Pilot Study of the Formation of Floating Mixed-valent Fe Hydroxide Films

GRATHOFFEAR-0545435我们在俄勒冈州沿海环境的湿地土壤和土壤渗漏中，以及其他人在威拉米特山谷和吕内堡海德（德国）的湿地土壤和土壤渗漏中，发现了一种新的混合价（铁-亚铁）水铁矿前体，一种经常被误认为油膜的漂浮铁膜。这种混合价氧化铁类似于绿色锈和硫铁矿。它的高还原能力使其在环境修复中具有吸引力，通过减少高毒性污染物，如六价铬。这层膜也可能在铁循环中发挥重要作用。例如，通过促进铁-一种限制性营养素-向海洋的运输。这种水铁矿的前体也可能是湿地和河岸带微生物群落的重要营养源。我们建议进一步表征这一阶段在一些自然环境中（沿海湿地，河岸地区，和高山湿地），并在实验室合成它，以确定其溶解度和热力学stability. ObjectiveandMethods：我们的目标是记录这种混合价铁膜在各种自然环境中的发生，并确定相的热力学和溶解度。在这项试验性研究中，我们将确定这种膜如何在三种环境中形成：1）在自然野外环境中，2）在实验室中仅使用无机试剂，3）在实验室中使用产生膜的现场采样土壤，包括任何相关的微生物和有机物。我们将使用XRD、FTIR、Moessbauer、SEM、HRTEM、ICPMS、AAS、IC和UV-Vis来表征膜和相关的沃茨。一旦我们建立了使用这种新材料的知识基础和技术，我们预计将提出额外的工作来确定其在一系列环境条件下的稳定性和溶解度（例如，pH值，氧化还原，和温度），以确定其还原能力和速率，并将此技术应用于现场环境cleanup.Broader影响：这种混合价氧化铁的控制合成将使我们能够确定相形成和持续的环境条件。这种基本信息将是有用的工人感兴趣的补救应用，如诱导形成这种铁氧化物上游污染羽流。固体亚铁Fe相是有价值的补救剂，因为它们将许多污染物还原为具有较低毒性或流动性的形式。这种污染物减少在不存在固体铁相的情况下不会发生。零价铁、蒙皂石中的结构铁（II）和吸附在针铁矿上的铁（II）都被证明可以减少氯代烃和六价铬。但目前，如果含水层中没有Fe，则没有替代方案。混合价铁膜的合成可以提供这样的替代方案。 拟议的工作将包括学生培训和公众教育。学生通常会将铁膜误认为是油膜。这使得它成为一个很好的材料，以探究为基础的学习经验。由于铁膜本身适合于铁还原的研究，它将用于粘土矿物学和化学水文地质学课程的实验室项目和实地作业。我们还计划在哈特菲尔德海洋科学中心创建公共展览。

GRATHOFFEAR-0545435A new mixed-valent (ferric-ferrous) precursor to ferrihydrite, a floating iron film often misidentified as an oil film, has been identified in wetland soils and soil seeps by ourselves in Oregon coastal settings and by others in the Willamette Valley and the Lueneburger Heide (Germany). This mixed-valent iron oxide is similar to green rust and fougerite. Its high reductive capacity makes it attractive for use in environmental remediation, by reducing highly toxic contaminants such as hexavalent chromium. The film may also play an important part in the iron cycle. For example, by facilitating transport of Fe - a limiting nutrient - to the ocean. This precursor to ferrihydrite may also be an important nutrient source for microbial communities in wetlands and riparian zones. We propose to further characterize this phase in a number of natural environments (coastal wetlands, riparian areas, and alpine wetlands) and to synthesize it in the lab in order to determine its solubility and thermodynamic stability.Objectives and Methods: Our objectives are to document the occurrence of this mixed-valent iron film in various natural environments and to determine the thermodynamics and solubility of the phase. In this pilot study, we will determine how this film forms in three settings: 1) in the natural field environment, 2) in the lab using only inorganic reagents and 3) in the lab using field-sampled soils that produce the film, including any associated microbes and organics. We will use XRD, FTIR, Moessbauer, SEM, HRTEM, ICPMS, AAS, IC, and UV-Vis to characterize the film and associated waters. Once we have established the knowledge base and techniques for working with this novel material, we anticipate proposing additional work to determine its stability and solubility over a range of environmental conditions (e.g., pH, redox, and temperature), to determine its reductive capacity and rate, and to apply this technique at a field site for environmental clean up.Broader impact: Controlled synthesis of this mixed-valent Fe oxide will allow us to determine the environmental conditions under which the phase forms and persists. Such fundamental information would be useful to workers interested in remedial applications, such as inducing formation of this Fe oxide upstream from contaminated plumes. Solid ferrous Fe phases are valuable remedial agent because they reduce many contaminants to forms with lower toxicity or mobility. Such contaminant reduction does not occur in the absence of a solid iron phase. Zerovalent Fe, structural Fe(II) in smectites, and Fe(II) adsorbed to goethite have all been shown to reduce chlorinated hydrocarbons andhexavalent chromium. But currently there is no alternative if there is no Fe present in the aquifer. Synthesis of the mixed-valent Fe film could provide such an alternative. The proposed work will include student training and public education. Students typically misidentify the Fe film as an oil film. This makes it an excellent material for inquiry-based learning experiences. Because the Fe film lends itself to study of Fe reductions, it will be used in lab projects and field-based assignments in Clay Mineralogy and Chemical Hydrogeology classes. We also plan to create public displays at the Hatfield Marine Science Center.