Bubble-particle detachment behavior during bubble coalescence: Role of bubble size

Studies have reported that bubble coalescence causes particle–bubble detachment in the flotation pulp and foam phases. Most coalescence experiments have been conducted using bubble pairs with the same diameter; however, this is not the case in real flotation. In this study, particle–bubble detachment behavior during the coalescence of two bubbles with different sizes was investigated using a high–speed camera, and the variation of the coalescing bubble area was fitted to a damped oscillatory equation and analyzed. To explore the intrinsic detachment mechanism of the bubble size effect, the flow field variation in the bubble periphery was simulated using COMSOL 6.1. Results show that the particle–bubble detachment probability decreased with increasing bubble size difference. The released energy is greatest when the two equal bubbles coalesced, thus leading to the strongest oscillation and highest detachment probability. The simulation results show that turbulent kinetic energy affects particle-bubble stability and is an important reason for inducing particle-bubble detachment. Notably, particle–bubble detachment did not occur at the maximum turbulent energy, because there was a delay due to the time required for the sliding contraction of the three–phase contact line. The research finding provides new insights into the mechanism of particle–bubble detachment.