Effect of bubble size on the kinetics of flotation of pyrite

The size distribution and mean volume (v) over bar(b) of nitrogen bubbles g enerated 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 incre ased linearly with the gas rate, and under all studied conditions the exper imental 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 diamete r were studied in a specially modified Hallimond tube at pH 6.0, at room te mperature. The observed first-order rate constant increases linearly with t he 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 ra te constant and the gas rate suggests that particle-bubble aggregates are f ormed by one particle attached to one bubble. Since the rate constant shoul d 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.