Attachment of fine gas bubbles onto a solid surface and electrokinetics of gas bubbles

Study of bubble attachment onto a solid surface (collector) is of fundamental importance to particle hydrodynamics and interfacial science. Interests in this subject stem from its relevance to flotation processes used extensively in many separation processes such as mineral extraction, potable water and wastewater treatment, and bitumen recovery. Despite decades of operation, questions (e.g., selective flotation) still remain regarding mechanisms behind bubble attachment process. In light of this, the attachment of fine bubbles onto model collector surfaces was quantitatively investigated using a well-controlled experimental system that is analogous to bubble-particle attachments in real flotation processes. Such an approach allows elucidation of the effects of colloidal forces on bubble attachment as well as the roles of hydrodynamics and gravity in bubble transport and capture.; This thesis presents results of both experimental investigation and theoretical modeling. On the experimental side, the well-established impinging jet technique is extended to the study of bubble attachment onto solid substrates. The experimental system is designed in such a way that fine bubbles (either Hydrogen or Oxygen bubbles) generated by electrodes are carried by flowing solution to go through a capillary tube and to impinge onto a collector surface. Thorough experiments were carried out to investigate bubble attachment under a wide range of hydrodynamic and physicochemical conditions. Moreover, as no commercial instrument was available for measuring the zeta potential of gas bubbles which is an important parameter for quantifying the electrostatic double layer interaction, an electrophoresis apparatus was therefore devised for such a purpose.; On the theoretical side of this study, an Eulerian based approach was used to derive a bubble transport equation that includes contributions from hydrodynamic convection, Brownian diffusion, migration under gravitational buoyancy force and DLVO colloidal forces (e.g., the van der Waals and electrical double layer interactions). It was found that the theoretical predictions are generally in reasonable agreement with the corresponding experimental data of bubble attachment to methylated glass, suggesting validation of the bubble transport model. However, the proposed model failed to predict bubble attachment onto untreated glass at low Reynolds numbers. Several possible mechanisms are suggested to account for such a discrepancy.