Flotation In A Fluidized Bed ? A New Paradigm For Flotation

In conventional flotation machines, the recovery is strongly related to particle size. As particle size increases, the recovery also increases, reaching a maximum in the range 20 to 120µm. Beyond this range however, the recovery declines quite quickly. The reason for the decline in recovery observed with coarse particles can be traced to the effect of turbulence. Bubbles trapped in turbulent eddies rotate rapidly, and when the centrifugal force on a particle exceeds the retaining forces due to surface tension, the particle detaches. Since the centrifugal force varies as the cube of the diameter of the particle, and the attachment force varies simply as the diameter, being proportional to the length of the contact line, it is clear that detachment forces will predominate as the particle size increases. The corollary is that the recovery of coarse particles can be improved if the level of the turbulence in the cell can be reduced to a minimum. In this paper, a new type of flotation machine will be described, in which the particles to be floated are suspended in a fluidized bed. An up flow of fluidizing water is provided, by recycling liquid from the top of the cell. The recycle stream is aerated in a high-energy device that disperses the air into fine bubbles that capture the fines and ultrafines. Results are presented for several minerals and coarse coal. Keyword: fluidized bed flotation