EAR-PF: Mechanisms and Isotopic Signatures of Iron-Silica Adsorptive Interactions in the Precambrian Ocean

EAR-PF：前寒武纪海洋中铁-二氧化硅吸附相互作用的机制和同位素特征

• 批准号: 1249898
• 负责人: Steven Chemtob
• 金额: $ 17万
• 依托单位: Chemtob Steven M
• 依托单位国家: 美国
• 项目类别: Fellowship Award
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-08-01 至 2015-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1249898&HistoricalAwards=false
• 关键词: EAR; PF; Mechanisms; Isotopic; Signatures

Dr. Steven Chemtob has been awarded an NSF Earth Sciences Postdoctoral Fellowship to carry out a research and education plan at Washington University in St. Louis. Dr. Chemtob will perform laboratory experiments to characterize the structures, chemistries and stable isotope compositions of primary iron-silica precipitates that contributed to banded-iron formation (BIF). The presence of BIFs, iron- and silica-rich chemical sediments found in Precambrian successions, is tied to the oxygenation of Earth's early oceans and the development of the photosynthesizing biosphere. An outstanding issue in the study of BIF genesis is the mechanism for transport of iron and silica to depositional centers. Silica could have been transported to the BIF deposition site by efficient adsorption on iron oxide surfaces; alternatively, Fe and Si could have coprecipitated as a single oxyhydroxide phase. The impacts of specific mechanisms of iron-silica interaction on observable geochemical signatures, such as Fe and Si isotope composition, are unknown. The objectives of the proposed work are to characterize the molecular mechanisms of silica adsorption on iron oxide surfaces using X-ray scattering techniques and to identify site-specific silicon isotope fractionation factors for each adsorptive mechanism. This research will reveal fundamental mechanisms of aqueous Fe-Si interaction in Precambrian oceans, assist in the interpretation of chemical and isotopic analyses of BIFs, and place quantitative constraints on the role of silica adsorption in BIF deposition. The proposed studies will provide insight into the chemistry of ancient oceans but are also applicable to problems relevant to water chemistry and human health. The silicon isotope composition of modern natural waters is frequently used as a proxy for chemical weathering; these results will allow for improved quantification of the weathering process. Additionally, aqueous silica competes with other aqueous chemical species for adsorptive sites, impacting the capacity of iron oxide to adsorb nutrients, trace elements and toxic contaminants. Understanding silica adsorption mechanisms in Fe- and Si-rich waters is important for predicting trace element behavior and for developing effective remediation techniques. Dr. Chemtob's education plan will include mentoring high school and undergraduate students on authentic research experiences, giving public lectures in the St. Louis area, and participating in a teaching-as-research program, culminating in the development and presentation of new course content using novel pedagogical techniques.

Steven Chemtob博士被授予NSF地球科学博士后研究金，以在圣路易斯华盛顿大学执行研究和教育计划。 Chemtob博士将进行实验室实验，以表征原代铁 - 硅基沉淀物的结构，化学和稳定的同位素组成，从而有助于带状铁形成（BIF）。 在前寒武纪继承中发现的BIF，铁和富含二氧化硅的化学沉积物的存在与地球早期海洋的氧合和光合作用的生物圈的发展有关。 BIF Genesis研究中的一个杰出问题是铁和二氧化硅向沉积中心运输的机制。二氧化硅本可以通过有效的氧化铁表面上的有效吸附到BIF沉积位点。另外，FE和SI可以将其共沉淀为单个氧化氧化物相。铁 - 二利相互作用的特定机制对可观察到的地球化学特征（例如Fe和Si同位素组成）的影响尚不清楚。拟议工作的目标是使用X射线散射技术来表征二氧化硅在氧化铁表面上的分子机制，并确定每种吸附性机制的位点特异性同位素分馏因子。这项研究将揭示Fe-SI相互作用在前寒武纪海洋中的基本机制，有助于解释BIF的化学和同位素分析，并对硅胶吸附在BIF沉积中的作用进行定量约束。拟议的研究将提供对古老海洋化学的见解，但也适用于与水化学和人类健康有关的问题。现代天然水的硅同位素组成经常用作化学风化的代理。这些结果将允许改善风化过程的定量。此外，二氧化硅水性与其他化学物种的吸附性位点竞争，从而影响氧化铁对吸附养分，微量元素和有毒污染物的能力。了解Fe-和Si-rich水域中的二氧化硅吸附机制对于预测痕量元素行为和开发有效的补救技术很重要。 Chemtob博士的教育计划将包括指导高中和本科生关于真实研究经验的教育，在圣路易斯地区进行公开讲座，并参加教学课程，最终使用新颖的教学技术来开发和展示新课程内容。