Flotation refers to an operation in which one solid is separated from another by floating one of them at or on the liquid surface. In the fourth flotation, the separation of a solid feed mixture depends upon the differences in surface properties of the materials involved.
This method is commonly used in mineral dressing. Mineral dressing refers to the method of treating ores at or near the mine site to produce one or more concentrates of valuable minerals and tailings composed of waste or less valuable minerals.
Froth flotation is used for treating the metallic ores that are finer than 48 - 65 mesh, or coal and certain nonmetallic that are finer than 10-48 mesh. It is not possible to treat a material feed by froth floatation as the same cannot be suitably mixed and suspended by a floating device. Â
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Operation PrincipleÂ
Separation of a mixture of solids using froth flotation techniques depends on the differential in surface properties of the materials involved. If the mixture is suspended in an aerated liquid, the gas bubbles will tend to adhere preferentially to the constituent which is more difficult to wet by the liquid (hydrophilic) and so its effective density will be reduced to such an extent that it will rise to the surface and the material which has an affinity for the liquid gets surrounded by the liquid and it will simply sink, thus achieving a separation.Â
Frothing agents inducing the formation of froth of sufficient stability are added to suspend or retain the particles in the froth on the surface before they are discharged.
Frothing agent in froth flotation separation
Frothing agents work with different types of promotors, collectors, and modifiers.
Almost all the minerals and inorganic solids are hydrophilic, as the surface of these solids gets easily wetted by water. Hydrophilic solids are un-floatable as air bubbles do not surround and cover them from a particle bubble aggregate. However, these solids can be made water-repellent with the help of reagents known as collectors or promotors. The collectors and promotors are the materials that selectively render the desired particles air avoid and water-repellent.
Promotors
Promotors are materials that are adsorbed on the surface of the particles forming an unimolecular layer. A commonly used promotor is sodium ethyl xanthate.
Collectors
Collectors are materials from surface films on the particles. A commonly used collector is pine oil.
Frothing agentsÂ
Frothing agents are materials that induce the formation of a froth of sufficient stability to retain the particles of the constituent which is to be floated to be discharged as an overflow. Commonly used frothers are liquid soaps, pine oil, acrylic acid, methyl amyl alcohol, and methylisobutylcarbinol.
 The valuable concentrates from froth flotation may be either the froth product which is collected and removed from the top or the underflow product. In the case of metallic sulfide ores of copper, zinc, nickel, lead, and native gold and silver, the valuable product collects in the froth and removed is from the top. In glass sand flotation, iron-bearing minerals collect in the froth while valuable product is removed as underflow products.
Flotation Cell Working Principle and Construction
Construction: The material the flotation cell is made from is also important. Some materials are better at resisting corrosion than others, so you’ll want to choose a material.
The agitated cell consists of a tank having a square or circular cross-section. It is provided with an agitator which violently agitates the pulp. The air from a compressor blower is introduced into the system through a downpipe surrounding the impeller shaft. The bottom of the tank is conical and is provided with a discharge for tailings. An overflow is provided at the top for mineralized froth removal.
Working Principle of Floating CellÂ
Water is taken into the cell, and material is fed to the cell. The promotors and frothers are added. Agitations are given and the air is bubbled in the form of fine bubbles. Air avid particles due to the reduction in their effective density, will rise to the surface and be held in the froth before they are discharged from the overflow. Hydrophilic particles will sink to the bottom and be removed from the discharge for tailings.
Also Read: Size ReductionÂ
Take these Notes is, Orginal Sources:Â Unit Operations-II, KA Gavhane