Surface pore tension and adsorption characteristics of polluted sediment

Most natural sediment particles have numerous pores and a complex surface texture which facilitates their adsorption of contaminants. Particle surface structure, therefore, is an important instrumental factor in the transport of contaminants, especially in water environments. This paper reports on the results of adsorption-desorption experiments to analyze polluted sediment surface pore tension characteristics performed on samples from the bottom of Guanting Reservoir. In our analysis, the Frenkel-Halsey-Hill (FHH) equation is applied to calculate the fractal dimensions of particles to quantify the surface roughness and pore tension characteristics. The results show that the surface fractal dimensions of sediment particle surfaces normally measure from 2.6 to 2.85. The volume of pores smaller than 10 nm changes significantly after being contaminated with pollutants and the fractal dimension decreases because the pores adsorb the contaminants. Supported by the National Science Fund for Distinguished Young Scholars (Grant No. 50325929) and the National Key Technology R&D Program during the 11th Five-Year Plan Period (Grant No. 2006BAB05B05)     

The mechanisms of contaminants release due to incipient motion at sediment-water interface

Sediments in many rivers and lakes are subjected to resuspension due to a combination of hydrodynamics.However,the roles of contaminant-contained dissolved and particulate sediments during the resuspension release are rarely studied.This study focuses on the release quantity of contaminants in both water phase and solid phase.Conservative tracer(NaCl)and reactive tracer(Phosphorus)were respectively added to cohesive fine-grained sediments and non-cohesive coarse-grained sediments.A range of typical shear stress was conducted to characterize the time-depended release of contaminants in a laboratory flume.When the sediment started to move,the concentration of contaminant in the overlying water increased with the bed shear stress,but the dissolved contaminants responded faster than the particulate ones.The observed contaminant release process can be divided into three main stages:the initial two hours fast mixing:the release contribution of pore water could reach up to 75%;the middle 4–6 h adsorption:the partitioning coefficient of contaminant between water phase and solid phase decreased over the time,and the adsorption of contaminates from resuspended sediment dominated the negative release;the last equilibrium stage:the desorption and adsorption reached equilibrium,and the reactive contaminant made an impact on the water quality in the solid phase.The existing formulas to evaluate the release flux are far from practice meaning as the sediment contaminants undergo a very complex release process.     

钼锑抗分光光度法对黄河表层沉积物中磷的形态分布及其吸附-解吸特征研究

采用标准测试程序(SMT)和钼锑抗分光光度法对黄河流域甘宁蒙段表层沉积物进行磷形态的提取和含量测定,同时模拟沉积物对磷吸附-解吸特性进行了探索。结果表明：对照不同的评价标准,12个采样点中总磷(TP)含量均处于不同程度的污染水平,特别是S12采样点磷具有较高的释放风险。TP、无机磷(IP)和钙结合态磷(HCl-P)之间及有机磷(OP)和铁/铝结合态磷(NaOH-P)之间分别呈现出较好的正相关性。沉积物的组成和理化性质对磷的赋存形态产生影响,OP和NaOH-P可能与As,Ni,Co和Pb有相同的污染源。表层沉积物对磷的吸附-解吸过程均符合伪二级动力学方程,主要受化学作用的控制,而磷的等温吸附符合Langmuir方程,且升高温度有利于磷的吸附。水相中离子浓度(KCl)小于0.02 mol·L-1时,吸附作用占优势,反之,解吸作用占优势。水土比的增大会提高沉积物对磷的吸附量。另外,磷的解吸量会随着温度的升高和扰动强度的增加而增大。揭示了黄河甘宁蒙段表层沉积物中磷的形态分布及其吸附–解吸特征,为黄河甘宁蒙段水环境治理和磷负荷调控提供依据。     

ICP-MS研究黄河河曲段表层沉积物对Pb(Ⅱ)和Cr(Ⅵ)的吸附-解吸特性

表层沉积物易于富集和释放水中重金属,是污染水体中重金属的源和汇,研究表明黄河河曲段水体中Pb和Cr重金属污染严重。以电感耦合等离子体质谱(ICP-MS)为检测手段,研究了在优化实验条件下,黄河河曲段表层沉积物对Pb(Ⅱ)和Cr(Ⅵ)的吸附特性和解吸特性。结果表明：黄河河曲段沉积物对Pb(Ⅱ)和Cr(Ⅵ)具有较强的吸附作用,在吸附初始5 min时吸附率均达到98%以上,且是自发的吸热过程(ΔG<0,ΔH>0)。动力学实验显示,两种离子的吸附过程均符合准二级吸附动力学。等温吸附方程拟合发现,Pb(Ⅱ)的吸附符合Langmuir模型,而Cr(Ⅵ)的吸附符合Freundlich模型。解吸过程符合Elovich方程,且受pH的影响较大。Pb(Ⅱ)和Cr(Ⅵ)二元体系竞争效应研究表明,Pb(Ⅱ)的吸附率大于Cr(Ⅵ),且均低于单离子吸附率。扫描电子显微镜(SEM)和孔径及比表面积分析显示,黄河河曲段表层沉积物表面结构不规则,且具有相对较高比表面积。该研究揭示了Pb(Ⅱ)和Cr(Ⅵ)在黄河河曲段沉积物上的吸附-解吸行为,对评估沉积物污染风险和污染修复、掌握重金属离子与沉积物之间的作用机理具有一定指导意义。     

光度法对不同水期黄河甘宁蒙段表层沉积物中磷积累程度和交换能力的比较研究

磷是水体富营养化的主要控制因素,在外源磷输入逐步得到控制后,作为内源磷主要来源的表层沉积物对黄河水体水质的影响作用不容忽视。掌握表层沉积物中磷的积累程度以及沉积物-水界面磷的交换能力,对区域内水环境的治理和磷负荷的调控具有重要的意义。选择黄河甘宁蒙段作为研究区域,分别采集丰水期(2011.07)、枯水期(2014.05)和平水期(2014.10)表层沉积物样品,使用标准测试程序(SMT)和钼锑抗分光光度法测定样品中磷赋存形态,并在实验条件下模拟表层沉积物对磷的等温吸附及吸附动力学过程。研究发现：(1) 相比于国内主要河流表层沉积物中磷的形态特征,黄河甘宁蒙段表层沉积物中有机磷(OP)和铁/铝结合态磷(NaOH-P)含量相对较低,钙结合态磷(HCl-P)含量较高;各形态磷含量的平均值均在丰水期最高,表明丰水期表层沉积物中磷的积累程度最高,黄河甘宁蒙段水环境受到沿程农业发展的冲击较大。因此,合理使用含磷化肥和优化灌渠退水水质是未来降低黄河水体磷污染风险的发展方向。(2) 基于低磷浓度下等温吸附中各采样点表层沉积物吸附-解吸平衡浓度(EPC₀)与判断水体发生富营养化的磷浓度阈值的比较发现,研究区域所有水期大多数采样点表层沉积物发挥着“磷源”的作用,存在向上覆水释放磷的趋势,且枯水期中多数采样点的EPC₀值较高,“磷源”作用更加明显;基于L模型和F模型对高磷浓度下等温吸附的拟合参数,显示丰水期表层沉积物对磷的持留能力最强,枯水期次之,平水期最小,所有采样点表层沉积物对磷的吸附过程均易发生;基于吸附动力学曲线的变化趋势可知,所选择的各采样点磷吸附量在反应开始的12 h内迅速增大,12~48 h内吸附量逐渐增加并趋于稳定;基于伪二级动力学方程对吸附动力学过程的拟合结果,表明表层沉积物对磷吸附过程的反应速率受化学吸附控制为主;从同一水期不同采样点吸附过程中的限速步骤不同及不同水期邻近采样点吸附过程中限速步骤均为微孔扩散的结果发现,表层沉积物组成和理化性质的差异对磷吸附速率的影响大于不同水期条件下上覆水流速和流量的变化。     

南海峡谷慕斯地层的近底声学探测

为测量南海深海表层沉积物反射特性,在探索一号TS12航次中,使用高频浅地层剖面仪搭载深海勇士号载人潜水器,潜水器下潜深度1578 m,高频浅地层剖面仪(110 kHz)近底作业高度约2 m,在南海北部琼东南盆地大陆坡峡谷进行了近底浅表沉积物反射测量。浅地层剖面图像表明峡谷海底表层2 m内沉积物存在5分层结构的慕斯地层。慕斯地层水-沉积物界面反射强度平均值-11.86 dB,标准差2.51 dB,原位取样结果测量得沉积物颗粒平均粒径7.2μm,反射系数与沉积物粒径结果均表明慕斯地层表面为泥质沉积物。慕斯地层处于大陆坡峡谷折弯处,其中的沉积物大量来自浊流输运,特殊的地理环境使不同时期经浊流输运而来的沉积物通过沉降形成了具有典型分层结构的慕斯地层。首次获得了慕斯地层的高分辨声学剖面图像,为研究海底表层沉积物的细致分层和声学特性提供了依据,同时由于慕斯地层汇聚了大量输运而来的沉积物,对海底沉积历史特性具有重要的研究价值。      

Sintering of a bcc structure of spherical particles of equal and different sizes

Solid-state sintering of a bcc structure of spherical particles has been studied numerically by use of simple shape parameters to describe the state of the unit cell. Both free and pressure-assisted sintering of particles of equal and different sizes for various ratios of boundary and surface diffusion have been considered. At low relative densities, the evolution of particle radius, interparticle junction radius and shrinkage predicted by the bcc model are rather similar to sintering of a simple row of particles. At higher densities, the porosity closes up; that is, the junctions start to interact, or the next-nearest neighbours in the particle structure attain contact. Quantative measures of the density at the transition from open pore space between the particles to closed porosity as well as the density at which the next-nearest neighbours start to touch are derived. Furthermore, different dihedral angles and the evolution of relative density and sintering stresses are studied.     

Variations of δ(15)N-Values and Hydrolyzable Amino Acids in Settling Particles in the Ocean

Abstract The modification of nitrogen isotopic signals during particle sedimentation in the sea is of great interest for the use of sedimentary δ(15)N-values as a paleoceanographic tool. The effect of organic matter degradation on such modification was studied by analyzing nitrogen, hydrolyzable amino acids (THAA) and δ(15)N-values in a suit of marine settling particles collected from the Bay of Bengal, Indian Ocean, by using time-series sediment traps, and in underlying sediments. The flux of settling particles showed temporal variations which are related to the monsoons, the major climatic feature of this marine region. During high flux periods settling particles are enriched in nitrogenous material that is less degraded and exhibit higher δ(15)N-values than particles showing characteristics of degradation. At the sediment surface more than 95% of the settling particulate nitrogen is lost and the δ(15)N-values of the residual sedimentary nitrogen are higher than those of settling particles. The observed increase is interpreted to be due to fractionation during degradation of organic matter.     

Water vapor sorption in starch granules

A mathematical model proposed for diffusion in spherical particles can be solved on a digital computer. The model includes particle size distribution and variable diffusion coefficient of the form D = Doe^αC, where D is the diffusion coefficient, D₀ and α are constants, and C is the moisture content. Isothermal experimental measurements were made gravimetrically on a Cahn electrobalance by vacuum sorption techniques. The model adequately predicts the absorption characteristics of water vapor in starch granules. Although swelling is neglected in the model, it does contribute to sorption characteristics.     

Pore-Resolving Simulations of Biomass Char Particle Combustion

Biomass char morphology affects combustion behavior at the particle scale for zone II conditions, in which both heterogeneous reaction and intra-particle diffusion govern the overall rate. Furthermore, particle-scale processes affect reactor-scale outputs, and reactor-scale simulations are sensitive to particle-scale models. However, most char particle combustion models employ coarse-grained, effective-continuum approaches, which treat all porosity at the subgrid-scale. Effective-continuum approaches are not valid or accurate in the presence of large, irregular pores which can approach the size of the particle. A 3-D, pore-resolving CFD simulation approach using real biomass char particle geometries obtained from X-ray micro-computed tomography (micro-CT) is therefore used to examine the impact of morphology on zone II combustion for pulverized (∼100 µm) biomass char particles for the first time. In contrast to larger, millimeter to centimeter sized particles, the sub-millimeter, high aspect ratio biomass char particles exhibited localized reactant penetration into the innermost regions of the particles, facilitated by the presence of large pores connected to the external surface. The oxygen mole fraction distributions were governed by the large pore morphology, were non-monotonic with distance from the surface, and achieved minima in thick microporous char regions surrounding the large pores. A comparison between the pore-resolving simulation and an equivalent, spatially resolved, effective-continuum simulation revealed that even in the microporous char, the effective-continuum model underpredicted reactant penetration. A careful comparison was then performed between 30 pore-resolving particle simulations and several effectiveness factor models that employed particle-specific parameters. Commonly used uniform cylinder models significantly underpredicted effectiveness factors for these real pulverized pine char particles, while accessible hollow cylinder models achieved less than 10% relative error when averaged over all 30 particles.     

活性炭吸附甲醛的格子Boltzmann模拟

基于孔隙尺度,结合活性炭与甲醛的真实物性参数,利用格子Boltzmann方法,选取热质耦合的LBGK模型对填充有球形活性炭的方腔内部双扩散混合对流、流固共轭传热及吸附特性进行数值模拟。分别采用二维D2Q9模型描述速度温度场,D2Q5模型描述浓度场,研究活性炭颗粒直径、孔隙率以及颗粒的排列方式对整个动态吸附性能的影响。结果表明：在孔隙率为0.85时,随着颗粒直径的增大,活性炭吸附甲醛的速率减小,达到饱和吸附状态所需的时间增长;当直径为0.43 mm时活性炭的吸附速率最大,达到饱和状态的时间最短;活性炭颗粒的吸附速率与达到吸附饱和所需的时间几乎与孔隙率无关;与活性炭颗粒的错列与顺列排列方式相比,随机且不粘连排列方式的动态吸附性能更好。     

低温流体在多孔表面的池沸腾研究综述

低温流体尤其是液氮在航天、电子冷却、低温生物医疗与超导磁体与电缆等领域有着广泛的应用.文中对光滑与多孔表面上的流体核态沸腾换热与临界热流密度的研究进行了归纳；总结了低温流体池沸腾的研究现状；比较了低温流体与常见制冷剂以及水在物性上的主要差异；综合分析了加热表面材料、多孔层厚度、孔隙率、烧结颗粒直径、平均孔隙直径与压力等...     

Variations of δ15N-Values and Hydrolyzable Amino Acids in Settling Particles in the Ocean

Abstract

The modification of nitrogen isotopic signals during particle sedimentation in the sea is of great interest for the use of sedimentary δ¹⁵N-values as a paleoceanographic tool. The effect of organic matter degradation on such modification was studied by analyzing nitrogen, hydrolyzable amino acids (THAA) and δ¹⁵N-values in a suit of marine settling particles collected from the Bay of Bengal, Indian Ocean, by using time-series sediment traps, and in underlying sediments. The flux of settling particles showed temporal variations which are related to the monsoons, the major climatic feature of this marine region. During high flux periods settling particles are enriched in nitrogenous material that is less degraded and exhibit higher δ¹⁵N-values than particles showing characteristics of degradation. At the sediment surface more than 95% of the settling particulate nitrogen is lost and the δ¹⁵N-values of the residual sedimentary nitrogen are higher than those of settling particles. The observed increase is interpreted to be due to fractionation during degradation of organic matter.     

Thermal diffusion in micropores by molecular dynamics computer simulations

This work focuses on the identification of the main microscopic processes that influence thermal diffusion (the Soret effect) in a fluid mixture confined in an uncorrugated slit pore. To achieve this purpose, a boundary driven nonequilibrium molecular dynamics scheme is applied on binary mixtures of super-critical Lennard–Jones (LJ) spheres representing methane and n-decane. Following previous work, we perform a systematic study of the influence of the parameters used to describe a model slit pore on an effective thermal diffusion factor. Among these parameters are: The nature of the reflection of the diffusing particles on the walls (specular or diffusive), the pore width with respect to the particle size and the fluid-wall potential strength. Simulations were run both on equimolar and non-equimolar mixtures. The results indicate that thermal diffusion is effectively lowered only for strong fluid–wall interactions. It is shown that the general trends, which are different under sub- and super-critical conditions, can be explained by a careful analysis of the relative sorption energies of the two compounds.     

Sorption and diffusion behaviours of strontium in sodium-type bentonite bed

Sorption and diffusion of Sr were examined using a typical Japanese bentonite. The experimental results showed that Sr sorption on the bentonite had linear relationship between the equilibrium Sr concentration and Sr sorption amount, i.e., Henry’s type of sorption, in wide initial Sr concentration from 1.1 × 10^?9 to 1.1 × 10^?4 mol L^?1 at pH 10. The Sr sorption also indicated pH dependence in pH range between 2 and 12. Sorption modelling calculation indicated that cation-exchange reactions contributed to Sr sorption in the pH range studied and a surface complexation reaction was predominant above pH 8. Diffusion of Sr in loosely compacted bentonite bed was described by pore and surface diffusion and surface complexation of Sr. Chemical-transport calculations reproduce the diffusion data at pH 5 using the cation-exchange parameters obtained in the analysis of the batch sorption experiment.     

Optical Properties of Ag and Au Nanoparticles Dispersed within the Pores of Monolithic Mesoporous Silica

The optical absorption of silver and gold nanoparticles dispersed within the pores of monolithic mesoporous silica upon annealing at elevated temperatures has been investigated. With decreasing particle size, the surface plasmon resonance position of the particles blue-shifts first and then red-shifts for silver/silica samples, but only red-shifts for gold/silica samples. This size evolution of the resonance position is completely different from that previously reported for fully embedded particles. We assume a local porosity at the particle/matrix interface, such that free surface of particles within the pores may be in contact with ambient air, and present a two-layer core/shell model to calculate the optical properties. These calculations also consider deviations from the optical constants of bulk matter to account for corresponding effects below about 10 nm particle size. From the good agreement between experimental results and model calculations, we conclude a peculiar particle/ambience interaction dominating the size evolution of the resonance. Because of the difference of core electron structure, the relative importance of the effects of local porosity and free surface, respectively, are different for silver and gold. For silver, the effect of the local porosity is stronger, but for gold the opposite is found.     

Sound absorption of cellular metals with semiopen cells

A combined experimental and theoretical study is presented for the feasibility of using aluminum foams with semiopen cells for sound-absorption applications. The foams are processed via negative-pressure infiltration, using a preform consisting of water-soluble spherical particles. An analytical model is developed to quantify the dependence of pore connectivity on processing parameters, including infiltration pressure, particle size, wetting angle, and surface tension of molten alloy. Normal sound-absorption coefficient and static flow resistance are measured for samples having different porosity, pore size, and pore opening. A theory is developed for idealized semiopen metallic foams, with a regular hexagonal hollow prism having one circular aperture on each of its eight surfaces as the unit cell. The theory is built upon the acoustic impedance of the circular apertures (orifices) and cylindrical cavities due to viscous effects, and the principle of electroacoustic analogy. The predicted sound-absorption coefficients are compared with those measured. To help select processing parameters for producing semiopen metallic foams with desirable sound-absorbing properties, emphasis is placed on revealing the correlation between sound absorption and morphological parameters such as pore size, pore opening, and porosity.     

Pore matrices prepared at supercritical temperature by computer simulations: matrix characterization and studies of diffusion coefficients of adsorbed fluids

We present series of molecular dynamics simulations to study the structure of different porous matrix configurations. The present simulations are an extension of recently reported data at a temperature below the critical. Here, we show how temperature modifies the structure and porosity of pore matrices during their preparation in comparison with the previous work. Moreover, in these studies at a higher temperature, we studied in more detail the structure of the porous matrix. Matrices were prepared by two different processes. The first method consisted of a single Lennard-Jones fluid simulated at a fixed density and at a supercritical temperature. Then, the matrix configuration was taken from the last configuration of the fluid. The second method was prepared from a binary mixture, where one of the components served as a template material. The final porous matrix configuration was obtained by removing template particles from the mixture. Matrices were prepared at two different densities and at different matrix particle interactions. The volume distribution, the cluster formation and the connectivity between the particles in the pore matrix were investigated. The importance of using template particles was clear since they produced larger voids and higher porosities. On the other hand, the temperature of preparation seems to modify the size of the voids and the porosity in the matrices. For instance, at this high temperature, the matrix porosity is higher when template particles are present in the system. These results point in the opposite direction compared to those found in a previous paper at a lower temperature. The diffusion of fluids immersed in the different matrices was also analysed by calculating the mean square displacements of their particles. It was observed that this quantity was higher when matrices were prepared with template particles. These results also point to different directions in contrast with pore matrices prepared at a lower temperature. Finally, the results show that temperature plays an important role in the pore matrix formation.     

Surface characterization by nitrogen adsorption of silica aerogels synthesized from various Si(OR)4 and R″Si(OR′)3 precursors

We report the surface characterization by nitrogen adsorption-desorption technique of organically surface-modified silica aerogels. These solids were prepared through a sol-gel process from various combinations of silicon precursors and co-precursors with the aim of obtaining identically modified materials. The silicon precursors are based on four identical hydrolysable alkoxy groups (methoxy or ethoxy) whereas one of the alkoxy groups in the co-precursors is substituted by a non-hydrolysable alkyl group (methyl, ethyl, n-propyl, iso-butyl, n-octyl, vinyl or phenyl). Obtained alcogels were dried under carbon dioxide supercritical conditions and their specific surface area, pore volume, mesoporosity and pore size distribution were investigated. Mesoporous materials exhibiting high specific surface areas and total pore volumes were obtained, revealing a decreasing porosity along with the use of co-precursors having larger side chains.