The effect of microhydrodynamics on bubble–particle collision interaction

Interactions between particles and bubbles are influenced by hydrodynamic forces of the aqueous medium in which the flotation process takes place. This paper investigates the effect of liquid hydrodynamic forces working at short inter-surface separation distance, referred to as microhydrodynamic forces, on the bubble–particle collision (encounter) interaction. The full equation of particle motion around an air bubble with either a mobile surface (e.g., the potential flow) or an immobile surface (e.g., the Stokes flow) has been solved and analyzed numerically. The effect of particle density, size and film thickness (i.e., inter-surface separation distance) on the bubble–particle collision angle and efficiency has been examined. The new results were compared against the results obtained under the condition that microhydrodynamic effect has been ignored (the conventional theory). The effect of microhydrodynamics on the collision angle and efficiency has been found significant. Generally, the microhydrodynamic effect decreases the collision efficiency due to retarding the particle approach to the rising bubble surface. There also exists a critical set of particle size and density, where the collision angle is minimal, for both the mobile and immobile bubble surfaces. Away from the critical particle size and density the collision angle increases to 90°.

Graphical abstractMicrohydrodynamics retards the particle approach to the air bubble surface and significantly affects the bubble-particle collision interaction.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Micro hydrodynamics (MH) works at short inter-surface separation distance. ► MH influences bubble–particle collision interaction in flotation. ► MH decreases collision efficiency for both immobile and mobile bubble surfaces. ► Collision angle first decreases and then increases with increasing particle size and density.