Overloading of gas bubbles in column flotation of coarse particles and effect upon recovery

This communication presents experimental results obtained in the column flotation of relatively coarse silica sand (d(80) = 190 mum) conditioned with dodecylamine. It is shown that air bubbles might become completely covered with particles giving rise to bubble-particle aggregate densities close to that of water. Under these circumstances, mineralised bubbles do not have enough buoyancy to rise along the column and tend to accumulate close to the bottom, giving rise to a gas holdup profile that decreases from bottom (50-60%, v/v) to top of the column (around 20%, v/v), and to a decrease in solids recovery (as low as 30% for the more severe conditions: J(t) = 1.5 cm/s and 35% solids slurry). It is postulated that the drop in recovery observed is due to both bubble coalescence caused by overloading (loss of bubble surface area) and to entrainment of mineralised bubbles in the tails stream. The occurrence and magnitude of the phenomenon was photographically documented. (C) 2003 Elsevier Science B.V. All rights reserved.