Sulfide flotation

Flotation of sulfide minerals is a popular topic in the literature dealing with flotation. It displays well the application of the different flotation reagents such as frothers, collectors, depressants, and activators. 

The adsorption of collectors on sulfide mineral occurs by two separate mechanisms chemical and electrochemical. The former results in the presence of chemisorbed metal xanthate (or other thiol collector ion) onto the mineral surface. The latter yields an oxidation product (dixanthogen if collector added is xanthate) that is the hydrophobic species adsorbed onto the mineral surface. The chemisorption mechanism is reported to occur with galena, chalcocite and sphalerite minerals, whereas electrochemical oxidation is reportedly the primary mechanism for pyrite, arsenopyrite, and pyrrhotite minerals. The mineral, chalcopyrite, is an example where both the mechanisms are known to be operative. Besides these mechanisms, the adsorption of collectors can be explained from the point of interfacial energies involved between air, mineral, and solution. 

The chemisorption mechanism can be well explained with the mineral, galena. The collector ion used is xanthate ion (C ). The mechanism of its adsorption occurs in the following steps  

The feasibility of the above reaction ensues from the data on the solubility products of lead sulfate and lead carbonate salts. Evidence abounds that both sulfate and carbonate ions are present. 

The electrochemical mechanism can be well explained with the mineral pyrite. The collector ion is xanthate ion (CT), a member in the anodic sulfydryl collectors group. Two electrochemical reactions occur on the surface of the pyrite. There is the formation of dixanthogen (C2) by anodic oxidation of xanthate ion (CT) on the surface of pyrite coupled with cathodic reduction of adsorbed oxygen. These reactions are shown below  

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Activators enhance the adsorption of collectors, eg, Ca " in the fatty acid flotation of siUcates at high pH or Cu " in the flotation of sphalerite, ZnS, by sulfohydryl collectors. Depressants, on the other hand, have the opposite effect they hinder the flotation of certain minerals, thus improving selectivity. For example, high pH as well as high sulfide ion concentrations can hinder the flotation of sulfide minerals such as galena (PbS) in the presence of xanthates (ROCSS ). Hence, for a given fixed collector concentration there is a fixed critical pH that defines the transition between flotation and no flotation. This is the basis of the Barsky relationship which can be expressed as [X ]j[OH ] = constant, where [A ] is the xanthate ion concentration in the pulp and [Oi/ ] is the hydroxyl ion concentration indicated by the pH. Similar relationships can be written for sulfide ion, cyanide, or thiocyanate, which act as typical depressants in sulfide flotation systems. 

Xanthates and dithiophosphates dominate sulfide flotation usage, though several other collectors including more recently developed ones are gaining acceptance rapidly (43). As of this writing, this is an active area of research. Many of the sulfide collectors were first used ia the mbber iadustry as vulcanizers (16). Fatty acids, amines, and sulfonates dominate the nonsulfide flotation usage. The fatty acids are by-products from natural plant or animal fat sources (see Fats and fatty oils). Similarly petroleum sulfonates are by-products of the wood (qv) pulp (qv) iadustry, and amines are generally fatty amines derived from fatty acids. 

The amount of collector used is necessarily very small because surface coverages of a monomolecular layer or less are required to impart sufficient hydrophobicity to the mineral. The usages typically range from 1—100 g of collector per ton of ore treated for sulfide flotation (typically 0.2—10% value metal content ia the ore) and 100—1000 g/1 for nonsulfide flotation (1—20% value mineral content) (10). 

Sulfide collectors ia geaeral show Htfle affinity for nonsulfide minerals, thus separation of one sulfide from another becomes the main issue. The nonsulfide collectors are in general less selective and this is accentuated by the large similarities in surface properties between the various nonsulfide minerals (42). Some examples of sulfide flotation are copper sulfides flotation from siUceous gangue sequential flotation of sulfides of copper, lead, and zinc from complex and massive sulfide ores and flotation recovery of extremely small (a few ppm) amounts of precious metals. Examples of nonsulfide flotation include separation of sylvite, KCl, from haUte, NaCl, which are two soluble minerals having similar properties selective flocculation—flotation separation of iron oxides from siUca separation of feldspar from siUca, siUcates, and oxides phosphate rock separation from siUca and carbonates and coal flotation. 

This part of the presentation embodies first a general treatment on surfactants followed by the elaboration of frothers, collectors and regulators. The text subsequently involves the area of sulfide flotation, which occupies a premier position in the field of flotation. The section is completed with some important examples of flotation of sulfides. The final section is devoted to natural hydrophobicity which, on its own accord constitutes an important and interesting area in the field of flotation. 

Some specific examples in the field of sulfide flotation will now be described. 

Sulfenyl chloride derivatives, 22 106 Sulfenyl chlorides, 23 645 Sulfidation, 23 506-507 Sulfide flotation, 26 649. See also Sulfide mineral flotation Sulfide mineral flotation... 

Richardson, P. E. Edelstein, D. L., "The Physical Chemsitry of Mineral-Reagent-Interactions in Sulfide Flotation," USBM Information Circular 8819, 1978, p. 72. 

The improved capabilities of LIX 64 N reagent for recovery, purification, and concentration of copper values from acidic leach liquors were described by DeMent and Merigold (DlO). The leaching of copper sulfide flotation concentrates with subsequent recovery of copper by LIX 64 N was shown to be technically feasible. This extractant loads and strips faster, is more effective in extracting copper from a lower pH solution, has considerably less secondary entrainment, has better iron rejection, and may be used at levels up to 30 vol. % in kerosene without aqueous entrainment. Use of the reagent in operating pilot and commercial plants is also discussed. 

The Dowa Mining Company (K9) in Kosaka, Japan has developed a hydrometallurgical process shown in Fig. 15 to treat 2400 metric tons/ month of copper-zinc sulfide flotation concentrates. The microscopically fine mixture of copper and zinc sulfides was separated from lead sulfide and barite by flotation. The flotation concentrate analyzed 8.7% Cu,... 

As regards cleaning, for example, a roast process can be applied to convert pyrite to a magnetic form, followed by its magnetic separation together with garnet and pyroxene. Another cleaning step in the presence of sulfide minerals would be a sulfide flotation. 

A and B values of the collectors and frothers commonly used in non-sulfide flotation... 

Competitive reaction between collector ion and hydroxyl ions in sulfide flotation... 

Sulfides as electronic conductors can act as donors of electrons and hence promote electrode reactions on mineral surfaces. Sulfide flotation systems constitute redox systems in... 

Trahar, W.J., 1983. The influence of pulp potential in sulfide flotation, principles of mineral flotation, The Wark Symposium, Aust. Inst. Min. Metall. Adlaide, Austalia, p. 117. 

Various starches have been used in industry for depressing talc, mica, natural sulfur, carbon gangue and sulfide minerals, and especially for depressing oxidized iron minerals in the reverse flotation of iron ore and the separation of Cu-Mo in the copper-molybdenite sulfide flotation. 

These dialkyl dithionocarbamates are characterized by low dosage (5-30 g/t) and high selectivity. They can be appUed in the polymetallic sulfide flotation. 

Pugh, R. J. 1989. Macromolecular organic depressants in sulfide flotation—A review, 2. Theoretical analysis of the forces involved in the depressant action. Int. J. Miner. Process. 25 131. 

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