Hydrodynamics interaction between air bubbles and particles in flotation revealed by high-speed visualization

A mineral separation process usually involves a flotation method which uses buoyancy forces on microbubbles. The important factors which determine the separation efficiency heavily relate to the intensity of occurrence of bubbleparticle collision. This occurrence is mainly controlled by the hydrodynamics interaction between the bubbles and mineral particles so that improved understandings on the underlying physics become the key point in improving the performance of separation process. In the present research the interaction between bubble and particles without interfacial modification is studied experimentally focusing on the mode of interaction, probability of collision and the angle of detachment. The test was done by using the experimental set up which consisted of a fluid container made of glass, syringe pump as bubble generator, particle feeder, illumination system, high speed video camera and image processing software. The bubble generator and particle feeder were carefully designed so that the bubble formation, as well as the particle feeding could be precisely controlled and water was used as the medium. The microhydrodynamics aspects which were observed and analyzed included the collision, attachment, detachment and particles movements. The results show that two modes subprocesses after the bubbleparticles collisions characterized the microhydrodynamics interactions between particle and bubble namely reflection and attachment with the former dominates the mechanism with higher probability of occurrence. Moreover, larger particles are influenced by the microhydrodynamics forces when they are below the bubbles which are floating upward. The collision efficiency is then influenced by the particles velocity toward the bubble within a very small distance. Here, the particles movement is affected by a fore- and aft-asymmetric motion of the fluid surrounding the bubbles. Further, the particles movement depends on the mobility of bubble surface and particles inertia.