Study interactions between fine particles and micron size bubbles generated by hydrodynamic cavitation

• Bubble generation by hydrodynamic cavitation and interactions with fine particles.
• Increased number of bubbles with increasing dissolved gas or fluid velocity.
• Critical hydrophobicity of contact angle 45° for bubble–particles attachment.
• Enhancement of bubble–particle attachment by micron bubbles on solid surfaces.
• Detrimental role of bubble aging in bubble/particle attachment.

Interactions between fine subbituminous coal particles and micron size bubbles generated by hydrodynamic cavitation were investigated. The experimental results showed that increasing fluid velocity increases the number counts of micron size bubbles. The number counts of microns size bubbles were found to increase with increasing the dissolved gas content. At a given fluid flow velocity, reducing the dissolved gas content by heating the liquid for 2 h at 80 °C reduced the number counts of micron size bubbles while saturating the liquid with CO2 led to a significant increase in the number counts of micron size bubbles. However, change in fluid velocity or dissolved gas content had little effect on the bubble size. Introducing micron size bubbles generated by hydrodynamic cavitation into flotation column was found to be a promising method to enhance the recovery of fine coal particles. The micron size bubbles were found to attach to the solids with contact angle of 45° or larger. The micron size bubbles frosted on the solid surface were proven to enhance the bubble–solid attachment. These findings further improved our understanding of the role of hydrodynamic cavitation in the attachment of flotation size bubbles to gas-nucleated fine particles and hence in fine particle flotation. The conclusions derived from this study provide scientific basis for the design of hydrodynamic cavitation assisted flotation devices.