Chemical effects of gases during froth flotation
APPLICATIONS OF NITROGEN: The chemical effects of gases during froth flotation have been studied early years [7]. Oxygen acting as an electron acceptor, contributes significantly in the flotation of sulphides by sulfhydryl collectors. The presence of nitrogen was found to shift the rest potential of pyrite electrodes to more cathodic values, whereas oxygen was found to maintain the mixed potential of the system pyrite-xanthate to more anodic values, favorable for the electro oxidation of xanthate to dixanthogen. As a result, bubble contact can be obtained [8, 9, 10, 11, 12].
In industrial flotation, the use of other gases than air has been reported from time to time [13]. Of all the gases nitrogen would appear to hold the greatest practical promise because of its readily availability, as a by product (from oxygen plants) being also cheap to produce. Since it is chemically inert and poorly soluble in water, it is unlikely to be consumed by the side reactions.
Although nitrogen does not interact either electrochemically or chemically with some of the constituents of the flotation pulp, it acts significantly influencing the behavior of sulfides during their flotation. This activity may be attributed to the ousting of dissolved oxygen from the flotation liquor that is successful when a current of nitrogen is passed through it for a sufficient extent of time. The following consequences can be considered as responsible:
- Changes in the hydration state of mineral surfaces.
- Effect of dissolved gases on the surface chemistry of minerals.
- Maintain the cathodic redox potentials.
- Influence the galvanic interactions.
The adsorption of a gas on a surface is possible by physical adsorption. The presence of a thin, gaseous film on a mineral surface decreases its wetting characteristics and alters significantly the further adsorption of flotation reagents. Also, such a gas film eases appreciably the attachment of a bubble on the mineral [14].
Separation of Molybdenite from Chalcopyrite
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