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41.
《Chemie der Erde / Geochemistry》2014,74(3):497-505
Chromium L3,2 energy loss near-edge structures (ELNES) of nine chromium compounds were measured in a transmission electron microscope to study the effect of valence state and site geometry of chromium on spectral features. The compounds studied represent a set of standards with given valence state and coordination. The chromium coordination is either octahedral or tetrahedral with different degree of distortion. The distortion of polyhedra results in a loss of the fine detail of spectral features in Cr L3,2 ELNES spectra. The effect of valence state manifests in a systematic chemical shift of the ELNES spectra by about 2 eV per oxidation state for octahedrally coordinated Cr and 0.4–1.4 eV per oxidation state for tetrahedrally coordinated Cr. On the basis of collected Cr L3,2 ELNES spectra we propose a simple quantification technique for the determination of chromium oxidation state in oxidic compounds which is independent of the coordination. 相似文献
42.
As part of a study on coastal sedimentary processes this paper presents the OSL dating of mixed coastal sediment samples from the southern North Sea island of Sylt (German Bight). During coring of the swash-bar (beach) sediments, five samples were presumably contaminated by younger overwash and aeolian sediments because of the sampling method employed. To obtain reliable burial ages for these swash-bar sediments, single-grain and small aliquot measurements were used together with the Finite Mixture Model (FMM) proposed by Roberts et al. (2000) to identify the grain population containing the largest doses (from the deepest part of the core). Before the FMM was applied to dating, the parameters and performance of the FMM were first investigated by systematically comparing small aliquot (∼20 grains) and single-grain measurements of an undisturbed aeolian and swash-bar sample and a laboratory mixture of both sediments. This test case demonstrates the advantage of selecting the time interval immediately following the initial luminescence signals for background subtraction because unsuitable quartz grains were removed from the dose distribution. It is concluded that the measurement of small aliquots can be regarded as a reliable proxy for single-grain dose distribution if the sediment contains only a small proportion of quartz grains emitting a luminescence signal and that the FMM results are relatively insensitive to changes of the over-dispersion parameter between 5–40% for small aliquots and 10–40% for single-grains.We show that the burial ages of the contaminated swash-bar samples resulting from the maximum age populations from equivalent dose distributions measured using small aliquots are consistent with the stratigraphy and with ages obtained from uncontaminated samples. 相似文献
43.
Assessing the effectiveness of nanoscale zero-valent iron particles produced by green tea for Cr(VI)-contaminated groundwater remediation 
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下载免费PDF全文 Nanoscale zero-valent iron particles (NZVI) produced by using green tea (GT) extract as a reductant can remove Cr(VI) from water effectively, which can be utilized in groundwater remediation. In order to define the reaction mechanism and removal effect in the aquifer, in this study, GT-NZVI particles were prepared and measured by some characterization methods to define their surface performance, and then batch and one-dimensional experiments were carried out to reveal the reaction properties of GT-NZVI and Cr(VI) in groundwater. The results showed that the prepared GT-NZVI particles were regular spherical with a diameter of 10–20 nm, which could disperse in water stably. The main component of GT-NZVI was α-Fe with superficial polyphenols as a stabilizer. GT-NZVI suspension had good ability to reduce the Cr(VI) to Cr(III) in water. When the concentration of GT-NZVI was 1 g/L, the removal efficiency of Cr(VI) with an initial concentration of 100 mg/L reached 92.8% in 1 h reaction. In column tests, GT-NZVI passed through the natural sand column successfully with an average outflow percentage of 71.2%. The simulated in-situ reaction zone (IRZ) with GT-NZVI was used to remediate Cr(VI) contaminated groundwater. The outflow concentration of Cr(VI) kept in 0.14–0.32 mg/L corresponding to the outflow rate below 0.32% within 15 days, and the removal efficiency of Cr(VI) by IRZ with GT-NZVI decreased with the increase of aquifer medium particle size, groundwater flow rate and ionic strength. Most of Cr(III) as reduzate was adsorbed or immobilized on the surface or in the lattice of GT-NZVI, which indicated effective immobilization for chromium. 相似文献
44.
山西省阳泉市山底河煤矿“老窑水”循环系统多年水质监测数据计算结果显示,煤矿酸性“老窑水”的Ca/Mg值普遍偏低,且存在Ca/Mg值随酸化程度的增强（SO42?含量增加或pH减小）而减小的规律。针对这一问题,结合研究区的地球化学物源条件,通过室内试验以及野外监测水样的石膏、方解石、白云石矿物饱和指数与pH变化关系,分析煤矿酸性“老窑水”低Ca/Mg值的成因机制。研究表明:区内石炭系－二叠系的煤系地层中碳酸盐岩夹层、分散状态分布的菱镁矿、黄铁矿是“老窑水”中Ca2+、Mg2+、SO42?的物质来源;在黄铁矿氧化水解形成的以硫酸根为主导的酸性溶液中（pH为2.0~4.5）,代表硫酸对石膏、方解石、白云石可溶解性的饱和指数排序为石膏>方解石>白云石,受石膏在高浓度硫酸活性降低并发生沉淀、方解石溶解受Ca2+同离子效应抑制和饱和状态的平衡调节的综合影响,使Ca2+相对含量减少,由于MgSO4溶度积大于CaSO4,故Mg2+含量未受上述约束（或较低）,脱白云岩化反应可因Ca2+含量随石膏沉淀而继续进行,加之区内有菱镁矿的溶解,使得Mg2+相对含量增加,最终出现了镁矿酸性“老窑水” Ca/Mg值低的结果。Ca/Mg值可作为煤矿酸性“老窑水”的污染特征指标,应用于环境影响评价。 相似文献
45.
In order to better understand the influence and mechanism of soil-derived humic acid (SHA) on adsorption of P onto particles in soils, the amounts of PO4 adsorbed by synthetic goethite (α-FeOOH) were determined at different concentrations of SHA, pH, ionic strength and order of addition of adsorbents. Addition of SHA can significantly reduce the amount of PO4 adsorption as much as 27.8%. Both generated electrostatic field and competition for adsorption sites were responsible for the mechanism by which SHA inhibited adsorption of PO4 by goethite. This conclusion was supported by measurement of total organic C (TOC), infrared spectral features and Zeta potential. Adsorption of PO4 onto goethite was inversely proportional to pH. Order of addition of PO4 and SHA can influence adsorption of PO4 as follows: prior addition of PO4 ⩾ simultaneous addition > prior addition of SHA. Iron and SHA apparently form complexes due to prior addition of SHA. Observations made during this study emphasized that PO4 forms different types of complexes on the surface of goethite at different pH, which dominated the interaction of SHA and PO4 adsorption on goethite. Based on these observations, the possible modes of SHA inhibition of PO4 adsorption on goethite were proposed. 相似文献
46.
《Marine pollution bulletin》2013,69(1-2):13-20
Many studies have investigated phototoxicity under controlled laboratory conditions, however, few have actually demonstrated it occurring in environmental samples. Here we report on the potential for UK marine coastal waters to demonstrate phototoxicity when tested using the oyster embryo (Crassostrea gigas) bioassay in the presence UV light. Subsurface water, sea surface microlayer samples and subsurface water samples that had been extracted through solid phase extraction (SPE) columns were analysed. Results demonstrated that the majority of samples failed to display any phototoxic potential. However, those collected from Belfast Lough did display an increase in toxicity when bioassays were performed in the presence of UV light when compared to identical samples assayed in the absence of UV light. Analysis of water samples at this location identified known phototoxic PAHs, pyrene and fluoranthene. These findings suggest the need to consider the potential UV light has when determining the toxicity of environmental samples. 相似文献
47.
Upper bound rigid block methods and finite element limit analysis are applied to investigate the undrained stability of rectangular tunnels. Solutions for a range of soil properties and tunnel geometries are obtained for situations in which the tunnel is wider than it is high. The upper and lower solutions for tunnel stability, which accurately bracket the true collapse load, are summarised in a series of stability charts for use in tunnel design. 相似文献
48.
《Marine pollution bulletin》2013,77(1-2):411-416
The concentrations of 16 polycyclic aromatic hydrocarbons (PAHs) were determined in mullet (Liza klunzingeri), water and sediment from northern part of Hormuz strait (Persian Gulf). The concentration levels of total PAHs in L. klunzingeri, water and sediment were 133.99–268.57 ng g−1 dry weight, 3.12–5.88 ng l−1 and 42.29–228.9 ng g−1 dry weight, respectively. Based on isomer ratios, analysis of the PAHs source in the sediment demonstrated that the PAHs come from pyrogenic and petrogenic origin. Risk assessment showed PAHs threshold concentrations to occasionally be exceeded in the study area. 相似文献
49.
We investigated the sensitivity change of multiple-elevated-temperature (MET) stimulated post-infrared infrared-stimulated luminescence (MET-pIRIR) signals as a response to irradiation, sunlight bleaching and heating using samples from the Mu Us Desert, central China. A strong dose dependence of MET-pIRIR signal sensitivity was observed. The intensity of the test-dose signals (Tx) increase with the pre-dose received. Furthermore, the signal sensitivity can be reset by sunlight bleaching or heating. This suggests that both the electron traps and hole centres in K-feldspar can be bleached by sunlight, and can, therefore, be used for dating. Using the test-dose signal as a monitor for sensitivity change, it was found that the sensitivity (or hole centres) saturate at a higher dose (D0 = ∼750 Gy) than the sensitivity-corrected signals (or electron traps) (D0 = ∼400 Gy). We propose a multi-aliquot regenerative-dose (MAR) MET-pIRIR dating protocol, which utilises the high saturation dose of hole centres. This protocol was tested using aeolian sediments from north China with ages ranging from 0 to 470 ka. It was found that, compared to the dose limit of ∼800–1000 Gy using the normal MET-pIRIR or pIRIR procedure, the new method can measure a natural dose of up to ∼1500 Gy and produce ages consistent with the expected ages for the samples investigated. 相似文献
50.
《Applied Geochemistry》2005,20(1):69-88
Surface sediments of the NW Aegean Sea were analyzed for clay mineral composition (94 samples), organic C and carbonate content, and major and minor elements (112 samples). Illite is the most abundant clay mineral, followed by smectite, chlorite and kaolinite. Clay minerals are preferentially deposited within the continental shelf and slope environment, due to the prevailing cyclonic circulation and the formation of flocs in the rivers’ pro-delta areas. The spatial distribution of major lithogenic elements (Si, Al, Ti, Fe) is substantially biased by the presence of relict sands located in the central-eastern part of the Thermaikos Gulf continental shelf. Biogenic elements (Ca, Sr) are noticeably pronounced on the northern flank of the North Sporades Islands. Organic C content and minor elements Cu, Zn, As and Pb are enriched markedly over the Thessaloniki Bay and Gulf suggesting substantial human impact, deriving largely from untreated or partly treated domestic and industrial effluents. The terrigenous component of the elements is preferentially contributed from the Axios River (Zn and Pb), the Aliakmon River (Cr, Co, Ni, Cu and As), and to a lesser extent from the Pinios River (V, Co, Ni and Cu); a considerable part of the metals originates in ultra-mafic and volcanic formations, which are abundant in the rivers’ catchment basins. Carbonate content exhibits great variability, with the highest values observed in biogenic sediments of the Sporades Basin. In the latter area, Mn (and Fe) oxides and hydroxides were found as coatings on calcite. The coatings were enriched in Cr, Co, Ni, Zn, As, Mo and Pb, due to adsorption or ion-exchange during early diagenesis. The combined influence of the river systems, the Thessaloniki metropolis, and the diverse sedimentological background, generates great patchiness in the distribution of major and minor elements. 相似文献