Collaborative Research: Recrystallization of Stable Iron Oxides in Reducing Environments

土壤、沉积物和岩石中含有丰富的铁(Fe)氧化物。像大多数矿物一样，氧化铁矿物会随着周围环境的变化而发生转化反应。这些转化会导致有毒的微量元素、金属和生物营养素的加入或释放，从而影响水质。这些变化还可能改变氧化物的同位素组成，这通常被用来重建地球上过去的环境条件。这项拟议的工作将研究最近发现的一种尚未得到充分描述的氧化铁转化反应：“稳定的氧化铁再结晶”。这一过程涉及一种固体氧化铁矿物，它在还原条件下与溶液中的溶解离子进行元素和同位素交换，令人惊讶的是，这一过程被证明在氧化物的结构、结构或颗粒大小没有任何明显变化的情况下发生。拟议工作的目标是确定两种常见的氧化铁矿物：针铁矿和磁铁矿如何以及在什么条件下发生稳定的氧化铁再结晶。该项目的结果可能从根本上改变我们对氧化铁矿物反应的理解，对现代和古代地球表面过程具有重要影响。为了研究这一过程，这个跨学科团队将把放射性同位素示踪实验与光谱分析、高分辨率显微分析和孔隙尺度分析相结合。这种方法将使我们能够跟踪几种不同粒度、微量元素含量和再结晶历史的天然和合成铁氧化物的再结晶速率、范围和空间分布。实现我们的研究目标将导致：(1)通过加强对氧化铁如何在一系列地球化学条件下与有毒痕量金属和放射性核素相互作用的了解，采取更有效的地下水修复战略；(2)通过研究氧化铁同位素特征如何随时间变化，改进对地球过去环境条件的评估；(3)深入了解对其他矿物观察到的类似的、知之甚少的重结晶过程。除了通过将这项研究纳入课程作业和同行评议的出版物来传播结果外，该项目还将支持为6-8年级学生实施为期一周的夏令营计划--“科学发掘：肮脏的细节”--该计划将为儿童、STEM重点本科生和K-12教师提供教育机会。

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.