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

[126018] ryan1 .为了了解自然系统中微量金属收支的人为变化，首先要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相关的自然环境。先前的研究记录了与超镁铁质岩石相关的土壤、植物和水中微量金属（如Cr、Ni和Co）的浓度升高——在某些情况下，其水平被认为对生态和人类健康有害。这些研究没有对含微量金属相的形态进行定量分析，而这是理解迁移率的关键组成部分。我们将采用最近开发的定量XRD方法结合顺序化学萃取（SCE）来评估痕量金属分配。SCE常用于依次溶解土壤中的矿物质和有机物。然而，只有结合先进的粉末XRD技术，顺序萃取才能准确地确定土壤中的矿物组成、结构和丰度。这类数据特别重要，因为它提供了以下方面的信息：(1)固相在土壤中的溶解度；(2)矿物组成和结构对元素浓度、形态和流动性的影响。除了XRD和SCE（使用ICP-AES）外，还将进行C-N分析以帮助确定土壤有机质含量，透射光和SEM分析将用于评估主-次矿物空间关系，激光衍射将用于评估各种土壤和矿物相的粒度。现场分析将包括Eh， pH， Cr和Ni的测量。这个项目的目的是描述水圈表层自然产生的微量金属的形态和浓度，包括超镁质岩石（新鲜的和化学改变的）、土壤（无机固体、有机物、土壤水）、地表水和河流沉积物。为了评估风化和这些岩石中微量金属释放的主要控制因素，我们将对来自各种风化机制的岩石、土壤和水样本进行取样和分析，包括(1)凉爽的温带，最近冰川覆盖的阿巴拉契亚北部（佛蒙特州），(2)凉爽的温带，未冰川覆盖的英国康沃尔，(3)半干旱和半湿润的加利福尼亚北部，以及(4)潮湿的热带哥斯达黎加。这种比较分析的结果将被应用于在广泛的环境中痕量金属物种形成的预测模型。

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.