Use of millimeter bubbles

It is easy to obtain millimeter bubbles, and the equipment to generate bubbles of this size already exists. 

There is the possibility of non-reagent flotation. Because of non-retardation of surfaces and a high velocity of bubble rising, the normal component of the hydrodynamic field of bubbles is sufficiently large to provide hydrodynamic pressing forces to ensure the electrostatic barrier is overcome (cf Fig. 10.8). 

The disadvantages is caused by the possibility of detached particles being deposited at the leading bubble surface and displaced along the bubble surface to the zone where the normal velocity component is directed from the bubble surface, and a detachment becomes possible. 

Appendix lOG Flotation with Bubbles between Millimeter and Centimicron 

The possibility of detachment of particles is critical when millimeter bubbles are used. If this cannot be prevented, centimicron particles should obviously be used. Millimeter bubbles can be combined with reagents whose adsorption on the particles surface prevents their detachment. 

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The use of millimeter bubbles is attractive because they are produced by existing technologies and because electrostatic repulsion can be overcome by hydrodynamic pressing forces. The latter advantage get lost if surfactant has to be added to modify the surface of the particle to prevent its detachment. 

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