共查询到20条相似文献，搜索用时 31 毫秒
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Aref Alshameri Alkhafaji R.Abood Chunjie Yan Akhtar Malik Muhammad 《Arabian Journal of Geosciences》2014,7(3):841-853
The bentonite deposit of Lahij Province, Yemen, has very promising commercial applications due to its mineralogy and physical and chemical properties. It was examined to determine its mineralogical composition, chemical and physical properties of the bentonite deposit, purity and sodium-exchanged bentonite. Modified bentonite was synthesized by exchanging cetyltrimethylammonium cations for inorganic ions on the bentonite and its adsorption properties for ammonium were characterized in batch experiments. Analytical methods were carried out to study the bentonite comprising X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared spectroscopy, chemical analysis and kinetic and isotherm models were also tested. The results have shown that the purification of bentonite resulted in a bentonite fractions of the total sample composed of montmorillonite and <5 % quartz. The XRD data showed that the interlayer spacing (d 001) of bentonite decreased from 15.3 to 12.5 Å and then increased to 19.7 Å. Moreover, high cation exchange capacity, good water absorption and high swelling capacity were also obtained. The results have shown that the modified bentonite was more effective than the natural bentonite for ammonium removal. In addition to that, pseudo-second-order kinetic model, Freundlich and the Langmuir models described the adsorption kinetics and isotherm well. It was concluded that Yemen (Alaslef) bentonite can be potential adsorbents for ammonium removal. 相似文献
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I. K. Chandra Y.-H. Ju A. Ayucitra S. Ismadji 《International Journal of Environmental Science and Technology》2013,10(2):359-370
The feasibility of natural bentonite and rarasaponin–bentonite for Evans blue removal from aqueous solution was studied. Rarasaponin is a natural surfactant obtained from Sapindus rarak DC was used as modifying agent for natural bentonite modification. Adsorption experiments were conducted in a batch system at various temperatures. Several temperature-dependent isotherm models (Langmuir, Freundlich, Sips and Toth) were used to represent equilibrium data. It was found that Toth model represents the adsorption equilibrium data better than other models. Kinetic data were best represented by the pseudo-first order model. The controlling mechanism of the adsorption of Evans blue onto natural bentonite and rarasaponin–bentonite was physical adsorption. 相似文献
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A. K. Mishra B. Kumar S. Vadlamudi 《International Journal of Environmental Science and Technology》2017,14(8):1625-1634
Owing to its low hydraulic conductivity, soil and bentonite mixture is applied as a liner material. However, the experimental determination of hydraulic conductivity, which is controlled by various physical, chemical and mineralogical factors, requires an expensive and time-consuming setup. In the present work, multigene symbolic, genetic programming was used to model functional relationships for hydraulic conductivity. The developed model was able to generalize highly nonlinear variations in data as well as predict system behavior from experimental observations. It was found that the predictions obtained from developed model agree well with experimental observations. 相似文献
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There is great incentive to reduce bentonite use in iron ore pelletization by improving its effectiveness. In order to make bentonite more effective, it is necessary to understand the actual binding mechanisms so that they can be properly taken advantage of. Bentonite use could also be reduced by replacing bentonite with even lower-cost binders, such as high-carbon fly-ash based binder (FBB). While FBBs can be used alone as binders, it was considered possible that mixtures of FBB and bentonite could exhibit superior binding properties. In this study, it was found that bentonite bonds by a physical mechanism, while FBB bonds by a chemical mechanism. These mechanisms were determined to be incompatible. Mixtures of the two binders resulted in reduced dry magnetite concentrate pellet compressive strengths below the industrially acceptable value of 22 N (5 lbf). Activators and accelerators, which were necessary components of the FBB, deactivated the bentonite. The compatibilities and mechanisms of the two binders are explained in this paper. The classical theory of the binding mechanism of bentonite binder is challenged by the bentonite fiber mechanism that was recently identified by the authors. 相似文献
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Setianto Samingan Agus Yulian Firmana Arifin Snehasis Tripathy Tom Schanz 《Acta Geotechnica》2013,8(2):155-165
This paper presents results of an experimental work to determine a relationship between swelling pressure and suction of heavily compacted bentonite–sand mixtures. For comparison, tests were also carried out on heavily compacted bentonite specimens. A series of swelling pressure tests were performed using multi-step constant-volume method where suction of the specimens tested was reduced in a stepwise manner toward a zero value. The suction reduction was induced using vapor equilibrium and axis-translation techniques. It is shown that compacted specimens did not exhibit any collapse upon suction decrease and exhibited maximum swelling pressures at zero-equilibrium suction. The development of swelling pressure with decreasing suction of the specimens showed threshold suctions below which a further reduction in suction yields an increase in the swelling pressure of the same magnitude. The magnitude of threshold suction was found to be a function of bentonite content in compacted specimens. 相似文献
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Thermal conductivity is an important parameter to consider when designing clay-based barriers for use in deep geological repositories (DGR). In the DGR environment, the infiltration of local saline groundwater can potentially change the pore fluid chemistry of a barrier over its lifetime. This change in chemistry is known to alter the thermal properties of the barrier materials. In order to examine the impact of pore fluid salinity on thermal conductivity, experiments were conducted under both distilled water and saline pore fluid conditions. The material mixtures were prepared at two different dry densities using two different salt types. Furthermore, five different thermal conductivity prediction models were selected and evaluated on their performance with respect to the experimental outcomes. In general, these results indicated that an increase in the constituent pore fluid’s salt concentration leads to a decrease in the thermal conductivity of the material. Additionally, the thermal conductivity values of the materials prepared at a high dry density were greater than of those compacted at a low dry density. 相似文献
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《Geomechanics and Geoengineering》2013,8(1):73-85
Bricks made of compacted sand–bentonite mixture are considered as a possible engineered barrier to isolate high-level radioactive waste at great depth. This work is aimed at investigating some specific effects related to the presence of discontinuities at the contact between the bricks and the excavation wall. In order to do this, an experimental device was developed in the laboratory. The model is made up of a specially designed infiltration cylinder which allows the precise definition of a planar discontinuity between the compacted specimen (a sand–bentonite mixture made up of sand and Kunigel clay from Japan) and a metal wall. During hydration and subsequent specimen swelling, the planar wall is filled, resulting in a healing process. Three total pressure gauges placed along the wall allow a detailed observation of the increase in total stress against the wall. After different periods of swelling, the maximum resistance of the specimen–wall interface to pressure was tested by imposing a pressure increase through a porous stone placed at one end of the cylinder. It was found that the maximum pressure supported by the interface is a function of the initial thickness of the discontinuity and the initial density of the specimen. It was also found that the maximum sustainable pressure depends linearly on the elapsed time. These results are of interest for optimizing water infiltration procedures in either mock-up tests or real disposal systems. If the maximum sustainable pressure at the interface is known, it is possible either to ensure homogeneous hydration of a mass of bricks by respecting the maximum injection pressure limit or to accelerate hydration by forcing water paths along the discontinuities. 相似文献
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In the present study, influence of wetting–drying cycles on swelling pressures of sand–bentonite mixtures used in the construction
of sanitary landfills to have an impermeable liner was investigated before and after lime treatment of the mixtures. Swelling
pressure tests were conducted to see if the swelling pressures were affected by wetting–drying cycles. First series of specimens
were prepared as a mixture of sand and bentonite only. In the first series of specimens, sand was mixed with bentonite in
various proportions with their optimum water contents and compacted by using standard proctor energy. In the second series
of the specimens, lime in various proportions was added to the mixtures of sand–bentonite. Then, the sand–bentonite mixtures
stabilized by lime were compacted with the standard proctor energy at their optimum moisture contents. Five wetting–drying
cycles were performed on each specimen and values of swelling pressures were measured at the end of each cycle. Results of
swelling pressure tests indicated that the swelling pressure is decreased when lime is added to the mixtures. In addition,
decrements were observed on swelling pressures by wetting–drying cycles. The results of the experiments of this investigation
showed that the beneficial effect of lime stabilization to control the swelling pressures was partly lost by the wetting–drying
cycles. However, the test results indicated that the swelling pressures of the specimens made of sand–bentonite mixtures stabilized
by lime were lower than the swelling pressures of the specimens made of only sand–bentonite mixtures. 相似文献
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Agapitus Ahamefule Amadi 《Environmental Earth Sciences》2013,70(6):2437-2442
Compacted soil–bentonite mixtures are finding wide application as buffer material for waste repositories for their favorable self-sealing qualities. The swelling properties of such materials which serve as a measure of their self-sealing capabilities and, thus, the efficiency of the repository in sealing off their contents from the environment are closely related to the chemistry of the leachate that emanate from the wastes. For this reason, the swelling parameters (namely swelling potential and pressure) of compacted lateritic soil–bentonite mixtures under consideration for use as barrier in municipal waste landfill were evaluated. Series of swelling potential and pressure tests were performed using variable content (0–10 %) of bentonite at predetermined optimum moisture content. Soil mixtures were compacted with British Standard Heavy compactive effort and saturated with processed tap water as well as three leachate solutions of varying ionic strength that were generated in active open dump landfills. Experimental results showed that swelling potential based on the free swell together with the maximum swell pressures of compacted soil mixtures measured at equilibrium increased approximately linearly with increase in the amount of bentonite when inundated with processed tap water and the three leachate solutions. On the other hand, these swelling parameters decreased as the ionic strength of the leachate solutions measured by their electrical conductivity increased for the various soil mixtures. These results provide an insight into the swelling behavior and the possible degradation in the efficiency of the proposed lateritic soil–bentonite mixtures in relation to their use as buffer material in waste landfills. 相似文献
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Effect of sand grain size and boundary condition on the swelling behavior of bentonite–sand mixtures
Wang Dong-Wei Zhu Cheng Tang Chao-Sheng Li Sheng-Jie Cheng Qing Pan Xiao-Hua Shi Bin 《Acta Geotechnica》2021,16(9):2759-2773
Deep geological repository is a favorable choice for the long-term disposal of nuclear wastes. Bentonite–sand mixtures have been proposed as the potential engineered barrier materials because of their suitable swelling properties and good ability to seal under hydrated repository conditions. To investigate the effects of sand grain size on the engineering performance of bentonite–sand mixtures, we prepare five types of bentonite–sand mixtures by mixing bentonite with sand of varying particle size ranges (0.075–0.25 mm, 0.25–0.5 mm, 0.5–1 mm, 1–2 mm and 2–5 mm, respectively). We carry out sequential oedometer tests under different simulated repository conditions, including constant vertical stress (CVS), constant stiffness (CS) and constant volume (CV) conditions. The microstructural heterogeneity and anisotropy of these soil mixtures are characterized through the quantitative analysis of micro-CT scanning results. Experimental results reveal that both sand grain size and boundary condition significantly influence the swelling of soil mixtures. Under three conditions, the temporal evolutions of swelling stress and strain follow similar trends that they increase faster at the beginning and gradually stabilize afterward. Comparing the ultimate values, swelling strains follow CVS?>?CS?>?CV, while swelling stresses follow CV?>?CS?>?CVS. Under CS boundary conditions, as the stiffness coefficient increases, the swelling pressure increases and the swelling strain decreases. CT results further indicate that mixtures with larger sand inclusions are more structurally heterogeneous and anisotropic, resulting in increased inter-particle friction and collision and a higher energy dissipation during the swelling process. Moreover, the non-uniform distribution of bentonite in local zones would be intensified, which plays an important role in compromising swelling behavior. Therefore, soil samples mixed with larger sand particles present a smaller swelling stress and strain values. This study may guide the choice of engineered barrier materials toward an improved design and assessment of geological repository facilities.
相似文献14.
Ryszard Kryza Jolanta Muszer Joanna Haydukiewicz Czesław August Marta Jurasik Nickolay Rodionov 《International Journal of Earth Sciences》2011,100(6):1227-1235
A Lower Carboniferous platform sedimentary sequence (the Paprotnia Beds) in the Bardo Unit of the central Sudetes (NE part
of the Bohemian Massif, SW Poland) is biostratigraphically well dated, based on rich macro- and micro-fossil evidence, as
Late Viséan (late Asbian, crenistria, Go III α zone). The beds contain several bentonite layers, one of which was dated using the U–Pb SHRIMP method on volcanic
zircons and yielded an age of 334 ± 3 Ma. This date fits well to the recently established chronostratigraphic limits of the
Viséan, and is consistent with the newest isotopic age constraints of 336.5–332 Ma for the Asbian boundaries. 相似文献
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In this study, an investigation was performed to determine if lime-stabilized sand–bentonite mixtures are appropriate for the construction of sanitary landfills liners. For this aim, the hydraulic conductivity tests were conducted in the laboratory on sand–bentonite mixtures and lime-stabilized sand–bentonite mixtures to evaluate the effect of wetting–drying cycles. The hydraulic conductivity tests were performed to see if their hydraulic conductivities are affected by wetting–drying cycles. First series of specimens have been prepared as a mixture of sand and bentonite only. In the first series of specimens, sand was mixed with bentonite in proportions of 20, 30, 40, and 50 %. In the second series of the specimens, lime in proportions of 1, 2 and 3 % by weight was added to the mixtures of sand–bentonite in proportions of 20, 30, 40, and 50 %. From the results of the tests, it was observed that while optimum water content increased, maximum dry density decreased with addition of lime to the sand–bentonite mixtures. Generally, the hydraulic conductivity increased with the addition of lime to the mixtures but at low percentages of lime (1–2 %), however, slight decreases in k were recorded. It was also observed that the wetting–drying cycles on the permeability test indicate cure effect on specimens with addition of lime which resulted in decreased the hydraulic conductivity. 相似文献
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Acta Geotechnica - Compacted Gaomiaozi bentonite–sand mixtures are regarded as attractive buffer/backfill materials for nuclear waste deep geological disposal. When the mixture blocks are... 相似文献
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以泥盆系占优势的南秦岭成矿带中存在有重要的Ｐｂ－Ｚｎ－Ａｇ，Ａｕ，Ｈｇ－Ｓｂ及Ｃｕ矿床。它们形成中晚古生带扬子地块北部被动大陆边缘的沉积盆地演化与造山期中，成矿系列显示出时间与空间的演化特征，构在了一个热水沉积成矿系列，成矿发生于一个热旋回中，各种矿化有相似的物源，每一种地质事件都有特定的金属富集及富集在型和大型矿床是该地区构造－岩浆变质变形作用的最终产物。 相似文献
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