Hydrodynamic collisions involving bubbles and mineral particles

The movement of bubbles inside a liquid and their interaction with other bubbles, solid particles, or surfaces has been a topic of intense research due to its importance to understand natural phenomena and improve industrial applications such as mineral flotation. For a long time, the mobility at the air-water interface was suggested to affect the flotation recovery, and this understanding was further advanced in the past few years with the development of experimental techniques. In this study, we review the recent experimental and theoretical understanding of the boundary conditions at the air-liquid interface, and how the surface mobility affects the rising speed of a single bubble and the coalescence of bubbles. Consequently, the flotation efficiency can be affected by the surface mobility by altering the probability of collision, attachment, and detachment between the bubble and valuable mineral particles. Recent works also show that the surface mobility is affected by the solution chemistry, the aging of the air-water interface, and the hydrodynamic flow. Therefore, it can be speculated that future techniques for mineral flotation can be developed by the controlled manipulation of surface mobility at the bubble surface. A freshly formed bubble has a mobile interface, but the presence of impurities or added surfactants at different concentrations can accelerate the immobilization of the air bubbles.