The formation and fate of intermediates during the oxidation of pyrite.

摘要

The goal of this study is to enhance the understanding of the mechanism, or mechanisms, involved in the oxidation of pyrite and to characterize the species that influence those mechanisms at the molecular scale. To develop this enhanced understanding, the formation and fate of intermediate species during the oxidation of pyrite have been investigated using a variety of geochemical and surface science techniques. The critical issues that have been evaluated throughout the presented study are the effect of reactive intermediate species, the influence of different oxidants, and the result of different photo-environments on the pyrite oxidation system.; Batch aqueous experiments measured micromolar aqueous concentrations of hydrogen peroxide and hydroxyl radical and show hydrogen peroxide concentrations persisting throughout the course of an oxidation experiment. Fourier transform infrared spectroscopy, utilizing a flow-through attenuated total reflectance reaction cell, observed multiple sulfoxyanion species (sulfate and thiosulfate) at the pyrite surface during oxidation, verifying the step-wise oxidation of disulfide.; Two novel experimental techniques were developed for this study and make up a significant component of this report. The first technique is an ultra-high vacuum mass spectrometry method for the analysis of low concentrations of hydrogen peroxide that independently verified the presence of hydrogen peroxide in the pyrite system. The second technique is a modified photochemical flow-through attenuated total reflectance reaction cell that allowed for the characterization of surface sulfoxyanions during pyrite oxidation under illumination showing the effect light has on the surface speciation of sulfoxyanions.; The experimental analysis of reactive intermediates in the pyrite system has revealed a capacity for the pyrite surface to perform and undergo reactions that were previously overlooked and represents an advance in the knowledge of the surface reactivity of pyrite. The spectroscopic characterization of sulfur oxidation products offers insight into the fundamental mechanisms that govern the oxidation of pyrite.; Overall, this study presents an increased understanding of the formation, stability, and fate of intermediate species in the pyrite system. From this, it is now conceivable to explore the implications of this reactivity in both early earth and present-day environments.