Frothers are used in flotation to aid generation of small bubbles, but little is known about the mechanisms that take place in the flotation machine to produce such an effect. Coalescence prevention is the common explanation, although the exact mechanism is obscure and almost no attention has been paid to a frother effect on bubble break-up, the other possible mechanism. This thesis presents a technique to study the effect of frothers on bubble coalescence at the generation stage (at a capillary tube) and a technique to study the effect of frothers on bubble coalescence and break-up in a turbulent field. The first technique is based on the sound bubbles emit when they form and coalesce. The sound signal was linked to bubble formation and coalescence events using high-speed cinematography. The technique has a resolution capable of detecting coalescence events that occur within 1-2 ms. The second technique allows discriminating between coalescence and break-up and is based on the exposure of a mono-size distribution of bubbles to a turbulent field generated by a three-bladed axial flow impeller. Analysis of bubble size distributions after contact with the turbulent field gives the coalescence and break-up fraction. The results show frothers reduce coalescence and alter the bubble size distribution of bubbles generated by break-up. / In the course of high-speed imaging an effect of frother on bubble shape and motion after formation was detected. Analysis of this forms the third major component of the work. A dependence of velocity on bubble aspect ratio is shown, which is in line with recent literature.

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The thesis presents a technique for and results of surface force measurements in a 3-phase system. The phases are a solid medium (mica), fluid (water and water-based electrolyte solutions) and gas (an air bubble). Analysis of deformation of the air bubble with respect to mutual position of the bubble and the mica surface, the capillary pressure of the undeformed bubble surface, the capillary pressure, and the disjoining pressure provide data for calculation of the air-liquid surface electrical potential. Furthermore, the information extracted from the deformation analysis made it possible to draw a conclusion regarding the nature of electrical double-layer forces in the system and, to some degree, about the effect of ion properties on the surface charging properties of the air-liquid interface. / Surface forces between an air bubble and a flat mica surface immersed in aqueous electrolyte solutions have been investigated using a modified surface force apparatus. This method allows forces to be detected in two regimes: at long range where the bubble is distorted slightly by the surface forces, and at short range where the force is manifest as disjoining pressure in a thin wetting film separating the bubble from the solid. The force was calculated from the equilibrium (or quasi-equilibrium) shape of the bubble surface. The experiments clearly show that long-range double-layer repulsion acts between mica and an air bubble in water and electrolyte solutions of different concentration. Double-layer repulsion indicates that the air bubble surface is negatively charged. However, there is clear evidence that charge regulation occurs at the air-water interface to maintain a constant surface potential, and as a result of this, the charge at this interface changes from negative to positive as the bubble approaches the negatively charged mica surface. Because of the attraction that arises due to the charge reversal, excessive force is required to separate the bubble from the mica, though the mica remains completely wetted by the aqueous phase. / The air-liquid surface potential has been evaluated from fitting a theoretically calculated shape to experimental measurements of bubble shape and film thickness, where the theoretical bubble shape was obtained from the numerical solution of the augmented Young-Laplace equation. Potential on the air bubble surface mainly depends on the concentration of electrolyte but is insensitive to the type of cation or anion within the low range of concentration investigated here. / The more important issue for such concentrations appears to be the electrostatic interaction between ions in solution and the air bubble interface. Therefore at the concentrations investigated, the potential on the gas-liquid interface arises due to the non-specific adsorption of ions to oriented water dipoles at the interface. / Thesis ([PhDApSc(MineralsandMaterials)])--University of South Australia, 2005.

Thesis (PhDApSc(MineralsandMaterials))--University of South Australia, 2001.

The relationship between operating parameters, cell hydrodynamics, flotation response and scale-up of flotation rates has been explored using three geometrically similar Rushton turbine flotation cells with volumes of 2.25, 10 and 50dm³. Mean energy dissipation values measured using Laser Doppler Velocimetry (LDV) and a torque turntable method were in good agreement. As the cell volume was increased, the mean energy dissipation was proportional to N³D, rather than N³D² as may be expected based on dimensional analysis. Possible reasons for this difference are discussed. Aeration resulted in a slight increase in mean energy dissipation. Bubble diameters were measured using a University of Cape Town bubble size analyser to determine the frother concentration at which a constant bubble diameter was achieved for all operating conditions and cell volumes. The critical frother concentration required to achieve this was 20 ppm MIBC.

Department of Chemical Engineering, University of Newcastle, N.S.W. Bibliography : leaves 22-238. "The hydrodynamic phenomena occurring inside the enclosed downcomer section of a plunging jet bubble column are described in this study".

Thesis (Ph.D.) -- McMaster University, 1999. / Includes bibliographical references (leaves 231-245). Also available via World Wide Web.

Thesis (Ph.D.)--University of Tulsa, 1991. / Bibliography: leaves 80-82.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1990. / Vita. Abstract. Includes bibliographical references (leaves 70-86). Also available via the Internet.