Surfactant adsorption froth flotation process

This type of adsorption is the basis for a number of important industrial processes, notably the separation of mineral ores by froth flotations (Somasun-daran, 1979), the de-inking of waste paper (Turai, 1982), the ultrapurification of fine powders for the chemical and ceramic industries (Mougdil, 1991), and the production of foamed concrete. In the last case, for the concrete to entrain air, it is not even necessary for the liquid phase to show any foaming. In most of the processes used above, surfactants, such as salts of long-chain carboxylic acids or long-chain amines, that adsorb with their polar or ionic heads oriented toward the solid and their hydrophobic groups oriented away from it, are used to make the surface of the solid hydrophobic. 

The process of froth flotation for the separation of minerals exploits the fact that either minerals differ naturally in their degree of wettability by surfactant solutions or their surface properties can be modified by adsorption. When air is blown through a suspension of finely ground ore in an appropriate surfactant solution, those particles which have the relevant surface properties become... 

This is very similar to the flotation procedure described under basic physical treatments. In the case of foam fractionation, not only are the pollutants raised to the surface where they can be skimmed off, but a froth, like beer foam, is produced in which the pollutants become concentrated. The key to the process is the adsorption of the pollutants onto the surface-active agents that cause the froth to form. Sometimes a surfactant is added so that non-surface-active components can be removed. 

In addition to inducing froth stability, frother specfes can take part in the overall process of adsorption on the mineral surface. Like the collector species, the ftother species also can be expected to migrate to the particle-gas interface during the time of contact and assist in establishing the attachment of the bubble to the particle. Coadsotption of ftother along with the collector species can be favorable for flotation, possibly because the neutral molecules adsorbed between charged collector ions can reduce the repulsion between the latter species and thereby enhance the overall surfactant adsoiption. 

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