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1.
Hyperfiltration of potassium nitrate through clay membranes under relatively low-head conditions 总被引：2，自引：0，他引：2
Megan Hart 《Geochimica et cosmochimica acta》2005,69(20):4817-4823
Much like reverse osmosis membranes, clays have been shown to exhibit reverse osmosis properties at high hydraulic heads. To determine if reverse osmosis was possible at lower hydraulic heads, potassium nitrate solutions were passed through thin clay layers at heads of 1.30 to 1.42 m. In each experiment, concentrations significantly increased due to partial solute rejection by the clay membranes. Concentration increases within the experimental cells were between 131% and 184%. Calculated values of the reflection coefficient ranged between 0.55 to 0.70, suggesting that these thin clay layers exhibited membrane effects. The results of these experiments suggest hyperfiltration may concentrate some dissolved contaminants from below to above regulatory limits in shallow aquifers bounded by a membrane-functioning aquitard or relatively low hydraulically conductive geologic strata. Hyperfiltration may also control nutrient distributions, creating subsurface microbial “hotspots”. Consideration of hyperfiltration effects may ultimately lead to a clearer understanding of many subsurface processes, both shallow and deep, including contaminant fate and transport, subsurface microbiology, natural bioremediation and attenuation, redox, rock-water interaction, and groundwater chemistry. 相似文献
2.
Hyperfiltration of Nacl Solutions Using a Simulated Clay/Sand Mixture at Low Compaction Pressures 总被引：1，自引：0，他引：1
It is widely recognized that clays and shales can demonstrate membrane properties. When a hydraulic head differential exists
across a membrane-functioning clay-rich barrier, some of the solute is rejected by the membrane. This process is known as
hyperfiltration. Some shallow geologic environments, including aquitards bounding shallow perched aquifers and unconfined
aquifers, some river and stream beds, and some lake bottoms contain clay–soil mixes. Many engineering structures such as landfill
liners, mixed soil augered barriers, and retention pond liners also consist of soil–clay mixes. No previous testing has been
performed to investigate the likelihood that hyperfiltration may occur in such mixed soils. Therefore, we performed five experiments
using different mixes of Na-bentonite and glass beads (100, 50, 25, 12 and 0% clay) to determine if any of these mixes exhibited
membrane properties and to investigate what effect clay content had upon the membrane properties of the soil. Each mixture
was compacted to 345 kPa and the sample mixtures were 0.58–0.97 mm thick. All the experiments used an approximately 35 ppm
Cl− solution under an average 103 kPa hydraulic head. Experimental results show that all the simulated clay–sand mixtures do
exhibit measurable membrane properties under these conditions. Values of the calculated reflection coefficient ranged from
a low of 0.03 for 12% bentonite to 0.19 for 100% bentonite. Solute rejection ranged from 5.2% for 12% clay to a high of over
30% for the 100% clay. The 100% glass bead sample exhibited no membrane properties. 相似文献
3.
Three relatively low-head hyperfiltration experiments were conducted to investigate clay membrane behavior at lower hydraulic heads. Dilute Cl− solutions (187 and 336 mg/L) were forced through thin layers of kaolinite (0.67–1.62 mm) under heads ranging between 1.45 and 1.89 m. At the end of each experiment, there was a Cl− concentration increase (15–29%) within the cell. The concentration increase is attributable to solute-sieving by the kaolinite. Calculated final concentration increases at the membrane face ranged between 1.51 and 1.65 times the initial concentration and the calculated values of the reflection coefficient ranged between 0.35 and 0.40. These experiments show that clays are capable of significant hyperfiltration effects at lower pressure heads more typical of natural aquifers. Consequently, hyperfiltration effects may need to be considered in a broad spectrum of shallow subsurface processes in which these effects have been regarded as inconsequential; particularly in perched aquifers. 相似文献
4.
Hyperfiltration is the ability of a membrane to retard the passage of a solute under a hydraulic head in excess of osmotic pressure. Disaggregated and recompacted shales, mudstones, clays and tuff have been shown to exhibit hyperfiltration-induced membrane effects in past experiments. However, limestone and dolomite have not previously been tested. Therefore, eight hyperfiltration experiments were performed on intact Burlington Limestone and Jefferson City Dolomite to assess the membrane properties of these lithologies. Four experiments were conducted on each lithology using 0.0050 and 0.0100 M Cl− solutions at heads of 0.50 and 1.00 m. Reflection coefficients, a measure of osmotic efficiency, ranged from 0.34 to 0.39 for the Burlington Limestone and 0.32 to 0.40 for the Jefferson City Dolomite. At the end of the hyperfiltration experiments, Cl− was concentrated within the cell above input concentrations by 85–95% for the Burlington Limestone and 79–105% for the Jefferson City Dolomite. An additional experiment passed 0.0020 M dissolved silica solution through the Burlington Limestone at a head of 0.965 bar (14 psi). The final concentration of silica within the cell was 0.0043 M dissolved silica at steady-state; a concentration 114% higher than the original input solution concentration. The reflection coefficient for this experiment was calculated to be 0.33. The results of these experiments suggest that membrane properties in these lithologies may be worthy of consideration in some geologic scenarios, including: (1) shallow or perched aquifers bounded by thin limestone or dolomite strata, (2) overpressured aquifers bounded by limestone or dolomite, (3) limestone or dolomite bounded aquifers with significant vertical components of flow, and (4) facies changes with significant lateral component of flow bounded by either lithology. Furthermore, the results suggest that silica cementation may be possible even under relatively low head conditions. Cementation due to hyperfiltration, even at shallow depths and low pressures should be further investigated. Similarly, other low permeability lithologies lacking a charged surface could potentially function as geologic membranes. 相似文献
5.
《Applied Geochemistry》1994,9(5):533-546
Experiments suggest that increasing electrolyte flux into a compacted smectite membrane may result in greater permeability of the membrane to the electrolyte. The influx of electrolyte into the membrane pores decreases the double layer thickness, therefore reducing the clay's ability to exclude anions. As a result, solute previously accumulated in the concentration polarization layer (CPL) may be able to dissipate through the membrane, producing a temporary situation where the effluent is more concentrated than the feed solution. Of course, at some juncture the CPL will diminish sufficiently so that the effluent concentration will be the same as that of the feed solution and a true state will be reached.The fact that increasing electrolyte concentration within the clay membrane decreases the membrane efficiency implies that the result of solute accumulation in geological basins, even though a portion of such accumulation is attributable to the solute filtering ability of low permeability rocks, is the ultimate cessation of membrane effects. At the start of the cycle, shale membranes have low solute concentrations and thus high rejection capabilities. The largest amount of solute accumulates deep in the basin center, where vertical flux rates are high. Because of greater solute concentration within the aquifer, the solute concentration in the centrally located membranes rises more quickly than that of those located near the basin margins. Therefore, the cessation of membrane effects occurs first in the deep center of the basin and gradually moves upward and outward toward the basin margins. The fact that membrane efficiency decreases as pore solute concentration increases might help explain why conclusive trends attributable to membrane effects have not been more commonly observed in the subsurface. 相似文献
6.
溶质在土工合成衬垫（GCL）长期入渗过程中具有明显的化学-渗透特性。室内渗透试验表明：阳离子之间的置换效应对GCL衬垫渗透系数影响较大,10 mM的CaCl2溶液使渗透系数上升至2.5×10-11 m/s,而30 mM的CaCl2溶液使渗透系数上升至5.6×10-11 m/s。渗透液体浓度的增加缩短了溶质穿透GCL的时间,且预饱和处理试剂对GCL渗透系数的变化影响较大,采用蒸馏水作为预饱和试剂处理GCL衬垫对其渗透系数的影响明显小于CaCl2溶液;建立了考虑膜效应和离子交换效应条件下溶质运移耦合动力学模型,并对GCL穿透试验过程中溶质浓度的变化进行了预测,仿真计算结果表明,10 mM和30 mM两种CaCl2溶液渗透条件下,Ca2+浓度变化的试验结果和计算结果均相吻合,验证了耦合动力学模型的可靠性;从Ca2+浓度及流量穿透曲线分布可知,化学-渗透效应可有效地延缓溶质的迁移速度。随着溶质浓度的降低,阻滞作用更显著。因此,在分析GCL衬垫中溶质入渗特征时,必须考虑化学-渗透效应的影响。 相似文献
7.
Flux equations for liquid and solute migration through clay barriers that behave as semi-permeable membranes used in waste containment and remediation applications, known as clay membrane barriers (CMBs), are discussed. The results of a simplified analysis of flow through a geosynthetic clay liner (GCL) using measured values for the chemico-osmotic efficiency coefficient (ω) of the GCL indicate a total liquid flux that counters the outward Darcy (hydraulic) flux due to chemico-osmosis associated with clay membrane behavior of the GCL. Also, the solute (contaminant) flux through the GCL is reduced relative to the solute flux that would occur in the absence of membrane behavior due to chemico-osmotic counter advection and solute restriction. Since diffusion commonly controls solute transport through GCLs and other low-permeability clay barriers, the implicit (empirical) correlation between ω and the effective salt-diffusion coefficient of the migrating contaminant is an important consideration with respect to contaminant restriction in CMBs. 相似文献
8.
Hyperfiltration is sometimes cited as a mechanism to explain high degrees of calcite cementation at shale/sandstone contacts. To test this cementation mechanism, a series of experiments were performed in which solutions undersaturated with respect to calcite were hydraulically forced through a Ca-bentonite at different flow rates. Calcite precipitate was observed on the bentonite membrane from hyperfiltrated stock solutions having initial calcite saturation indices of 0.91 and 0.59. Supersaturation conditions at the clay's high-pressure interface are likely provided by establishment of a concentration polarization layer.In the subsurface, the driving force for hyperfiltration is a differential hydraulic pressure gradient acting across a shale membrane. This hydraulically-induced flux of solution causes a build-up of solute at the shale's high-pressure interface to levels that may exceed saturation indices of common cementing minerals like calcite. Although the source of the hydraulic pressure is likely due to compaction within the sedimentary pile, directional flow constraints suggest that hyperfiltration-induced precipitation of calcite occurs at sand/shale boundaries away from areas of active compaction. 相似文献
9.
Megan Hart 《Hydrogeology Journal》2013,21(2):481-489
Membrane behavior in naturally occurring and engineering systems refers to the restriction of solute migration through a membrane relative to the migration of the solvent. Hyperfiltration is the net flux that results when two solutions of different concentration are separated by a membrane and an external force is applied in excess of the osmotic pressure. Clay membranes containing layered fabric have higher efficiencies than membranes with random fabrics. Therefore, low-permeability rocks with a foliated fabric might exhibit membrane properties. Four hyperfiltration experiments were conducted on samples of Darrington Phyllite from the Easton Metamorphic Suite of the Northwest Cascades, Washington (USA). Chloride solutions were passed through thin, intact discs at relatively low heads. At the end of the experiments, dissolved chloride concentrations had increased 110–140 % and calculated reflection coefficients ranged from 0.87 to 0.88; this was attributed to partial solute rejection by the phyllite. Natural scenarios in which phyllite might exhibit membrane properties include (1) shallow perched aquifers bounded by phyllite, (2) overpressured aquifers bounded by phyllite, (3) phyllite-bounded aquifers with significant vertical groundwater flows, and (4) ultrafiltration during metamorphic devolatilization at depth. Membrane processes exhibited by phyllite may also contribute to the formation of some low-temperature ore bodies. 相似文献
10.
局域化改进集合卡尔曼滤波（EnKF）可以克服EnKF方法在使用小集合时,对参数识别精度较低的缺陷,其能同化
地下水位观测数据有效识别渗透系数场。实际工作中,溶质运移数据也较容易获得。崔凯鹏（2013）尝试增加溶质运移
数据以改进只同化水流数据对渗透系数的估计结果,但是精度提高有限。本文在其基础上修改模型,进一步增加溶质注
入井,探究同时同化水头和溶质运移数据,对渗透系数场识别效果,之后对比了局域化EnKF与非局域化EnKF参数识别结
果,并分析了溶质影响范围与参数识别的关系。结果表明：同时同化溶质运移和水头资料,比同化单一种类观测数据识别
的渗透系数精度更高;相同实现数目下,局域化EnKF比EnKF对渗透系数场的估计结果与真实场更为接近;仅考虑溶质影
响范围内的渗透系数,同化水头数据在最后时刻参数识别结果好于同化溶质运移数据参数识别结果,但差别不大。 相似文献
11.
Osmotic phenomena refer to water and solute transport processes that occur when transport of solute molecules or ions is restricted by the porous medium relative to that of water molecules. Chemical osmosis and reverse osmosis/ultrafiltration are osmotic phenomena. The studies of “coupled flow” caused by chemical osmosis have been widely applied in many fields, such as earth science, environmental science and civil engineering. This paper provided a review of the considerable advances in the field of chemical osmosis and clay semipermeable membrane since the 1950s. We summarized the research progress of chemical osmosis in clayey sediments into three aspects: theoretical basis, experimental research and numerical model. In particular, the laboratory equipment and measurement methods of the chemico-osmotic efficiency coefficient σ were described,. The existing discontinuous models based on the ‘diffusive double layer’ theory were summerized, as well as the various control factors of σ. It increases with Cation Exchange Capacity (CEC), compaction pressure and decreases by the increasing of porosity and solution concentration. This paper also summerized the contimuum models based on non-equilibrium thermodynamics, which are used to explain and predict anomalies of hydraulic head pressure and salinity in clayey environments. For the future development of this discipline, it is critical to find a reliable method to confirm the σ value. It is also critical to emphasize the research on chemical osmosis in complex conditions and the influence of chemical osmosis on groundwater flow and solute transpotation. China has just stepped into this research area and more efforts should be made if significant progress is desired. This review will be helpful to further research on groundwater numerical simulation integrated with chemical osmosis in China. 相似文献
12.
13.
Earthen barriers or clay liners are a major concern in geo-environmental engineering. They are designed to preclude or reduce leachate migration. Hence, a low hydraulic conductivity (k) is an important parameter in the design of clay liners. Materials such as bentonite and lateritic clays, which have a low hydraulic conductivity at high dry densities, are used in the construction of clay liners. Compacted expansive clays which are high in montmorillonite content also have a very low hydraulic conductivity. When expansive clays are blended with fly ash, an industrial waste, the hydraulic conductivity further reduces as the ash-clay blends result in increased dry densities at increased fly ash contents. Hence, fly ash-stabilised expansive clay can also be proposed as an innovative clay liner material. It is, therefore, required to study various physical and engineering properties of this new clay liner material. Liquid limit (LL) and free swell index (FSI) are important index properties to be studied in the case of this clay liner material. The hydraulic conductivity of this new clay liner material depends on the fly ash content in the blend. Further, parameters such as solute concentration and kinematic viscosity also influence hydraulic conductivity of clay liners. This paper presents experimental results obtained on hydraulic conductivity (k) of fly ash-stabilised expansive clay liner at varying fly ash content and solute concentration. The tests were performed with deionised water (DIW), CaCl2, NaCl and KCl as permeating fluids. Fly ash content in the blend was varied as 0, 10, 20 and 30 % by weight of the expansive clay, and the solute concentration was varied as 5 mM (milli molar), 10, 20, 50, 100 and 500. It was found that hydraulic conductivity (k) decreased with increasing fly ash content, solute concentration and kinematic viscosity. Further, hydraulic conductivity (k) was correlated with LL and FSI of the clay liner material for different fly ash contents and solute concentrations. Useful correlations were obtained. 相似文献
14.
Sudhakar M. Rao T. Thyagaraj P. Raghuveer Rao 《Geotechnical and Geological Engineering》2013,31(4):1399-1404
Compacted expansive clays swell due to crystalline swelling and osmotic/double layer swelling mechanisms. Crystalline swelling is driven by adsorption of water molecules at clay particle surfaces that occurs at inter-layer separations of 10–22 Å. Diffuse double layer swelling occurs at inter-layer separations >22 Å. The tendency of compacted clay to develop osmotic or double layer swelling reduces with increase in solute concentration in bulk solution. This study examines the consequence of increase in solute concentration in bulk solution on the relative magnitudes of the two swelling modes. The objective is achieved by inundating compacted expansive clay specimens with distilled water and sodium chloride solutions in free-swell oedometer tests and comparing the experimental swell with predictions from Van’t Hoff equation. The results of the study indicate that swell potential of compacted expansive clay specimens wetted with relatively saline (0.4, 1 and 4 M sodium chloride) solutions are satisfied by crystalline swelling alone. Comparatively, compacted clay specimens inundated with less saline solutions (0.005–0.1 M sodium chloride) require both crystalline and osmotic swelling to satiate the swell potential. 相似文献
15.
16.
为了研究岩溶管道中溶潭对溶质运移的影响,在实验室内构建水箱-管道系统,在不同管道结构和水流条件下进行定量示踪实验并得到相应的穿透曲线(BTCs);采用Qtracer2软件分析溶质运移参数,采用滞后系数R分析实验结果与一维经典对流弥散方程解析解之间的差别。实验结果显示:随着水箱数量的增加,示踪剂(NaCl)峰值质量浓度逐渐降低,弥散系数和弥散度逐渐增加,穿透曲线拖尾逐渐增长,表明水箱的瞬态存储使溶质运移滞后;与不对称水箱相比,对称水箱BTC拖尾较长;峰现时间随着不对称水箱数量的增多明显滞后;出口流量增加时,弥散度减小,BTC拖尾变短。一维经典对流弥散方程解析解仅对单管道最大流量条件下的BTC拟合较好,对流量较小的单管道和水箱-管道系统的BTC拟合较差,需研究适用的模型解释其拖尾现象。 相似文献
17.
Consolidation of clayey contaminant barriers such as landfill liners has been postulated as a cause of early breakthrough of contaminants. In this paper we theoretically investigate this proposition. For this purpose a sophisticated one‐dimensional, large‐deformation model of coupled mechanical consolidation and solute transport is employed. This new model is a generalization of existing coupled consolidation and solute transport models described in the literature. It takes into account both non‐linearities in geometry as well as constitutive relations. The latter relate the compressibility, hydraulic conductivity and coefficient of effective diffusivity to the deformation of the soil. The model is applied to a case study of a clay liner and geomembrane system. Results obtained from numerical solution of the model equations are compared with those from various simplified models, including a ‘diffusion only’ (i.e. a rigid soil) model traditionally used in contaminant barrier design. For barriers incorporating low compressibility soils (as for many well compacted clays), there is little difference between contaminant transit (i.e. breakthrough) times predicted by the two models. However, for contaminant barriers incorporating more compressible soils, consolidation is shown to significantly accelerate transport. These results indicate the potential importance of accounting for the effects of soil consolidation and highlight the limitations of existing models when modelling solute transport through composite barriers utilizing soft soils. Based on these limited results, we suggest a possible way of taking into account soil consolidation using simplified models. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
18.
为了探究冻结作用下黏土中水盐迁移特性,采用室内单向冻结试验装置,基于TDR技术对添加不同溶质（NaCl）浓度的土样进行了土中温度、含水率及电导率（EC）的同时连续测量。结果表明：溶质的添加引起土中孔隙水冰点下降,造成土中成冰量减少,从而导致含溶质土样的冻结深度大于不含溶质土样;在封闭系统中随着溶质浓度的增大,土中水分迁移量和溶质迁移率均有增大趋势,距离冻结锋面越远,水分、溶质迁移量就越少;冻结锋面附近液态水凝结成冰,引起冻结锋面附近溶质浓度变化剧烈,溶质浓度急剧增大。 相似文献
19.
An analytical solution for one-dimensional contaminant diffusion through multi-layered media is derived regarding the change
of the concentration of contaminants at the top boundary with time. The model accounts for the arbitrary initial conditions
and the conditions of zero concentration and zero mass flux on the bottom boundary. The average degree of diffusion of the
layered system is introduced on the basis of the solution. The results obtained by the presented analytical solutions agree
well with those obtained by the numerical methods presented in the literature papers. The application of the analytical solution
to the problem of landfill liner design is illustrated by considering a composite liner consisting of geomembrane and compacted
clay liner. The results show that the 100-year mass flux of benzene at the bottom of the composite liner is 45 times higher
than that of acetone for the same composite liner. The half-life of the contaminant has a great influence on the solute flux
of benzene diffused into the underlying aquifer. Results also indicates that an additional 2.9–5.0 m of the conventional (untreated)
compacted clay liner under the geomembrane is required to achieve the same level of protection as provided by 0.60 m of the
Hexadecyltrimethylammonium (HDTMA)-treated compacted clay liners in conjunction with the geomembrane. Applications of the
solution are also presented in the context of a contaminated two-layered media to demonstrate that different boundary and
initial conditions can greatly affect the decontamination rate of the problem. The method is relatively simple to apply and
can be used for performing equivalency analysis of landfill liners, preliminary design of groundwater remediation system,
evaluating experimental results, and verifying more complex numerical models. 相似文献
20.
近年来,国内外对复杂地层绳索取心钻具的研究取得了长足进步,但是未能很好解决卡心构件对岩心入管的阻碍和底喷式钻头易产生“泥垫”现象,从而影响取心质量和钻进效率的关键技术问题。以普通S95绳索取心钻具为研究对象,通过在内管里增设0.7 mm厚度的不锈钢衬管,封隔卡簧等卡心构件装置,增加底喷式钻头水孔数量并增大水槽体积,设计可供选择的发夹式和卡簧式岩心提断器等技术改造,研制一款用于复杂地层钻进,具备隔水、隔卡、自动锁心的三层管绳索取心钻具。选用发夹式岩心提断器在水敏性强的破碎地层中试验,平均回次进尺1.13 m,获取岩心采取率94.48%,对比附近同类地层钻孔的岩心采取率提高了50%以上;选用卡簧式岩心提断器在裂隙发育的泥质地层中试验,卡簧卡心如同普通钻具上的卡簧一样可靠。试验结果表明:用衬管封隔卡心构件的取心技术方案可行,解决了卡心构件对软弱松散岩心入管的阻碍,有利于保护岩心的原状性;所用底喷式钻头孔底冲洗效果好,降低了钻头“泥垫”现象对钻进速度的影响。该钻具操作方便,使用成本低廉,有望在我国现行绳索取心机台推广应用,具有较强的普适性和广泛的应用前景。 相似文献