Direct visualisation of bubble-particle interactions in presence of cavitation bubbles in an ultrasonic flotation cell

In this study, the role of cavitation bubbles in the bubble-particle interaction dynamics was investigated using high-speed imaging. A lab-scale conceptual flotation cell was designed involving an ultrasonic field with adjustable power output and a continuous liquid recirculation stream. Coarse size range hydrophobic glass Ballotini particles were suspended in the cell by the combined action of a confined vortex and turbulence created by periodic ultrasonic pulses. Ultrasonic pulses in the liquid medium led to the generation of numerous fine size range cavitation bubbles which were observed to form particle clusters. These particle clusters were observed attaching to relatively larger size carrier bubbles forming stable bubble-particles aggregates, which subsequently floated. It was noted that a favourable state of bubble-particle interactions was achievable to produce such stable bubble-particles aggregates by suitably controlling the input power and period of the applied ultrasonic pulse.