Determination of precious metals in geological samples by continuous powder introduction microwave induced plasma atomic emission spectrometry after preconcentration on activated carbon

A novel method was developed for analysing geological materials for Au, Ag, Pd and Pt by continuous powder introduction microwave induced plasma atomic emission spectrometry (CPI-MIP-AES). The preconcentration of the trace metals on activated carbon (AC) was performed before conducting MIP-AES measurements in order to obtain accurate and precise analytical results. The method proposed is based on the selective sorption of precious metals that are subsequently introduced to the plasma as a dry particulate aerosol consisted of analytes collected on the sorbent. The technical design and operating conditions of the novel sample introduction system based on the fluidized-bed concept has been optimized. The microwave excitation source with integrated rectangular cavity TE₁₀₁ and vertically positioned plasma torch has been used. The signal stability proved to be adequate for sequential mode of measurements due to the vertical plasma configuration as well as the MIP-AES system compatibility with the CPI technique. Calibration was done using home-made standards obtained by sorption of metals of interest from standard solutions on activated carbon. Precision is typically 1-4% relative standard deviation at the 1 μg g⁻¹ level. Under measurement conditions the detection limits for Ag, Au, Pd and Pt were 24, 43, 57 and 550 ng per 1 g of AC, respectively. The proposed procedure was used for Au, Ag, Pd and Pt determination in the platinum ore SARM-7 as well as Au and Ag in the Chinese soil GBW-07405 certified reference materials. The standard addition technique was used and recoveries revealed that the proposed method shows good accuracy and precision.     

Sequestration of organometallic compounds by natural organic matter. binding of trimethyltin(IV) by fulvic and alginic acids

The binding capacity of fulvic and alginic acids towards trimethyl tin(IV) cation was quantitatively determined in order to evaluate the sequestering ability of toxic organometallic compounds by natural organic matter. Investigations were performed in the pH range of natural waters (5–8.5) where the carboxylate groups, largely present in both sequestering agents, are the main binding sites. A chemical interaction model, according to which both the protonation of polyelectrolyte ligands and the hydrolysis of the organotin cation in NaCl aqueous solution were considered, was used to define the speciation of the systems under investigation. Measurements performed at different ionic strength values (0.1, 0.25, 0.5 and 0.7 mol L^?1, NaCl) allowed us to consider the dependence of stability constants on the ionic strength, and to calculate the formation constants at infinite dilution. Results obtained show the formation of the complex species TMT(L), TMT(L)₂ and TMT(L)(OH) for L = fulvic acid and TMT(L) for L = alginic acid, respectively. In order to compare the strength of interaction of these natural poly electrolytes with other analogous synthetic polyelectrolytes, measurements were also carried out on the trimethyltin(IV)–polyacrylate (5.1 kDa) system, and in this case the formation of TMT(L), TMT(L)₂ and TMT(L)(OH) species was found. Results show the following trend of stability for the species TMT(L) in the systems investigated: TMT–fulvate ≈ TMT–polyacrylate > TMT–alginate. On the basis of the stability data obtained, the lowest concentration of fulvic and alginic acids, able to act as sequestering agents towards triorganotin(IV) cation in the conditions of natural waters, was also calculated. Copyright © 2006 John Wiley & Sons, Ltd.     

Generic strength model for dry jointed rock masses

A new nonlinear thermo-mechanical model for heavily jointed rock masses is presented. The model describes poroelasticity, shear-enhanced compaction and brittle–ductile transition in dry porous rocks. The key input parameters of the model, such as elastic moduli, tensile and compressive strength are expressed as functions of the reference porosity of the rock. These functions are based on empirical data for limestones and sandstones and assume that the medium is isotropic. The effect of joints is modeled by scaling down the key model parameters. The scaling rules are found with the help of explicit numerical modeling of randomly jointed media.     

超临界CO_2-水两相流与CO_2毛细捕获:微观孔隙模型实验与数值模拟研究

CO_2毛细捕获机制是CO_2地质封存中的关键科学问题,然而有关孔隙尺度下(微米极)超临界CO_2毛细捕获的研究较少.采用高压流体-显微镜-微观模型实验装置,开展超临界CO_2条件(8.5 MPa,45?C)下CO_2驱替水(排水)和水驱替CO_2(吸湿)实验,采用高分辨率照相机采集CO_2水两相流运动图像,并借助光学显微镜直接观测孔隙尺度下CO_2毛细捕获特征.同时,采用计算流体动力学方法对实验过程进行三维数值模拟.数值模拟不仅反映了实验过程中两相流驱替锋面的推进过程,还刻画了孔隙尺度下被捕获的CO_2液滴/团簇三维空间形态特征.最后,基于数值模拟给出了CO_2初始饱和度与残余饱和度曲线,即毛细捕获曲线,并对比分析了3种毛细捕获曲线预测模型(即Jurauld模型、Land模型和Spiteri模型)的优劣.分析表明,Jurauld模型的描述能力稍优于Land模型,Spiteri模型的描述能力较弱.由于Land模型只需单个参数,且参数具有明确的物理意义,因此在实际工程中,建议优先采用Land模型.     

Raman spectroscopic study of the magnesium‐carbonate minerals—artinite and dypingite

Magnesium minerals are important in the understanding of the concept of geosequestration. The two hydrated hydroxy magnesium‐carbonate minerals artinite and dypingite were studied by Raman spectroscopy. Intense bands are observed at 1092 cm⁻¹ for artinite and at 1120 cm⁻¹ for dypingite, attributed ν₁ symmetric stretching mode of CO₃²⁻. The ν₃ antisymmetric stretching vibrations of CO₃²⁻ are extremely weak and are observed at 1412 and 1465 cm⁻¹ for artinite and at 1366, 1447 and 1524 cm⁻¹ for dypingite. Very weak Raman bands at 790 cm⁻¹ for artinite and 800 cm⁻¹ for dypingite are assigned to the CO₃²⁻ν₂ out‐of‐plane bend. The Raman band at 700 cm⁻¹ of artinite and at 725 and 760 cm⁻¹ of dypingite are ascribed to CO₃²⁻ν₂ in‐plane bending mode. The Raman spectrum of artinite in the OH stretching region is characterised by two sets of bands: (1) an intense band at 3593 cm⁻¹ assigned to the MgOH stretching vibrations and (2) the broad profile of overlapping bands at 3030 and 3229 cm⁻¹ attributed to water stretching vibrations. X‐ray diffraction studies show that the minerals are disordered. This is reflected in the difficulty of obtaining Raman spectra of reasonable quality, and explains why the Raman spectra of these minerals have not been previously or sufficiently described. Copyright © 2008 John Wiley & Sons, Ltd.     

基于向量空间模型的岩屑LIBS光谱分类识别方法

向量空间模型最初用于文献检索,该模型是通过对文献内容进行特征文本提取后,将文献转换到文本向量空间,然后在文本向量空间中通过计算文献的特征文本向量与检索文本的特征文本向量的相似度,实现文献的检索,该方法基于模式识别中模板匹配的最近邻原则。针对光谱数据的特点和模式识别中模板匹配的基本原则,将向量空间模型引入基于样品光谱的分类识别。通过训练集中光谱数据获得各样品的光谱数据模板,提取训练集中各样品光谱数据模板特征峰的波长和相对强度信息,构建特征峰信息数据库,计算获得特征峰信息权值,将光谱数据转换到特征峰向量空间,获得各样品光谱数据模板的特征峰向量,构建样品特征峰向量数据库。同理获得预测集样品光谱的特征峰向量,在特征峰向量空间中通过计算预测集样品特征峰向量与样品特征峰向量数据库中各样品模板特征峰向量的余弦值,完成对预测集样品的分类识别。以岩屑样品的LIBS光谱为研究对象,将向量空间模型应用于LIBS光谱的分类识别。分类结果表明,该方法能够实现对岩屑样品LIBS全谱的快速分类识别,且在对预测集光谱数据进行平均处理后,分类准确率为100%。提出的基于向量空间模型的LIBS光谱分类方法可以拓展应用于其他光谱数据的分类识别。     

CO2 Injection in Geological Formations: Determining Macroscale Coefficients from Pore Scale Processes

Carbon dioxide (CO₂) injections in geological formations are usually performed for enhanced hydrocarbon recovery in oil and gas reservoirs and storage and sequestration in saline aquifers. Once CO₂ is injected into the formation, it propagates in the porous rock by dispersion and convection. Chemical reactions between brine ions and CO₂ molecules and consequent reactions with mineral grains are also important processes. The dynamics of CO₂ molecules in random porous media are modeled with a set of differential equations corresponding to pore scale and continuum macroscale. On the pore scale, convective–dispersive equation is solved considering reactions on the inner boundaries in a unit cell. A unit cell is the smallest portion of a porous media that can reproduce the porous media by repetition. Inner boundaries in a unit cell are the surfaces of the mineral grains. Dispersion process at the pore scale is transformed into continuum macroscale by adopting periodic boundary conditions for contiguous unit cells and applying Taylor-Aris dispersion theory known as macrotransport theory. Using this theory, the discrete porous system changes into a continuum system within which the propagation and interaction of CO₂ molecules with fluid and solid matrix of the porous media are characterized by three position-independent macroscopic coefficients: the mean velocity vector , dispersivity dyadic , and mean volumetric CO₂ depletion coefficient .     

长江三峡工程库区千将坪滑坡地质特征及成因分析

 千将坪滑坡体位于三峡库区长江支流青干河的左岸,距三峡工程坝址44km。2003年7月13日零时20分,三峡库区秭归县千将坪村发生了山体基岩滑坡,造成15人死亡、9人失踪,4家乡镇企业被摧毁。文章通过对滑后详细地质调查,阐述了千将坪滑坡区地质条件,描述了滑坡发生的前兆现象以及滑坡发生滑动的过程,仔细分析了千将坪滑坡各要素的特征。根据滑坡体物质组成和结构的差异,把滑体物质自滑坡后缘至前缘分为块石堆积区、基岩裂解区、土夹块石区、漂砾卵石区。同时,文中研究了滑带土的物理力学性质,分析了滑坡体的成因机制,从地形地貌、岩性组合、构造条件详细论述了斜坡失稳的内因,认为导致斜坡失稳的外部因素有集中降雨、农田灌溉以及三峡蓄水3个方面的影响。     

汶川大地震后水坝建设中若干问题的思考

应用参数摄动法对可压缩N-S方程进行渐近展开,并取其零阶近似对高压下微管道液体流动 特性进行了分析．对任意截面形状和面积的微管道,在等温流动假设下将其截面形状、滑移 长度等对解的贡献转化为求解该截面的格林函数,并给出等截面圆形微管道流动的零阶近似 解．以此分析可压缩性、黏性以及壁面滑移等因素对高压下液体微管道流动特性的影响,进 一步揭示了高压驱动下液体微管道流动偏离经典Hagen-Poiseuille(HP)理论的原因．