Contact-angle, flotation

Fig. 9. Correlation of contact angle, flotation recovery, surface coverage by collector, and 2eta potential. Solid, quart2, collector reagent, 4 x 10 Af dodecylammonium acetate. = recovery, % A = zeta potential, mV Q — contact angle, degrees and = surface coverage, % of one monolayer. Ref.

FIGURE 39.2 Correlation of adsorption density, contact angle, flotation response and zeta potential for quartz as a function of dodecylammonium acetate concentration at pH 6 to 7, 20 to 25°C [5]. 

Contact angle is proportional to (ysv - 7sl), therefore addition of a surfactant that adsorbs at the solid-solution interface should decrease ysL d therefore increase the quantity above and make 6 smaller. Yet such addition in flotation systems increases 6. Discuss what is inconect or misleading about the opening statement. 

The 2eta potential and contact angle as well as flotation recovery correlate well in some flotation systems as shown in Figure 9 (20). 

CMC), reverses the effect that the surfactant has on contact angle at lower concentrations, and at or above the CMC there is no further lowering of surface tension. At the higher concentrations, the surfactant loses some of its beneficial effect on dewateriag, as shown ia Figure 5. The beneficial effects of surfactants on dewateriag are most pronounced ia cakes that have been partially deslimed or ia cakes of partially hydrophobic particles (eg, flotation concentrates) that are adsorbed onto each other. Surfactants at or above CMC have Httle practical effect on extremely fine cakes, where pores are small and the cake has no further opportunity to consoHdate. A number of filter cakes do not respond to surfactant addition at any level. 

Figure 3.9 Anodic current and contact angle as a function of potential for sulphidized pyrite compared with flotation recovery (Heyes and Trahar, 1984)...

Flotation leads to separation of ores from the mixtures. It has been suggested that, among other surface forces, the contact angle plays an important role. The gas (air or other gas) bubble as attached to the solid particle should have a large contact angle for separation (Figure 5.14). Further, it should be stable at the surface. 

Contact angle measurements are of fundamental importance in a range of industrial and everyday processes such as flotation, painting (i.e. the paint must wet the substrate) and weather-proofing. In the flotation process a solid block of the powdered mineral to be floated is often studied using a wide range of collector (i.e. surfactant) solutions to determine optimum flotation conditions. 

The practical importance of monolayer formation is generally because of its relationship to reduction of surface tension. Air—water surface tension can affect such important phenomena as contact angle with a solid surface (affecting flotation), rate of wetting of a solid, or foaming (with applications in enhanced oil recovery or fire extinguishers), just to name a few. Reduction of air—water surface tension could, for example, cause a liquid to spread on a solid instead of beading up on it. 

FIG. 7.19 Schematic illustration of several configurations of three phases useful in the discussion of detergency and flotation. The shaded region represents the soiled spot in detergency and 0, is the relevant contact angle the shaded region is an air bubble in flotation, and 02 is the appropriate contact angle. The arrows in (b) and (d) indicate flow in the adjacent phase. 

BORONCOMPOUNDS - BORON OXIDES, BORIC ACID AND BORATES] (Vol 4) -contact angles m water [FLOTATION] (Vol 11)... 

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