Mineral pyrite-xanthate

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 ... 

Copper sulfldes, chalcopyrite, chalcocite, bomite, covellite Pyrite, pyrrhotite, other sulfide minerals, quartz Xanthates, dithiophosphates... 

The pH of the pulp to the flotation cells is carefliUy controlled by the addition of lime, which optimizes the action of all reagents and is used to depress pyrite. A frother, such as pine oil or a long-chain alcohol, is added to produce the froth, an important part of the flotation process. The ore minerals, coated with an oily collected layer, are hydrophobic and collect on the air bubbles the desired minerals float while the gangue sinks. Typical collectors are xanthates, dithiophosphates, or xanthate derivatives, whereas typical depressants are calcium or sodium cyanide [143-33-9] NaCN, andlime. 

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. 

Janetski et al. (1977) used voltammetry to study the oxidation of pyrite electrode in solution at different pH in the absence and presence of ethyl xanthate to demonstrate that the oxidation of pyrite itself increases as the pH is increased. At high pH condition, the oxidation of pyrite occurs at a potential cathodic to that for xanthate oxidation and hence, only the mineral will be oxidized at the mixed potential and flotation will be depressed. 

The depression by hydrosulphide ion is in a similar manner as hydroxyl depression, i.e. there is a critical pH for each HS ion concentration at a constant xanthate concentration above which no flotation is possible. In the case that the hydrophobic entity is disulphide, the mineral will be depressed when the reaction (3-5a) or (3-6a) occurs before the reaction (1-3). Thus for the pyrite /ethyl xanthate system, pyrite will be depressed if the oxidation reaction (3-5a) takes place prior to the oxidation reaction (4-35). 

Janetski et al. (1977) also studied the behavior of a pyrite electrode in a solution of cyanide concentration in the absence and presence of xanthate using voltammetric technique. They reported that on increasing the concentration of cyanide at constant pH and xanthate concentration, the oxidation wave of xanthate is shifted to more anodic potential indicating that the presence of cyanide, which may react with the mineral surface to form an insoluble iron cyanide complex will result in the inhibition of the electrochemical oxidation of xanthate and the depression of pyrite. 

The flotation separation of galena, sphalerite and pyrite in Fankou lead-zinc mine is very complicated because these three minerals are finely disseminated. The OPCF technology is also successfully applied to this plant to separate these three minerals. Here, pH is modified to 12 by lime and pulp potential is maintained as less than 170 mV. The mixture of xanthate and DDTC is used as a collector in flotation of galena. CUSO4 is used as a collector in the flotation of sphalerite. The principal flowsheet of OPCF for flotation separation of Fankou lead-zinc ore is given in Fig. 10.20. The comparison of results of plant production for OPCF and old flowsheet is listed in Table 10.16. It can be seen that the OPCF technique... 

Natarajan, K. A., Riemer, S. C., Iwasaki, I., 1984. Influence of pyrrhotite on the corrosive wear of grinding balls in magnetite ore grinding. Inter. J. Miner. Process, 13(1) 73-81 Nesbitt, H. W., Bancroft, G. M., Pratt, A. R., Scaini, M. J., 1998. Sulfur and iron surface states on fractured pyrite surfaces. American Mineralogist, 83 1067 - 1076 Neeraj, K. M., 2000. Kinetic studies of sulphide mineral oxidition and xanthate adsorption. Doctor thesis of Virginia Polytechnic Institute and State University. A Bell Howell Company UMI dissertation Services... 

O Dell, C. S., Walker, G. W., Richardson, P. E., 1986. Electrochemistry of the chalcocite-xandiate system. J. Appl. Electrochem., 16 544-554 Opahle, I., Koepemik, K., Eschrig, H., 2000. Full potential band stracture calculation of iron pyrite. Computational Materials Science, 17(2 - 4) 206 - 210 Page, P. W. and Hazell, L. B., 1989. X-ray photoelectron spectroscopy (XPS) studies of potassium amyl xanthate (KAX) adsorption on precipitated PbS related to galena flotation. Inter. J. Miner. Process, 25 87 - 100... 

Pozzo, R. L., Malicsi, A. S., Iwasaki, L, 1988. Pyrite-pryyhotite-grinding media contact and its effect on flotation. Minerals Metallurgical Processing, 5(1) 16-21 Pozzo, R. L., Malicsi, A. S., Iwasaki, I., 1990. Pyrite-pyrrhotite-grinding media contact and its effect on flotation. Minerals Metallurgical Processing, 7(1) 16 - 21 Prestidge, C. A., Thiel, A. G., Ralston, J., Smart, R. S. C., 1994. The interaction of ethyl xanthate with copper (II)—activated zinc sulphide kinetic effects. Colloids Surfece, A. Physicochem. Eng. Aspects, 85 51 - 68... 

Trahar, W. J., Senior, G. D., Heyes, G. W., Creed, M. D., 1997. The activation of sphalerite by lead—a flotation perspective. Inter. J. Miner. Process, 49 121 - 148 Usui, A. H. and Tolun, R., 1974. Electrochemical study of the pyrite-oxygen-xanthate system. Inter. J. Miner. Process, 1 135 - 140... 

The flocculation results on the individual mineral suspensions are shown in Figure 2 (A B). These graphs show the effect of polyacrylic acid dispersant before (PAA) Figure 2A, and after xanthation (PAAX) Figure 2B, on the flocculation-dispersion behavior of individual suspensions of coal and pyrite with Purifloc-A22 flocculant. 

Beside defects from mineral genesis, grinding of a mineral can produce roentgen amorphous states or a new crystalline phase. This leads to the formation of surfaces which differ morphologically and energetically from equilibrium surfaces. Relations were also observed between the degree of crystallinity and particle size on one side and surface reactivity with water or a surfactant on the other side. For example, the adsorption of xanthates on a very pure surface of pyrite monocrystals occurs much slower than on fine crystalline samples5. ... 

K. C. Pillai and V.Y. Young,/. Colloid Interface Sci 103 103 (1985). X-ray photoelectron spectroscopy study of xanthate adsorption on pyrite mineral surfaces. 

Table 4.2 lists the values of rest potential for a few minerals in potassium ethyl xanthate solutions (6.25 X 10 mol/1, pH 7) and infrared identifications of surface reaction products (Allison et al., 1972). Only those minerals such as chalcopyrite and pyrite have surface reaction product of dixanthogen. 

Leppinen [483] studied the adsorption of EX on nonactivated pyrite, pyrrhotite, chalchopyrite, and sphalerite and on the same minerals activated with copper sulfate. He used the particle-bed electrode (Fig. 4.51) [513, 514] under open-circuit conditions. The IR results were compared to the flotation data. Dixanthogen was found on nonactivated pyrite, pyrrhotite, and chalchopyrite. Iron xanthate... 

Figure 7.27. ATR spectra of pyrite particles after conditioning at two different concentrations of potassium ethyl xanthate (KEX). Reprinted, by permission, from J. O. Leppinen, Int. J. Miner. Process. 30,245 (1990), p. 251, Fig. 4. Copyright 1990 Elsevier Publishers B.V.

ATR on Mineral-Bed Electrodes. ATR at a mineral-bed electrode was employed to study the anodic oxidation of ethyl xanthate (EX) on chalcocite, chalcopyrite, pyrite, and galena [513, 514]. The optical scheme of the SEC cell is shown in Fig. 4.51. Prior to the addition of xanthate to the buffer, the electrode was polarized cathodically in order to remove any oxidation products that are formed during sample preparation. After a polarization period of 15 min at the selected potential, the electrode was pressed against a Ge IRE and the spectrum was measured while applying a potential less than or equal to -l-0.1 V. Otherwise, the spectra were recorded at open-circuit potential (OCP) just after the polarization to avoid corrosion of the Ge IRE. 

As shown in Fig. 1.7, sodium mercapto-benzothiazole performs strong collecting capability toward galena, but weak collecting capability toward pyrite. Comparison of sodium mercapto-benzothiazole and hulyl xanthate in the flotation of galena mineral is as follows ... 

The functional mechanism of thiocarbamates had been discussed briefly in Chap. 3 (Volume 1) and Chap. 6 (Volume 1). It was reported that [20], the adsorption of thiocarbamate on pyrite is weaker than that of xanthate, and fliio-carbamate is prone to desorb from pyrite surface in water. But thiocarbamate adsorbs on towanite firmly. Based on potentiometry of A.B. Glembotski, thiocarbamate adsorbs on towanite and molybdenite via chemical adsorption. And the chemical adsorption between thiocarbamate and towanite is obvious at pH 8. But chemical adsorption cannot take place between thiocarbamate and pyrite. Compared with thiocarbamate, there exists chemical adsorption occurring between xanthate and the above minerals. And the chemical adsorption of xanthate weakens with increasing the pulp pH. 

Sulfide minerals are relatively easier to separate by chemisorption because they can use the major collectors such as xanthates and dithiosphophates. Certain special additives with high surface energy capabilities can also be added to separate different grades of sulfides (e.g., to sink pyrite while floating chalcopyrite). 

Figure 27 presents the flotation recovery curves of Richardson and Walker" for chalcocite, bomite, chalcopyrite, and pyrite. The results for chalcocite are similar to those shown in Fig. 25. The onset of flotation of bornite and chalcopyrite was found" to coincide with the potentials at which UV-vis spectroscopy showed xanthate to begin to be abstracted from solution. This indicated that attachment of xanthate to the surface was responsible for inducing flotation for both minerals. As pointed out in Section VII, these potentials are below the values at which copper xanthate or dixanthogen are formed but correspond to values at which chemisorption is expected.

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