Micelles flotation process

The examples in the preceding section, of the flotation of lead and copper ores by xanthates, was one in which chemical forces predominated in the adsorption of the collector. Flotation processes have been applied to a number of other minerals that are either ionic in type, such as potassium chloride, or are insoluble oxides such as quartz and iron oxide, or ink pigments [needed to be removed in waste paper processing [92]]. In the case of quartz, surfactants such as alkyl amines are used, and the situation is complicated by micelle formation (see next section), which can also occur in the adsorbed layer [93, 94]. 

A more plausible explanation for anionic surfactant adsorption on silica gel is found in the presence of about 0.2 wt.% alumina in the silica gel. The alumina pz-c is about pH=8.0, so it would be positively charged at the pH of the experiments. If the alumina is uniformly distributed through the silica, all of the adsorption could be accounted for provided a close-packed mono-layer of surfactant is formed on the alumina. This circumstance would also be consistent with the shape of the toe of the isotherm. Gaudin and Fuerstenau (25) advanced the idea of hemimicelle formation (two-dimensional micelles on a surface) to account for similar observations in flotation processes. 

Flotation processes are an important part of water treatment technologies in modern water treatment plants. Flotation is based on the principle of adhesion of insoluble particles to air bubbles and adsorption of dissolved surfactants at the surface of air bubbles. Flotation allows for different kinds of admixtures to be removed from water bulk in a physical and chemical manner. In this way, suspended and colloidal particles, emulsions of oils and fats, the separate surfactant molecules and their micelles, complexes of surfactants with colloid rust, and multivalent ions of heavy metals can be removed. At present, the flotation processes and equipment for their realization are widely described in the literature [12]. Flotation involves the injection of small bubbles of air or other gas into the water bulk. Surface-active impurities are adsorbed at the bubble surface and transferred through the water bulk to its surface. As a result, the foam concentrate is formed on the surface of bubbling water. It contains surfactants, suspended solid particles (water impurities), emulsified substances, bacterial cells, etc. This foam is evacuated from the surface by means of special scrapers and other devices. 

Surfactants find a variety uses in analytical processes. One is the formation of micelles (or microemulsions) which can provide protective environments for analytes or reagents which may enhance stability, or luminescence intensity, for example, or allow reagents to act in conditions not normally accessible to them. They also find application in sample pretreatment including flotation procedures, electro-analytical measurements (e.g. suppression of polaro-graphic maxima) and flow systems. 

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