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UBC Theses and Dissertations

Humid oxidation of pyrite Stenhouse, James Fairley

Abstract

A study of the humid oxidation of pyrite, that is, oxidation of pyrite in aqueous medium under oxygen pressure, was undertaken to learn something of the reaction kinetics and mechanism Involved in the primary humid oxidation reactions. The method of investigation is based on measuring the oxygen consumption by the reaction and using this measurement to determine the reaction rates. Experimentally, this measurement is accomplished by recording the change in pressure in an oxygen storage bottle feeding the reaction. Based on the experimental results of this Investigation, a model for the oxidation process is proposed. During the reaction, a stable oxide layer forms on the surface of the pyrite particle and in the model for the oxidation process, the following steps are proposed: 1. Adsorption of oxygen molecules to the surface of the particle and dissociation of the molecules to atoms on the surface. 2. Transfer of electrons from sulfur atoms, through the oxide layer, to adsorbed oxygen atoms. 3. Interstitial diffusion of sulfur ions through the oxide layer to the surface of the particle. 4. Reaction between sulfur ions and oxygen on the surface and desorption of the products of this reaction into solution. 5. Diffusion of lattice defects created at the pyrite oxide interface by sulfur removal to the surface of the particle and diffusion of oxygen atoms into the oxide layer. The mathematical expressions which are developed for the effect of reaction variables are based on this model and are supported by experimental results.

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