Adhering bubble methods

Another widely used method is the measurement of contact angles from sessile drops or adhering bubbles. Because of its simplicity, various procedures have been developed, as we shall describe below. 

The separation of a mixture using flotation methods depends on differences in the surface properties of the materials involved. If the mixture is suspended in an aerated liquid, the gas bubbles will tend to adhere preferentially to one of the constituents-the one which is more difficult to wet by the liquid-and its effective density may be reduced to such an extent that it will rise to the surface. If a suitable frothing agent is added to the liquid, the particles are held in the surface by means of the froth until they can be discharged over a weir. Froth flotation is widely used in the metallurgical industries where, in general, the ore is difficult to wet and the residual earth is readily wetted. Both the theory and practical application of froth flotation are discussed by Clarke and Wilson 44. ... 

Mineral flotation is a method for selective separation of mineral components out of polymineral dispersions of ground ores in water (ca. 5-35 vol.% of the solid) by using dispersed gas (usually air) bubbles. The method consists in the different adhesion of hydrophobized and hydrophilic mineral particles to an air bubble. Hydrophobized mineral particles adhere to the air bubble and are carried out as a specifically lighter aggregate to the surface of the mineral dispersion where they form a foam (froth) layer. This foam, called concentrate, is mechanically removed (Fig. 1A). A mineral is hydrophobized by adsorption of a suitable surface-active compound (surfactant, collector) on the surface of the mineral component to be flotated. All other nonhydrophobized particles remain dispersed in the mixture (Fig. IB). 

There are static and dynamic methods. The static methods measure the tension of practically stationary surfaces which have been formed for an appreciable time, and depend on one of two principles. The most accurate depend on the pressure difference set up on the two sides of a curved surface possessing surface tension (Chap. I, 10), and are often only devices for the determination of hydrostatic pressure at a prescribed curvature of the liquid these include the capillary height method, with its numerous variants, the maximum bubble pressure method, the drop-weight method, and the method of sessile drops. The second principle, less accurate, but very often convenient because of its rapidity, is the formation of a film of the liquid and its extension by means of a support caused to adhere to the liquid temporarily methods in this class include the detachment of a ring or plate from the surface of any liquid, and the measurement of the tension of soap solutions by extending a film. 

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. 

The density of melts is usually measured by weighing a platinum body in air and in the melt. Gas bubbles adhering to the body are the main source of errors involved in the method. It is also possible to measure directly a volume of the melt (Volarovich and Leonteva, 1936) or with high-density glasses to weigh the melt in a platinum vessel in molten salts, e.g. NaCl (Hanlein, 1932). 

Since surface forces depend on the magnimde of the area, the drops tend to be as spherical as possible. Distortions due to gravitational forces depend on the volume of the drop. In principle, it is however possible to determine the surface tension by measurement of the shape of the drop, when gravitational and surface tension forces are comparable. Two principally different methods must be taken into account. There are methods based on the shape of a static drop lying on a solid surface or a bubble adhering underneath a solid plate, and dynamic methods, based on continuously forming and falling drops. It should be noted that all the principles described here for drops are valid also for bubbles. 

Basket USP 1 EP basket JP method 1 BP 1 Rotating stirrer Dosage form confined leads to consistent solid/liquid interface Floating products kept immersed Limited sink conditions Trapped bubbles in basket can slow dissolution rate Inadequate mixing at slow speed Floating dosage forms Dosage forms that tend to adhere to the vessel surfaces... 

By analyzing the tracks produced by individual particles in cloud chambers, stacks of photographic emulsions, and bubble chambers, and by other methods of detecting particles, the decay of individual particles has been studied, and it has been found that in every case there is conservation of mass-energy and conservation of momentum. Other conservation principles have also been found to be adhered to rigorously, as follows ... 

Flotation is a technical process in which suspended particles are clarified by allowing them to float to the surface of the liquid medium (Fuerstenau et al., 1985 Klimpel, 1995 Rao et al., 1995 Yoon et al., 1990). The material can thus be removed by skimming at the surface flotation is found to be a highly versatile method for physically separating particles based on differences in the ability of air bubbles to selectively adhere to specific mineral surfaces (as determined by surface forces). This is economically much cheaper than any other process. If the suspended particles are heavier than the liquid (such as minerals), then one uses gas (air or CO2 or other suitable gas) bubbles to enhance the flotation. 

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