| 1. |
- Bouchelaghem, Fatiha, et al.
(författare)
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Fluid flow and effective conductivity calculations on numerical images of bentonite microstructure
- 2017
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Ingår i: Applied Clay Science. - : Elsevier. - 0169-1317 .- 1872-9053. ; 144, s. 9-18
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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.
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| 2. |
- Breen, C., et al.
(författare)
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Exploring the interactions between starches, bentonites and plasticizers in sustainable barrier coatings for paper and board
- 2019
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Ingår i: Applied Clay Science. - : Elsevier Ltd. - 0169-1317 .- 1872-9053. ; 183
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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.
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| 3. |
- Cedeno, Daniel Grings, et al.
(författare)
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An experimental study on smectites as nitrogen conveyors in subduction zones
- 2019
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Ingår i: Applied Clay Science. - : Elsevier. - 0169-1317 .- 1872-9053. ; 168, s. 409-420
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Tidskriftsartikel (refereegranskat)abstract
- We performed high pressure and high temperature (HPHT) experiments on NH4-doped montmorillonite (similar to 2 wt % of NH4) under pressures of 2.5, 4.0, and 7.7 GPa and temperatures from 200 to 700 degrees C. Each experiment was analyzed with XRD, FTIR, CHN elemental analysis, and SEM in order to determine the NH4-Smectite phase changes and their morphology, and the presence of ammonium in the runs. Our results show that smectite can easily transport nitrogen, speciated as ammonium (NH4+), incorporated into the smectite interlayer in mildly reducing environments to deeper levels in the Earth through cold thermal regime subduction zones. NH4-Smectite transforms into NH4-enriched micaceous phase (tobelite) through a NH4+-enriched interlayered I/S phase in relatively low pressures and temperatures (around 2.5 GPa and 500 degrees C). Tobelite is stable until more extreme conditions (7.7 GPa and 700 degrees C), together with lesser amounts of buddingtonite (an ammonium-bearing feldspar) kyanite, and garnet. Our experiments also show the effect of nitrogen in the feldspar stability, as potassic and sodic feldspar are stable up to similar to 5 GPa, while buddingtonite, is observed to be stable up to 7.7 GPa. Nitrogen can return to the surface once the stability of these nitrogen-enriched minerals is reached due to pressure or temperature increasing.
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| 4. |
- Dessirier, Benoît, et al.
(författare)
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Reconstruction of the water content at an interface between compacted bentonite blocks and fractured crystalline bedrock
- 2017
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Ingår i: Applied Clay Science. - : Elsevier BV. - 0169-1317 .- 1872-9053. ; 142, s. 145-152
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Tidskriftsartikel (refereegranskat)abstract
- High-density sodium bentonite combines a low permeability with a swelling behavior, which constitute two important qualities for engineered barriers in geological disposal of spent nuclear fuel. For example, the KBS-3V method developed in Sweden and Finland is planned to include compacted bentonite as the buffer material to embed canisters containing the spent nuclear fuel packages in deposition holes in deep crystalline bedrock. The partially saturated bentonite buffer will then swell as it takes up groundwater from the surrounding rock. It is important to quantify the water content evolution of the installed buffer to correctly predict the development of the swelling pressure and the prevailing conditions (thermal, mechanical, chemical and biological). This study aimed at quantifying the water content profile at the surface of a cylindrical bentonite parcel retrieved after in situ wetting in fractured crystalline bedrock. We demonstrate the possibility of using regression-kriging to quantitatively include spatial information from high-resolution photographs of the retrieved bentonite parcel, where more water saturated areas appear as relatively dark shades, along with bentonite samples, where detailed measurements of water content were performed. The resulting reconstruction is both exact regarding local sample measurements and successful to reproduce features such as intersecting rock fracture traces, visible in the photographs. This level of detail is a key step to gain a deeper understanding of the hydraulic behavior of compacted bentonite barriers in sparsely fractured rock. An improved scanning procedure could further increase the accuracy by reducing errors introduced by the geometrical transformations needed to unfold and stitch the different photographs into a single gray scale map of the bentonite surface. The application of this technique could provide more insights to ongoing and planned experiments with unsaturated bentonite buffers.
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| 5. |
- Hatem, Mohammed, et al.
(författare)
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Interaction of clay and concrete relevant to the deep disposal of high-level radioactive waste
- 2015
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Ingår i: Applied Clay Science. - : Elsevier BV. - 0169-1317 .- 1872-9053. ; 118, s. 178-187
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Tidskriftsartikel (refereegranskat)abstract
- A concept for the disposal of highly radioactive waste at depth in the Earth’s crust using very deep bore-holes requires that the upper 2 km’s of the 800 mm diameter, steeply drilled holes, be effectively sealed. This can be achieved by using dense smectitic clay where the rock is weakly fractured and strengthening with concrete when fracture zones are encountered. Earlier investigations have shown that chemical reactions between the clay and concrete can be expected both in the upper part where the temperature is lower than 90oC and in the deeper section where the temperature reaches up to 150oC. To study further this interaction, hydrothermal experiments were conducted using mixed-layer (illite/smectite) Holmehus clay and a low pH slag-based concrete placed in contact under isothermal conditions at 21°C, 100oC and 150oC for a period of 8 weeks. The sample sets, which consisted of two clay discs separated by concrete cast on the lower clay disc, were extracted in undisturbed form and exposed to uniaxial pressure for measuring the compressive strength at successively increasing pressures. Compression tests underenhanced thermal conditions led to strengthening of both the clay and concrete. X-ray diffraction and electron microscopy analysis of the material revealed an increasing degree of cation exchange at higher temperatures with the cement, whereby Ca replaced Na in the interlayer sites of smectite layers. Dissolution of illite/smectite was also evident occurring at enhanced temperatures, with a decrease in K, Mg and Fe content with advanced alteration. The enhanced strength of clay can be partly attributed to the precipitation of cement phases from circulating fluids, including precipitation of gypsum.
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| 6. |
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| 7. |
- Lopez-Fernandez, Margarita, et al.
(författare)
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Microbial community changes induced by uranyl nitrate in bentonite clay microcosms
- 2018
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Ingår i: Applied Clay Science. - : Elsevier. - 0169-1317 .- 1872-9053. ; 160, s. 206-216
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Tidskriftsartikel (refereegranskat)abstract
- Deep geological repository (DGR) is one of the internationally accepted options to dispose radioactive wastes. Bentonite formations from Almeria, Spain, were selected as reference material for artificial barriers for the future Spanish repository. However, the safety of this long-term disposal could be compromised not only by physicochemical factors but also by microbial processes. The highly radioactive waste must be safely stored at least for 100,000 years for the radioactivity to decrease to similar levels to those of natural uranium. To simulate a scenario where the mobilization of radionuclides from the repository to the host formations may occur, long-term microcosms were studied. After being exposed to uranyl nitrate for 5 months, the response of the bentonite microbial community to the addition of this radionuclide was evaluated. High throughput 16S rRNA gene sequencing revealed that the structure of the microbial community after the uranyl nitrate treatment differs to that of the control microcosms. The microbial diversity was dominated by Firmicutes and Proteobacteria. Moreover, after the uranyl nitrate treatment OTUs annotated as Paracoccus and Bacillus were highly enriched. The mineralogy of bentonites was not affected by the uranyl nitrate treatment as was demonstrated by X-ray diffraction analysis. In addition, the study of uranium-bacteria interaction revealed the ability of isolates to biomineralize uranium as uranium phosphate mineral phases. Thus, the changes induced by the release of uranium in the microbial population may also affect the mobility of this radionuclide, making it less mobile and therefore less harmful for this environment.
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| 8. |
- MacGregor-Ramiasa, M., et al.
(författare)
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Magnetic alignment of nontronite dispersions
- 2015
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Ingår i: Applied Clay Science. - : Elsevier BV. - 0169-1317. ; 116-117, s. 167-174
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Tidskriftsartikel (refereegranskat)abstract
- The time dependent alignment of exfoliated nontronite dispersions subjected to moderate magnetic field strengths (B.
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| 9. |
- Mauroy, Henrik, et al.
(författare)
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Anisotropic clay–polystyrene nanocomposites: Synthesis, characterization and mechanical properties
- 2015
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Ingår i: Applied Clay Science. - : Elsevier BV. - 1872-9053 .- 0169-1317. ; 108, s. 19-27
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Tidskriftsartikel (refereegranskat)abstract
- Recent studies on clay–polymer nanocomposites have shown prominent improvements in thermal and mechanical propertieswith the addition of quite small amounts of nanometer sized clay particles. The present work presents characterization of anisotropic clay–polystyrene nanocomposites synthesized via a guided self-assembly technique, employing electric fields to align the clay particles into chain-like structures inside the polymer matrix. Four different kinds of surface modified clay were used as particle additives, namely Hectorite, Laponite, Na-Montmorillonite and Li-Fluorohectorite. The microstructure of the nanocomposites was examined with wide angle X-ray scattering (WAXS), X-ray computed microtomography (XMT) and transmission electron microscopy (TEM). Thermogravimetric analysis (TGA) was further employed to examine the high-temperature resilience of the nanocomposites before determination of the mechanical properties during compression. The results showed that the nanocomposites were of the intercalated type with the clay dispersed as ~15–70 nm thick crystallites which in turn aggregated into micrometer sized particles. Alignment of the clay particles into chains inside the polymer matrix led to differences in mechanical properties compared to nanocomposites having a randomorientation of the clay particles. In particular the aligned polystyrene–fluorohectorite nanocomposite displayed large improvements compared to its non-aligned counterpart. It was also observed that differences in yield strength depended on the compression direction.
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| 10. |
- Norrfors, Knapp Karin, et al.
(författare)
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Montmorillonite colloids : II. Colloidal size dependency on radionuclide adsorption
- 2016
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Ingår i: Applied Clay Science. - : Elsevier. - 0169-1317 .- 1872-9053. ; 123, s. 292-303
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Tidskriftsartikel (refereegranskat)abstract
- Bentonite is a strong radionuclide (RN) adsorbent. As a consequence, it is proposed as one of the engineered safety barriers in many nuclear waste disposal concepts in granite formations. Despite the many beneficial effects of bentonite, in contact with groundwater of low ionic strength montmorillonite colloids may be released from the bentonite buffer and transported towards the biosphere carrying the RNs bound to it. During the transport of colloids in bedrock fractures, size separation of clay colloids may occur, which may further affect RN mobility. In this work, RN adsorption (Th(IV), U(VI), Np(V), Tc(VII) and Pu(IV)) onto size fractionated montmorillonite colloids was studied in a synthetic, carbonated groundwater. Fractionation was done by simple settling procedures and sequential centrifugation. We combined batch adsorption experiments and geochemical modelling for the adsorption studies. U(VI), Np(V) and Tc(VII) did not adsorb to montmorillonite in the synthetic groundwater. Adsorption of Th(IV) and Pu(IV) is strong but, within experimental uncertainties, not significantly affected by the fractionation process. Montmorillonite colloids obtained by fractionation of the raw clay material but in the presence of organic matter during the initial separation step present significantly reduced uptake of Th and Pu. Based on the results, implementation of an "average log K-D" (i.e. average distribution coefficients) for all colloidal sizes in reactive transport modelling codes would be acceptable.
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