Microflotation of fine oil droplets by small air bubbles: Experiment and theory

A trajectory analysis accounting for hydrodynamic interactions and van der Waals attractions was performed to predict the kinetic constant for capture of fine but non-Brownian oil droplets by small air bubbles under creeping- flow conditions. For the range of bubble (40 mum less than or equal to 2 al pha (1) less than or equal to 80 mum) and droplet (3 mum less than or equal to 2 alpha (2) less than or equal to 20 mum) diameters of interest, the th eoretical kinetic constant scales as k proportional to phi alpha (-0.86)(1) alpha (1.21)(2), where phi is the gas holdup, alpha (1) is the bubble radi us, and alpha (2) is the droplet radius. Experiments with a batch flotation cell support these scalings, but the quantitative predictions for the capt ure rate are about three times higher than the measured values. Smaller bub bles are more efficient collectors because they have higher surface area pe r volume and cause weaker hydrodynamic interactions, whereas smaller drople ts are floated less efficiently because they tend to flow around the rising bubbles.