Foam flotation

Prior to about 1920, flotation procedures were rather crude and rested primarily on the observation that copper and lead-zinc ore pulps (crushed ore mixed with water) could be benefacted (improved in mineral content) by treatment with large amounts of fatty and oily materials. The mineral particles collected in the oily layer and thus could be separated from the gangue and the water. Since then, oil flotation has been largely replaced by froth or foam flotation. Here, only minor amounts of oil or surfactant are used and a froth is formed by agitating or bubbling air through the suspension. The oily froth or foam is concentrated in mineral particles and can be skimmed off as shown schematically in Fig. XIII-4. 

A. N. Clark and D. J. Wilson, Foam Flotation Theory and Applications, Marcel Dekker,... 

D. J. Wilson and A. N. Clarke, Topics in Foam Flotation, Marcel Dekker, Inc., New York, 1983. 

Among the existing separation techniques, some - due to their intrinsic characteristics - are more adapted than others to processing large amounts of material. Such processes, which already exist at industrial level, can be considered in order to perform an enantioselective separation. This is the case for techniques such as distillation and foam flotation, both of which constitute well-known techniques that can be adapted to the separation of enantiomers. The involvement of a chiral selector can be the clue which changes a nonstereoselective process into an enantioselective one. Clearly, this selector must be adapted to the characteristics and limitations of the process itself. 

Separation Techniques, Academic, New York, 1972 Lemhch, Adsub-ble Methods, in li (ed.). Recent Developments in Separation Science, vol. 1, CRC Press, Cleveland, 1972, chap. 5 Grieves, Chem. Eng. J., 9, 93 (1975) Valdes-Krieg King, and Sephton, Sep. Purif Methods, 6,221 (1977) Clarke and Wilson, Foam Flotation, Marcel Deldcer, New York, 1983 and Wilson and Clarke, Bubble and Foam Separations in Waste Treatment, in Rousseau (ed.). Handbook of Separation Processes, Wiley, New York, 1987. 

There are numerous surfactant applications. Cahn and Lynn [206] list about 50 types. Most of these applications can be classified in terms of surfactant action to promote emulsification, foaming, flotation, suspension, detergency or wetting. 

Finally, unit operations (gas absorption, distillation) may cause foaming or are even based on foaming (flotation, foam fractionation). 

The parameter Cm can provide important data to be used in estimating the antifoam efficiency, in determining the minimum (threshold) surfactant concentration in the purification of solutions by foam flotation [53], in analysing the causes of foam formation in extraction systems and in establishing the optimum conditions of effective extraction [68]. 

Foam films are usually used as a model in the study of various physicochemical processes, such as thinning, expansion and contraction of films, formation of black spots, film rupture, molecular interactions in films. Thus, it is possible to model not only the properties of a foam but also the processes undergoing in it. These studies allow to clarify the mechanism of these processes and to derive quantitative dependences for foams, O/W type emulsions and foamed emulsions, which in fact are closely related by properties to foams. Furthermore, a number of theoretical and practical problems of colloid chemistry, molecular physics, biophysics and biochemistry can also be solved. Several physico-technical parameters, such as pressure drop, volumetric flow rate (foam rotameter) and rate of gas diffusion through the film, are based on the measurement of some of the foam film parameters. For instance, Dewar [1] has used foam films in acoustic measurements. The study of the shape and tension of foam bubble films, in particular of bubbles floating at a liquid surface, provides information that is used in designing pneumatic constructions [2], Given bellow are the most important foam properties that determine their practical application. The processes of foam flotation of suspensions, ion flotation, foam accumulation and foam separation of soluble surfactants as well as the treatment of waste waters polluted by various substances (soluble and insoluble), are based on the difference in the compositions of the initial foaming solution and the liquid phase in the foam. Due ro this difference it is possible to accelerate some reactions (foam catalysis) and to shift the chemical equilibrium of some reactions in the foam. The low heat... 

It has been suggested the methods of separation involving adherence of particles of different dispersity on bubble surface as a result of adsorption or adhesion, to be named adsorptive-bubble (adsubble) methods [27,28]. The methods of surface separation are termed differently in the different publications in the case of surfactant extraction they are referred to as adsorption flotation, foam flotation, foam fractionation, foam separation or adsorptive accumulation in the case of ion extraction, they are called ion flotation, foam flotation of hydrophobic precipitates, etc. 

All these methods have many features in common but at the same time they bear noticeable differences. For example, in foam flotation of macroscopic particles (suspensions),... 

The MoS2 in ores is concentrated by the foam flotation process the concentrate is then converted by roasting into Mo03 which, after purification, is reduced with hydrogen to the metal. Reduction with carbon must be avoided because this yields carbides rather than the metal. 

In the context of a study of foam flotation of powdered activated carbon (PAC), Zouboulis et al. [143] noted large and different pH effects when an anionic surfactant was used instead of a cationic one. For the cationic surfactant, best recovery (at low surfactant concentration) was achieved at the highest pH, in agreement with electrostatic arguments (see Section IV.B.l) for the anionic surfactant, an intermediate pH was the best. The authors also measured the zeta potential of the carbon in the presence and absence of the surfactants and concluded that the specific chemical nature and the dissociation of each surfactant. 

The dependence of the values for surface concentrations of DBS in the presence > " in the absence ( dbS Cu(OH)2, on the initial DBS concentrations is depicted in Fig. 3. The figure actually shows the DBS separation in precipitate flotation in the presence of Cu(OH)2, as well as its recovery in the foam flotation. Surface concentrations of DBS obtained in the DAF system in the presence of Cu(0H)9 are about 10—30 times higher if compared to the DIS system. This is again the consequence of a smaller amount of air involved in the DAF system, which causes the total bubble surface to be lower. It is evident that the Tjjgg values in both systems are about 2—10 times lower from same time the recoveries of pure DBS are lower and... 

D.J. Wilson, E. L. Thackston, Foam flotation treatment of industrial wastewaters Laboratory and pilot scale, EPA-600/2-80-138, June 1980. 

As mentioned in Chap. 7, molecular imprinting of polymers15 can also be used to prepare hosts for the removal of the desired optical isomer from racemates. Foam flotation with imprinted polymers has been used in chiral separations.16 Flotation is often used to separate minerals from their ores. The polymers can be reused repeatedly. This may turn out to be the lowest-cost method of resolution. 

The above flotation when conducted for microscopic size species that are naturally surface ective is called foam flotation. It has been used undar laboratory condilioex for the removal of microorganisms, dyes, and so on. 

Separation by foam flotation techniques can be performed in several different modes of operation. These are summarized in Table 17.1-2, Lem itch s book,9 Adsorptive Bubble Separation Techniques, provides a discussion of the ndvantages and disadvantages of these varicos inodes of operation. 

Similarly, another practical problem in the commercial use oF foam flotation Ireaimenr is the recovery and reuse of the surfactant. The concept of competitive ndsorption also affords hope in this aree one displaces the surfactant from the sludge in the collapsed fosmale by addition of a competing ion such as OH" or COj" so that the surfactant conld be recovered from the sludge and recycled. 

Otber areas related to energy can use foam flotation techniques. For example, this technology provides a means of separating (he oils in sand tats and on water resulting from spills. A mobile unit was tested for held applicability of this idea by the U.S. EPA 7 The unit wonld arrive at the spill and clean up oil-conlaminated beeches, then relocate as necessary. 

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