Sphalerite activator

At pH = 9.5, the cyclic voltammogram of the sphalerite activated by CUSO4 is relatively complex. At the upper limit of the scan potential shown in Fig. 6.1, a series of anode peaks appearing in forward scan sequentially correspond to reaction (6-9) and other reactions as follows ... 

Fereshteh, R., Caroline, S., James, A. F., 2002. Sphalerite activation and surface Pb ion concentration. Inter. J. Miner. Process, 67 43 - 58 Fierro, R. E., Tryk, D., Scherson, D., Yeager, E., 1988. Perovskite-type oxides oxygen electrocatalysis and bulk structure. Journal of Power Sources, 22 (3 - 4) 387 - 398... 

Kartio, I. J., Basilio, C. I., Yoon, R. H., 1996. An XPS study of sphalerite activation by copper. In R. Woods, F. Doyle, P. E. Richardson (eds.), Electrochemistry in Mineral and Metal Processing IV. The Electro-Chemical Society, 25 - 34 Kelebek, S., 1987. Wetting behaviow, polar characteristics and flotation of inherently hydrophobic minerals. Trans. MM, Sec. C, 96 103 - 107... 

However, sphalerite activation hy copper sulfale is the result of ndsorption of copper ions on the surface of this mineral, due to ion-exchange processes. The effect of activators also can be dne to tbeir reactions with the collectors to form compounds of low-solubiliiy product.7... 

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. 

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 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... 

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 mineral, sphalerite, on account of its resistance to oxidation, contributes very little of Zn2+ through dissolution. In this case, zinc sulfate is added and the reaction, which is shown in the parenthesis, is pressed into proceeding from right to left (i.e., PhS + Zn2+ —> ZnS +Pb2+). This is equivalent to saying deactivation of sphalerite. Besides Pb2+, Cu2+ is also known to give rise to activation. In this case, cyanide ions are introduced into the system. The stability of Cu(CN)2, relative to Zn(CN)2- results in ratios of dissolved Cu to Zn such that activation cannot occur. 

Several reviews on ore processing by flotation are available.17-21 In addition to providing details of the chemistry of collectors they describe the use of activators and depressants. The former usually convert the surfaces of an ore particle which does not bind strongly to conventional collectors to one that does. The addition of Cu2+ ions to enhance the flotability of minerals such as sphalerite, a zinc sulfide, has been exploited for some time.4 Formation of a surface layer of CuS has been assumed to account for this, but the mechanisms and selectivities of such processes continue to be investigated.18,22,23... 

A mixed polarization diagram (where the polarization behavior of the two different electrodes is represented) for the sphalerite-hypersteel combination is given in Fig. 1.10 (Vathsala and Natarajan, 1989), in which the cathodic polarization curves for the sphalerite and the anodic polarization curves for the hypersteel ball material are seen to overlap. The active nature of the ball material is evident. The current values were observed to be lower in the absence of oxygen which indicated a lower anodic dissolution of the hypersteel grinding medium in the absence of oxygen. 

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