Collaborative Research: Recrystallization of Stable Iron Oxides in Reducing Environments

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Iron (Fe) oxides are abundant in soils, sediments, and rocks. Like most minerals, Fe oxide minerals undergo transformation reactions as their surroundings change. These transformations can result in the incorporation or release of toxic trace elements, metals, and biological nutrients, which affect water quality. The transformations may also alter an oxide's isotopic composition, which is often used to reconstruct past environmental conditions on Earth. The proposed work will investigate a recently identified, insufficiently characterized Fe oxide transformation reaction: "stable Fe oxide recrystallization". This process involves a solid Fe oxide mineral that undergoes elemental and isotopic exchange with dissolved ions in solution under reducing conditions, which surprisingly has been shown to occur without any obvious changes in the oxide's structure, texture, or particle size. The goal of the proposed work is to determine how and under what conditions stable Fe oxide recrystallization occurs for two common Fe oxide minerals: goethite and magnetite. The outcomes of this project could fundamentally change our understanding of Fe oxide mineral reactions with important implications for earth surficial processes on both modern and ancient Earth.To study this process, this interdisciplinary team will combine radioactive isotope tracer experiments with spectroscopic, high-resolution microscopic, and pore-scale analyses. This approach will allow us to track recrystallization rates, extents, and spatial distributions for several natural and synthetic Fe oxides with different particle sizes, trace element contents, and recrystallization histories. Achieving our research goal would lead to: (i) more effective groundwater remediation strategies by improving knowledge of how Fe oxides interact with toxic trace metals and radionuclides under a range of geochemical conditions; (ii) improved assessments of past environmental conditions on Earth by examining how Fe oxide isotopic signatures change over time; and (iii) insights into similar, poorly understood recrystallization processes observed for other minerals. In addition to disseminating results through the incorporation of this research into coursework and peer-reviewed publications, this project will support the implementation of an annual week-long summer camp program for grade 6-8 students - "Science Unearthed: The Dirty Details" - which will provide educational opportunities for children, STEM focused undergraduates, and K-12 teachers.