Floating particles

Similarly, small (0.2—0.6 mm) air bubbles are introduced into a 2.6-m Deister Flotaire column at an intermediate level allowing rapid flotation of readily floatable material in the upper recovery zone. The bottom air permits longer retention time of the harder-to-float particles in the presence of micrometer-sized bubbles at a reduced downward velocity. The first commercial unit went on stream in 1986. It was used to improve the recovery of <0.6 mm (—28 mesh) coal in the plant s tailings. An average of 5.5% increase in coal recovery resulted from its use (14). The second commercial use processed <0.15 mm (—100 mesh) coal feed. 

The first study utilizing this method was reported by Schuller in 1966 [65]. Schuller used polystyrene latex beads that were spread on a salt-containing aqueous subphase in order to keep the particles at the interface. tt-A plots of the floating particles were determined, which showed several phase regions with reproducible transition points. The author determined the particle diameters from the A-value, at which a steep rise in the isotherm occurred. Moreover, Schuller also spread millimeter-sized Styropor particles and found isotherms of similar shape [66]. By taking pictures at different surface pressure, he was able to correlate the shape with different states of order in the monolayer. Shortly after that. 

At the lowest measurable compression (point Q) the molecular area is 21 8 A. and the film is perfectly mobile, allowing floating particles of dust to move about freely. As compression is applied... 

In contrast, most of the conventional foam separation techniques use large bubbles, requiring relatively high gas flow rates to generate sufficient interfacial area for adhesion of solid particles to bubbles. This causes turbulence at the foam/liquid boundary and, in order to prevent redispersion of floated particles, a rather tall foam column is required (ref. 36). 

A metallic bond occurs when a pool of electrons forms a bond with the atoms of a metal. The atoms that make up a piece of metal are cations rather than neutral atoms. The valence electrons of metals surround the cations. Valence electrons in a metal are freely floating particles, sometimes called a sea of electrons, that move around the cations. The valence electrons are attracted to the cations, forming metallic bonds. Metallic bonds hold particles of metals together. 

Figure 7.1 In a plasma, electrons are stripped away from atoms and become free-floating particles.

As discussed in Section 1.2.2 the bubble shapes in fairly dry foams and froths (4 gas > 0.83, approximately) are not spheres or distorted spheres, but polyhedrons. In practice there will be distributions of both gas-cell sizes and shapes. In addition to the gas bubbles, froth contains the floated particles, pulp liquor, and a fraction of (hydrophilic) particles that did not float due to bubble attachment, but which were mechanically entrained in the froth. The pulp liquor and these latter particles all have to be allowed to drain back out of the froth. The rate of this drainage will be greatest at the froth-pulp interface (i.e., the bottom of the froth layer) and slowest near the top of the froth layer. Froth drainage equations are discussed elsewhere [53]. The froth needs to be a stable enough foam that some time can be allowed for these drainage processes, and also so that the upper layer(s) of the froth can be swept out of the flotation cell. On the other hand, the froth should not be too stable as a foam so that it will break easily after collection. In addition to the role of the frother, froth stability is also promoted by increasing liquid viscosity. 

The floated particles are ultimately separated from the fibres by rising to form a froth that can be skimmed off. Either the flotation surfactants, or others added during the processing, are also needed to help prevent redeposition on the fibres later [779]. A number of reviews are available on flotation de-inking [53,551,767,779] and on the kinds of flotation cells used [53,551,767]. 

Allow large particles to settle to the bottom of the bottle. Pipette off any froth and floating particles. 

If a precipitate or a crystalline meal has formed it must be drained in a filter funnel. First pour off the liquid (see Note 2) — through the filter if necessary, so as to save any floating particles of the solid — then pour the main part of the damp solid into the filter. A considerable part, of the solid will adhere to the dish ... 

Fig. 14. S-FFF apparatus designed by Giddings group (A) the separation principle with smaller particles (X), bigger particles (7) and floating particles (Z) with a density smaller than that of the solute [These particles are equally well separated as retention depends on Ap I (B)]. C Fractogram of a separation of polystyrene latexes of different sizes at two different rotational speeds. The ability to shift retention by changing the rotational speed is demonstrated. D The same mixture analyzed by a programmed field run demonstrating that a wider particle size range can be condensed into a reasonable elution span. Reproduced from [14] with kind permission of the American Association for the Advancement of Science...

FIGURE 5.17 Flotation (a, c, e) and immersion (b, d, f) lateral capillary forces between two particles attached to fluid interface (a) and (b) are two similar particles (c) is a light and a heavy particle (d) is a hydrophibc and a hydrophobic particle (e) is small floating particles that do not deform the interface (f) is small particles captured in a thin liquid film deforming the interfaces due to the wetting effects. 

To distinguish between the capillary forces in the case of floating particles and in the case of partially immersed particles on a substrate, the former are called lateral flotation forces and the latter, lateral immersion forces. - " These two kinds of force exhibit similar dependence on the interparticle separation but very different dependencies on the particle radius and the surface tension of the liquid (see References 35 and 212 for comprehensive reviews). The flotation and immersion forces can be both attractive (Figures 5.17a and b) and repulsive (Figures 5.17c and d). This is... 

As already mentioned, the weight of micrometer-sized and sub-micrometer floating particles is not sufficient to deform the fluid interface and to bring about capillary force between the particles... 

The overlap of the meniscus around a floating particle with the meniscus on a vertical wall gives rise to a particle-wall interaction, which can be both repulsive and attractive. An example for a... 

FIGURE 5.21 Experimental setup for studying the capillary interaction between a floating particle (1) and a vertical hydrophobic plate (2) separated at a distance, x. The edge of the plate is at a distance, H, lower than the level of the horizontal liquid surface far from the plate (3) and (4) are micrometric table and screw (see References 249 and 250 for details). 

Granulometric analysis of fractions 1, 2, 3 (Fig. 6) clearly shows that particles are mainly supracolloids, between 1 to 100 xm, with a mode value close to 30 xm. The fraction 4 (at the bottom of the Imhoff cone) presents the widest range size with particle larger than 100 im, and a multi-modal distribution. After 1 h of settling, the separation of settleable matter is achieved, as fractions 1 to 3 do not contain particles of size above 100 xm, even if, in the first fraction, some millimetric floating particles are present. One can note that no colloidal population is detected by laser granulometry. 

Place the flask in the microwave. Heat on high until the solution is completely clear and no small floating particles are visible (about 2min). Swirl the flask frequently to mix the solution and prevent the agarose from burning (see Fig. 5A). 

Fill a saucer, or broad basin, with water, and let fall upon it camphor reduced to the fineness of coarse sand. The floating particles of camphor will instantly begin to move, and acquire a progressive rotatory motion, which continues for some minutes and finally subsides. 

The tableting Section shall be free from dust and floating particles. For this purpose it is desirable that each tablet machine is connected to an exhaust system and isolated into cubicles. 

In case of operation involving floating particles of fine powder, a suitable, exhaust system shall be provided. Workers should be provided with suitable masks during operation. 

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