Flotation describes the is the buoyancy of particulate matter. Both, specific lighter substances than water and specific heavy substances can be separated from the water. With the latter substances, gas bubbles are deposited on these substances, causing them to float. As with sedimentation, Stoke’s law applies, except, the settling speed is negative.
The smaller the gas bubbles are (50 - 80μm, pressure release floatation) and the more hydrophobic the surface of the particles is, the better the attachment of the gas bubbles. Microthrix parvicella (filamentous bacterium) is hydrophobic and could be washed out by flotation.
Frequently, substances are added to enhance the flotation effect, so-called collectors. The water-facing parts of the molecule then become hydrophobic.


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