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 博士获得了美国国家科学基金会地球科学博士后奖学金，以在圣路易斯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-二氧化硅沉淀物的结构、化学性质和稳定同位素组成。 BIF（前寒武纪演替中发现的富含铁和二氧化硅的化学沉积物）的存在与地球早期海洋的氧化和光合作用生物圈的发展有关。 BIF成因研究中的一个突出问题是铁和硅向沉积中心的迁移机制。二氧化硅可以通过氧化铁表面的有效吸附被输送到 BIF 沉积位点；或者，Fe 和 Si 可以共沉淀为单一羟基氧化物相。铁-硅相互作用的具体机制对可观测的地球化学特征（例如铁和硅同位素组成）的影响尚不清楚。拟议工作的目的是利用 X 射线散射技术表征二氧化硅在氧化铁表面吸附的分子机制，并确定每种吸附机制的特定位点硅同位素分馏因子。这项研究将揭示前寒武纪海洋中水相铁硅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相关的问题。现代天然水体的硅同位素组成经常被用作化学风化的代表。这些结果将有助于改进风化过程的量化。此外，水性二氧化硅与其他水性化学物质竞争吸附位点，影响氧化铁吸附营养物、微量元素和有毒污染物的能力。了解富含铁和硅的水中的二氧化硅吸附机制对于预测微量元素行为和开发有效的修复技术非常重要。 Chemtob 博士的教育计划将包括指导高中生和本科生获得真实的研究经验、在圣路易斯地区进行公开讲座以及参与教学即研究项目，最终利用新颖的教学技术开发和呈现新的课程内容。