Structural controls on Fe oxide formation: A crystallographic analysis of the growth of hematite versus goethite

Fe 氧化物形成的结构控制：赤铁矿与针铁矿生长的晶体学分析

基本信息

批准号：
1925903
负责人：
Peter Heaney
金额：
$ 47.49万
依托单位：
Pennsylvania State Univ University Park
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2019
资助国家：
美国
起止时间：
2019-08-15 至 2024-07-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1925903&HistoricalAwards=false
关键词：
Structural controls Fe oxide formation

项目摘要

Dating back to the earliest hominids, the minerals hematite and goethite (both iron oxides) have provided us with durable, non-toxic red, yellow, and brown pigments, and today these minerals are synthesized in the millions of tons. They also are of critical economic importance because they serve as the primary reserves used to extract iron, and iron accounts for 90% of the world's metal consumption. Moreover, they can control the ability of soils to remove contaminants from groundwater because they frequently form as coatings on other soil minerals, such as quartz and feldspar. Even as only a microscopic veneer, they can attract and remove toxic metals, which otherwise would not react with the quartz or feldspar hosts. In spite of their economic and environmental significance, geologists continue to debate how they form and what mechanism determines which of either hematite or goethite is likely to crystallize. Understanding this formation process matters because some scientists have used hematite and goethite ratios to infer the climatic conditions that generated ancient soils. This project strives to determine the chemical conditions that dictate whether hematite or goethite will form in natural environments by using an innovative X-ray scattering technique that allows researchers to monitor iron oxide minerals at the atomic scale as they crystallize from fluids. In addition to this research helping scientists design more accurate historical (and predictive) climate models, the Investigators will also develop an interactive program that focuses on the geological and technological significance of iron oxides. These exercises will take advantage of a Smithsonian Learning Center called Q?rius, which attracts approximately 100,000 school children each year, and the U.S. National Museum of Natural History's extensive collection of iron oxide specimens to explain the important role of these minerals for maintaining the nation's technological and economic welfare.Over the past decade, several studies have argued that the ratio of hematite to goethite in soils can yield quantitative estimates of mean annual precipitation, raising the possibility that hematite/goethite ratios in paleosols may serve as proxies for ancient climate. The application of hematite/goethite proxies to Ordovician paleosols has, however, conflicted with the results of well-established climatic indicators. Recent research by the Principal Investigators has revealed that the crystallization of hematite relative to goethite is determined by a complex interplay of solution pH, temperature, and time. The PIs hypothesize that the formation of goethite is outcompeted in certain conditions by the metastability of 'hydrohematite,' a mineral discovered 175 years ago and discredited in the 1920s. Specifically, they suggest that the reaction of ferrihydrite to hydrohematite is favored in alkaline systems (pH ~8) at low to moderate temperatures (below 130oC). The composition of hydrohematite falls halfway between those of the goethite and hematite endmembers, and the transition from hydrohematite to stoichiometric hematite involves structural discontinuities suggestive of the onset of magnetic coupling between neighboring iron atoms. The PIs will combine state-of-the-art, synchrotron X-ray diffraction techniques with computational methods to understand the factors that control the relative thermodynamic stabilities in this system of iron (hydr)oxide nanophases. Accurate applications of hematite/goethite proxies for paleoclimate reconstruction require a rigorous understanding of the rates at which ferrihydrite alters to goethite and hematite and on the variables that influence which reaction products form. The series of research thrusts outlined in this proposal will provide important constraints on the character and the rates by which iron (hydr)oxides evolve in maturing soils. The results thus will improve the utility of hematite and goethite as a climate indicator, and they will reveal the relationship between the defect states and the physical properties and behaviors of iron oxides.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

可以追溯到最早的人类，矿物质赤铁矿和乙铁矿（两种铁氧化物）为我们提供了耐用，无毒的红色，黄色和棕色的颜料，如今，这些矿物质已在数百万吨中合成。它们也具有至关重要的经济意义，因为它们是用于提取铁的主要储量，铁占世界金属消耗的90％。此外，他们可以控制土壤从地下水中去除污染物的能力，因为它们经常形成其他土壤矿物质（例如石英和长石）上的涂料。即使仅是微观饰面，它们也可以吸引和去除有毒金属，否则它们不会与石英或长石宿主反应。尽管具有经济和环境意义，但地质学家仍继续辩论其形成方式以及哪种机制决定了赤铁矿或魔铁的哪种机制可能会结晶。理解这种形成过程很重要，因为一些科学家使用了赤铁矿和谷石比来推断产生古老土壤的气候条件。该项目致力于确定通过使用创新的X射线散射技术在自然环境中决定是否会在自然环境中形成的化学条件，该技术使研究人员可以从原子量表中监测氧化铁矿物质，因为它们从流体中结晶。除了这项研究帮助科学家设计更准确的历史（和预测性）气候模型外，研究人员还将开发一个互动程序，该程序侧重于铁氧化铁的地质和技术意义。 These exercises will take advantage of a Smithsonian Learning Center called Q?rius, which attracts approximately 100,000 school children each year, and the U.S. National Museum of Natural History's extensive collection of iron oxide specimens to explain the important role of these minerals for maintaining the nation's technological and economic welfare.Over the past decade, several studies have argued that the ratio of hematite to goethite in soils can yield quantitative estimates of mean annual precipitation, raising the古溶质中的赤铁矿/谷石比的可能性可能是古代气候的代理。然而，赤铁矿/谷石的代理在奥陶纪古代物中的应用与建立良好的气候指标的结果相抵触。首席研究者的最新研究表明，赤铁矿相对于绿铁矿的结晶取决于溶液pH，温度和时间的复杂相互作用。 PI假设在某些情况下，在175年前发现的一种矿物的矿物质的矿物质的亚ottain矿在某些条件下，在某些条件下，对谷杆菌的形成量越来越多。具体而言，他们建议在低至中等温度（低于130oC）下，在碱系统（pH〜8）中有利于铁硫酸盐对氢干燥岩的反应。氢钛矿的组成落在谷石和赤铁矿末端的一半，以及从氢去盐酸盐到化学计量的赤铁矿的过渡涉及结构性不连续性，暗示了邻近铁原子之间磁耦合的结构不连续。 PI将结合最新的，同步加速器X射线衍射技术与计算方法，以了解控制这种铁（Hyd）氧化物纳米相系统中相对热力学稳定性的因素。赤铁矿/谷石代理在古气候重建中的准确应用需要严格了解铁硫酸铁石的变化速率和赤铁矿和赤铁矿以及影响哪种反应产物形成的变量。该提案中概述的一系列研究推力将对铁（Hyd）氧化物在成熟土壤中演变的特征和速率提供重要限制。因此，结果将改善赤铁矿和谷石作为气候指标的效用，它们将揭示缺陷状态与铁氧化铁的物理特性和行为之间的关系。该奖项反映了NSF的法定任务，并被认为是值得通过基金会的知识分子和更广泛影响的审查审查标准来通过评估来通过评估来支持的。