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

Steven Chemtob博士被授予NSF地球科学博士后奖学金，在圣路易斯的华盛顿大学开展研究和教育计划。Chemtob博士将进行实验室实验，以表征有助于带状铁形成（BIF）的原生铁-硅沉淀物的结构，化学和稳定同位素组成。 在前寒武纪地层中发现的富含铁和二氧化硅的化学沉积物BIF的存在与地球早期海洋的氧化作用和光合作用生物圈的发展有关。铁、硅向沉积中心的迁移机制是BIF成因研究中的一个突出问题。二氧化硅可以通过在氧化铁表面上的有效吸附被运输到BIF沉积位点;或者，Fe和Si可以作为单个羟基氧化物相共沉淀。铁-硅相互作用的具体机制对可观察到的地球化学特征（如Fe和Si同位素组成）的影响尚不清楚。拟议的工作的目标是表征分子机制的二氧化硅吸附在氧化铁表面上使用X-射线散射技术，并确定网站特定的硅同位素分馏因子为每个吸附机制。这项研究将揭示前寒武纪海洋中水Fe-Si相互作用的基本机制，有助于解释BIF的化学和同位素分析，并对BIF沉积中二氧化硅吸附的作用进行定量限制。拟议的研究将提供对古代海洋化学的深入了解，但也适用于与水化学和人类健康有关的问题。现代天然沃茨的硅同位素组成经常被用作化学风化的替代物;这些结果将允许改进风化过程的量化。此外，含水二氧化硅与其他含水化学物质竞争吸附位点，影响氧化铁吸附营养素、微量元素和有毒污染物的能力。了解二氧化硅在富铁和富硅沃茨中的吸附机理对于预测微量元素的行为和开发有效的修复技术具有重要意义。Chemtob博士的教育计划将包括指导高中和本科生进行真实的研究体验，在圣路易斯地区进行公开讲座，并参与教学研究计划，最终使用新颖的教学技术开发和展示新的课程内容。

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.