| 1. |
- Svensson, Daniel, et al.
(författare)
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Freezing and thawing of montmorillonite - A time-resolved synchrotron X-ray diffraction study
- 2010
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Ingår i: Applied Clay Science. - : Elsevier BV. - 1872-9053 .- 0169-1317. ; 49:3, s. 127-134
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Tidskriftsartikel (refereegranskat)abstract
- The evolution of phases over time during freezing and thawing of unconfined Na- and Ca-montmorillonites (Wyoming, MX-80) was studied with time-resolved synchrotron X-ray diffraction. The clay samples were: (i) powder equilibrated to ambient atmosphere and (ii) pastes of 30 mass% montmorillonite in pure water. The phases were characterised in-situ using a stream of nitrogen gas for temperature control. The behaviour of montmorillonite during freezing and thawing is important in final repositories for spent nuclear fuel that are using bentonite as a buffer material. The Na-montmorillonite equilibrated to ambient atmosphere (one-layer hydrate) was unaffected by freezing down to -50 degrees C. The Ca-montmorillonite equilibrated to ambient atmosphere (two-layer hydrate) showed a minor decrease in basal spacing (0.11 angstrom) by freezing down to 50 degrees C. The magnitude of the decrease in basal spacing was high compared to the thermal contraction of the similar minerals muscovite and pyrophyllite and some dehydration of the clay was likely to be involved. Wet Na-montmorillonite in pure water was highly affected by freezing causing the osmotic phase to collapse during ice formation to 19 angstrom (three-layer hydrate) and later to a mixture of two and three-layer hydrates (-15 degrees C) and at lower temperatures to twolayer hydrate (16 angstrom, 50 degrees C). The Ca-montmorillonite in pure water was present as a 19 angstrom three-layer hydrate at + 20 degrees C and expanded upon cooling, producing two partly overlapping 001 reflections corresponding to three and four-layer hydrates prior to the ice formation. A mean d-value of the 002 peaks of the four-layer hydrate was determined to be 10.8 angstrom, which corresponded to a basal spacing of 21.6 angstrom. To our knowledge this is the first time a distinct four-layer-water hydrate is reported for Ca-montmorillonite in pure water. After the ice formation started, the montmorillonite was dehydrated to three-layer hydrate and at -15 degrees C to a mixture of two and three-layer hydrates. At -50 degrees C only two-layer hydrate was present. The ice formation and the dehydration of the montmorillonite occurred simultaneously. The effects of freezing on the montmorillonite were shown to be reversible during the thawing. The two dimensional diffraction rings gave information on the ice texture. The highly dispersed Na-montmorillonite (high surface area) in pure water facilitated the nucleation of the ice crystals and gave rise to uniformly sized crystals, while the Ca-montmorillonite (not dispersed, lower surface area) gave rise to non-uniformly sized ice crystals. (C) 2010 Elsevier B.V. All rights reserved.
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| 2. |
- Svensson, Daniel, et al.
(författare)
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Hurlbutite, the first Be mineral from Vastana iron mine, Skane, Sweden
- 2002
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Ingår i: GFF. - 2000-0863. ; 124:1, s. 41-43
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Tidskriftsartikel (refereegranskat)abstract
- Hurlbutite has been identified as the first Be mineral from the Vastan (a) over circle iron mine, Sk (a) over circle ne, Sweden. The mineral is yellowish to whitish and its microscopic habit is platy and porous. Associated minerals are pinkish apatite, hematite, quartz and svanbergite. The unit cell dimensions calculated from powder X-ray diffraction data are: a = 8.321(8) Angstrom, b = 8.834(8) Angstrom, c = 7.881(7) Angstrom, beta = 90.38(6)degrees. Energy dispersive X-ray analyses of Ca, Sr and P indicated the formula (Ca0.93Sr0.07)Be-2(PO4)(2). The presence of Be and O was qualitatively confirmed by parallel electron energy loss spectroscopy, and traces of B were also detected.
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| 3. |
- Svensson, Daniel, et al.
(författare)
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Intercalation of smectite with liquid ethylene glycol - Resolved in time and space by synchrotron X-ray diffraction
- 2010
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Ingår i: Applied Clay Science. - : Elsevier BV. - 1872-9053 .- 0169-1317. ; 48:3, s. 358-367
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Tidskriftsartikel (refereegranskat)abstract
- Using synchrotron X-ray powder diffraction we studied the reaction of liquid ethylene glycol and smectite, i.e. (i) the time-resolved glycolation of Mg-smectite (Georgian Ibeco Seal M-90) films equilibrated to form hydrates with 0-3 water layers, and (ii) time and spatially resolved glycolation of homoionic Li-, Na-, K-, Mg-, and Ca-montmorillonite powders (Wyoming MX80) equilibrated to ambient atmosphere and packed in glass capillaries. The films in (i) were approximately 65 run thick and complete reaction was achieved within minutes. The relative intensity of the 17 angstrom-smectite-glycolate varied linearly with the square root of time and the effective diffusion coefficients were determined to be of the order of 10(-11) m(2)/s. In the one-layer hydrate experiment the basal spacing increased from 12.5 to 14.5 angstrom during the reaction, which indicated a redistribution of water in the sample. The capillaries in (ii) were 1.5 mm in diameter and were investigated along their length using a 1 x 1 mm X-ray beam. The wet part contained the 17 angstrom-montmorillonite-glycolate in all cases. In the dry part, close to the wetting front, a 0.5-2 mm zone with increased basal spacing was observed in all cases, except for the K-form. The zone with increased hydration contained: more two-layer-hydrate (Li, Na), four-layer-hydrate (Mg) and three-layer-hydrate (Mg, Ca). Further from the liquid the montmorillonite was present in its original hydration state as one-layer-hydrate (Li, Na,K) or two-layer-hydrate (Mg, Ca). The transport of liquid glycol into the montmorillonite in the tube was thus coupled to a transport of water on the mm-scale. (C) 2010 Elsevier B.V. All rights reserved.
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| 4. |
- Svensson, Per Daniel, et al.
(författare)
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Combined Salt and Temperature Impact on Montmorillonite Hydration
- 2013
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Ingår i: Clays and Clay Minerals. - 0009-8604. ; 61:3-4, s. 328-341
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Tidskriftsartikel (refereegranskat)abstract
- Bentonite is to be used as a sealing material for long-term storage of radioactive waste. During permafrost periods the buffer may freeze, causing the following: montmorillonite dehydration, ice formation, and pressure build-up that may fracture the surrounding rock. No previous study has been done on freezing of bentonite in saline water. Using small and wide angle X-ray scattering, the present study aimed to increase understanding of the combined impact of salt and temperature on the hydration (swelling) of Wyoming montmorillonite. The basal spacing of the Na-montmorillonite was very dependent on the water content, while this was not the case for the Ca-montmorillonite(after reaching 19 angstrom). The basal spacing of the free-swelling Na-montmorillonite (34-280 angstrom) was estimated successfully using simple calculations. During freezing of Na-montmorillonite in NaCl solution, both ice and hydrohalite formed (at -50 and -100 degrees C). At starting concentrations >= 1.5 M the basal spacing was not affected by freezing. During freezing of Ca-montmorillonite in CaCl2 solution, ice formed; antarcticite formed only sporadically. The basal spacing of the Ca-montmorillonite at high NaCl concentrations (>1 M) was greater at -50 and -100 degrees C (18 angstrom) than at 20 degrees C (16 angstrom). The opposite was observed at low concentrations. This change was attributed to small amounts of salts introduced into the montmorillonite interlayer, hence changing the interlayer water properties. The montmorillonite hydration was also temperature dependent; decreasing temperature increased the hydration (as long as no ice was formed) and increasing the temperature decreased the hydration. This was attributed to the temperature impact on the entropy of the hydration reaction. This observation was also reproduced in an experiment up to 90 degrees C. A small amount of salt in the groundwater was noted to reduce significantly the potential problem of ice formation in bentonite sealings.
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| 5. |
- Svensson, Per Daniel, et al.
(författare)
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Redox Chemistry in Two Iron-Bentonite Field Experiments at Äspö Hard Rock Laboratory, Sweden: An XRD and Fe K-Edge XANES Study
- 2013
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Ingår i: Clays and Clay Minerals. - 0009-8604. ; 61:6, s. 566-579
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Tidskriftsartikel (refereegranskat)abstract
- Excavated bentonite from two large iron-bentonite field experiments at Aspo Hard Rock Laboratory in Sweden was investigated with respect to iron redox chemistry and mineralogy. The iron redox chemistry was studied by Fe K-edge X-ray absorption near edge structure spectroscopy and the mineral phases were studied using X-ray diffraction. Bentonite is to be used as a buffer material in high-level radioactive waste repositories to protect the waste containers from their surroundings. Montmorillonite, which is responsible for the sealing properties in the bentonite, is susceptible to redox reactions. A change in the montmorillonite iron redox chemistry may affect its layer charge and hence its properties. The experiments included are the first Alternative Buffer Material test (ABM1) and the Temperature Buffer Test (TBT). The clays were heated to a maximum of similar to 130 degrees C (ABM1) or similar to 150 degrees C (TBT) for 2.5 and 7 y, respectively. In the central part of the compacted clay blocks was placed an iron heater and the distance from the heater to the rock was similar to 10 cm (ABM1) and similar to 50 cm (TBT), respectively. Eleven different clay materials were included in the ABM1 experiment and five were analyzed here. In the ABM1 experiment, the Fe(II)/Fe(III) ratio was increased in several samples from the vicinity of the heater. Kinetic data were collected and showed that most of the Fe(II)-rich samples oxidized rapidly when exposed to atmospheric oxygen. In the TBT experiment the corrosion products were dominated by Fe(III) and no significant increase in Fe(II) was seen. In ABM1, reducing conditions were achieved, at least in parts of the experiment; in TBT, reducing conditions were not achieved. The difference was attributed to the larger scale of the TBT experiment, providing more oxygen after the installation, and to the longer time taken for water saturation; oxidation of the samples during excavation cannot be ruled out. Minor changes in the bentonite mineral phases were found in some cases where direct contact was made with the iron heater but no significant impact on the bentonite performance in high-level radioactive waste applications was expected as a result.
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