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贵州铜仁坝黄磷矿中铀赋存状态的逐级化学提取研究 总被引：1，自引：1，他引：0
贵州铜仁坝黄磷块岩矿床富集放射性元素铀,利用逐级化学提取分析方法对该地区黄磷矿中铀的赋存状态进行探究,有助于进一步探讨磷块岩型铀矿的分布规律、成矿机理及铀资源的综合开发。本文采用经修改的Tessier法流程,提取了水溶态、可交换离子态、碳酸盐结合态、铁锰氧化物结合态、有机质黄铁矿态、强酸提取态和残渣态等七种不同形态的铀。研究发现:黄磷矿中的铀主要以独立铀矿物和类质同象置换的形式存在,分别占37.83%、37.21%,少量铀(占24.96%)以分散吸附形式存在。分析表明:独立铀矿物在富磷、黄铁矿脉和镜面擦痕发育的岩层中含量较高,说明热液活动有利于独立矿物形式铀的富集;类质同象铀与黄磷矿中的磷含量呈正相关关系,铀元素可能是以离子置换的方式赋存于胶磷矿的晶格缺陷中;吸附形态铀的含量受到岩石中黏土矿物含量和黄铁矿脉的影响,有机质黄铁矿态是吸附形态铀存在的主要方式,少量铀通过扩散作用吸附于黏土矿物表面。除类质同象铀因其存在形式不易被提取利用外,独立铀矿物及吸附形态铀对于未来优化资源配置具有现实意义。 相似文献
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混合价态和中间价态硫的Ｆｅ、Ｐｂ和Ｚｎ化合物在带状闪锌矿、黄铁矿－胶黄铁矿和方铅矿中形成普遍的包体和残留物。带状硫化物的品位常随带状的混合价和中间价态硫化物的提高而提高，后者具有纤维状的微细结构。纤维状微细结构同样存在于比利时和波兰Ｚｎ－Ｐｂ矿床中的带状闪锌矿和黄铁矿中。 相似文献
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不同类型黄铁矿对金的吸附实验 总被引：16，自引：1，他引：16
在稀溶液状态下的Ａｕ的吸附实验，较好地体现了地质热液过程中吸附作用在金矿成矿方面的重要性。黄铁矿与金的硫氢配合物的作用结果截然不同于黄铁矿与金的氯配合物的作用结果。黄铁矿对金的硫氢配合物的吸附是通过表面络合和静电吸附完成的，且不同类型黄铁矿有明显的吸附差异。矿物表面特性及非均匀催化可能在吸附过程中起了重要作用。金矿中常见的Ａｕ、Ａｓ和ｐ型黄铁矿三位一体的现象可能与Ａｓ对吸附作用的影响有较大关系。而 相似文献
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已知黄铁矿和方铅矿的导电性可划分为空穴导电、电子导电、离子导电和混合型导电性。在硫化物矿床中,黄铁矿和方铅矿的导电性类型具有明显的垂直分带性,可作为判断矿床侵蚀程度的标志。对许多硫化物矿床中的黄铁矿和方铅矿测试表明,其总的分带规律性是:下部层位中的黄铁矿和方铅矿以电子导电性为特征;中部变为混合型导电性;上部以空穴导电性为主。如果在金矿床的地表,电子导电性的黄铁矿与空穴导电性的 相似文献
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硫化物矿物标准物的研制 总被引：2，自引：0，他引：2
《岩矿测试》1995,14(2):81-113
研制的黄铁矿、黄铜矿、方铅矿和闪锌矿４个标准物质是国内首次成功研制的硫化物矿物成分分析标准物质，样品采用重选，磁选和电磁选等选矿技术提纯矿物，获得纯度大于９５％的单矿物样品。黄铁矿和闪锌矿用棒磨机少量多级粉碎至０．１４７ＭＭ，方铅矿和黄铜矿用于小型玛瑙球磨机粉碎至０．０９７ＭＭ。经单因素方差分析检验，均匀性符合要求，采用小包装在干燥，充氩气气氛中保存样品，使样品稳定性有足够保证。连续４年定期监测了 相似文献
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聚氨酯泡塑对不同价态金吸附性能的研究及应用 总被引：7，自引：0，他引：7
研究了聚氨酯泡沫塑料对不同价态金的吸附行为，选择了泡塑吸附和硫脲解脱以及用原子吸收法测定的最佳条件。方法已应用于黄铁矿和毒砂单矿物中价态金的测定，黄铁矿中各价态金的加和与总金量相符，加标回收实验Au(Ⅲ），Au(Ⅰ),Au(0)的回收率分别为98＝5％，98．8％和104％，为矿样中痕量金的价态分析提供了一个可靠的方法。 相似文献
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Carrick M Eggleston Andrew G Stack Kevin M Rosso Angela M Bice 《Geochemical transactions》2004,5(2):33
The reactivity of a mineral surface is determined by the variety and population of different types of surface sites (e.g.,
step, kink, adatom, and defect sites). The concept of "adsorbed nutrient" has been built into crystal growth theories, and
many other studies of mineral surface reactivity appeal to ill-defined "active sites." Despite their theoretical importance,
there has been little direct experimental or analytical investigation of the structure and properties of such species. Here,
we use ex-situ and in-situ scanning tunneling microcopy (STM) combined with calculated images based on a resonant tunneling model to show that observed
nonperiodic protrusions and depressions on the hematite (001) surface can be explained as Fe in an adsorbed or adatom state
occupying sites different from those that result from simple termination of the bulk mineral. The number of such sites varies
with sample preparation history, consistent with their removal from the surface in low pH solutions. 相似文献
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《Geochimica et cosmochimica acta》2005,69(2):389-398
Mn2+(aq) oxidation as promoted by hematite in the presence of molecular oxygen has been studied as a function of hematite particle size. This system is a good candidate to serve as a test of the change of particle reactivity as a function of size due not only to its importance in Earth/environmental processes, but also because it involves electronic coupling between the hematite and adsorbed manganese. The properties of nanoscale hematite, including size quantization of the electronic structure and the relative proportions of terrace vs. edge/kink sites, are expected to change significantly with the particle size in this size range. Experimental results from this study suggest that the heterogeneous manganese oxidation rate is approximately one to one and a half orders of magnitude greater on hematite particles with an average diameter of 7.3 nm than with those having an average diameter of 37 nm, even when normalized to the surface areas of the particles. The acceleration of electron transfer rate for the reactions promoted by the smallest particles is rationalized in the framework of electron transfer theory. According to this theory, for a reaction such as heterogeneous Mn oxidation, the rate depends on three factors: the electronic coupling between initial and final electronic states, the substantial reorganization energy for solvent and coordinated ligands between initial and final states, and the free energy of reaction (corrected for work required to bring reactants together). The adsorbed Mn is electronically coupled with the solid during the electron transfer, and changes in the electronic structure of the solid would be expected to influence the rate. The Lewis base character of surface oxygen atoms increases as the electronic structure becomes quantized, which should allow increased coupling with adsorbed Mn. Finally, as demonstrated previously by in situ AFM observations, the reaction proceeds most readily at topographic features that distort the octahedral Mn2+ coordination environment. This has the effect of lowering the reorganization energy, which effectively controls the magnitude of the transition state barrier. Previous studies of <10 nm diameter hematite nanoparticles have demonstrated a decrease of symmetry in the average coordination environment of surface atoms, supporting the idea that smaller sizes should correspond to a decrease in reorganization energy. 相似文献
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In a previous study, we described proximity effects on surfaces of the semiconducting minerals galena and pyrite, whereby a chemical reaction at one surface site modifies the reactivity of a remote surface site several Ångstroms or even nanometers away (Becker et al., 2001). The modification of interest does not arise because of a direct “through space” interaction between the two sites, but rather an indirect interaction via the electronic structure of the substrate. Here we investigate the distance and direction dependence of proximity effects using quantum mechanical modeling. The direct and indirect interactions between co-adsorbed oxygen atoms and between adsorbed oxygen atoms and point defects on vacuum-terminated galena (100) surfaces were modeled. Density functional theory cluster and plane wave pseudopotential calculations were used to calculate the modifications to the adsorption energy as a function of separation. Energy-distance plots indicate that the proximity effect energy can become very strong at separations decreasing below about 5 to 6 Å, and persist at increasing separations up to 12 Å in a slowly decaying form. A strong attractive indirect interaction out-competes direct electrostatic repulsion for O-vacancy interactions. An oscillatory asymptotic behavior is found for co-adsorbed O-O indirect interactions, which indicates that the proximity effect energy can vary with surface crystallographic direction. It implies the presence of a strong organizing force on like adatoms that may explain the progressive oxidation of certain sulfide minerals by patchwork growth. These findings begin to pave the way for improved adsorption isotherms and extended surface complexation models that will include the specific influence of semiconductor-type proximity effects. 相似文献
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WU Daqing DIAO Guiyi YUAN Peng PENG Jinlian 《《地质学报》英文版》2006,80(2):192-199
The adsorption of pentachlorophenol （PCP） onto quartz, kaolinite, illite, montmorillonite and iron oxides has been investigated by batch equilibrium techniques. The pH-dependent isotherms are curves with peak values, the position of which is at about pH = 5-6 depending on the mineral species. Based on distribution of both speciation of surface hydroxyls on minerals and PCP in solution a surface reaction model involving surface complexation and surface electrostatic attraction is presented to fit the pH-dependent isotherms, and both reaction constants are calculated. The results show that on quartz and phyllosilicate minerals the predominant adsorption reaction is surface complexation, meanwhile both of surface electrostatic attraction and surface complexation are involved on the iron oxide minerals. The reaction constants of surface electrostatic adsorption are usually one to three orders in magnitude, larger than that of surface complexation. The concentration-dependent isotherms can be well fitted by Langmnir equation with the correlation coefficient R〉0.93 for kaolinite and iron oxides. The maximum adsorption is found in the order： hematite 〉 lepidocrocite 〉 goethite 〉 kaolinite 〉 quartz 〉 montmorillonite ≈ illite, which can be interpreted by consideration of both reaction mechanism and surface hydroxyl density. The significant adsorption of PCP onto mineral surfaces suggests that clay and iron oxide minerals will play an important role as HIOCs are adsorbed in laterite or latertoid soil, which is widespread in South China. 相似文献
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Uranium(VI), which is often elevated in granitoidic groundwaters, is known to adsorb strongly to Fe (hydr)oxides under certain conditions. This process can be used in water treatment to remove U(VI). To develop a consistent geochemical model for U(VI) adsorption to ferrihydrite, batch experiments were performed and previous data sets reviewed to optimize a set of surface complexation constants using the 3-plane CD-MUSIC model. To consider the effect of dissolved organic matter (DOM) on U(VI) speciation, new parameters for the Stockholm Humic Model (SHM) were optimized using previously published data. The model, which was constrained from available X-ray absorption fine structure (EXAFS) spectroscopy evidence, fitted the data well when the surface sites were divided into low- and high-affinity binding sites. Application of the model concept to other published data sets revealed differences in the reactivity of different ferrihydrites towards U(VI). Use of the optimized SHM parameters for U(VI)-DOM complexation showed that this process is important for U(VI) speciation at low pH. However in neutral to alkaline waters with substantial carbonate present, Ca–U–CO3 complexes predominate. The calibrated geochemical model was used to simulate U(VI) adsorption to ferrihydrite for a hypothetical groundwater in the presence of several competitive ions. The results showed that U(VI) adsorption was strong between pH 5 and 8. Also near the calcite saturation limit, where U(VI) adsorption was weakest according to the model, the adsorption percentage was predicted to be >80%. Hence U(VI) adsorption to ferrihydrite-containing sorbents may be used as a method to bring down U(VI) concentrations to acceptable levels in groundwater. 相似文献
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In order to understand the adsorption mechanism of metal atoms to semiconducting surfaces, we have studied, as a model system, the vapor phase adsorption of Ag, Au, and Cu on the (001) surface of molybdenite (MoS2) and the subsequent surface diffusion of these adsorbates. Our scanning tunneling microscopy (STM) images show that, depending on the type of metal atom that is adsorbed, islands of a characteristic size (2 nm for Ag, 8 to 10 nm for Cu, two distinct sizes of 2 nm and 8 to 10 nm for Au), shape (well rounded in the lateral extension) and thickness (one monolayer for Ag, 1 to 1.5 nm for Cu) are formed during the initial stages of deposition. Whole islands are observed to surface diffuse without loss of size or shape. Despite the relatively large size of the copper islands on molybdenite, these islands surface diffuse extensively, suggesting that the Cu-S interaction is weak. Surface diffusion is only hindered once individual islands start to coalesce. As copper islands accumulate, the size and shape of the original islands can still be recognized, supporting the conclusion that these characteristics are constant and that monolayer growth occurs by the aggregation of islands across the surface.The strength and the nature of the Ag-S(MoS2) bond were further investigated by using molecular orbital calculations, ultraviolet photoelectron spectroscopy (UPS) and scanning tunneling spectroscopy (STS). By applying quantum mechanical approaches using a two-dimensional periodic molybdenite slab and hexagonal MoS2 clusters of different sizes with metal atoms adsorbed to them, it is possible to calculate the electron transfer between the mineral surface and the metal atom as well as the adsorption energy as a function of surface coverage. In addition, we used the results from the quantum mechanical runs to derive empirical potentials that model the characteristics of the forces within the crystal, within the adsorbed islands, and the metal and mineral surface. The combination of quantum mechanical calculations and empirical force field calculations explain the electronic structure and the highest stability of Ag islands that have seven atoms in diameter, which exactly agrees with the size of experimentally observed islands. UPS results also suggest that a specific new state is formed (approximately 4.5 eV into the valence band) which may describe the Ag-S bond because it does not occur in pure silver or molybdenite.This study shows how the combination of microscopic (STM), spectroscopic (STS, UPS), compositional (X-ray photoelectron spectroscopy, XPS) and molecular modeling (quantum mechanical and empirical) techniques is a useful approach to understand the nature of the metal to sulfide bond. Further insights may be gained concerning the natural association of certain metals with sulfides. 相似文献
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Nano-scale spatial confinement can alter chemistry at mineral–water interfaces. These nano-scale confinement effects can lead to anomalous fate and transport behavior of aqueous metal species. When a fluid resides in a nanoporous environments (pore size under 100 nm), the observed density, surface tension, and dielectric constant diverge from those measured in the bulk. To evaluate the impact of nano-scale confinement on the adsorption of copper (Cu2+), we performed batch adsorption studies using mesoporous silica. Mesoporous silica with the narrow distribution of pore diameters (SBA-15; 8, 6, and 4 nm pore diameters) was chosen since the silanol functional groups are typical to surface environments. Batch adsorption isotherms were fit with adsorption models (Langmuir, Freundlich, and Dubinin–Radushkevich) and adsorption kinetic data were fit to a pseudo-first-order reaction model. We found that with decreasing pore size, the maximum surface area-normalized uptake of Cu2+ increased. The pseudo-first-order kinetic model demonstrates that the adsorption is faster as the pore size decreases from 8 to 4 nm. We attribute these effects to the deviations in fundamental water properties as pore diameter decreases. In particular, these effects are most notable in SBA-15 with a 4-nm pore where the changes in water properties may be responsible for the enhanced Cu mobility, and therefore, faster Cu adsorption kinetics. 相似文献
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C. W. Yong M. C. Warren I. H. Hillier D. J. Vaughan 《Physics and Chemistry of Minerals》2003,30(2):76-87
The adsorption of alkali metal cations on a hydroxylated corundum surface was investigated using high-level electronic structure
calculations, with both cluster Hartree–Fock and periodic density-functional theory approaches. The work concentrates on the
structural aspects of binding sites with threefold oxygen coordination at the basal (0001) surface. It was found that adsorption
at different sites can give rise to a wide range of adsorption energies, which strongly depends on the freedom of surface
hydrogen atoms to adjust their positions. Alkali metal adions from Li+ to Cs+ were studied with the cluster method, periodic plane-wave pseudopotential calculations being carried out for K+ adsorption to validate the cluster results. A site above an octahedral interstice was found to be the least preferred for
cation adsorption, despite having the lowest repulsion from surface aluminium atoms. The strongest adsorption was found over
an aluminium atom in the second layer, because the hydroxyl groups could reorient towards the neighbouring octahedral interstices,
and hence significantly decrease repulsion with the cation. The adsorption energy and the first three interlayer spacings
parallel to the basal surface change systematically with ionic size for each adsorption site. Many of these trends extend
to adsorption of Ca2+, Co2+ and Pb2+, which were also investigated, although a redistribution of 3d electrons in Co2+ results in strong adsorption even at an unfavourable site. The results suggest that it may be possible not only to predict
adsorption behaviour for a wide range of elements, but also to use experimental measurements of interplanar separations to
gain information about contaminated surfaces.
Received: 29 April 2002 / Accepted: 23 October 2002
Acknowledgements The authors thank the Natural Environment Research Council for support in carrying out this work. 相似文献