A study on the mechanism and suppression of iron disulfide oxidation

Oxidation of metalsulfides results in the production of sulfuric acid and the mobilization of toxic metals, a process commonly known as acid mine drainage (AMD). In order to propose successful remediation strategies a thorough knowledge of the reaction mechanism is necessary. The goal of this work was to study the mechanism of iron disulfide oxidation by monitoring reactions at a model surface with modern surface science techniques. It is envisioned that the knowledge resulting from this investigation would aid any future remediation strategies.; By using photoelectron spectroscopies and ion scattering spectroscopy, methods sensitive to surface chemistry and structure, it was found that variance in preparation methods, such as cleaving or acid washing the natural surface of pyrite, caused little effect on initial reactivity at the surface. However, a higher concentration of iron at the {lcub}111{rcub}, relative to the {lcub}100{rcub} pyrite surface, was found to cause an increase in reactivity. Based upon these results, that oxidation is initiated at defect ferric iron sites on the surface, pyrite was exposed to phosphate, a proposed abatement chemical, and through chelation of surface iron, oxidation was reduced. However, exposure of this surface to simulated sunlight negated any suppression and brought the reaction rate back to that of the unexposed surface. Furthermore, any drop in pH below 4 solubilized the iron phosphate and also increased the oxidation rate.; A method of iron disulfide thin film development was introduced and applied to a surface sensitive infrared technique, attenuated total reflectance. By using this technique on marcasite thin films (a structural pseudomorph of pyrite), sulfur oxidation products were differentiated on the surface that were previously indistinguishable using photoelectron techniques. Intermediates, such as thiosulfate, were found and a reaction mechanism was proposed.; Some of the results of this work have helped develop a framework from which a new direction for remediation strategies was proposed. It was found that the hydrophilic/hydrophobic packing, exhibited by lipids upon hydration, leads to a dense bilayer-lipid coating on the pyrite surface limiting the interaction of aqueous oxidants with the mineral and dramatically reduces oxidation (up to 80%) even in extreme pH (2–3.5).