Foams froth flotation processes

Type of flow pattern(s) involved in an adsorptive bubble separation system depends on the type of process used. For example, bubble fractionation involves two-phase (gas-phase and liquid-phase) bubble flow, while solvent sublation involves multiphase bubble flow in their vertical bubble cells. Foam fractionation involves a two-phase bubble flow in the bottom bubble cell, and a two-phase froth flow in the top foam cell. However, all froth flotation processes (i.e., precipitate flotation, ion flotation, molecular flotation, ore flotation, microflotation, adsorption flotation, macroflotation, and adsorbing colloid flotation) involve multiphase bubble flow and multiphase froth flow. 

Undesirable foams Producing oil well and well-head foams Oil flotation process froth Distillation and fractionation tower foams Fuel oil and jet fuel tank (truck) foams... 

In industry, froth flotation processes are used to separate particles and/or droplets gas by attaching them to gas bubbles, which rise in a flotation vessel to form a product layer of foam teimed froth. The most common type of froth flotation is induced gas flotation (also termed scavenging flotation), in which gas bubbles are injected (sparged) into the flotation medium. Variations include dissolved gas flotation, in which gas is dissolved in water after which microbubbles come out of solution, attach to the dispersed species of interest and cause them to float (see also Section 8.3 and Chapter 10). 

In the froth flotation process, air is bubbled through a water suspension containing the crushed minerals to form a foam or froth. The wetted particles (those that are hydrophilic) remain in the water suspension, whereas hydrophobic particles collect at the air bubble/water interface and can be removed from the liquid. Various agents, such as amino acids (having a high molecular weight), can be used to enhance the relative wettability of the solids in a... 

Foam Production This is important in froth-flotation separations in the manufac ture of cellular elastomers, plastics, and glass and in certain special apphcations (e.g., food products, fire extinguishers). Unwanted foam can occur in process columns, in agitated vessels, and in reactors in which a gaseous product is formed it must be avoided, destroyed, or controlled. Berkman and Egloff (Emulsions and Foams, Reinhold, New York, 1941, pp. 112-152) have mentioned that foam is produced only in systems possessing the proper combination of interfacial tension, viscosity, volatihty, and concentration of solute or suspended solids. From the standpoint of gas comminution, foam production requires the creation of small biibbles in a hquid capable of sustaining foam. 

The first application which comes into mind when thinking about liquid foams is in cleaning processes, such a shampoo or shaving foams. More important, however, are liquid foams in mineral froth flotation and, a closely related process, the de-inking of recycled paper. Other uses include fire fighting. In food we often find foams such as whipped cream or egg whites. 

For example, in mineral flotation, surfactant can be added to adsorb on metal ore particles, increasing the contact angle, so they attach to gas bubbles, but the surfactant does not adsorb much on silicates, so these do not attach to gas bubbles. The surfactant may also stabilize a foam containing the desired particles facilitating their recovery as a particle-rich froth that can be skimmed. Flotation processes thus involve careful modification of surface tension and wettability. 

Foams and emulsions may also be encountered simultaneously [114]. Figure 1.5 shows an example of an aqueous foam with oil droplets residing in its Plateau borders (see Section 5.6.7). In addition to containing gas, an aqueous phase, and an oleic phase, foams can also contain dispersed solid particles. Oil-assisted flotation of mineral particles provides one example (Chapter 10). Oil-sand flotation of bitumen provides another (Chapter 11). In the case of oil-sands flotation, an emulsion of oil dispersed in water is created and then further separated by a flotation process, the products of which are bituminous froths that may be either air (and water) dispersed in oil (from primary flotation) or air (and oil) dispersed in water (from secondary flotation). In either case, the froths must be broken and de-aerated before the bitumen can be upgraded to synthetic crude oil. (See Section 11.3.2). 

Suspensions are created at an early stage of processes used to separate valuable minerals or oil by froth flotation (Chapter 10). Suspensions are also quite important and widespread in the petroleum industry (Chapter 11) and, like emulsions and foams, suspensions may be encountered throughout each of the stages of petroleum recovery and processing (in reservoirs, drilling fluids, production fluids, process-... 

Froth flotation is an application of foams that is used to separate mineral components from each other based on their having different surface properties, typically their wettability and surface electrical charge. For example, froth flotation is the classic process used to separate copper from lead ore. The process involves having hydrophobic particles attach to gas bubbles which rise through a turbulent suspension to create a surface foam called a froth. Figure 10.2 shows an illustration of a mechanical flotation cell. This is the classic flotation device [53,91,625], First, the flotation feed particles are well dispersed into a particle suspension. Together with chemical flotation aids, such as collectors and frothers, this constitutes what is called the flotation pulp. In a mechanical flotation cell, air is fed in the form of fine bubbles and introduced near the impeller (see Figure 10.2). In addition to mechanical flotation cells, there are also pneumatic cells and cyclone flotation cells. Pneumatic... 

Shaw, R.C. Czarnecki, J. Schramm, L.L. Axelson, D. Bituminous Froths in the Hot-Water Flotation Process in Foams Fundamentals and Applications in the Petroleum Industry, Schramm, L.L., Ed., American Chemical Society Washington, 1994 pp. 423-459. 

Foams are dispersions of gas in a relatively small amount of liquid. When they are still on the surface of the which they were formed, they also are called froths. Bubbles range in size from about 50 fim to several mm. The data of Table 20.1 show densities of water/air foams to range from 0.8 to 24g/L. Some dissolved or finely divided substances may concentrate on the bubble surfaces. Beer froth, for instance, has been found to contain 73% protein and 10% water. Surface active substances attach themselves to dissolved materials and accumulate in the bubbles whose formation they facilitate and stabilize. Foam separation is most effective for removal of small contents of dissolved impurities. In the treatment of waste waters for instance, impurities may be reduced from a content measured in parts per million to one measured in parts per billion. High contents of suspended solids or liquids are removed selectively from suspension by a process of froth flotation. 

Flotation is the term used to describe a process in which the species being separated from the bulk liquid media are insoluble particulates. Froth flotation is another one of the two foam separation processes. It also involves the production of foam in a heterogeneous aqueous system, and has a great deal of potential for the water and wastewater treatment. Froth flotation can be subdivided into at least seven categories (42,43,84), including precipitate flotation, ion flotation, molecular flotation, microflotafion, adsorption flotation, ore flotation, macroflotation, and adsorbing colloid flotation. They are described separately below. 

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. 

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