Flotation of Extreme Particle Sizes

Abstract

Flotation is effective over a narrow particle size range. As particle sizes increase above ~150 µm, body detachment forces overcome surface attachment forces, while, at the same time, mineral liberation decreases, reducing attachment force increasing the detachment probability. As particle sizes decrease below ~20 µm, the collision probabilities between bubbles and particles decrease because fine particles follow streamlines around bubbles due to their low inertia. In this work, Jig Flotation and Two Liquid Flotation (TLF) are developed to extend the maximum and minimum particle size of flotation, respectively. The Jig Flotation process reduces detachment probabilities using an intermittent fluidized bed instead of a mechanically agitated flotation cell for bubble-particle collision. The pulsion and suction cycles creating the intermittent fluidization allow for the formation of a froth phase, allowing Jig Flotation to be selective for both fine and coarse particles. The jigging mechanism allows particles to be separated by density independent of particle size. This mechanism is enabled by the attachment of bubbles to selectively hydrophobized minerals, reducing their apparent density and enhancing their density difference with gangue minerals. In the present work, several Jig Flotation cells have been designed and tested, and encouraging results achieved on chalcopyrite ore. The TLF process uses recyclable oils instead of air bubbles to recover ultrafine coal particles. Oil, having higher contact angles than air bubbles, enhances the recovery of ultrafine particles. The TLF process has produced coal with below 5% ash and below 2% moisture with recoveries greater than 80% from fine coal wastes.