Investigation of particle-bubble interactions with a new experimental setup

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Doctoral thesis (monograph)
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Flotation is one of the most widely used processes in mineral beneficiation industry. Research on flotation circuit modelling and optimisation has for long time been of major importance. Flotation is mainly driven by surface chemical properties of the particles attaching to air bubbles. Earlier flotation models are based solely on dynamic consideration, but in the recent years serious research effort has been focused on finding surface chemical parameters, which may improve the existing flotation models. Parameters were mainly obtained from measurements performed with surface force apparatus, thin film balance techniques and atomic force microscopy. This thesis work aimed to design and develop a new experimental apparatus, suitable for in-depth study of particle-bubble interactions. The experimental results of this work provide additional data for the improvement of existing, and development of new flotation models. The new experimental setup named Colloidal Interaction Force Measurement Apparatus (CIFMA) is based on AFM force measurement principle. The apparatus eliminates the limitations caused by the small measurement range of commercial instruments and provides several new features that facilitate the in-depth investigation of particle-bubble interactions. In connection with the instrument design, the errors and problems associated with the technique are reviewed. The experiments conducted with CIFMA were focused on ultrapure, electrolyte containing and gas saturated aqueous systems. In addition the effects of approach velocity, applied load and contact time on the particle-bubble adhesion were studied. The results among others revealed, that the particle-bubble interaction process is time dependent, highly dynamic phenomena. The jump-in force and the adhesion decrease with time. Increased load and contact time enhance the adhesion of the particle to the air bubble even if no three-phase contact is formed. The nanometer-sized roughness of the particle surfaces has a significant effect on the particle-bubble adhesion. In ultrapure system a very long-range jump of the bubble towards the particle occurred, that was detected by optical means. With increasing electrolyte concentration this effect disappeared. These results emphasize the importance of reassessment of existing flotation models and development of new ones by taking into consideration the observed effects.
particle-bubble interactions, CIFMA, adhesion, applied load, contact time, time dependent effect
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