Effect of bubble loading on the recovery of coarse mineral particles by flotation

Experiments are described in which the recovery of chalcopyrite particles in a fluidized bed froth flotation machine was determined as a function of particle size. The machine has been developed to capture particles over a wide size range, from zero up to a top size determined by the properties of the mineral. Coarse particles are captured in a fluidized bed low-energy environment. Fines and ultra-fines are captured in a separate high-shear zone. The device has two product streams: a froth layer that discharges into a launder as in conventional cells, and another product withdrawn from the pulp below the froth layer on a screen. In the experiments, the chalcopyrite recovery was essentially 100 % for size fractions from 0 to 1400 µm. Here we present experimental results and observations not previously described in the field of flotation: Some bubble-particle aggregates that rise in the pulp in the column, are seen to accumulate beneath the froth layer. These aggregates fail to enter the froth while others rise into the froth and are removed as froth product. Particles from the accumulated layer beneath the froth can be removed from the column in the recycle stream and captured on a screen, forming the screen product. As the particle size increases, the proportion of total product captured in the froth decreases, with corresponding increase in the fraction captured on the screen. Even for the coarsest sizes, the fraction in the froth product is significant. Initially, bubbles loaded with hydrophobic particles that have risen out of a fluidized bed into the pulp phase fail to rise, until they can attach to clean bubbles rising subsequently out of the bed.