Liquid-solid flotation principles

On this subject notice that, possibly combined with various heating methods, several physical effects may be considered which allow free flotation of solid and even liquid matter. Materials may be levitated for instance by a jet of gas, by intense sound waves or by beams of laser light. Conductors levitate in strong radiofrequency fields, charged particles in alternating electric fields, magnets above superconductors or vice versa. A review on levitation in physics with the description of several techniques and their principles and applications was made by Brandt (1989). 

Flotation. The use of ak or gas bubbles to separate mineral particles by preferential attachment and subsequent flotation has been a feature of the mineral processing industry for many decades, but the application of the principle to solid-liquid separations is of more recent origin. The techniques have similarities but differences. In mineral flotation it is more common to use chemicals to enhance the collection of the particles and the stability of the ffoth and to produce the bubbles by beating air into the suspension, but in solid liquid separation it is more usual to dissolve air into the liquid under pressure, allowing the gas to expand out of solution under the lower pressure of the separation chamber, producing bubbles for the preflocculated particles to collect on without the need for further chemical addition. 

Flotation is a technique to separate finely dispersed solid particles based on different surface wettabilities. The principle of flotation is illustrated in Figure 8.11. Air bubbles are blown through a slurry of solid particles dispersed in a liquid. In the case of an aqueous liquid, the more hydrophobic particles attach to the air bubbles that pass through the liquid and arrive in the froth, leaving the hydrophilic particles behind in the bulk liquid. 

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