Adsorptive bubble separation methods adsorption

Robert Lemlich/ Ph.D./ P.E./ Profe.s.sor of Chemical Engineering Emeritus, University of Cincinnati Fellow, American In stitute of Chemical Engineers Member, American Chemical Society, American Society for Engineering Education Fellow, American As.sociation for the Advancement of Science. (Adsorptive-Bubble Separation Methods)... 

Principle The adsorptive-bubble separation methods, or adsub-ble methods for short [Lemlich, Chem. Eng. 73(21), 7 (1966)], are based on the selective adsorption or attachment of material on the surfaces of gas bubbles passing through a solution or suspension. In most of the methods, the bubbles rise to form a foam or froth which carries the material off overhead. Thus the material (desirable or undesirable) is removed from the liquid, and not vice versa as in, say, filtration. Accordingly, the foaming methods appear to be particularly (although not exclusively) suited to the remov of small amounts of material from large volumes of hquid. 

The droplet analogs to the adsubble methods have been termed the adsoplet methods (from adsorptive droplet separation methods) [LeiTilich, Adsorptive Bubble Separation Methods, Ind. E/ig. Chem., 60(10), 16 (1968)]. They are omitted from Fig. 22-41, since they involve adsorption or attachment at liquid-liquid interfaces. Among them are emulsion fractionation [Eldib, Foam and Emulsion Fractionation, in Kobe and McKetta (eds.). Advances in Petroleum Chemistry and Refining, vol. 7, Interscience, New York, 1963, p. 66], which is the analog of foam fractionation and droplet fractionation [Lemlich, loc. cit. and Strain, J. Phys. Chem., 57, 638... 

A few simple differences in the properties of immiscible phases make possible their relative displacement. Most simply, if the phases have different densities they will automatically acquire a relative motion in a gravitational field. Thus in adsorptive bubble separation methods, bubbles injected into a column of liquid rise toward the upper surface. Separation occurs by combining the relative enrichment of components at the bubble interface with the continuous displacement of bubbles through the liquid [33-35]. 

Of the five types of interfaces mentioned above, adsorption at gas-liquid (e.g., air-water) interfaces is of interest in all adsorptive bubble separation methods. In the liquid pool, a molecule is acted upon by molecular attractions, which are distributed more or less symmetrically about the molecule. However, at the air-water interface, a water molecule is only partially surrounded by other like molecules as a consequence, an attraction tends to draw the surface molecules inward, and in doing so makes the water behave as if it were surrounded by an invisible membrane. This behavior of the surface is called surface tension. Surface-active substances possess the ability to lower the surface tension of water even at low concentrations. 

B. Karger, 11, R. B. Grieves, R. LemUch, A. J. Rubin, and F. Sebba, Nomenclature recommendations for adsorptive bubble separation methods. Separation Science 2, 401 (1967). M. H. S. Wang, Separation of Lignin from Aqueous Solution by Adsorptive Bubble Separation Processes, Ph.D. Thesis, Rutgers University, New Brunswick, NJ, 1972. 

The contributions of Dr. Joseph D. Henry (Alternative Solid/Liquid Separations), Dr William Eykamp (Membrane Separation Processes), Dr. T. Alan Hatton (Selection of Biochemical Separation Processes), Dr. Robert Lemlich (Adsorptive-Bubble Separation Methods), Dr. Charles G. Moyers (Crystallization from the Melt), and Dr. Michael P. Thien (Selection of Biochemical Separation Processes), who were authors for the seventh edition, are acknowledged. 

In adsorptive bubble separation methods, surface active material collects at solution interfaces and, thus, a concentration gradient between a solute in the bulk and in the surface layer is established. If the (very thin) surface layer can be collected, partial solute removal from the solution will have been achieved. The major application of this phenomenon is in ore flotation processes where solid particles migrate to and attach themselves to rising gas bubbles and literally float out of the solution. This is essentially a three-phase system. 

Foam fractionation (6), a two-phase adsorptive bubble separation method, is a process where natural or chelate-induced surface activity causes a solute to migrate to rising bubbles and thus be removed as a foam. Two government-... 

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