Mechanism of the hydrophobic particles with different sizes detaching from the oscillating bubble surface

Abstract

Turbulence plays a critical role in flotation, as it has a marked impact on bubble-particle interactions, i.e., collision, attachment, and detachment. However, the detachment mechanisms of bubble-particle aggregates in a turbulent field are still not well understood. Particularly, the oscillatory detachment mechanism of bubble-particle aggregates lacks direct experimental evidence. For this reason, this study focuses on the study of the detachment mechanism of hydrophobic particles with different sizes on an oscillating bubble surface. In this study, vertical capillary forces of particles with different sizes were measured by surface force apparatus. The bubbles with attached particles were made to vibrate vertically by the oscillatory detachment measurement system, and the critical detachment amplitudes of particles were measured. Images of the dynamic detachment process of particles were captured by a high-speed camera. Then, the detachment mechanism of particles with different sizes on the oscillating bubble surface was further investigated by image analysis, displacement and acceleration measurement, and comparison of experimental and theoretical vertical critical vibration forces. The results show that although the capillary force increases with the increase of particle size, the critical detachment amplitude decreases significantly. It was also observed that the particles with different sizes have different detachment behaviors on the oscillating bubble surface due to the difference of inertia. Compared with the vertical detachment of coarse particles, the approximately tangential detachment of fine particles is the main reason for the decrease of vertical capillary force, which leads to the conclusion that the experimental value of vertical critical vibration force of fine particles is far less than the theoretical value. The present study is expected to provide a fundamental understanding of the bubble-particle detachment mechanism in a turbulent field.