Electrochemical pyrite oxidation

Electrochemical pyrite oxidation is the sum of anodic (electron release) and cathodic (electron consumption) reactions occurring at the surface. The anodic process is a complex collection of oxidation reactions in which the pyrite reacts mainly with water to produce Fe3+, sulfates, and protons,... 

Williamson, M. A. and J. D. Rimstidt, 1994, The kinetics and electrochemical ratedetermining step of aqueous pyrite oxidation. Geochimica et Cosmochimica Acta 58, 5443-5454. 

Pyrite oxidation includes biological and electrochemical reactions, and varies with pH p02, specific surface, morphology, presence or absence of bacteria and/or clay miner-... 

Williamson M. A. and Rimstidt J. D. (1994) The kinetics and electrochemical rate-determining step of aqueous pyrite oxidation. Geochim. Cosmochim. Acta 58, 5443—5454. Witzke T. (1999) Hydrowoodwardite, a new mineral of the hydrotalcite group from Konigswalde near Annaberg, Saxony/Germany and other localities. Neues Jahrb. Mineral. Mh., 75-86. 

Figure 12.20 The rate of oxidation of pyrite (r = rf(FeS2l/t/< in mo /m s) near 25"C and 1 bar pressure. Whole model and leverage plots for multiple linear regression analysis of published and measured rate data for the aqueous oxidation of pyrite (a) Oxidation of pyrite by dissolved oxygen (b) Oxidation of pyrite by ferric iron under an N2 atmosphere and (c) Oxidation of pyrite by ferric iron in the presence of dissolved oxygen. Reprinted from Geochim. et Cosmochim. Acta, 58, M. A. Williamson and J. D. Rimstidt, The kinetics and electrochemical rate-determining step of aqueous pyrite oxidation, 5443-54, 1994, with permission from Elsevier Science Ltd., The Boulevard, Langford Lane, Kidlington 0X5 1GB, U.K.

The electrochemistry of single-crystal and polycrystalline pyrite electrodes in acidic and alkaline aqueous solutions has been investigated extensively. Emphasis has been laid on the complex anodic oxidation process of pyrite and its products, which appears to proceed via an autocatalytic pathway [160]. A number of investigations and reviews have been published on this subject [161]. Electrochemical corrosion has been observed in the dark on single crystals and, more drastically, on polycrystalline pyrite [162]. Overall, the electrochemical path for the corrosion of n-EeS2 pyrite in water under illumination has been described as a 15 h" reaction ... 

Lalvani SB, Shami M (1986) Electrochemical oxidation of pyrite slurries. J Electrochem Soc133 1364-1368... 

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 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 ... 

Janetski et al. (1977) used voltanunetric method to study the electrochemical behavior of a pyrite electrode in ethyl xanthate solution containing various concentration of sodium sulphide. They observed an additional anodic wave due to the oxidation of the dissolved sulphide species present and that the wave appeared at potential cathodic to xanthate oxidation. Therefore, they concluded that the presence of sulphide in solution introduced an anodic process which occurred in preference to xanthate oxidation and hence dixanthogen would not be formed and the pyrite would not be rendered floatable. 

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. 

Abstract The flotation mechanism is discussed in the terms of corrosive electrochemistry in this chapter. In corrosion the disolution of minerals is called self-corrosion. And the reaction between reagents and minerals is treated as inhibition of corrosion. The stronger the ability of inhibiting the corrosion of minerals, the stronger the reagents react with minerals. The two major tools implied in the research of electrochemical corrosion are polarization curves and EIS (electrochemistry impedance spectrum). With these tools, pyrite, galena and sphalerite are discussed under different conditions respectively, including interactions between collector with them and the difference of oxidation of minerals in NaOH solution and in lime. And the results obtained from this research are in accordance with those from other conventional research. With this research some new information can be obtained while it is impossible for other methods. 

Kostina, G. M. and Chernyak, A. S., 1979. Investigation of the mechanism of electrochemical oxidation of arsenopyrite and pyrite in caustic soda solution. Zhumal Prikladnoi Khimii, 52 1532- 1535... 

Mustin C., et al. (1992) Corrosion and electrochemical oxidation of a pyrite by Thiobacillus ferrooxidans. Appl. Environ. Microbiol. 58, 1175-1182. 

The oxidation of pyrite can occur when the mineral surface is exposed to an oxidant and water, either in oxygenated or anoxic systems, depending on the oxidant. The process is complex and can involve chemical, biological, and electrochemical reactions. The chemical oxidation of pyrite can follow a variety of pathways involving surface interactions with dissolved O2, Fe, and other mineral catalysts (e.g., Mn02). Oxidation of pyrite... 

Holmes P. R. and Cmndwell F. K. (2000) The kinetics of the oxidation of pyrite by ferric ions and dissolved oxygen an electrochemical study. Geochim. Cosmochim. Acta 64, 263 -274. 

The stability zone of Fe4[Fe(CN)6]3 in Fig. 4.58 is in agreement with the condition of depression of pyrite with cyanide in Fig. 4.47. In fact, the presence of cyanide results in the inhibition of the electrochemical oxidation of the xanthate. 

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