Analysis of fine bubble attachment onto a solid surface within the framework of classical DLVO theory

Fine bubble attachment onto a solid surface in an impinging jet flow was analyzed within the framework of DLVO theory. The effects of hydrodynamic convection, van der Waals (VDW) interaction, electrostatic double-layer (EDL) interaction, and gravitational force on bubble attachment rate (in terms of the Sherwood number) were examined in detail. The analyses showed that due to large Peclet number and gravity number for gas bubbles the behavior of the bubble attachment is significantly different from that of colloidal particle deposition in some aspects. Specifically, it was demonstrated that within a certain range of physicochemical conditions, gas bubbles can attach onto a solid surface despite the existence of repulsive VDW interaction force and the fact that the surfaces of both the bubble and the solid collector carry the same sign of electrostatic potentials. This is attributed to the role played by the short-range attractive asymmetric EDL interaction and the strong hydrodynamic and gravity forces, without any need for the so-called hydrophobic interaction force. In addition, it was also shown that the models derived for the impinging jet system can be used to evaluate transport of fine gas bubbles onto a large particle surface, suggesting that the information extracted from the impinging jet geometry can be applied to the analysis of flotation processes. (C) 1999 Academic Press.