The phenomenon of bubble coalescence is encountered along with the interaction of hydrophobic particles in metallurgical industries and flotation processes. In the context of steel making industries where inert gas bubbles are used to remove inclusions from steel, coalescence of bubbles was expected to show an effect on the stability of the particles or agglomerates at the bubble interface. This was verified by carrying out experiments using a cold model with polymeric low density polyethylene particles which are hydrophobic in nature. The effect of particle size and particle loading on coalescence of two equal sized bubbles, one bare and the other coated with particles has been investigated. It has been found that individual particles remained stable to bubble surface oscillations, however, agglomerated particles were unstable and their detachment had a dependency in particle size and loading fraction on the bubble.

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Particle coated bubble and its stability plays a major role during particle recovery in flotation process. A rising bubble undergoes shape oscillations which are subjected to change when particles are coated on the surface of a bubble. Experiments were performed to understand the effect of particle coating on a rising bubble in a liquid column. Hydrophobic Low density polyethylene particles were used to coat the bubble surface and water was used as liquid medium. Two images (one direct and mirror image) were taken for all position during rise of the bubble. Effect of different fraction of particle coating on the bubble surface oscillations was studied. It is observed that the shape oscillations of bubbles are arrested as coating fraction increased from 10% to 50% with the latter undergoing almost no deformation in shape. The bubble in this case behaves like a rigid body and exhibits pure rotation as it moves up.