Activation sphalerite

Aetivators. These are used to make a mineral surface amenable to collector coating. Copper ion is used, for example, to activate sphalerite (ZnS), rendering the sphalerite surface capable of absorbing a xanthate or dithiophosphate collector. Sodium sulfide is used to coat oxidized copper and lead minerals so that they can be floated by a sulfide mineral collector. 

The copper sulfide formed on the surface of the sphalerite mineral reacts readily with the xanthate, and forms insoluble copper xanthate, which makes the sphalerite surface hydro-phobic. Such a reaction for activating sphalerite occurs whenever the activating ions are present in the solution. It is thus necessary to deactivate sphalerite (to prevent the occurrence of natural activation) in the case of some ores. With lead-zinc ores, for example, natural activation occurs due to Pb2+ in solution... 

The electrochemical mechanism of cupric sulphate activating sphalerite has been studied. The measured cyclic voltammogram curves in aqueous solution at different pH with sphalerite compound electrode are shown as solid lines in Fig. 6.1. 

Aciivators are chemical reagenls. which alter the surface of a sulfide so that it can absorb a collector and final. Cupric sulfate is the most widely used activator. For example, xamhatc as a collector will not readily float sphalerite, but the addition of cupric sulfate to the pulp changes the surface of the sphalerite particles to copper sulfide. Xamhate then will readily fioat the activated sphalerite as it behaves similarly to copper sulfide. 

Figure 2 Variation of the extent of deactivation of copper-activated sphalerite as function of the cyanide concentration (after Marsicano et at., ref. 12)...

A deactivating agent for copper-activated sphalerite is any species that has sufficient affinity for copper(I) or (II) to compete for it with sulfide ions in the surface lattice of the mineral, thus removing it from the surface. Ligands such as cyanide or ethylenediamine, which coordinate strongly to copper, have therefore been found to be the most effective. A knowledge of the stability of the species present in a system composed of and CN ions has enabled ... 

T. N. Khmeleva, W. Skinner, and D. A. Beattie, Depressing mechanisms of sodinm bisulphite in the coUectorless flotation of copper-activated sphalerite, Internat. J. Mineral Processing 76(1-2) (2005). 

The galena would be floated first under conditions of alkaline pH (pH 8-10) using a low concentration of an alkyl xanthate as the collector, sodium sulfite to depress the zinc minerals and a short-chain alcohol as a frother. After galena flotation, the pH would be raised to 11-12 (to depress gangue iron sulfides) copper sulfate is added to activate sphalerite and marmatite additional alkyl xanthate is added to float these two minerals. The final lead concentrate should be more than half lead with minimal zinc content the final zinc concentrate should be more than half zinc with minimal lead content. 

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. 

Activators promote the reaction of the coUector with some minerals. For example, ordinarily xanthates do not bind to sphalerite, but pretreatment of the sphalerite using copper sulfate enables it to adsorb the xanthate. Thus it is possible to float the sphalerite from lead—zinc ores after the galena has been recovered. 

Zinc ores are generally floated at the mine (18). In the case of simple zinc sulfide ores, flotation is carried out by treatment with copper sulfate to activate the sphalerite causing it to be wet by the organic collector (eg, xanthate). The now-hydrophobic zinc ore particles attach themselves to the rising bubbles. Oxidized ore particles present must be sulftdized with sodium sulfide to be floated (19). Flotation produces concentrates which are ca 50—60% zinc. In mixed ore, the lead and copper are usually floated after depressing the sphalerite with cyanide or zinc sulfate. The sphalerite is then activated and floated. 

The value of the activity coefficients of FeS in sphalerite determined for temperatures above 300°C can be extrapolated to lower temperatures. As stated by Barton and Toulmin (1966), ypeS does not depend on temperature above about 270°C. However, the activity coefficient below 270°C has not been studied. Scott and Kissin (1973) have stated that activity coefficients for FeS in sphalerite at low temperatures may be substantially different from those at higher temperatures. 

Figure 1.95. Activity of component ZnCOs versus /oj. Carbonate containing ZnCOs is in equilibrium with sphalerite. Thermochemical calculation was made under the following conditions temperature = 200°C, ionic strength = 1, ES = 10 m, and pH = 5. (1) CH4 and H2S region. (2) H2CO3 and H2S region. (3) H2CO3 and (Na, K) SOj region (Shikazono, 1977b).

Figure 1,188. Typical sulfur activity and temperature ranges for Japanese auriferous vein (dotted) and gold-silver vein (hatched) deposits. I.so-FeS content curves for sphalerite were drawn based on the equation of Barton and Skinner (1979). py pyrite, po pyrrhotite (Shikazono and Shimizu, 1987).

Opaque minerals identified from active geothermal areas are pyrite, sphalerite, galena, chalcopyrite, and tetrahedrite from Okuaizu, Fushime, and Nigorikawa (Japan), Salton Sea (U.S.A.) and Broadlands (New Zealand). 

Back-arc spreading center 1 North Fiji Basin, Station 4 (16°59 S. 173°55 E) 1980 Axial graben at topographic high of north-central segment near triple junction. Sheet lava floor. Active (r = 290°C) anhydrite chimneys standing on dead sulfide mound. Forest of dead sulfide chimneys. Anhydrite, amorphous silica in dead chimneys pyrite, marcasite, chalcopyrite, sphalerite, wurtzite, goethite. 

Central Mariana Trough (18 02 N. 144 "45 E) 3675 Crest of an axial ridge where the relief is greatest (ca. 800 m). A low mound, 20-30 m in diameter. Several active chimneys surrounded by a low mound of hydrotlrernial precipitates. Sphalerite, barite, amorphous silica. 

Activators are those reagents which act in a manner converse to the action of depressants, i.e., they render those minerals floatable which either have been temporarily depressed or would not float without their assistance. They are generally soluble salts which ionize in the aqueous medium. The ions then react with the mineral surface, providing a monomolecular coating and thereby making the mineral surface favourably disposed to the collectors. Sphalerite (ZnS) is essentially not floatable with common collectors. The addition of Cu2+ to the solution, however, alters the mineral surface to CuS, which can adsorb collector. This feature is described elaborately in a later section. 

The flotation of sphalerite, the sulfidic mineral source of zinc, is next considered as an example to illustrate the role of activators. This mineral is not satisfactorily floated solely by the addition of the xanthate collector. This is due to the fact that the collector products formed, such as zinc xanthate, are soluble in water, and so do not furnish a hydrophobic film around the mineral particles. It is necessary to add copper sulfate which acts as an... 

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