Bubble and Foam Separations - Waste Treatment

Departments of Chemistry and Environmental Engineering Vanderbilt University Nashville, Tennessee ANN N. CLARKE 

In today s world of waste treatment, bubble and foam separations lemain lelatively little used techniques. Dissolved or induced air flotation is the most commonly used variation, havii been enqiloyed for many years in the treatment of wastewaters for the separation of suspended sc, oils, greases, fibeis, and other iow-density solids as well as fbr the thickening of activated sludge and flocculated chemical sludges. The most active commercial use was and is in ore flotation—as discussed in Chapter 16. The potential Cor the use of these separation techniques, however, is veiy high in both the areas of traditional and hazardous waste management. 

This chapter provides an overview of the various bubble and foam separation techniques. The overview includes not only the results of laboratory and larger-scale studies but also the mathematical models that can be employed to optimize removal efficiencies and predict removal behavior. 

Ore flotation developed and grew in the three decades beginning in 1915. - Our areas of interest—ion, molecular, precipitate, and adsorbing colloid flotation—are relatively new subjects. While Adamson s original text on surface chemistry provided an excellent introduction to basic principles, Sebba s book in 1962 first discussed ion flotation and solvent sublation in detail. Biketman s book provides detailed information on foam characteristics. 

As will be seen in the later sections of this chapter, research in bubble and foam separations has continued to be performed throughout the world. Major centers of effort have developed in the United States, France, Israel, Italy, and Japan, as well as Poland and the Soviet Union. Indeed, a very large number of foam separation techniques have been developed in recent years. The most commonly employed nomenclature was recommended in 1967 by Karger et al. This discussion also uses that nomenclature. 

Tbe basis Tor (be separation by bubbles and foam (adsorptive bubble separalion) is the difference in the surface activities of the various materials present in the solution or the suspension of interest. The material mey be cellular or colloidal substances, crystals, minerals, ionic or molecular compounds, precipitates, proteins, or bactemi, but in any case it must be surface active at the air-liquid interface (Fig. 17.1-1) These surface-active meterials tend to attach preferentially to (he air-liquid interfaces of the bubbles or fonme, As the bobbies or fonms rise throngh the columa or pool oftiquid, the attached material is removed. When this combination reachas the surface, the meierial can be removed in the relatively smell volume or collapsed foam or surface scum.  

When it is aseessary to remove a substance that is ant surface active, it can be adsorbed onto a surface-active collector. This combination wben correctly selected is surface active at the air-liquid interface and can be removed as described above. The substance of interest which is removed is called the colii-gend.  

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