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Potentiodynamic sweeps, cyclic voltammetry, and the rotating ring-disk technique were used to study the anodic dissolution of pyrite. Pyrite behaves as a metal in the potential region investigated. The dissolution was shown to be kinetically controlled. At low overpotentials a total of three electrons were transferred and selective dissolution of Fe3* occurs with the formation of a metal-deficient sulfide layer. At large overpotentials this passivating sulfide layer is oxidized in an overall 15 electron-transfer reaction. Oxygen reduction at pyrite was studied in the pH range 1 to 3 using the rotating ring-disk technique. Hydrogen peroxide was detected at the ring and mechanistic analyses of the data show that the reaction can proceed by two paths, one involving solution-soluble hydrogen peroxide and one involving only adsorbed intermediates. The amount of hydrogen peroxide formed during the course of reaction diminishes as the pH decreases. InfroductionThe electrochemistry of pyrite has been extensively studied"2 since knowledge of its behavior in aqueous solution is important for its many applications, for example, in flotation, leaching, and as a material for photoelectrochemical and photovoltaic solar cells. The anodic dissolution has been investigated by various electrochemical techniques3-5 and the surface products have been examined by x-ray photoelectron spectroscopy (XPS)'-' and Raman spectroscopy.9 In acid solution it is generally accepted that the overall oxidation reactions involve the formation of sulfur or a metal-deficient sulfide at low overpotentials and sulfate at high overpotentia1s.3'°'12 However, there are some questions of fundamental importance that still need some clarification, for example: (i) what is initially oxidized? (ii) does Fe2 enter the solution? (iii) in what potential region can solution soluble products be detected? and (iv) how many electrons are involved in the total reaction? The anodic dissolution of pyrite was studied in this work with these questions in mind.Potentiodynamic sweeps, cyclic voltammetry, and rotating ring-disk measurements were used for this purpose.The rotating ring-disk technique was also used to study oxygen reduction on pyrite. Oxygen reduction constitutes the cathodic reaction coupled to mineral oxidation in leaching and to collector oxidation in flotation. While the anodic dissolution of pyrite has been extensively studied, only a few investigations have been made on the reduction of oxygen on pyrite.'18 In a recent series of papers'9 the mechanism of oxygen reduction on galena and pyrite was studied with the aid of the rotating ring-disk technique.The emphasis was on the correlation between the flotation properties of these minerals and the kinetics of oxygen reduction, It was concluded that the first electron transfer was rate determining and that soluble hydrogen peroxide was formed as an intermediate. The amount of hydrogen peroxide formed was dependent on the mineral and on the surface properties.1' In this work the oxygen reduction was studied i...

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The objective was to study the influence of natural organic matter (NOM) on the corrosion and by-product release of iron and copper. The corrosion was studied using potentiodynamic sweeps, coupon tests and field measurements in different Swedish municipalities. For iron it was found that the corrosion rate decreases in the presence of NOM. The results are explained in terms of surface complexation and a good correlation is found between theoretical calculations and experimental results. In the case of copper it was found that NOM both increases the corrosion rate and the content of copper in the water after one night of stagnation. The results are compared with equilibrium calculations and a good correlation is achieved.