JAPANESE JOURNAL OF MULTIPHASE FLOW

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A novel flotation using microbubbles was developed. At the bottom of the flotation column, the spiral liquid flow microbubble generator was attached. The mean diameter of dispersed microbubbles was ca. 63 μm in spite added surfactants. The fine particles of carbon were used as suspension in liquid phase. The carbon particles were concentrated in foam layer at the top of the column using microbubble flotation. The concentration of carbon particles in the foam presented a maximal value when the concentration of surfactant in solution is 5 % of cmc. On the other hand, the concentration of the carbon particles in liquid phase decreased exponentially to 1/10 for 50 minutes. To design the microbubble flotation column, a theoretical model was proposed for the removal of suspended fine particles with microbubbles and remixing from foam layer, where two empirical parameters were decided for this system.
The presented microbubble flotation can be possible to remove carbon fine particles suspended in liquid with much less dilute surfactant.

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Recently, micro-bubbles are generated by some methods and used at various situations. However, physical characteristics for micro-bubbles are not understood very well. In this study, micro-bubbles generated by the pressurizing dissolution method are compared with those generated by the shear method, and the relation between some bubble size populations and their effects of oxygen supplying are discussed. We found that the bubbles generated by the pressurizing dissolution method, which are very small, have advantageous to the effect of oxygen supplying at the same air flow rate, but it is not so effective considering the flow rate through the interfacial area of bubbles. We also presented the relation between four parameters and the overall volumetric mass transfer coefficient.

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