Collaborative Research: Recrystallization of Stable Iron Oxides in Reducing Environments

合作研究：还原环境中稳定氧化铁的再结晶

• 批准号: 1451253
• 负责人: Philip Larese-Casanova
• 金额: $ 14.07万
• 依托单位: Northeastern University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-08-01 至 2018-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1451253&HistoricalAwards=false
• 关键词: Collaborative; Research; Recrystallization; Stable; Iron

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.

土壤、沉积物和岩石中富含铁 (Fe) 氧化物。与大多数矿物一样，氧化铁矿物随着周围环境的变化而发生转变反应。这些转化可能导致有毒微量元素、金属和生物营养素的掺入或释放，从而影响水质。这些转变还可能改变氧化物的同位素组成，该组成通常用于重建地球上过去的环境条件。拟议的工作将研究最近发现的、尚未充分表征的氧化铁转化反应：“稳定的氧化铁重结晶”。该过程涉及固体铁氧化物矿物，在还原条件下与溶液中溶解的离子进行元素和同位素交换，令人惊讶的是，这种情况在氧化物结构、质地或颗粒尺寸没有任何明显变化的情况下发生。这项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。该项目的成果可能从根本上改变我们对氧化铁矿物反应的理解，对现代和古代地球的地表过程具有重要意义。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、高分辨率微观和孔隙尺度分析结合起来。这种方法将使我们能够跟踪几种具有不同粒径、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：（i）通过提高对铁氧化物如何在一系列地球化学条件下与有毒微量金属和放射性核素相互作用的了解，制定更有效的地下水修复策略； (ii) 通过检查铁氧化物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； (iii) 对其他矿物观察到的类似的、人们知之甚少的重结晶过程的见解。除了通过将这项研究纳入课程作业和同行评审出版物来传播研究结果外，该项目还将支持为 6-8 年级学生实施为期一周的年度夏令营计划——“科学出土：肮脏的细节”——该计划将为儿童、专注于 STEM 的本科生和 K-12 教师提供教育机会。