A long time ago, OSTWALD proposed a hyphothesis on the presence of increased concentration of reagents in the zone of the three-phase perimeter of wetting, and this hyphothesis was subsequently confirmed experimentally by Talmud, and later by Klassen. A more detailed description of their work is given in Section III. Here, mention is made that the increased reagent concentration obviously assists the attachment of particles to bubbles. Such action by collectors is noticeable even with very small additions of reagents, since they are concentrated on small portions of the surface. If it is assumed that, under optimal conditions, the concentration of reagents in the three-phase perimeter of wetting is the most thermodynamic state of the system, then any extension or contraction of this perimeter will cause an increase in the free energy of the system. Consequently, the concentration of collector along the three-phase perimeter of wetting should stabilize its dimension and attach the particles to the bubbles.
A special case of particle attachment arises when air bubbles are covered by ‘crusts’ consisting of a number of particles. Owing to the hydrophobicity of their surfaces and the presence of collector on them, these particles become aggregated. Under similar conditions, the stability of such a ‘crust’ increases if it consists of particles of various dimensions, since the small particles fill the intervening space between large particles, thereby imroving their coalescence. This is probably the explanation of somewhat paradoxical phenomenon, often observed in flotation processes, when the addition of very fine particles to the pulp improves flotation of large particles.
In all above considerations reference has often been made to forces separating particles from air bubbles. It is necessary, at least, to mention the reasons which cause the separation of attached particles from air bubbles under real conditions of flotation. In mineral dressing literature, two particular approaches are considered.: (1)correlating the separating forces with the accelerated rise of mineralized bubbles (Volkova); (2)considering the slippage if the particle along the bubble (Bogdanov and Eigeles). Beloglazov discussed the effect of the forces on gravity on fine particles at contact angles less than 15 degrees is represented by a vector equal to the height of the spherical segment which disappears on attachment of the particle. The magnitude of this vector equals delta^2/8r (where r is the radius of the bubble and delta is the diameter of the area of attachment). Under these conditions the work, A, of gravity is equal to ?
