EAGER: Development of Tellurium Stable Isotopes as Paleoredox Indicator

EAGER：开发碲稳定同位素作为古氧化还原指示剂

• 批准号: 1660600
• 负责人: Thomas Johnson
• 金额: $ 9.84万
• 依托单位: University of Illinois at Urbana-Champaign
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-09-01 至 2019-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1660600&HistoricalAwards=false
• 关键词: EAGER; Development; Tellurium; Stable; Isotopes

Tellurium (Te) is a toxic element that is used in photovoltaic solar panels, is concentrated in some mine wastes, and is a key constituent of some types of gold ore deposits. Its chemical properties vary with conditions: In oxygen-poor, "reducing" conditions it tends to be immobilized in solid forms, but when exposed to atmospheric oxygen it can dissolve in water. In the modern environment, measurements that detect when and where Te transitions from its oxidized, mobile form to its reduced, immobile form can help us predict its mobility and toxicity. Such measurements should also improve understanding of Te-bearing ore deposits. In piecing together the history of life on earth, measurements of ancient rocks that reveal the presence or absence of Te oxidation can provide evidence for changes in biologically critical oxygen concentrations in the earth's atmosphere and oceans over time. This project will develop a new way to trace Te oxidation and reduction, using novel measurements of small variations in Te stable isotope ratios (128Te/125Te). This new geochemical tool should be useful in a range of applications aimed at modern environments, ore deposits, and earth history. A doctoral student will be trained in advanced geochemistry applied to both ancient rocks and the modern environment. The project plans to recruit an undergraduate student from an underrepresented group in STEM; the student will be introduced to the field of environmental geochemistry. K-12 students will learn to collect and analyze river waters to determine if seeps from a local coal ash impoundment affect river water quality.The objectives of this exploratory project are to establish if (1) isotopic shifts occur in modern weathering environments and (2) if Te stable isotopes can serve as a paleoredox proxy of Precambrian oxygenation. The new analytical method uses hydride generation MC-ICPMS and a double spike (120Te and 124Te) to obtain highly precise measurements of 128Te/125Te ratios while requiring very small amounts of Te (10 ng). Measurements of modern soils, weathered shales and mine tailings will reveal the magnitude of 128Te/125Te shifts imparted during redox cycling in active weathering environments. Measurements of ancient ironstones, shales, and paleosols will provide a record of Te isotopic shifts, or lack thereof, in ancient environments. Te isotopes should provide a new paleoredox proxy with an intermediate redox threshold between those of the U isotope and Cr isotope proxies, and thus, may provide new insights into O2 levels during the Neoproterozoic. Such a tool could provide valuable information about the rise of oxidizing conditions and the proliferation of multicellular life.

碲 (Te) 是一种用于光伏太阳能电池板的有毒元素，集中在一些矿山废物中，并且是某些类型金矿床的关键成分。 其化学性质随条件而变化：在缺氧、“还原”条件下，它往往以固体形式固定，但当暴露于大气中的氧气时，它可以溶解在水中。 在现代环境中，检测碲何时何地从氧化的移动形式转变为还原的固定形式的测量可以帮助我们预测其移动性和毒性。 此类测量还可以增进对含碲矿床的了解。 在拼凑地球上生命的历史时，对古代岩石的测量揭示了碲氧化的存在或不存在，可以为地球大气和海洋中生物临界氧浓度随时间的变化提供证据。 该项目将开发一种追踪碲氧化和还原的新方法，利用碲稳定同位素比（128Te/125Te）微小变化的新测量方法。这种新的地球化学工具应该可用于针对现代环境、矿床和地球历史的一系列应用。 博士生将接受应用于古代岩石和现代环境的高级地球化学培训。 该项目计划从 STEM 领域代表性不足的群体中招募一名本科生；将向学生介绍环境地球化学领域。 K-12 学生将学习收集和分析河水，以确定当地煤灰蓄水池的渗漏是否影响河流水质。该探索性项目的目标是确定 (1) 现代风化环境中是否发生同位素变化，以及 (2 ）如果 Te 稳定同位素可以作为前寒武纪氧化的古氧化还原代理。 新的分析方法使用氢化物​​发生 MC-ICPMS 和双尖峰（120Te 和 124Te）来获得 128Te/125Te 比率的高精度测量，同时需要非常少量的 Te（10 ng）。 对现代土壤、风化页岩和尾矿的测量将揭示活跃风化环境中氧化还原循环过程中产生的 128Te/125Te 位移的大小。 对古代铁矿石、页岩和古土壤的测量将提供古代环境中碲同位素变化或缺乏的记录。 Te 同位素应该提供一种新的古氧化还原代理，其氧化还原阈值介于 U 同位素和 Cr 同位素代理之间，因此可能为新元古代时期的 O2 水平提供新的见解。 这样的工具可以提供有关氧化条件的上升和多细胞生命增殖的有价值的信息。

项目成果

Measurements of mass-dependent Te isotopic variation by hydride generation MC-ICP-MS

• DOI: 10.1039/c9ja00244h
• 发表时间: 2020-02
• 期刊: Journal of Analytical Atomic Spectrometry
• 影响因子: 3.4
• 作者: N. Wasserman;T. Johnson