Non-sulphide entrainment was modelled and the convex relationship between their recovery and that of water was explained. Selectivity of true flotation was evaluated for sphalerite with respect to pyrite. Selectivity decreased as either the overall transfer rate increased or froth thickness decreased. Overall selectivity was found to depend more on hydraulic entrainment than true flotation.;The transfer rate of different size classes of galena was measured as a function of AFR, in the presence of a froth phase of controlled thickness. Under this operating mode, the flotation rate is a function of the transfer rate of material from the slurry to the froth and of the transfer rate from the froth to the concentrate. The flotation rate constant was found to decrease as either froth thickness increased or AFR decreased. The transfer rate of material from the froth over the cell lip was calculated, and decreased as either particle size or froth thickness increased, and as AFR decreased. Hence the decreased recovery of +60 (mu)m galena in flotation plants could be caused by the slow kinetics of transport from the froth to the concentrate launder more than that of transport from the slurry to the froth, as previously postulated. AFR affected the kinetics of transport from the froth phase to the concentrate more than the kinetics of transport from the slurry to the froth.