Bubble movement in a rotating eddy: The implications for particle-bubble detachment

Abstract

Bubbles are an essential part of the froth flotation process for the separation of mineral particles. However, little information is available on the behaviour of bubbles in the turbulent flows in a flotation machine. It has been noted in flotation kinetics studies that the behaviour of bubbles in turbulent eddies is a significant factor in bubble-particle collision, attachment and detachments. In this paper, the performance of single bubbles and groups of bubbles inside a rotating eddy have been studied experimentally. Bubbles were released into a turbulent rotating field in a wall cavity, where a confined eddy was developed by controlling the water flow into the water channel over the open mouth of the wall cavity. To study the behaviour of particles attached to bubbles in the turbulent eddies, particle-bubble aggregates were generated in an external fluidized bed and introduced into the rotating eddy with no frothers added. The process of particle detachment due to centrifugal movement was captured by a high-speed camera. The traditional theory of particle-bubble detachment, which assumes a centrifugal motion of the attached particle on the surface of the bubble, was experimentally verified. However, other modes were also observed. For example, bubbles carrying particles can be brought together in a turbulent vortex, resulting in bubble coalescence and consequent detachment of particles. Inertial detachment modes are also seen, due to rapid changes in the trajectory of the bubble, or because of oscillations of the bubble’s surface.