Intracrystalline Swelling of Mixed-Layer Illite-Smectite in K-Bentonites

Müller-Vonmoos, Max; Kahr, G.; Madsen, Fritz T.

doi:10.1180/claymin.1994.029.2.06

Cited by 9 publications

(6 citation statements)

References 17 publications

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“…This is primarily because the heating led to an average charge of the I/S that is not much higher than that of smectite (Mfiller-Vonmoos et al 1994), indicating that a large part of the smectite remained intact and that high-charge illite layers were formed in close association of the smectite stacks. Secondly, the particle morphology does not speak against neoformation ofillite.…”

Section: Discussionmentioning

confidence: 95%

Aspects on the Illitization of the Kinnekulle Bentonites

Pusch

1995

Clays and clay miner.

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Abstract--Earlier interpretations of the conversion of the virgin smectite of the Ordovician Kinnekulle K-bentonites into the present mixed-layer illite/smectite imply that it took place through charge increase of the smectite with subsequent uptake and fixation of potassium. Recent analyses show that the layer charge of the smectite component of the I/S is in fact low and they suggest that neoformation of a separate illite phase took place. Pytte's kinetic model gives good agreement with the actual conversion rate for an activation energy of about 25-27 kcal/mole, depending on the adopted rate parameters, temperature history and assumed potassium source. In the KinnekuUe case the rate-controlling factor appears to have been the supply of potassium, which is concluded to have required large-scale, heat-induced groundwater convection.

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Section: Discussionmentioning

confidence: 95%

Aspects on the Illitization of the Kinnekulle Bentonites

Pusch

1995

Clays and clay miner.

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“…The particle size of the exfoliated volclay was determined by centrifugal sedimentation of an aqueous dispersion19 and the data are plotted in Figure 1 (median diameter = ca. 100 nm).…”

Section: Resultsmentioning

confidence: 99%

“…3% feldspars. Its particle size has been reported 19. Li–Volclay was prepared by exchanging the surface cations with Li + in an aqueous dispersion.…”

Section: Methodsmentioning

confidence: 99%

Reinforcement of poly(dimethylsiloxane) networks by montmorillonite platelets

Osman¹,

Atallah²,

Kahr

et al. 2001

J of Applied Polymer Sci

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A PDMS network, synthesized from a vinyl-terminated precursor, was reinforced by plate-like montmorillonite (volclay) particles with different surface cations. The optimal ratio of crosslinker-to-PDMS precursor was ascertained from the mechanical properties of networks prepared with different crosslinker concentrations. The elastic modulus of the polymer was enhanced by the montmorillonite particles. The increase in modulus was higher in the Li-than in the Na-volclay composites. The ultimate strength of the composites was also strongly enhanced by the small platelets, especially in presence of surface Li ϩ . The stronger influence of Li-volclay on the mechanical properties of the composites can be attributed to the partial formation of an intercalated structure, which leads to thinner particles with a high aspect ratio. Both composite strength and modulus were proportional to the filler-volume-fraction, but the increase in strength was limited by rising particle agglomeration at high loading. In contrast to organic-modified montmorillonite, the inorganic surface of volclay catalyzed the thermal degradation of PDMS.

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“…In this process, interlayer charge increases mainly by isomorphous substitution of Si 4+ by A13+. Following the adsorption of K § the interlayer of the montmorillonite collapses and bentonites transform into potassium bentonites (K-bentonites) as described by Miiller-Vonmoos et al (1994). Pusch & Madsen (1993 also postulated the neoformation of high-charge illite layers in the illite-smectite mixed-layers.…”

Section: Mineralogical Longevitymentioning

confidence: 99%

Clay mineralogical investigations related to nuclear waste disposal

Madsen

1998

Clay miner.

229

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Mineralogical and geotechnical investigations on the possible use of compacted bentonite as a buffer material in nuclear waste repositories are reported. The swelling capacity is highly dependent on the density of the compacted bentonite. Swelling pressures >30 MPa were measured for dry densities of ~2.0 g/cm3. Added iron or magnetite powder up to 20 wt% had no influence on the swelling capacity. Compacted mixtures of 20 wt% ground set cement and bentonite showed higher swelling pressures but lower swelling strain capability than compacted bentonite alone. Steam lowered the swelling pressure of compacted bentonite to ~60% of the original value. The influence was, however, reversible by ultrasonic treatment. The thermal conductivity of saturated compacted bentonite at a density of 2.0-2.1 g/cm3is ~1.35-1.45 W/m°K The volumetric heat capacity ranges from 3.1 x 106to 3.4 x 106j/m3°C The saturated hydraulic conductivity of the compacted bentonite is <10-12m/s. The apparent diffusion coefficients for various ions in compacted bentonite for water contents in the range of 20 to 25 wt% are: K+: 5 x 10-11, Cs+: 6 x 10-12, Sr2+: 3 x 10-11, UO22+: <10-13, Th4+: <10-13, Fe2+: 4 x 10-11, Fe3+: 4 x 10-11, Cl-: 1 x 10-10and I-: 1 x 10-10m2/s. The 'breakthrough time' for an apparent diffusion coefficient of 10-11m2/s in compacted bentonite 1 m thick was estimated to be ~3000 years. The mineralogical longevity was investigated on natural K-bentonites from Kinnekulle, Sweden, and Montana, USA. Although these materials have undergone considerable changes during diagenesis and contain various amounts of mixed-layer illite-smectite, they still have a substantial swelling and adsorption capacity. The investigations demonstrate that although the properties of bentonite are negatively influenced to a certain extent by heat, hot steam, iron and cement, compacted bentonite is still the best choice to act as a buffer material in a nuclear waste repository.

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Intracrystalline Swelling of Mixed-Layer Illite-Smectite in K-Bentonites

Cited by 9 publications

References 17 publications

Aspects on the Illitization of the Kinnekulle Bentonites

Aspects on the Illitization of the Kinnekulle Bentonites

Reinforcement of poly(dimethylsiloxane) networks by montmorillonite platelets

Clay mineralogical investigations related to nuclear waste disposal

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