Collisional interaction process between a bubble and particles with different hydrophobicity

Abstract

The collisional interaction process between bubbles and particles is considered to play an important role in flotation. This paper aims to investigate the effect of particle hydrophobicity on the bubble-particle collision and subsequent interaction process. Four types of bubble-particle interaction behaviors were observed, namely the non-collision, the collision but without attachment, the attachment with jump-in after collision, and the attachment without jump-in after collision. The ‘jump-in’ event was interpreted as the rupture of the water film, providing the formation and growth of a ‘three-phase contact line’ (TPCL). The mildly hydrophobic particle could attach to the bubble surface without the rupture of the water film, whereas the highly hydrophobic particle had the higher collision and attachment probability. The significant effect of particle hydrophobicity was found in the observed particle trajectories and velocities. The distance between the bubble and the particle of weakly hydrophobicity and mildly hydrophobicity remained almost constant in the particle sliding process on the bubble surface. However, the highly hydrophobic particle was observed to jump in instantaneously after a short interaction time. Influenced by hydrodynamic drag, the maximum sliding velocity of any particles near the bubble’s equatorial plane was higher than the particle terminal velocity, and highly hydrophobic particle had a higher difference. The analysis of the individual force components of particle provides valuable insights into the kinematic properties of particle as it slides. The hydrodynamic drag coefficient decreased with an increase in the particle contact angle, implying the highly hydrophobic particle had a smaller hydrodynamic drag. Additionally, the reaction force was introduced for the first time to satisfy the radial force balance relationship, and explanations were proposed in terms of its source.