| 1. |
- Jansson, Mats, et al.
(författare)
-
LOT : in situ diffusion experiments using radioactive tracers
- 2003
-
Ingår i: Applied Clay Science. - 0169-1317 .- 1872-9053. ; 23:1-4, s. 77-85
-
Tidskriftsartikel (refereegranskat)abstract
- An experiment series at Aspo Hard Rock Laboratory, called "Long Term Test of Buffer Material", LOT, are carried out at Aspo Hard Rock Laboratory to validate models of clay buffer performance at standard KBS-3 repository conditions and to quantify clay buffer alteration processes at adverse conditions. In conjunction with the tests of the bentonite, cation diffusion tests using caesium and cobalt are performed. Each test contains 38 cylindrical blocks of bentonite clay with a hole in the middle which are placed around a copper rod in a vertically drilled hole at a depth of 450 m. In each test, four identical cylindrical bentonite plugs, doped with 1 MBq Co-57 and Cs-134, respectively, are inserted in the fifth block from the bottom. The system was left to be saturated with ground water before heating of the central copper rod started to simulate the thermal activity of radioactive waste. The experiments continued for 14 months before the bentonite blocks were drilled out using over-core drilling technique. The lowest blocks were cut up, sparsely in the outer layer, and in cubic centimeters, big samples closer to where the activity was inserted. All samples were analyzed using a gamma spectrometer to get a three-dimensional picture of the activity distribution. The system was then fitted to a diffusion model to obtain apparent diffusivities for the two cations. The apparent diffusivity for cobalt agrees well with those obtained in other in situ experiments and in laboratory studies, while the value for caesium is lower than expected. This can be due to that the clay was not fully water saturated during the experiment.
|
|
| 2. |
- Molera, Mireia, et al.
(författare)
-
Anion diffusion pathways in bentonite clay compacted to different dry densities
- 2003
-
Ingår i: Applied Clay Science. - 0169-1317 .- 1872-9053. ; 23:1-4, s. 69-76
-
Tidskriftsartikel (refereegranskat)abstract
- Diffusion of the anions Cl- and I- in MX-80 compacted bentonite has been studied at different ionic strengths (0.01, 0.1 M NaClO4) and clay density (0.4, 0.8, 1.2, 1.8 g cm(-3)) at the buffered pH of bentonite 8.2 using a through-diffusion technique with measurement of breakthrough curves and concentration profiles in the bentonite. Apparent diffusivities and capacity factors (alpha=epsilon+rhoK(d)) are obtained from diffusion simulations using the computer code ANADIFF. Two diffusion processes, both with density and ionic strength dependent apparent diffusivities and capacity factors, were observed. The diffusion processes observed are ascribed to diffusion in intralayer and interparticle water. The experimental data indicate that intralayer water constitutes the dominating part of water in bentonite compacted to dry the densities 0.4-1.8 g cm(-3) studied in this work.
|
|
| 3. |
- Wold, Susanna, et al.
(författare)
-
Diffusion of lignosulfonate colloids in compacted bentonite
- 2003
-
Ingår i: Applied Clay Science. - 0169-1317 .- 1872-9053. ; 23:04-jan, s. 43-50
-
Tidskriftsartikel (refereegranskat)abstract
- Colloids, as humic acid, are known to be strong complexing agent for radionuclides. If such colloids are introduced into the bentonite barrier in a repository for spent fuel, the diffusivities for radionuclides can change. The colloid complexed radionuclides diffusivities will be governed by the colloidal diffusivities, and the transport of strongly bentonite sorbed radionuclides might be facilitated into the biosphere. The diffusive properties of Lignosulfonate (LS) colloids dissolved in 0.01 and 0.1 M NaClO4 in bentonite of dry densities 0.6, 0.8, 1.0, 1.2, 1.5, and 1.8 g/cm(3) are studied. LS is used as a model substance for humic acid. Independent of ionic strength and of dry density apparent diffusivities in the order of 10(-8) cm(2)/s were obtained. The ratios of effective diffusivity/apparent diffusivity are in accordance with the porosities of the bentonite. The diffusing colloids were not found to be hindered by ionic exclusion or by filtering effects. The results indicate that the LS diffuse through the bentonite as small uncharged colloids. It seems that ionic strength greater than or equal to 0.01 M NaClO4 provides enough ions to shield the charged sites on the colloids, and the colloids can coil into smaller units.
|
|
| 4. |
- Al-Taie, Laith, et al.
(författare)
-
Hydraulic properties of smectite rich clay controlled by hydraulic gradients and filter types
- 2014
-
Ingår i: Applied Clay Science. - : Elsevier BV. - 0169-1317 .- 1872-9053. ; 87, s. 73-80
-
Tidskriftsartikel (refereegranskat)abstract
- The common practice in geotechnical laboratories is to apply high hydraulic gradients for getting results in reasonable time but this can jeopardize the accuracy. In this paper, the hydraulic conductivity of a smectite rich clay from Iraq was determined under different hydraulic gradients (5 to 10000 m/m) using several densities and two permeants. Also, two types of filters were used, ordinary stainless steel sintered filter and sand/silt filter, in order to examine the possible effect of clogging by dragged clay gel particles. It was concluded that the outflow filter can affect the evaluated conductivity especially when applying high hydraulic gradients. For sintered filters the hydraulic conductivity was reduced as the gradient increased, while the conductivity increased as the hydraulic gradient increased when using sand/silt filters. For salt water the impact of the gradient was less obvious than for distilled water. A theoretical model was derived for selecting safe hydraulic gradients as a function of dry density, hydraulic gradient, swelling pressure and permeant type. A major conclusion was that the gradient in laboratory testing should not exceed 100 m/m.
|
|
| 5. |
- Al-Taie, Laith, et al.
(författare)
-
Natural smectitic soils for protective liners in arid climate
- 2014
-
Ingår i: Applied Clay Science. - : Elsevier BV. - 0169-1317 .- 1872-9053. ; 102, s. 104-112
-
Tidskriftsartikel (refereegranskat)abstract
- Compacted clay liners (CCL) can be used to isolate hazardous wastes like the soil and military scrap contaminated with depleted uranium that emanated from the Iraqi wars in 1991 and 2003. Near-surface repositories for such dangerous waste can preferably be located in the Iraqi deserts, which make up 60% of the territory of Iraq. CCLs are usually constructed using a mixture of clayey soil and coarse material compacted in air-dry form or suitably wetted. In the present study, two smectitic soils from Iraq, termed Green and Red clays, were investigated for potential use in CCLs. The shear strength, swelling pressure, hydraulic conductivity and creep properties were determined and used for preliminary design of top and bottom liners. The engineering properties were determined for various dry densities and water contents ranging from air-dry to fully saturated conditions. The results showed that mixtures of sand and 30-50% Green clay, and mixtures of sand and 40-60% Red clay are suitable for constructing top liners with a hydraulic conductivity between 1×10-10 - 1×10-9 m/s. For bottom liners, mixtures of sand and 70% Green clay and mixtures of sand and 80% Red clay can be considered. They were found to have a hydraulic conductivity of 1×10-11 m/s for a density at saturation of 2.1 g/cm3 (dry density 1.7 g/cm3). As to the slope stability of top liners, the shear strength for different clay percentages was found to guarantee slope stability for 18o inclination under both air-dry and water saturated conditions.
|
|
| 6. |
- Awad, Mahmoud E., et al.
(författare)
-
Modeling of the adsorption of a protein-fragment on kaolinite with potential antiviral activity
- 2020
-
Ingår i: Applied Clay Science. - : Elsevier. - 0169-1317 .- 1872-9053. ; 199
-
Tidskriftsartikel (refereegranskat)abstract
- This work aimed at studying the potentiality of interactions between kaolinite surfaces and a protein-fragment (350–370 amino acid units) extracted from the glycoprotein E1 in the transmembrane domain (TMD) of hepatitis C virus capsid. A computational work was performed for locating the potential electrostatic interaction sites between kaolinite aluminol and siloxane surfaces and the residues of this protein-fragment ligand, monitoring the possible conformational changes. This hydrated neutralized kaolinite/protein-fragment system was simulated by means of molecular modeling based on atomistic force fields based on empirical interatomic potentials and molecular dynamic (MD) simulations. The MD calculations indicated that the studied protein-fragment interacted with the kaolinite surfaces with an exothermic process and structural distortions were observed, particularly with the hydrophilic aluminol surface by favorable adsorption energy. The viral units isolation or trapping by the adsorption on the kaolinite nanoparticles producing structural distortion of the peptide ligands could lead to the blockage of the entry on the receptor and hence a lack of viral activity would be produced. Therefore, these findings with the proposed insights could be an useful information for the next experimental and development studies in the area of discovering inhibitors of the global challenged hepatitis and other pathogenic viruses based on the phyllosilicate surface activity. These MD studies can be extended to other viruses like the COVID-19 interacting with silicate minerals surfaces.
|
|
| 7. |
- Blanchart, P., et al.
(författare)
-
Mechanism of traditional Bogolan dyeing technique with clay on cotton fabric
- 2010
-
Ingår i: Applied Clay Science. - : Elsevier BV. - 0169-1317 .- 1872-9053. ; 50:4, s. 455-460
-
Tidskriftsartikel (refereegranskat)abstract
- Bogolan is a traditional dyeing technique deeply rooted in Mali It uses local clays from Niger River region and a leave extract from N galama trees (Anogeissus leiocarpa) The clay contains a significant amount of iron (hydr)oxides mainly akaganeite It reacts with N galama coating onto cotton to form black or brown colors UV/Vis and IR spectroscopy indicated very similar behavior of N galama leaves extract and carboxylic aromatic acids mainly ellagic or gallic acids which form dark colored complexes with iron Since iron (hydr) oxides are coated on clay mineral particles they contribute to the fixation of the Clay mineral particles and also cause the dark color X-ray diffraction of oriented tissue and SEM observations confirmed the presence of clay particles attached on the fiber surface.
|
|
| 8. |
- Bouchelaghem, F., et al.
(författare)
-
Diffusion calculations on numerical images of bentonite microstructure
- 2020
-
Ingår i: Applied Clay Science. - : Elsevier. - 0169-1317 .- 1872-9053.
-
Tidskriftsartikel (refereegranskat)abstract
- Effective diffusion tensors were computed for tracer diffusion through compacted water-saturated bentonite at two distinct scales by combining random microstructures and microstructures obtained by Transmission Electron Microscopy. The original micrographs have been thresholded by considering four distinct phases at the mesoscopic scale, and image analysis techniques have been employed in order to characterize the morphology and in particular the texture anisotropy of grains, clay gels and macrovoids. The Homogenization of Periodic Media approach employed is based on the local description ion diffusion at both the microscopic level of clay platelets (assuming variable diffusivity and ion sorption) and the mesoscopic level of clay aggregates and macropores. The local problems were successively solved using randon and TEM-based numerical microstructures in order to investigate the contribution to macroscopic diffusion of soft gels, dense gels and macrovoids under various configurations. Comparisons were made with existing diffusion data for montmorillonite and natural bentonite, and a particular attention was given to the anisotropy of the macroscopic diffusion tensor in connection with morphological characteristics of the underlying microstructure. The effect of clay matrix diffusivity on the magnitude and orientation of the macroscopic diffusion tensor has been investigated, and the principal axes of diffusion have been compared with the index of fabric orientation. Computations were also performed on microstructures of increasing size in order to investigate the model implicit assumption of existence of a Representative Elementary Volume.
|
|
| 9. |
- Bouchelaghem, Fatiha, et al.
(författare)
-
Fluid flow and effective conductivity calculations on numerical images of bentonite microstructure
- 2017
-
Ingår i: Applied Clay Science. - : Elsevier. - 0169-1317 .- 1872-9053. ; 144, s. 9-18
-
Tidskriftsartikel (refereegranskat)abstract
- Hydraulic conductivities of compacted water-saturated bentonite were computed based on the real microstructure. The Homogenization of Periodic Media approach employed fully acknowledges the heterogeneous and multiscale microstructure of clay, as well as locally varying physical flow properties. Consequently, three levels of description were considered : the microscopic level of clay particles, the mesoscopic level of clay aggregates, mineral grains and inter-aggregate porosity, and the macroscopic level of the sample subjected to fluid pressure gradients in the laboratory. Starting from the local description of fluid flow, the expression of the effective hydraulic conductivity tensor was derived. The soft and dense gels and the open voids may form a connected flow path or remain occluded. The local problems were solved on the microstructure obtained from a digitalized micrograph by image analysis. The contribution to macroscopic flow by the soft and dense gels was investigated in various configurations, and comparisons were made with hydraulic conductivity data for MX-80 bentonite.
|
|
| 10. |
- Breen, C., et al.
(författare)
-
Exploring the interactions between starches, bentonites and plasticizers in sustainable barrier coatings for paper and board
- 2019
-
Ingår i: Applied Clay Science. - : Elsevier Ltd. - 0169-1317 .- 1872-9053. ; 183
-
Tidskriftsartikel (refereegranskat)abstract
- Effective food packaging is a major factor in the current global drive to minimise food waste. Starch is an excellent oxygen barrier for packaging but it is brittle and moisture sensitive. The addition of layered minerals and plasticizers can significantly improve the moisture barrier and flexibility of the resulting composite. Some combinations of starch and plasticizer are incompatible but our results show that the addition of bentonite ensures the formation of coherent starch films with much improved moisture barrier regardless of the starch-plasticizer compatibility. It was clearly demonstrated that improvement of the moisture barrier was critically dependent on the layer charge of the bentonite used. Starch was readily accommodated in the interlayer space of bentonites with a layer charge of <0.4 electrons per formula unit but was not adsorbed if the layer charge was above this value. Starch-bentonite-plasticizer coatings prepared using bentonites with the lower layer charge routinely produced higher barriers to water vapour. The water vapour transmission rate (WVTR) of the base paper was reduced from 780 to 340 ± 20 g m2 day−1 when coated with starch alone. This was further reduced to 48 or 66 g m2 day−1 if glycerol or lower charge bentonite, respectively, was added to the starch. Optimised coatings of starch-lower charge bentonite-plasticizer provided WVTR values of ≤10 g m2 day−1 whereas WVTR values for comparative coatings prepared using the higher charge bentonites were three to four times higher (35 ± 7 g m2 day−1). Scanning electron micrographs provided clear evidence for the presence of 60 nm thick supramolecular layers formed from starch-bentonite-plasticizer in the samples coated on either glass or paper. The WVTR values for these low-eco footprint coatings are competitive with proprietary coatings prepared using petroleum derived resins.
|
|
