RUI: Quantitative XRD-Sequential Extraction Analysis of Trace Metal Speciation in Ultramafic-Derived Soils and Waters

0126018瑞安为了了解自然系统痕量金属收支的人为变化，首先必须了解这些系统的矿物学和化学特征。一种富含微量金属的系统是与超镁铁质岩石共生的自然环境。此前的研究证明，与超镁铁质岩石有关的土壤、植物和水中的铬、镍和钴等痕量金属浓度升高，在某些情况下，浓度被认为是对生态和人类健康有害的水平。这些研究没有做的是对微量金属相的形态进行定量分析，这是了解迁移性的关键组成部分。我们将应用最近开发的定量X射线衍射法结合顺序化学萃取(SCE)来评估痕量金属的分配。姐妹染色单体交换常用于土壤中矿物质和有机物的顺序溶解。然而，只有与先进的粉末X射线衍射技术相结合，连续提取才能准确地确定土壤中的矿物组成、结构和丰度。这种类型的数据特别重要，因为它提供了关于(1)固相在土壤中的溶解度，以及(2)矿物组成和结构对元素浓度、形态和流动性的影响的信息。除了X射线衍射仪和电子探针(使用电感耦合等离子体发射光谱仪)，还将进行C-N分析以帮助确定土壤有机质含量，将使用透射光和扫描电子显微镜分析来评估原生-次生矿物的空间关系，并将使用激光衍射法来评估不同土壤和矿物相的粒度。野外分析将包括Eh、pH、Cr值和Ni值的测量。该项目的目的是表征水圈表面自然存在的痕量金属的形态和浓度，包括超镁铁质岩石(新鲜的和化学蚀变的)、土壤(无机固体、有机物、土壤水)、地表水和水系沉积物。为了评估这些岩石的风化和痕量金属释放的主要控制因素，我们将对来自各种风化制度的岩石、土壤和水样进行取样和分析，这些风化制度包括(1)凉爽的温带最近冰化的阿巴拉契亚山脉北部(佛蒙特州)；(2)凉爽、温带、未冰川的英格兰康沃尔；(3)加利福尼亚北部的半干旱和亚湿润地区；以及(4)潮湿的热带哥斯达黎加。这一比较分析的结果将被应用于广泛环境中痕量金属形态的预测模型。

0126018 RyanIn order to understand anthropogenic alterations to the trace metal budget of natural systems, it is first important to understand the mineralogical and chemical features of such systems. One type of system enriched in trace metals is the natural environment found in association with ultramafic rocks. Previous studies have documented elevated concentrations of trace metals such as Cr, Ni and Co in soils, plants and waters associated with ultramafic rocks-- in some cases, at levels considered to be detrimental to ecological and human health. What these studies have not done is quantitatively analyze speciation of trace metal-bearing phases, which is a crucial component of understanding mobility. We will apply a recently developed quantitative XRD method in conjunction with sequential chemical extractions (SCE) to assess trace metal partitioning. SCE is often used to sequentially dissolve minerals and organic matter in soil. However, it is only when combined with advanced powder XRD techniques that sequential extractions can be used to accurately determine mineral composition, structure, and abundance in the soil. This type of data is especially important because it provides information on (1) the solubility of solid phases in the soil, and (2) the influence of mineral composition and structure on elemental concentration, speciation and mobility. In addition to XRD and SCE (using ICP-AES), C-N analyses will be performed to aid in determinations of soil organic matter content, transmitted light and SEM analyses will be used to assess primary-secondary mineral spatial relationships, and laser diffraction will be used to assess particle size of various soils and mineral phases. Field analyses will include measurements of Eh, pH, Cr and Ni.The intent of this project is to characterize the speciation and concentration of naturally-occurring trace metals in surficial aspects of the hydrosphere, including ultramafic rock (fresh and chemically altered), soil (inorganic solids, organic matter, soil water), surface water, and stream sediment. In order to assess the main controls on weathering and release of trace metals from these rocks, we will sample and analyze rock, soil and water specimens from a wide range of weathering regimes, including (1) the cool temperate, recently glaciated northern Appalachians (Vermont), (2) cool, temperate, unglaciated Cornwall, England, (3) semiarid and subhumid northern California, and (4) humid tropical Costa Rica. Results of this comparative analysis will be applied to a predictive model of trace metal speciation in a wide range of environments.