Influence of floatation bubble size on detachment mechanism of coarse-grained particles from air bubbles in turbulent vortex

Air bubbles is an indispensable factor that plays an important role in flotation process, and their size has a significant bearing on the interaction between bubbles and particles. However, the influence of bubbles size on mechanism of detachment of coarse-grained particles from bubbles in turbulent vortex still remains unclear. To deal with this situation, a self-made bubble-particle confined turbulent detachment testing platform is utilized to explore the detachment behavior of bubble-particle aggregates at different bubble sizes in turbulent eddies. The dynamic parameters involved in particle detachment during the testing are measured and analyzed using the Image-Pro Plus image processing software. As revealed by test results, while ensuring the bubble buoyance, reducing bubble size can lead to significantly improved stability of mineralized aggregates of bubbles and coarse-grained particles in turbulent vortex flow; the detachment of bubble-particle aggregates in this case takes place as a result of fluid shear or bubble oscillation or particle centrifugation; the change of vortex structure within the wall chamber plays a crucial role in detachment mode of bubble-particle aggregates; opposite from what is assumed in the traditional centrifugal detachment theory, it proves that the particles undergo a high-velocity centrifugal motion on surface of bubbles driven by turbulent eddies together with bubbles rather than an independent action alone; when smaller bubbles and particles rotate together within the wall chamber, the particles at bubble′s periphery tend to move at a velocity close to that of bubble′s core, causing a higher stability of aggregate, and hence less occurrence of centrifugal detachment of particles; conversely, for the aggregate formed with larger bubbles, the significant difference in relative velocity between the particles at the periphery and core of the bubble cause the particles to undergo a faster motion relative to the bubble, allowing the particles to have a more chance to come off the bubble due to the higher centrifugal force to which the particles are subjected. The work made in the paper may offer a basic insight into the mechanism of detachment of coarse-grained particle from bubbles in a turbulent vortex flow field.