ETBC: Hidden Iron Oxide Redox Processes During Biogeochemical Iron Cycling: Controls on Nanoscale Transformations and the Fate of Contaminants

ETBC：生物地球化学铁循环过程中隐藏的氧化铁氧化还原过程：对纳米级转化和污染物命运的控制

• 批准号: 0818354
• 负责人: Jeffrey Catalano
• 金额: $ 34.05万
• 依托单位: Washington University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-08-15 至 2012-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0818354&HistoricalAwards=false
• 关键词: ETBC; Hidden; Iron; Oxide; Redox

Intellectual Merit: Biogeochemical iron cycling involves primarily the alternation of iron between Fe(II) and Fe(III) oxidation states. This iron redox cycling is connected to the biogeochemical cycles of carbon, oxygen, phosphorus, and sulfur, and plays an important role controlling the fate of contaminants such as arsenic, uranium, and trichloroethylene. Aqueous Fe(II) and Fe(III) oxide minerals often coexist during biogeochemical iron cycling, and secondary abiotic reactions between these species may transform poorly crystalline iron oxides into more crystalline phases, fractionate iron isotopes, affect contaminant fate and speciation, and possibly acts as a negative feedback on microbial iron reduction. As these secondary processes have important geochemical and environmental implications, we need to obtain a mechanistic understanding of the fundamental reactions that occur between aqueous Fe(II) and Fe(III) oxides. Recent studies have observed electron transfer and atom exchange between aqueous Fe(II) and crystalline Fe(III) oxides. Preliminary measurements reveal that the reaction of Fe(II) with hematite (α-Fe2O3) varies with crystallographic orientation, with the (001) surface experiencing growth and other surfaces dissolution. Similar effects were seen at pH 3 and 7. As these reactions appear to be independent of Fe(II) adsorption and do not affect the bulk mineralogy or fluid composition, they are effectively ?hidden? redox processes. We hypothesize that Fe(II) serves a catalytic role, with iron atoms transferring to (001) surfaces through solution as Fe(II), and electrons transferring away from this surface through the hematite structure. The objectives of this proposal are to: (1) characterize the nature of the dynamic hematite surface redox processes operating in the presence of Fe(II), including how they vary with solution conditions and time and whether they are continuous of self-limiting; (2) determine how this coupled growth and dissolution is affected by the presence of the common inorganic species aluminum, phosphate, and silicate, all known hematite growth modifiers; (3) determine how these processes affect the speciation of structurally compatible [Ni(II)] and incompatible [As(V)] contaminants; and (4) investigate whether these processes can be activated during reductive dissolution by sulfide, an important process in marine sediments. These studies are expected to demonstrate a new complex abiotic interfacial redox process that occurs when biogeochemical iron cycling creates systems with coexisting Fe(II) and Fe(III) species. These studies may also provide new insight into iron biomineralization and nanoparticle synthesis. Finally, similar processes may occur for many elements that coexist in different oxidation states having different solubilities, such as S, Mn, or U; the expected results may thus serve as a guide for exploring complex redox processes in other geochemical systems. Broader Impacts: This project will facilitate the training of two new graduate researchers in the field of biogeochemistry. It will also allow a number of undergraduate researchers (2-3 per year) to be educated in the practice of science, training them in the formulation of research questions and the use of the tools and methods needed to answer scientific questions. Each graduate researcher will be given the opportunity to mentor an undergraduate student as part of their preparation as future educators. Results of this research will be incorporated into a graduate course taught by the PI. This research also may have societal impacts, as the studies of contaminant fate during these surface redox reactions may provide the basis for future development of new remediation strategies or methods to recharge water filtration systems.

智力优势：生物地球化学铁循环主要涉及铁在铁(II)和铁(III)氧化态之间的交替。这种铁氧化还原循环与碳、氧、磷和硫的生物地球化学循环有关，并对砷、铀和三氯乙烯等污染物的命运起着重要的控制作用。Fe(II)和Fe(III)氧化物矿物在生物地球化学铁循环过程中经常共存，它们之间的二次非生物反应可能会使结晶较差的氧化铁转变为更多的晶相，形成更多的铁同位素，影响污染物的去向和形态，并可能对微生物还原铁起到负反馈作用。由于这些次级过程具有重要的地球化学和环境影响，我们需要从机理上了解水中Fe(II)和Fe(III)氧化物之间发生的基本反应。最近的研究观察到了Fe(II)水溶液和晶态Fe(III)氧化物之间的电子转移和原子交换。初步测量表明，Fe(II)与赤铁矿(-Fe_2O_3)的反应随晶体取向的不同而不同，其中(001)表面发生生长，其他表面发生溶解。在pH值为3和7时也有类似的影响。由于这些反应似乎不依赖于Fe(II)的吸附，也不影响整体矿物学或流体组成，因此它们被有效地隐藏起来。氧化还原过程。我们假设Fe(II)起催化作用，铁原子以Fe(II)的形式通过溶液转移到(001)表面，电子通过赤铁矿结构转移到(001)表面。本建议的目的是：(1)描述在Fe(II)存在下赤铁矿表面氧化还原过程的性质，包括它们如何随溶液条件和时间变化，以及它们是否连续或自限；(2)确定常见无机物种铝、磷酸盐和硅酸盐的存在如何影响这种耦合的生长和溶解，所有已知的赤铁矿生长改进剂；(3)确定这些过程如何影响结构上相容的[Ni(II)]和不相容的[As(V)]污染物的形态；以及(4)研究这些过程在硫化物还原溶解过程中是否被激活，硫化物是海洋沉积物中的一个重要过程。这些研究有望展示一种新的复杂的非生物界面氧化还原过程，当生物地球化学铁循环产生Fe(II)和Fe(III)共存的体系时，就会发生这种过程。这些研究也可能为铁的生物矿化和纳米颗粒的合成提供新的见解。最后，存在于不同氧化态、具有不同溶解度的元素，如S、锰或铀，也可能发生相似的氧化还原过程，从而为探索其他地球化学系统中复杂的氧化还原过程提供指导。更广泛的影响：该项目将促进生物地球化学领域两名新的研究生研究人员的培训。它还将允许一些本科生研究人员(每年2-3人)接受科学实践方面的教育，培训他们提出研究问题以及使用回答科学问题所需的工具和方法。每个研究生研究人员都将有机会指导一名本科生，作为他们未来教育工作者准备的一部分。这项研究的结果将被纳入国际和平研究所教授的一门研究生课程。这项研究还可能产生社会影响，因为对这些表面氧化还原反应中污染物去向的研究可能为未来开发新的修复策略或方法来补充水过滤系统提供基础。