Impurities, Stoichiometry, Heterogeneity: Influences on Pyrite Crystal Properties, Oxidation Mechanisms, and Kinetics

黄铁矿是地壳中最丰富的硫化物矿物，其电学性质是其在各种地质和材料科学背景下的重要性的核心。微量元素含量和化学计量失衡控制着黄铁矿的半导体行为，但已发表的黄铁矿氧化模型并没有明确表达微量元素在控制电子转移中的作用。本研究将有助于了解Co、Ni和As如何通过对黄铁矿电子性质的影响来影响其氧化动力学和反应机理。这将通过在混合流反应器、间歇反应器和大气氧化研究中使用控制成分的天然黄铁矿和合成黄铁矿的系统研究来完成。高温合成产生的均质自体晶体适合进行电学测量（电导率、半导体特性和载流子浓度）、空间分辨化学表征（电子探针微分析、激光烧蚀- icp - ms）、结构分析（晶格参数、微量元素在晶体结构中的位置）以及氧化实验。不同掺杂浓度（包括未掺杂的黄铁矿）晶体产生的氧化速率将作为黄铁矿电导率、微量元素浓度和霍尔迁移率的函数进行分析，以评估这些潜在的反应速率依赖源和依赖顺序。将固体化学与黄铁矿氧化及相关微量元素释放机制联系起来，将从根本上提高我们对固溶界面地球化学途径的理解。了解微量元素如何影响黄铁矿的反应性可能对其工业应用具有重要意义，例如光伏应用。黄铁矿氧化过程中释放的砷和其他微量元素是地表水和地下水中的重要毒素；本研究建立的新的黄铁矿氧化模型将明确区分微量元素在促进电子转移中的作用，从而更好地预测这些环境中的释放速率。通过化学、物理和工程部门的设施，促进跨学科研究。一个新的跨学科环境科学项目的博士生将得到支持；本科生也将参加。学生将获得实验和分析技术的经验，以及写作和正式展示研究成果。

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.