Bubble-particle aggregate

Fig. 16.2-1, in the presence of air that is sucked or fed into the impeller zone where the air is well dispersed owing to the intense agitation in that zone. The air bubbles collide with pardcles and are attached to those that are hydrophobic or heve acquired hydrophobicity. The bubble-particle aggregates hue to the rop of the cell and are removed by skimming. Various types of machine that ase used by the industry have been described in detail by Harris in a recent publication on flotation.1... 

The traditional treatment of flotation in which the emphasis is on the formation of the bubble-particle aggregate and on the physical chemistry of flotation reagents is insufficient for solution of a number of technological problems of flotation, in particular of flotation technology of small particles (less than 20-40pm in size). As applied to water purification, the behaviour of such small particles is of interest in the elementary flotation act. Since flotation of small particles by small bubbles is a qualitatively new process, it is quite natural to use a special term microflotation (Clarke Wilson 1983). 

As the size of particles and bubbles decreases, the inertia forces affecting the process of their approach to each other, the formation of a bubble-particle aggregate, and the destruction of this aggregate decrease drastically. As the inertia forces decrease, the influence of viscous forces on... 

Both possibilities have been taken into account in the theory of flotation of weakly stable dispersions of spherical particles with a smooth surface. The sign of Hamaker s constant is important here. The bubble-particle aggregate is not formed in the absence of attraction forces or at h = 0. 

The clarification of reasons for the slow flotation of large particles is very important for the improvement of technology. A priori three factors decrease the flotation rate of bigger particles. The first is connected with the BCS stage, the second with the ACS stage, and the third with the stability of the bubble/particle aggregate. The effect of the first factor is illustrated by the lower curve in Fig 11.9. Beyond a particle size of 40 - 50pm the collision... 

The application of cationic surfactants was proposed initially by Deqaguin Dukhin (1961) in order to decrease the electrostatic barrier which prevents particle from approaching the bubble surface. This barrier is not important in flotation of normal size particles because they overcome the barrier due to gravity. However, the application of cationic surfactants is recommended in flotation of normal size particles, because it increases the stability of the bubble-particle aggregate by the increase the IT, - % -value. 

Thus, the mechanism of the supporting influence of cationic surfactants on microflotation and flotation can be different. In microflotation the electrostatic barrier can be decreased, in flotation the contact angle can be increased. Naturally, both effects manifest themselves simultaneously. Li Somasundaran (1990, 1992) observed a bubble recharge due to adsorption of multivalent inorganic cations. Thus, their application is recommended in order to increase the contact angle and to stabilise bubble-particle aggregates. Naturally, selective adsorption of multivalent ions at the water-air interface is important. But even in the absence of adsorption selectivity under equilibrium conditions a deviation from equilibrium can happen due to the increase of adsorption within the r.s.c. This is important for the precalculation of increase of the contact angle caused by cation adsorption. 

The main characteristic of the stability of bubble-particle aggregates is the contact angle v /. The equation... 

Flotation. After screening, washing, and dilution (flooding), the suspension pumped to primary flotation vessels comprises bitumen droplets, aerated bitumen globules, dispersed coarse and fine solids, and probably bubble-particle aggregates. This suspension is fed into a point somewhat higher than the center of the vessel as shown, for a continuous extraction circuit vessel, in Figure 21. The aim of the process here is to selectively separate the dispersed aerated bitumen droplets... 

Gas-bubble/mineral-particle attachment also occurs for the fraction of mineral particles that are not hydrophilic, so that some bubble-particle aggregates also form, float upwards, and become incorporated in the froth. An important goal of the flotation process is to produce bituminous froth without entraining large amounts of solids. Since the entrained... 

The flotability of particles, i.e., the formation of bubble particle aggregates and the enrichment of these aggregates in the foam layer, is given by a complex relationship of interfacial properties, particle size and hydrodynamic conditions [11]. The two parameters, surface properties and particle size, can be controlled with the aid of surface-active chemicals, such as surfactants or polymers. 

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