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1.
Batch experiments were conducted to study the sorption of uranium on selected clay minerals (KGa-1b and KGa-2 reference kaolinite,
SWy-2 and STx-1b reference montmorillonite, and IBECO natural bentonite) as a function of pH (4–9) and 0.001, 0.01, and 0.025 M
NaCl in equilibrium with the CO2 partial pressure of the atmosphere. Uranium concentrations were kept below 100 μg L−1 to avoid precipitation of amorphous Uranium-hydroxides. Solely PTFE containers and materials were used, because experiments
showed significant sorption at higher pH on glass ware. All batch experiments were performed over a period of 24 h, since
kinetic experiments proved that the common 10 or 15 min are in many cases by far not sufficient to reach equilibrium. Kaolinite
showed much greater uranium sorption than the other clay minerals due to the more aluminol sites available. Sorption on the
poorly crystallized KGa-2 was higher than on the well-crystallized KGa-1b. Uranium sorption on STx-1b and IBECO exhibited
parabolic behavior with a sorption maximum around pH 6.5. Sorption of uranium on montmorillonites showed a distinct dependency
on sodium concentrations because of the effective competition between uranyl and sodium ions, whereas less significant differences
in sorption were found for kaolinite. The presence of anatase as impurity in kaolinite enhanced the binding of uranyl-carbonate
complexes with surface sites. The kinetic of uranium sorption behavior was primarily dependent on the clay minerals and pH.
A multisite surface complexation model without assuming exchange is based on the binding of the most dominant uranium species
to aluminol and silanol edge sites of montmorillonite, respectively to aluminol and titanol surface sites of kaolinite. For
eight surface species, the log_k was determined from the experimental data using the parameter estimation code PEST together
with PHREEQC. 相似文献
2.
An approach for predicting swelling pressure of bentonites based on thermodynamic relationships between swelling pressure and suction is presented in this paper. The proposed method requires sorption isotherm data of the bentonites. A series of swelling pressure tests were performed on compacted specimens of bentonite-sand mixtures with different bentonite contents, water contents, and dry densities. The sorption isotherm of the pure bentonite was measured using a chilled-mirror hygrometer. It is found that the method works well for the bentonite-sand mixtures tested. Several published data on bentonites that have been proposed to be used as buffer and sealing material for nuclear waste repository were collected and used to verify the method. The proposed method is found to be also applicable for other bentonites of different types and therefore, can be used to predict swelling pressure of bentonites. 相似文献
3.
为验证土工合成黏土衬垫（Geosynthetic Clay Liners,GCL）作为煤矸石处置场衬垫层建设材料的可行性,采用垂直式双筒扩散装置进行室内扩散试验,研究了煤矸石淋滤液中典型污染物Zn2+、Mn2+和SO42-在人工钠化膨润土GCL中的扩散性能,使用有限层法模拟软件POLLUTE V7对污染物随时间变化的曲线进行拟合,确定3种污染物在人工钠化膨润土GCL中的扩散系数。研究结果表明,污染物在GCL中的扩散系数低于它们在传统压实黏土衬垫层中的扩散系数,从而能更有效地控制煤矸石淋滤液中污染物在GCL中的扩散迁移行为。 相似文献
4.
《Geochimica et cosmochimica acta》1999,63(3-4):325-336
In some previous work titration and Ni/Zn sorption edge/isotherm measurements carried out under a wide variety of experimental conditions on purified Na-montmorillonite were modelled in terms of cation exchange and surface complexation mass action equations. A major objective of the experimental/modelling programme is to understand and predict sorption in commercial bentonite systems. Since montmorillonite is the dominant clay mineral in bentonite and is often present in a mixed Na/Ca form, a natural extension to the previous investigations was to study Ni/Zn sorption on a conditioned Ca-montmorillonite. An important open question was whether the same basic parameters such as site types, site capacities, and acidity constants could be used for both materials and to see to what extent the Ni and Zn surface complexation constants were influenced by the form of the montmorillonite. Sorption edges for Ni and Zn at different Ca(NO3)2 background electrolyte concentrations, together with sorption isotherms measured over a range of pH values, are presented and modelled using the MINSORB code. The parameters characterising the sorption of Ni and Zn on Na- and Ca-montmorillonite systems are compared. Finally, examples are given that illustrate how the modelling can provide insight into the sorption processes. 相似文献
5.
6.
Diffusion and sorption experiments using a DKS permeameter 总被引：2，自引：0，他引：2
The analysis of contaminant transport through clay liner is a relevant aspect in the design of industrial, urban and mining waste disposal systems, since these areas must be designed and operated to prevent contaminating substances from reaching underground water systems in unacceptable concentrations. The design requires an estimate of the potential contaminant transport rate. However, before any attempt at quantification can be made, values for transport mechanism control parameters must be established. Clayey materials are frequently used as contaminant barriers. In these materials, which have low hydraulic conductivity, the main contaminant transport mechanism is molecular diffusion. Parameters controlling transport for these conditions are the diffusion coefficient and sorption parameters. These parameters depend on soil constituents and characteristics as well as on the chemical constitution of the contaminant. The great complexity of the factors involved makes it necessary to determine the parameters of each type of soil. This paper discusses an equipment called DKS permeameter (diffusion, convection, sorption), for the study of soil-contaminant transport mechanisms, designed at the Institute for Soil Mechanics of the Ruhr-University Bochum, and some results obtained from its use at COPPE/Federal University of Rio de Janeiro (UFRJ), Brazil. This equipment determines the effective diffusion coefficient and sorption parameter with a better reflection of field conditions. The soil under study is a mix of sodium–bentonite that has low hydraulic conductivity (k=10−9 cm/s) with adequate liner characteristics. The result indicated the relevance of determining sorption parameters for structured soils, since the sorption perceived from batch test results using pulverised soil represents maximum soil capacity. Designs based on this parameter would overestimate the attenuation capacity of the liner. 相似文献
7.
A new multichamber device was developed to study sorption/desorption reactions of metals on different competing sediment components
and the influence of environmental factors on these reactions. The system consists of a central chamber connected with six
external chambers and separated by 0.45-μm-diameter membranes.
The diffusion kinetics of metals between the single chambers were determined. Equilibrium was attained within 24 h. Algal
cell walls (Scenedesmus quadricauda), bentonite, aluminium oxide, managese oxide, quartz powder, and goethite were used as model sediment components. Determination
of metal sorption on the solid phases resulted in a significant enrichment on the algal cell walls, particularly for Cu and
Cd. It was concluded that sorption depends not only on ion exchange but also on complexing reactions which lead to relatively
stable surface binding. A second series of experiments investigated the effect of seawater on sediment components and dredged
mud. Cadmium was remobilized from all solid components, but Cu was not remobilized from algal cell walls and bentonite.
The dominant role of organic substrates in the binding of metals such as Cd andCu is of particular relevance for the transfer
of these elements into biological systems. Even relatively small percentages of organic substrates, if involved in metabolic
processes, may constitute a major pathway by which metals are transferred within the food chain. 相似文献
8.
Over the last decade, waste disposal has become a particularly sensitive issue in Algeria. New legislation concerning landfill
liner design has been adopted. Traditional methods of landfill liner characterization involve soil sampling and chemical analysis,
which are costly, destructive and time-consuming. New techniques are currently being investigated that aim to provide nondestructive
liner characterisation. This paper details technical aspects associated with electrical conductivity measurements within landfill
liners and presents experimental work to show the direct application of electrical techniques to track ionic movement through
a sand bentonite liner under chemically induced flow. Samples of sand bentonite were mixed and compacted with NaCl electrolytes
at different concentrations. The electrical conductivities of compacted specimens were measured with a two-electrode cell.
The effects of frequency and electrolyte concentration on the conductivity measurement were explored. The relationship between
the soil electrical conductivity and the NaCl electrolyte concentration in interstitial pore fluid was determined. The conductivity
measurements were used to quantify the pore fluid concentration and effective diffusion coefficient of sand bentonite liners.
It is concluded here that the electrical conductivity of compacted specimens depends mainly on the salt concentration in the
pore fluid, and that this approach could therefore be used to track ionic movement through liners during diffusion. 相似文献
9.
铀在北山花岗岩中的吸附迁移影响因素研究 总被引：1，自引：0，他引：1
运用水文地球化学模拟软件PHREEQC-Ⅱ,对铀元素进入中国高放废物处置预选场研究区地下水后的状况进行了模拟和预测。模拟得到核素铀进入研究区地下水后的元素浓度分布和迁移情况及外界因素变化引起地下水中铀迁移的行为,同时采用批式法测定不同条件下铀在甘肃北山花岗岩中的分配系数,研究了岩石粒径、溶液初始浓度、水相pH和温度对分配系数的影响,实验结果表明花岗岩对铀的吸附能力较弱,其中溶液初始浓度、粒径、温度影响较小,pH值对岩石的吸附性能有较大影响,在接近中性条件下影响达到最大,这与采用模拟软件模拟结果基本吻合。通过模拟和实验对比,能更好地研究在北山预选区处置条件下地下水-废物-岩石的相互作用过程中核素的迁移行为,从而为处置库系统安全评价提供有关依据。 相似文献
10.
Mohsen Hamidpour Mahmoud Kalbasi Majid Afyuni Hossein Shariatmadari Gerhard Furrer 《Environmental Earth Sciences》2011,62(3):559-568
This study deals with the use of the natural, low-cost sorbents bentonite and zeolite for the removal of lead from aqueous
solutions. The mineral material is from large deposits of bentonite and zeolite that have been discovered recently in Iran.
Experimental and modeling data from our kinetic and equilibrium investigations reveal that (1) the pseudo-second-order kinetic
model gave the best fit, and (2) the Koble–Corrigan sorption model describes the interaction between Pb(II) and the two mineral
materials better than the Freundlich and Langmuir models. However, the sorption of Pb(II) ions by zeolite and bentonite is
complex and probably involves several mechanisms. The experimental data show that natural zeolite and bentonite used in this
study exhibited a reasonable sorption capacity for Pb(II), and thus may be useful for the immobilization of Pb(II) from polluted
sites. 相似文献
11.
12.
H. Sepehrian M. Samadfam Z. Asadi 《International Journal of Environmental Science and Technology》2012,9(4):629-636
In this paper, the sorption of uranium onto nanoporous silica adsorbent in the presence of nitrate, sulfate, chloride, fluoride and phosphate was studied. The effect of contact time between the nanoporous sorbent and aqueous solution, pH and initial concentration of uranium was also investigated. Uranium sorption onto nanoporous silica adsorbent is a very fast process as sorption rate increases with pH increment. Optimum pH for uranium sorption was 4?C8. Experimental sorption isotherm is successfully described by Langmuir and Freundlich models. The results obtained by batch experiments showed that the presence of high concentration of nitrate, sulfate, chloride and phosphate anions alone had no interference with uranium recovery. However, the presence of fluoride ions (>250?mg/L) decreases uranium sorption by about 55?%. The results also showed that the presence of phosphate ions (about 300?mg/L) in solution could remove fluoride interference completely. Finally, the efficiency of the nanoporous silica adsorbent for uranium recovery from wastewater of the uranium conversion facility was investigated. 相似文献
13.
扩散是低渗透系数情况下溶质迁移的主要方式,目前尚没有测定高塌落度防渗墙填料扩散系数的试验方法。根据沥出试验原理,将处于流动状态的填料用半透膜包裹进行透析试验,通过有限圆柱中溶质迁移解析解对溶质迁移过程进行拟合求其扩散系数,探讨了试验和数据处理的相关问题,研究了膨润土含量和盐浴浓度对扩散系数的影响规律。结果表明,随拟合天数增加,填料中NaCl有效扩散系数减小,而误差增大;高塌落度填料中溶质迁移明显比压实土样中快,按拟合误差小于0.5%作为试验数据取舍依据,这一误差要求实际上是对溶质迁移以扩散为主导这一条件的量化,保证了采用纯扩散解析解进行数据拟合的合理性;扩散系数随填料中膨润土含量增加而减小,随盐浴浓度增加而减小,但在试验范围内数值变化不大,透析试验是快速测定防渗墙填料中溶质有效扩散系数的可行方法。 相似文献
14.
79Se is a potentially mobile long-lived fission product, which may make a dominant contribution to the long-term radiation exposure resulting from deep geological disposal of radioactive waste. Its mobility is affected by sorption on minerals. Selenium sorption processes have been studied mainly by considering interaction with a single mineral surface. In the case of multi-component systems (e.g. soils), it is difficult to predict the radioelement behaviour only from the mineral constituents. This study contributes to the understanding of multi-component controls of Se concentrations towards predicting Se behaviour in soils after migration from a disposal site. This goal was approached by measuring selenite sorption on mono and multi-phase systems physically separated by dialysis membranes. To the best of the authors’ knowledge, very few studies have used dialysis membranes to study the sorption competition of selenite between several mineral phases. Other workers have used this method to study the sorption of pesticides on montmorillonite in the presence of dissolved organic matter. Indeed, this method allows measurement of individual Kd in a system composed of several mineral phases. Dialysis membranes allowed (i) determination of the competition of two mineral phases for selenite sorption (ii) and determination of the role of humic acids (HAs) on selenite sorption in oxidising conditions. Experimental results at pH 7.0 show an average Se(IV) sorption distribution coefficient (Kd) of approximately 125 and 9410 L kg−1 for bentonite and goethite, respectively. The average Kd for goethite decreases to 613 L kg−1 or 3215 L kg−1 in the presence of bentonite or HA, respectively. For bentonite, the average Kd decreases slightly in the presence of goethite (60 L kg−1) and remains unchanged in the presence of HA. The experimental data were successfully modelled with a surface complexation model using the PHREEQC geochemical code. The drastic decrease in Se(IV) sorption on goethite in a multi-phase system is attributed to competition with dissolved silica released by bentonite. As with Si the HA compete with Se for sorption sites on goethite. 相似文献
15.
Using some uranium deposits and recent U-bearing sediments as examples, it is shown that all U-bearing rocks are characterized by an association of organic matter and calcium phosphate, irrespective of the quantitative relationship between these components. A considerable proportion of these components was delivered into sediments with remains of marine planktonic and nektonic organisms. Along with organic matter, calcium phosphate played a significant role in uranium concentration. This is related to a high sorption ability of the calcium phosphate. Uranium accumulated during diagenesis as a result of diffusion exchange between bottom and interstitial waters. The combination of anoxic bottom environment with high bioproductivity in upper aerated waters, a typical phenomenon in oceanic upwelling zones, is the most favorable factor of uranium concentration in the sedimentary process. This determines the stable paragenetic association of organic matter, phosphorus, and uranium in marine sediments, such as black shales and organogenic phosphate deposits. 相似文献
16.
为寻找有效且简单的克服基体效应的方法,我们研究了树脂吸附铀的行为:742阴离子树脂具有孔径大,吸附洗脱快等优点,本文择其吸附快之长处,对少量粉末状742树脂(280目以上)吸附铀的可能性进行了探索试验,富集分离效果良好。最终拟定在硫酸介质中以742阴离子树脂静态吸附分离铀,X-射线测量的方法,操作简单易行,方法灵敏度高、稳定。适应于地质、选冶样品中0.00X～X% 相似文献
17.
在苗儿山地区已知花岗岩型铀矿床上的试验结果显示,在矿化规模较大、品位较高的钻孔岩心剖面上观察到了分布范围大大超过矿体,且强度较高的210Po异常。据此认为,在勘探最后阶段通过测定钻孔岩心的210Po可以判断钻孔深部以及周围是否还存在隐伏矿体,以指导进一步钻探。本技术有望用于花岗岩型铀矿床的勘查工作。 相似文献
18.
J. A. Cooper 《Australian Journal of Earth Sciences》2013,60(4):483-486
Discordant uranium‐lead isotope measurements are reported for a sample of Nabarlek pitchblende. These are compared with earlier measurements on uranium minerals from the South Alligator River area. New interpretations suggest that regional uranium mineralisation took place either 710 or 815 m.y. ago; the lower of these calculations is based on the assumption of modern episodic lead loss, and the higher assumes lead loss by continuous diffusion. 相似文献
19.
Interpretation of carbon dioxide diffusion behavior in coals 总被引：3，自引：1，他引：3
Nikolai Siemons Karl-Heinz A.A. Wolf Johannes Bruining 《International Journal of Coal Geology》2007,72(3-4):315-324
Storage of carbon dioxide in geological formations is for many countries one of the options to reduce greenhouse gas emissions and thus to satisfy the Kyoto agreements. The CO2 storage in unminable coal seams has the advantage that it stores CO2 emissions from industrial processes and can be used to enhance coalbed methane recovery (CO2-ECBM). For this purpose, the storage capacity of coal is an important reservoir parameter. While the amount of CO2 sorption data on various natural coals has increased in recent years, only few measurements have been performed to estimate the rate of CO2 sorption under reservoir conditions. An understanding of gas transport is crucial for processes associated with CO2 injection, storage and enhanced coalbed methane (ECBM) production.A volumetric experimental set-up has been used to determine the rate of sorption of carbon dioxide in coal particles at various pressures and various grain size fractions. The pressure history during each pressure step was measured. The measurements are interpreted in terms of temperature relaxation and transport/sorption processes within the coal particles. The characteristic times of sorption increase with increasing pressure. No clear dependence of the characteristic time with respect to the particle size was found. At low pressures (below 1 MPa) fast gas diffusion is the prevailing mechanism for sorption, whereas at higher pressures, the slow diffusion process controls the gas uptake by the coal. 相似文献
20.
According to the present concept for final storage of spent nuclear fuel in Sweden, the spent fuel, encapsulated in copper or copper/steel canisters, will be placed in tunnels in a deep rock formation. The canisters will be surrounded by compacted bentonite clay acting as a buffer material. In connection with a safety analysis of such a storage facility, the total solubility of certain elements (e.g., uranium) as well as the transport properties (e.g., retardation due to sorption on mineral surfaces) of the long-lived radionuclides released from the canister have to be predicted or measured. The chemical conditions, governing the solubility and speciation of trace elements encountered in and around the repository depend on interactions between the ground water and the engineering materials in the repository and a production of oxidants due to radiolysis in the spent fuel. In the present study the speciation and solubility of uranium and neptunium in a bentonite-ground water system and in ground waters with compositions measured at a site at äspö, SE Sweden, have been calculated. The calculations have been carried out using a recent version of the geochemical computer code PHREEQE and the database HATCHES 5.0. Predictions of the uranium and neptunium concentrations in the ground water in the vicinity of a damaged high level waste repository have also been performed. The uranium concentration in the water in the bentonite barrier is predicted to be of the same order of magnitude or lower than that found in some granitic ground waters. For neptunium the calculations are uncertain due to the small amount of experimentally determined thermodynamic data and few verifications under the conditions (pH - Eh - carbonate concentration) considered. The predicted concentrations (ca 10–12 m, corresponds to ca 0.006 Bq/l) may be regarded as high, considering the high toxicity of neptunium and its long half-life. 相似文献