ABSTRACT
The process of bubble-particle encounter is very similar to the approach of a particle towards the surface of fibers or particle collectors in depth filtration. The important practical differences include the gas-liquid surface of bubbles in flotation, which changes the particle-surface interaction significantly. For example, the van der Waals interaction is repulsive between a bubble and a particle, but is attractive between the particle and a collector surface in filtration. The gas-liquid surface can be mobile, in the sense that the tangential component of liquid velocity at the gas-liquid interface is non-zero. The gas-liquid interface can be penetrated, rupturing the liquid film and resulting in the motion of the three-phase contact line. Because of these key differences the analysis of the particle-surface interaction in flotation is not the same as that in filtration. For instance, unlike the modem analysis for collector-particle approach in filtration, the bubble-particle encounter in flotation is considered not to be influenced by surface forces and the liquid film. The bubble-particle encounter is usually understood as the approach of particles and bubbles:
• Under the influence of long range forces only, such as long-range hydrodynamic and gravitational forces involving inertial and drag forces, particle gravity and buoyancy forces, and
186 Chapter 9
• To a particle-bubble inter-center distance of the order equal to the range of intennolecular and surface forces between particle and bubble.
