Pyrite is the most abundant sulfide mineral in the earth's crust, and its electrical properties are central to its importance in a variety of geological and materials science contexts. Trace element content and stoichiometric imbalances control pyrite's semiconducting behavior, but published pyrite oxidation models have not included explicit expressions of the role of trace elements in governing electron transfer. This research will contribute to basic understanding of how Co, Ni and As, through their effects on pyrite's electronic properties, influence its oxidation kinetics and reaction mechanisms. This will be accomplished through a systematic study using natural pyrite and synthetic pyrite of controlled composition in mixed flow reactor, batch reactor, and atmospheric oxidation studies. High temperature synthesis produces homogeneous, euhedral crystals suitable to carry out electrical measurements (conductivity, semiconducting character and carrier concentration), spatially resolved chemical characterization (electron probe microanalysis, laser ablation-ICP-MS), and structural analysis (lattice parameters, position of trace elements in the crystal structure), as well as oxidation experiments. The oxidation rates generated from crystals of different dopant concentrations (including undoped pyrite) will be analyzed as a function of pyrite conductivity, trace element concentration, and Hall mobility to assess these potential sources of reaction rate dependencies and order of dependence.
Linking solid-state chemistry with mechanisms of pyrite oxidation and associated trace element release will fundamentally improve our understanding of geochemical pathways at the solid-solution interface. Understanding how trace elements contribute to pyrite reactivity could have important implications for its industrial use, such as photovoltaic applications. Arsenic and other trace elements released during pyrite oxidation can be significant toxins in surface and ground waters; new pyrite oxidation models developed from this research will explicitly distinguish the role of trace elements in facilitating electron transfer, enabling better prediction of release rates in these environments. Cross-disciplinary research will be promoted as facilities in chemistry, physics, and engineering departments are engaged. A doctoral student in a new interdisciplinary Environmental Science program will be supported; undergraduates will also participate. Students will gain experience in experimental and analytical techniques, as well as in writing and formally presenting research results.
