Effect of bubble size on the kinetics of flotation of pyrite

The size distribution and mean volume (v) over bar(b) of nitrogen bubbles generated through porous plates was determined for porosities in the range 4-160 mu m at superficial gas rates of 0.35-2.11 cm/s. The mean volume increased linearly with the gas rate, and under all studied conditions the experimental bubble concentration had a constant value of 0.92+/-0.08 bubbles/cm(3). The kinetics of flotation of pyrite particles of 127 mu m mean diameter were studied in a specially modified Hallimond tube at pH 6.0, at room temperature. The observed first-order rate constant increases linearly with the gas rate and with the increase of the mean volume of the bubbles in the range (v) over bar(b) = 1.05-6.4 mu l. The linear dependency between the rate constant and the gas rate suggests that particle-bubble aggregates are formed by one particle attached to one bubble. Since the rate constant should not change at constant bubble concentration, the observed increase with (v) over bar(b) must be ascribed to the increase in probability of effective collisions that form stable particle-bubble aggregates. (C) 1999 Elsevier Science B.V. All rights reserved.