This thesis describes a kinetib study of the oxidation of pyrite in aqueous suspension by molecular oxygen. The reaction is found to proceed by several simultaneous paths, the direct dissociation by molecular oxygen being predominant, i.e. , FeS₂ + O₂ (aq) fast → FeS₂. O₂ FeS₂. O₂ + O₂ (aq) slow →FeS₂. 2O₂→ FeO₄+ S° In accord with this mechanism the overall rate of oxidation is found to be proportional to the pyrite surface area and to the oxygen partial pressure and independent of the solution composition. The rate Constant k₃ = 0.125 exp -13,300/RT m.cm.¯² atm.¯¹ min.¯¹ . The products of oxidation were found to be both ferrous and ferric sulphate, sulphuric acid and elemental sulphur. Solution composition did affect the distribution of products. High temperatures and low acidities favoured the formation of sulphuric acid while the opposite conditions favoured the formation of elemental sulphur. A separate study of the aqueous oxidation of ferrous sulphate by molecular oxygen revealed a second order dependence on ferrous ion and a first order dependence on molecular oxygen, i.e., (d[Fe⁺⁺]/dt) = k[Fe⁺⁺]²[O₂] k = 6 x 10⁹ exp -16,500/RT 1. m.¯¹ atm.¯¹ min.¯¹ This reaction was found to be catalyzed by small amounts of cupric Ion according to the following observed kinetics -(d[Fe⁺⁺]/dt) = k[Fe⁺⁺]²[O₂] +k₂ Fe+ k2[Fe⁺⁺]²[O₂] [Cu⁺⁺]½ k₂= [equation omitted] Although ferric sulphate was found to be an adequate oxidizing agent for pyrite, the contribution of this reaction to the over-all dissociation of pyrite in the presence of molecular oxygen was not significant since the rate of reoxidation of ferrous sulphate was found to be comparatively slow. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

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. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

Thesis (B.S.)--University of Missouri, School of Mines and Metallurgy, 1912. / The entire thesis text is included in file. Typescript. Illustrated by authors. Title from title screen of thesis/dissertation PDF file (viewed March 26, 2009) Includes bibliographical references.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 132-140). Also available via the Internet.

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Thesis (B.S.)--University of Missouri, School of Mines and Metallurgy, 1909. / Paging in original text incorrect. Numbering jumps from leaf 9 to leaf 11. Year the degrees were granted determined from "1874-1999 MSM-UMR Alumni Directory." The entire thesis text is included in file. Typescript. Title from title screen of thesis/dissertation PDF file (viewed Apr. 22, 2009).

Thesis--Institut scientifique chérifien, Rabat, Morocco. / Bibliography: p. 101-102.

Thesis--University of Pennsylvania.

Thesis (Ph. D. in Environmental Science)--Vanderbilt University, Aug. 2007. / Title from title screen. Includes bibliographical references.

Rest potential measurements, cyclic voltammetry, linear sweep voltammetry and constant potential coulometry were used to determine the electrochemical response of arsenopyrite in the absence and in the presence of cyanide and to determine its dissolution chemistry. Surface oxidation of arsenopyrite is proposed to proceed by a two-step reaction sequence. FeOOH, H₂AsO₃⁻, and Sᵒ, are produced in the initial step. Oxidation of Sᵒ to SO₄²⁻, and H₂AsO₃⁻ to HAsO₄²⁻ account for the second step. Coulometric results confirmed that 14 electrons are involved in the overall reaction. The implications of these results on the cyanidation of arsenical gold-bearing concentrates were also investigated. The response of four different concentrates to various cyanidation techniques was examined. Alkaline pressure oxidation in 1 M NaOH, at 200°C and under 500 psi of oxygen overpressure followed by conventional cyanidation resulted in 81% gold extraction from a concentrate that yielded only 2% gold extraction after direct cyanidation.