加速溶剂萃取-流体控制系统净化-高分辨气相色谱/高分辨质谱定量测定底泥中的二噁英

采用高分辨气相色谱/高分辨质谱(HRGC/HRMS)定量测定了底泥中的17种2,3,7,8位多氯代二噁英和呋喃(PCDD/Fs) ,并测定了四至八氯取代的二噁英和呋喃总量。样品经加速溶剂萃取,然后通过流体控制系统（FMS）自动过硅胶柱、氧化 铝柱和碳柱净化,最后浓缩。以HRGC/HRMS电压选择离子检测模式对样品中的PCDD/Fs进行了定性分析,采用同位素稀释 技术定量,该方法可精确定量到pg/g水平。结果表明该方法分析的17种二噁英和呋喃异构体的检出限可达0.1 pg/g。同 位素标准的回收率为49.8%～85.3%,样品中各异构体的回收率为93.2%～115.6%。该方法不但满足国际标准的要求,还大 大提高了分析速度,使分析周期从原来的2周缩短到2 d以内。     

鱼咀及丁坝对长江口航道分流分沙的影响

利用水平二维水流、盐度、泥沙数学模型研究了长江口航道整治工程(一期)实施前后,航道的分水分沙特点,重点讨论了束水丁坝的长度、潜堤的方向对航道分流比、分沙比的影响．数值模拟结果表明,双导堤工程减少了航道的分沙量,这有利于维护航道的畅通,但同时也使航道的分流比减小．航道分流分沙比的改变可通过调整各水工建筑物的布置或尺寸来实现．与束水丁坝长度的影响相比,鱼咀工程潜堤方向的改变对航道分流分沙比的影响更大．     

振荡流底层拟序结构及其与泥沙相互作用研究

湍流拟序结构与泥沙及床面相互作用的机理, 是目前国内外泥沙学术界研究的热点领域. 本文针对单向流和振荡流底边界层的湍流拟序结构与泥沙相互作用研究状况进行了综述, 重点论述了振荡流底边界层湍流研究的概况与今后需要开展的重点研究内容.      

Two-dimensional sediment transport models for sand-bed rivers

The problem of determining the specific mass flow of sediment entrained by a liquid flow passing above the sand bottom is studied. The boundary-value problem for a two-phase mixture of the liquid and solid particles in the active bottom layer is solved, and a general formula for determining the specific mass flow of sediment is derived. Constraints imposed on the rheological model of a moving mixture, which allow the phenomenological parameter (concentration of particles in the active layer of the mixture) to be eliminated from the model, are found. Within the framework of the proposed rheological model, the equation of riverbed deformations in the case of a sand bottom is obtained. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 3, pp. 131–139, May–June, 2009.     

黄茅海波-流共同作用下的三维悬沙数值模拟

针对黄茅海河口区波流相互作用显著、三维空间结构明显及泥沙运动复杂等特点,联合第3代海浪模式SWAN,建立了波流共同作用下的三维悬沙数学模型.在水流计算中,考虑了波浪产生的辐射应力影响,波浪依赖的表面风应力影响及波浪影响下的底部剪切应力,并采用k-kl紊流闭合模型提供垂向涡粘系数和垂向扩散系数.悬沙扩散方程中的源函数利用切应力法确定,泥沙沉降速度考虑絮凝作用,从而提高黄茅海悬沙场数值模拟精度.通过含沙量实测资料验证,模拟值与实测值符合较好.在模型验证的基础上,讨论了不考虑波浪与考虑波浪两种情况下黄茅海的悬沙分布特征,为工程实际研究提供了依据.     

Mössbauer spectroscopic study on chemical changes of iron compounds with the aid of sulfate-reducing bacteria

⁵⁷Fe Mössbauer spectra were measured of reaction products formed during an incubation experiment with sulfate-reducing bacteria, which were isolated from estuarine sediments of the Tama River in Tokyo. The spectrum of the product incubated for several days showed some overlapping sextets. This product had a different chemical form from amorphous iron monosulfide produced by inorganic reaction between ferrous and sulfide ions. It was estimated that the structure of nearest neighbor of iron in this product was similar to that of pyrrhotite (Fe_1?x S). After several months of incubation, other singlet and doublet appeared successively on the spectrum, corresponding to mackinawite (FeS_1?x ) and new sulfide, respectively. Both values of isomer shift and quadrupole splitting of new sulfide increased with increasing incubation time and approached those of pyrite (FeS₂). Extended X-ray absorption fine structure (EXAFS) showed that iron atoms were coordinated by sulfur in the incubation product.     

Comparison between Total Determination and Extractable Heavy Metals from River Sediments using Conventional and Microwave Accelerated Leaching Tests

Abstract

In the present study the concentration of heavy metals (Cu, Cr, Ni, Pb and Zn) in sediments collected from different sampling stations of the Leça river (Portugal) was determined, using Flame Atomic Absorption Spectrometry. In order to estimate the potential mobility of metals in these samples, the results of the total digestion were compared with those obtained by single extractions using EDTA and acetic acid as extractant solutions; in all samples studied, Cu and Zn were found to be the most mobile elements; Ni and Pb showed a smaller mobility in presence of either acidic medium and complexing ligands; Cr was found the least mobilizable element, given that the low extractability obtained with the two extractants tested in this work. In the single extraction tests, microwave energy was also employed to replace the conventional treatment and only in the case of the EDTA the results obtained were similar to those of the conventional procedure (recoveries between 90.16 and 98.76%); the precision (RSD, n=3) of the proposed microwave procedure for EDTA extractions was comparable to those of the conventional method with values always lower than 8% for all metals.     

The Determination of Arsenic in Soil and Sediment Digests by Graphite Furnace Atomic Absorption Spectrometry

Abstract

A method for the determination of As in siliceous materials from a fluoboric acid matrix by GFAAS is described. The basic analytical procedure also permits the measurement of major, minor and other trace elements by flame or graphite furnace AAS as appropriate. For As analysis, the incorporation of matrix modification with Ni and of corrective measures to overcome interference by Al, Na and Si are discussed. The validity of the method is demonstrated by the accurate analysis of four international standard reference materials and agreement with instrumental neutron activation analysis results for As in environmental samples. One application to the study of As geochemistry in lacustrine sediments is presented.     

Influence of the grain size on the quality of standardless WDXRF analysis of river Nile sediments

In multichannel wavelength-dispersive X-ray fluorescence spectrometry (WDXRF) the fluorescence intensity might depend on grain size and heterogeneity of the sample. Six river Nile sediment samples were collected two meters below the water surface from different locations covering the greater Cairo, Egypt. Each sample was dried at 65 °C for 48 h and divided into four grain size fractions: < 32 μm, 32–63 μm, 63–125 μm and 125–200 μm using different sieves. The dry sediment samples were mixed with low contamination binder (Wax, C₆H₈O₃N₂) in a mass ratio of wax:sample = 4:0.9 g. Sample pellets were made using a hydraulic press at a pelletizing pressure of 120 KN cm^{− 2}. The results show that the XRF intensities of the K_α radiation might increase or decrease with decreasing grain size, depending on the atomic number of the analyte. In the present thick pelletized samples, the penetration depth of the characteristic radiation increases at low grain sizes, and consequently the probability of the grain-size effect on the characteristic radiation decreases. Depending on the experimental data, a general theoretical equation, relating fluorescence intensity, grain size and atomic number, was derived by using cubic spline interpolation. The fractions were identified by WDXRF using standardless quantitative analysis, depending on the fundamental parameter approach. According to the present statistical analysis and the Certified Reference Material (CRM) results, the quantitative analysis results were found acceptable when the grain size of the river Nile sediments less than 32 μm. At a grain size > 63 μm, standardless analysis using fundamental parameter approach was found to be useful for qualitative and semi-quantitative analysis only whereas there are a strong positive correlations.     

Improvements on bed‐shear stress formulation for pier scour computation

This paper introduces an improved formula for the bed‐shear stress by applying the vorticity effect and its application in a 3D flow and sediment model to estimate scouring around bridge piers. Up to now, the sediment transport formulae used for computing pier scour were developed based on the general scouring in unobstructed flow. The capability for numerical models to predict local scour around bridge piers was severely restricted by the sediment transport formulae. The new formula introduced in this paper can take into account vortices that affect the local scour process by adding some terms into the classic bed‐shear stress equation. The 3D numerical model system used in this study consists of three modules: (a) an unsteady hydrodynamic module; (b) a sediment transport module; and (c) a Fation module. The hydrodynamic module is based on the 3D RANS equations. The sediment transport module is comprised of semi empirical models of suspended load and non‐equilibrium bed load. The bed‐deformation module is based on the mass balance for sediment. The model was used to simulate pier scour in tree different test cases: (1) a circular pier; (2) a square pier; and (3) a rectangular pier, by applying the ordinary sediment equation and the newly introduced sediment equation. Results of both numerical simulations were compared against laboratory measured data and also in case 1 with result of Olsen and Melaaen (J. Hydraul. Eng. 1993; 119 (9):1048–1054). Comparisons show that the new sediment formula could predict the scour more accurately than the ordinary one. Copyright © 2010 John Wiley & Sons, Ltd.