9 - Collection and Attachment of Particles by Air Bubbles in Froth Flotation

Summary

Introduction

Froth flotation has a long history (over 100 years) of development and widespread applications. Essentially, the process involves the attachment of finely dispersed hydrophobic particles to air bubbles to produce so-called “three-phase froths” on the surface of the flotation cell with the hydrophilic particles remaining dispersed in the suspension. In this way, the particles are separated, based on their differences in surface wettability. Although froth flotation includes several major elementary sub-processes, one of the most important operations involves the interaction of the selected suspended particles with a chemical reagent (a flotation collector) in order to make the surfaces sufficiently hydrophobic and become “targets” for bubbles generated in the cell. The “gangue” particles remain hydrophilic and do not interact with the collector reagent but remain dispersed in the suspension.

The following unit processes are also important:

1. (i) Generation and dispersion of gas bubbles in the presence of a surfactant (frother) in the pulp and the formation of the froth layer.

2. (ii) Collision of hydrophobic particles with gas bubbles.

3. (iii) Adhesion of hydrophobic particles to gas bubbles and the formation of particle–bubble aggregates.

4. (iv) Ascension of particle–bubble aggregates from the pulp into the three-phase froth.

Both the fundamental and practical aspects of froth flotation have been well studied and developed but the process still undergoes modification and advancement.