Flotation method, solid foams

In the broad sense, adsorption is the selective accumulation of chemical species at all types of phase interfaces. However, only the adsorption of solutes from a fluid phase (gas or liquid) onto a fluid-solid interface will be dealt with here. Such separation methods as froth flotation (Dl) and foam fractionation (S3) will not be considered. 

Mineral flotation is a method for selective separation of mineral components out of polymineral dispersions of ground ores in water (ca. 5-35 vol.% of the solid) by using dispersed gas (usually air) bubbles. The method consists in the different adhesion of hydrophobized and hydrophilic mineral particles to an air bubble. Hydrophobized mineral particles adhere to the air bubble and are carried out as a specifically lighter aggregate to the surface of the mineral dispersion where they form a foam (froth) layer. This foam, called concentrate, is mechanically removed (Fig. 1A). A mineral is hydrophobized by adsorption of a suitable surface-active compound (surfactant, collector) on the surface of the mineral component to be flotated. All other nonhydrophobized particles remain dispersed in the mixture (Fig. IB). 

The ability of plastics to float on the surface of a beaker of tap water at 20°C is related to their density at that temperature. The density of water at 20°C is approximately 1 g cm-3. If a small sample floats on the surface of the water, it has a density lower or equal to one at the same temperature if it sinks, it has a density greater than one. Polyethylene, polypropylene and polystyrene float on water while other plastics sink, Bakelite and casein having the highest densities. The flotation test is a rough method to identify plastics since results are dependent on the physical form of the plastic. Foams contain cells filled with air, so their densities will be lower than a solid block of the same type of plastic. 

The flotation test is a rough method to identify plastics since results are dependent on the physical form of the material. Foams contain cells filled with air, so their densities will be lower than a solid block of identical dimensions of the same type of plastic. Water-sensitive or absorbent fillers such as paper... 

Therefore, the technological challenge is large, particularly in the case of particle mixtures with near similar physical properties such as size and size distribution, density and morphology. Then, differences in surface chemistry can be exploited to separate the particles,for instance via flotation [33],L-L interfacial partitioning [34-36], foam and gas aphrons (stabilised micro-bubbles) fractionation, and electrophoretic and electrostatic techniques. This whole field, despite its maturity in other industries such as metallurgy and solid waste fractionation, is totally imderdeveloped for fine-chemical and biotechnological production methods. 

Bubbles are formed in the sintered glass as air, or other suitable gas (Nj, CO2, etc.) is bubbled through the solution containing the solid suspension. A flotation agent (a suitable surface-active agent) is added and the air is bubbled. Surface-active pollutants in wastewater have been removed by bubble film separation methods. Especially very minute concentrations are easily removed by this method, which is more economical than more complicated methods (such as active eharcoal, filtration, and other chemical methods). This method is now commercially available for such small systems as fish tanks, etc. (Birdi, 2009, 2010a). The principle in this procedure is to create bubbles in wastewater tank and to collect the bubble foam at the top. Figure 1.56. 

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