Inverse flotation: a new method of fine particle beneficiation

Conventional froth flotation involves the attachment of hydrophobic particles to rising air bubbles and the concentration of those particles through the drainage of a froth product. This paper describes preliminary experimental findings of a new technology hereby given the term Inverse Flotation. This technology involves the replacement of rising air bubbles with falling drops, and the replacement of the water based suspension of feed particles with a gas-based dispersion. Our preliminary work described in this paper was based on individual drops of water. Fine particles of silica less than 90 microns were shaken through a sieve creating a dispersed cloud of particles. A test drop, attached to a syringe, was passed through the cloud and then examined under the microscope. Large numbers of the hydrophilic silica particles were evident inside the drop. When the experiment was conducted using fine coal there were no particles found within the drop however a careful search revealed an aggregate on the outer surface of the drop. Then, experiments were conducted using a mixture of silica and coal. Large numbers of silica particles were observed to be inside the test drops, while there was some evidence of fine coal at the surfaces of the drops. In general, the silica particles were very efficient in passing through the interface to join the bulk of the drops, while the hydrophobic particles showed little tendency to associate with the drops. These findings support the proposition that hydrophobic particles can be concentrated in a dry form using Inverse Flotation.