Validity of critical coalescence concentration in dynamic conditions

• We posed that the concept of CCC is only valid in static conditions.
• We designed a setup to monitor the same batch of bubbles during formation and rising.
• The size distribution of bubbles was compared with the CCC results observed in flotation cell.
• In static conditions, the minimum bubble size is reached around the CCC.
• In dynamic condition, coalescence occurred above the CCC.

The aim of the study was to confirm that the concept of the critical coalescence concentration (Cho and Laskowski, 2002) is only applicable to static conditions.A new experimental setup was developed. The experimental idea was to sample the same batch of bubbles at their formation point and later, during the bubble rise in static and dynamic conditions. The difference in the measured bubble size in the two sampling areas gives indication on the effect of frothers on bubble coalescence and breakup that takes place after the bubble creation due to the dynamic conditions.Three commercial frothers, DF200, NF240 and DF250, were tested in the experiments.In static conditions, the size of the forming and rising bubbles became equal at the frother concentration equal to the critical coalescence concentration (CCC) observed previously in mechanical flotation cell. On the other hand, in dynamic conditions, the size of rising bubbles was significantly larger than the size of freshly formed bubbles not only below the CCC as expected based on the literature. This finding confirms the hypothesis that the CCC is only applicable in static conditions, or in conditions where hydrodynamic forces do not contribute to bubble coalescence or breakup. The results showed that the frothers have a major effect on bubble size already at the early stage of bubble formation.

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