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）是一种有毒元素，用于光伏太阳能电池板，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。 它的化学性质随条件而变化：在缺氧的“还原”条件下，它倾向于以固体形式固定，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Te从氧化的移动的形式转变为还原的非移动的形式的时间和地点的测量可以帮助我们预测其流动性和毒性。 这种测量还应提高对含碲矿床的认识。 在拼凑地球上生命的历史时，对揭示碲氧化存在或不存在的古代岩石的测量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Te氧化和还原的新方法，使用Te稳定同位素比值（128 Te/125 Te）微小变化的新测量方法。这种新的地球化学工具应该是有用的，在一系列的应用，旨在现代环境，矿床和地球历史。 一名博士生将接受适用于古代岩石和现代环境的高级地球化学的培训。 该项目计划从STEM代表性不足的群体中招募一名本科生;学生将被介绍到环境地球化学领域。K-12学生将学习收集和分析河流沃茨，以确定是否从当地煤灰蓄水池渗漏影响河流水质。这个探索性项目的目标是建立（1）同位素变化发生在现代风化环境和（2）如果Te稳定同位素可以作为前寒武纪氧化作用的古氧化还原代理。 这种新的分析方法使用氢化物发生MC-ICPMS和双加标（120 Te和124 Te）来获得128 Te/125 Te比率的高精度测量，同时需要非常少量的Te（10 ng）。 现代土壤，风化页岩和尾矿的测量将揭示在活跃的风化环境中的氧化还原循环过程中赋予的128 Te/125 Te移位的幅度。 测量古代铁矿石，页岩和古土壤将提供一个记录的Te同位素的变化，或缺乏，在古代环境。 Te同位素应该提供一个新的古氧化还原代理与中间氧化还原阈值之间的U同位素和Cr同位素代理，因此，可能会提供新的见解，在新元古代O2水平。 这样的工具可以提供有关氧化条件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