Zeolites--A Potential New Tool for Environmental Studies? Isotope and Elemental Studies of Zeolites

沸石——环境研究的潜在新工具？

• 批准号: 9628402
• 负责人: Xiahong Feng
• 金额: $ 13.99万
• 依托单位: Dartmouth College
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1996
• 资助国家: 美国
• 起止时间: 1996-08-01 至 2000-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9628402&HistoricalAwards=false
• 关键词: Zeolites; Potential; New; Tool; Environmental

Feng 9628402 This proposal describes a three year project that studies natural zeolites and their relationship to environmental change. Since the exchange rate between zeolite and the environment is affected by many factors, our approach includes collecting samples from a number of different environments and using chemical and isotope tracers that respond to various environmental factors with different sensitivity. These tracers are oxygen, hydrogen and nitrogen isotopic compositions, K/Ar dating, and major and trace elements. Our initial efforts will be focused on Yucca Mountain drill core samples for two reasons. First, preliminary results on oxygen isotopic compositions of zeolites and clay minerals and the K/Ar dates have provided very affirmed indication for the feasibility of the project. Oxygen isotope compositions show that clinoptilolite from Yucca Mountains is out of equilibrium with the current temperature and fluid conditions. The results also imply a possibility to determine groundwater level variations since zeolite formation. The second and an obvious reason is that there has been a great amount of interdisciplinary research done for the site as a result of the site characterization efforts of the nation's first high-level nuclear wastes repository. A number of other zeolite-containing units will also be sampled to do a comparative study. These units will include the John Day Formation of Oregon, The Barstow Formation, Mud Hills and Lake Tecopa of Inyo County, California, and few zeolite ore deposits in Northeast China. These sites vary in age, diagenetic history and hydrological environments, and can be compared to the Yucca Mountain site. For each tracer, we will study mineral separates of zeolites and other authigenic minerals that are much less exchangeable, such as feldspars and clay minerals. These less exchangeable minerals can be considered to have preserved the formational information, and can be used to derive the conditions and environments (temperat ure and chemical and isotopic compositions of fluid) at the time of zeolite formation. If we assume that all the authigenic minerals formed at the same time and from the same fluid, the current compositions of zeolites may be related to the environmental changes occurred after their formation. For zeolites, we will also study, if possible, the chemical and isotopic compositions of different size fractions. This would help us understand the mechanisms (diffusion versus recrystallization) of exchange between zeolite and fluid, and determine whether zeolite has reached equilibrium with the current pore fluid and at the current temperature. Experimental studies will be conducted to understand the mechanism for chemical and isotopic exchange between zeolites and the environmental fluid, and to determine the physical constants (such as diffusivity and rate constants) necessary for quantifying the rate of exchange from the analytical data of natural zeoliltes.

冯9628402本提案描述了一个为期三年的项目，该项目研究天然沸石及其与环境变化的关系。由于沸石与环境之间的交换速率受许多因素的影响，我们的方法包括从许多不同的环境中收集样本，并使用对不同环境因素反应不同的敏感性不同的化学和同位素示踪剂。这些示踪剂包括氧、氢和氮同位素组成、K/Ar定年、常量元素和微量元素。我们最初的努力将集中在尤卡山钻芯样品上，原因有两个。首先，沸石和粘土矿物的氧同位素组成和K/Ar年龄的初步结果为该项目的可行性提供了非常肯定的迹象。氧同位素组成表明丝兰山斜发沸石在现今的温度和流体条件下处于不平衡状态。这一结果也暗示了确定沸石形成以来地下水位变化的可能性。第二个也是一个显而易见的原因是，由于美国第一个高级别核废料储存库的场地鉴定工作，已经为该场地进行了大量跨学科的研究。其他一些含沸石的单元也将被抽样进行对比研究。这些单元将包括俄勒冈州的John Day组，加利福尼亚州Inyo县的Barstow组，Mud Hills和Lake Tecopa，以及东北中国的少数沸石矿床。这些遗址的年代、成岩历史和水文环境各不相同，可以与尤卡山遗址相比较。对于每种示踪剂，我们将研究沸石和其他不可交换的自生矿物的矿物分离，如长石和粘土矿物。这些交换性较差的矿物可以被认为保存了形成信息，并可用于推断沸石形成时的条件和环境(流体的温度和化学和同位素组成)。如果我们假设所有的自生矿物都是在同一时间和同一流体中形成的，那么沸石目前的组成可能与其形成后发生的环境变化有关。对于沸石，如果可能的话，我们还会研究不同粒度组分的化学和同位素组成。这将有助于我们了解沸石与流体之间的交换机制(扩散和重结晶)，并确定沸石是否在当前的孔道流体和当前温度下达到平衡。将进行实验研究，以了解沸石与环境流体之间的化学和同位素交换机理，并根据天然沸石的分析数据确定量化交换速率所需的物理常数(如扩散系数和速率常数)。