Hydrodynamics of Flotation: Experimental Studies and Theoretical Analysis, 1997 Recycling Symposium Proceedings

Flotation deinking involves hydrodynamic interactions between ink particles and air bubbles during the subsequent steps of collision, attachment and removal of the particle-bubble aggregates. The mechanisms of ink aggregation onto the air bubbles are mainly driven by physico-chemical interactions, while collision and removal of the inked bubbles are driven by hydrodynamics.

The technological parameters relating to the aeration, mixing and separation steps were studied on a laboratory flotation cell designed to produce variable bubble sizes. Experimental evidence concerning the first-order kinetics of ink removal, with respect to flotation time and consumed air, was obtained for different particle and bubble sizes. Small bubbles were shown to be more effective, but led to higher fibre losses than large bubbles for a given ratio of consumed air.

These results were in agreement with more fundamental investigations on hydrodynamics of flotation, but could not be used to validate the theoretical relations since the different aeration conditions produced bubbles in a large size range which was dependent on the turbulence generated in the flotation cell.

The design of the experimental cell was then completely modified in such a way as to produce calibrated air bubbles of different sizes, and to investigate separately the effect of turbulence generated in the flotation cell. The results, obtained on different inks and specks showed that the relation between the flotation rate constant and bubble size depends on particle size and confirmed that large amounts of small air bubbles achieve the highest flotation efficiencies....