Induction and Coverage Times for Crude Oil Droplets Spreading on Air Bubbles

The interactions between crude oil droplets and air bubbles were studied by the droplet-bubble micromanipulator technique. Eight crude oils were investigated, and some aspects of the involved mechanisms were discussed. The induction time was measured for air bubbles approaching crude oil droplets in different aqueous phases. Distinct differences were observed in the presence and absence of salts, which showed the importance of long-ranged electrostatic repulsive forces on thin-film stability. The results also suggested that adsorption of dissolved hydrocarbons at air bubble surfaces may increase the potential energy barrier in the thin liquid film. Furthermore, the time needed for crude oil droplets to spread over the air bubble surfaces (referred to as coverage time) was determined for the crude oils. The results showed that the spreading velocity decreased with increasing viscosity of the crude oil. The detailed understanding of this type of interaction is considered to be a precursor for improving the oil removal efficiency during the flotation process.