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  • 1.
    García García, Sandra
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Wold, Susanna
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Jonsson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Effects of temperature on the stability of colloidal montmorillonite particles at different pH and ionic strength2009In: Applied Clay Science, ISSN 0169-1317, E-ISSN 1872-9053, Vol. 43, no 1, p. 21-26Article in journal (Refereed)
    Abstract [en]

    The effect of temperature at different pH and ionic strengths on the aggregation kinetics of colloidal montmorillonite particles in aqueous dispersions was investigated. For a given temperature and pH, the rate constant for aggregation increased with increasing ionic strength. At pH:54 the rate constant for colloid aggregation increased with increasing temperature, regardless of ionic strength. At pH 10 the aggregation rate constant decreased with increasing temperature as a general trend. In the intermediate pH interval, the aggregation rate constant apparently decreased with increasing temperature except at the highest ionic strength, where it increased with increasing temperature. The aggregation rate constant decreased at alkaline pH compared with the acidic pH range. This effect became more pronounced at higher ionic strengths and higher temperatures but could not be observed at 4 degrees C. These observations are in qualitative agreement with DLVO calculations taking temperature, pH and ionic strength into account.

  • 2.
    Holmboe, Michael
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Wold, Susanna
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Jonsson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Free porosity investigation of compacted Bentonite using XRDIn: Applied Clay Science, ISSN 0169-1317, E-ISSN 1872-9053Article in journal (Other academic)
    Abstract [en]

    Many countries intend to use compacted bentonite as abarrier in their deep geological repositories for nuclearwaste. In order to describe and predict hydraulicconductivity or radionuclide transport through thebentonite barrier, fundamental understanding of themicrostructure of compacted bentonite is needed. Thisstudy examined the interlayer swelling and overallmicrostructure of Wyoming Bentonite MX-80 and thecorresponding homo-ionic Na+ and Ca2+ forms, usingXRD with samples saturated under confined swellingconditions and free swelling conditions. For thesamples saturated under confined conditions, theinterparticle, or so-called free porosity was estimatedby comparing the experimental interlayer distancesobtained from one-dimensional XRD profile fittingagainst the maximum interlayer distances possible forthe corresponding water content. The results showedthat interlayer porosity dominated total porosity,irrespective of water content, and that free porositywas lower than previously reported in the literature. Atcompactions relevant for the saturated bentonitebarrier (1.4-1.8 g/cm3), the free porosity was estimatedto ≤ 3%.

  • 3.
    Holmboe, Michael
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Wold, Susanna
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Jonsson, Mats
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    García García, Sandra
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Effects of gamma-irradiation on the stability of colloidal Na+-Montmorillonite dispersions2009In: Applied Clay Science, ISSN 0169-1317, E-ISSN 1872-9053, Vol. 43, no 1, p. 86-90Article in journal (Refereed)
    Abstract [en]

    In many concepts for final storage of spent nuclear fuel bentonite will be used as an engineered barrier, mainly due to its inertness, plasticity and ability to retard transport of radionuclides by adsorption. In the event of water-bearing fractures making contact with the bentonite barrier, generation and transport of colloidal particles will strongly depend on groundwater composition and the surface properties of the colloidal particles. The bentonite barrier will unavoidably be exposed to ionizing radiation from the spent nuclear fuel but very little is known about effects of ionizing radiation on bentonite concerning colloidal stability. In this work we have studied the effect of gamma-radiation on the stability of dilute colloidal Na+-montmorillonite dispersions using a Cs-137 gamma-source (doses of 0-53.2 kGy). Aggregation kinetics and sedimentation experiments revealed significant radiation effects, evident as increased colloid stability. The only rationale for this is a gamma-radiation induced increase in surface potential. The effects appeared to depend on the Na+-montmorillonite concentration in the irradiated dispersions, indicating that the change in surface potential is induced by aqueous radiolysis products.

  • 4.
    Jansson, Mats
    et al.
    KTH, Superseded Departments, Chemistry. KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Eriksen, Trygve E
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    Wold, Susanna
    KTH, Superseded Departments, Chemistry. KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
    LOT: in situ diffusion experiments using radioactive tracers2003In: Applied Clay Science, ISSN 0169-1317, E-ISSN 1872-9053, Vol. 23, no 1-4, p. 77-85Article in journal (Refereed)
    Abstract [en]

    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.

  • 5.
    Kirabira, John Baptist
    et al.
    Makerere University.
    Jonsson, Stefan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Byaruhanga, Joseph Kadoma
    Makerere University.
    Laboratory Benefication And Evaluation of Mutaka Kaolin from the Lake Victoria Region, UgandaIn: Applied Clay Science, ISSN 0169-1317, E-ISSN 1872-9053Article in journal (Other academic)
  • 6.
    Larsson, Stefan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Rothhämel, Mirja
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Jacks, Gunnar
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630).
    A laboratory study on strength loss in kaolin surrounding lime-cement columns2009In: Applied Clay Science, ISSN 0169-1317, E-ISSN 1872-9053, Vol. 44, no 1-2, p. 116-126Article in journal (Refereed)
    Abstract [en]

    This study evaluated property changes in laboratory-prepared kaolin surrounding lime-cement columns. The parameters investigated included geotechnical parameters such as undisturbed undrained shear strength, remoulded shear strength, water content, and Atterberg limits. In addition the exchangeable Ca2+, Na+ and K+ ion concentrations were assessed. Four types of small-scale lime-cement columns were manufactured using different production methods and binder blending ratios. Tests were performed 7, 14, 30 and 90 days after installation. The migration of Ca2+, Na+ and V ions from the lime-cement columns into the surrounding soil has been confirmed through the chemical analysis on a large number of samples taken. The results illustrate that the undrained shear strength properties in the surrounding kaolin were significantly affected by the migration of Ca2+, Na+ and K+ ions. An increase in the Na+ and K+ ion concentrations in the front of the migrated Ca2+ ions was observed. The tests illustrate that, under the experimental conditions chosen, the remoulded undrained shear strength decreased in a thin zone as a result of the migrated Na+ and K+ ions. The magnitude of the strength loss depended on the binder blending ratio in the lime-cement columns.

  • 7.
    Molera, Mireia
    et al.
    KTH, Superseded Departments, Chemistry.
    Eriksen, Trygve E
    Jansson, Mats
    KTH, Superseded Departments, Chemistry.
    Anion diffusion pathways in bentonite clay compacted to different dry densities2003In: Applied Clay Science, ISSN 0169-1317, E-ISSN 1872-9053, Vol. 23, no 1-4, p. 69-76Article in journal (Refereed)
    Abstract [en]

    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.

  • 8.
    Norrfors, Knapp Karin
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics. Karlsruhe Institute of Technology (KIT), Germany.
    Bouby, Muriel
    Heck, Stephanie
    Finck, Nicolas
    Marsac, Rerni
    Schaefer, Thorsten
    Geckeis, Horst
    Wold, Susanna
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Montmorillonite colloids: I. Characterization and stability of dispersions with different size fractions2015In: Applied Clay Science, ISSN 0169-1317, E-ISSN 1872-9053, Vol. 114, p. 179-189Article in journal (Refereed)
    Abstract [en]

    Bentonite is planned to be used as a technical barrier in the final storage of spent nuclear fuel and high level vitrified waste. In contact with ground water of low ionic strength, montmorillonite colloids may be released from the bentonite buffer and thereby enhance the transport of radionuclides (RNs) sorbed: In the present case, clay colloids represent aggregates of several clay mineral layers. It is of major importance to determine RN sorption properties for different sizes of montmorillonite aggregates, since size fractionation may occur during particle transport in natural media. In this study, a protocol for size fractionation of clay aggregates is developed, by sequential and direct centrifugation, in the presence and absence of organic matter. Seven colloidal fractions of different mean aggregate sizes are obtained ranging, when considering the mean equivalent hydrodynamic sphere diameter (ESD), from similar to 960 nm down to similar to 85 nm. Applying mathematical treatments (Jennings and Parslow, 1988) and approximating the clay aggregates to regular disc-shaped stacks of clay mineral sheets result in mean surface diameters varying from similar to 1.5 mu m down to similar to 190 nm. All these colloidal fractions are characterized by XRD, IC and ICP-OES where they are found to have the same chemical composition. The number of edge sites (aluminol and silanol) is estimated (in mol/kg) for each colloidal fraction according to (Tournassat et al., 2003). It is calculated from the mean particle sizes obtained from AsFlFFF and PCS measurements, where the clay aggregates are approximated to regular disc-shaped stacks of clay mineral sheets. The estimated number of edge sites varies significantly for the different clay dispersions. In addition, stability studies using the various clay colloidal fractions are performed by the addition of NaCl, CaCl2 or MgCl2, in the presence or absence of organic matter, where no difference in stability is found.

  • 9.
    Norrfors, Knapp Karin
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry. Karlsruhe Institute of Technology (KIT), Germany.
    Marsac, Remi
    Bouby, Muriel
    Heck, Stephanie
    Wold, Susanna
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Luetzenkirchen, Johannes
    Schäfer, Thorsten
    Montmorillonite colloids: II. Colloidal size dependency on radionuclide adsorption2016In: Applied Clay Science, ISSN 0169-1317, E-ISSN 1872-9053, Vol. 123, p. 292-303Article in journal (Refereed)
    Abstract [en]

    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.

  • 10.
    Wold, Susanna
    et al.
    KTH, Superseded Departments, Chemistry.
    Eriksen, T. E.
    Diffusion of lignosulfonate colloids in compacted bentonite2003In: Applied Clay Science, ISSN 0169-1317, E-ISSN 1872-9053, Vol. 23, no 04-jan, p. 43-50Article in journal (Refereed)
    Abstract [en]

    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.

  • 11.
    Yang, Guomin
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Neretnieks, Ivars
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Moreno, Luis
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology.
    Wold, Susanna
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Density functional theory of electrolyte solutions in slit-like nanopores II. Applications to forces and ion exchange2016In: Applied Clay Science, ISSN 0169-1317, E-ISSN 1872-9053, Vol. 132, p. 561-570Article in journal (Refereed)
    Abstract [en]

    An extended reference fluid density approach/weighted correlation approximation (RFD/WCA) of density functional theory (DFT) for size-asymmetric electrolytes presented in part I is applied to calculate the forces and the ion exchange for Ca- and Na-montmorillonite systems in equilibrium with salt solutions. Our modeling shows that the DFT calculations are in excellent agreement with Monte Carlo simulations and experimental results. The results indicate that the ion size plays an important role in force-distance relation. Due to the excluded volume effect, the osmotic pressure curve predicted by DFT is shifted towards larger separation distances with increasing the diameter of counterions. Additionally, the interaction can be switched from attraction to repulsion with increasing diameter of counterions from standard to hydrated ionic size. Furthermore, the quantitative characterization of the exchange of calcium for sodium at room temperature on Wyoming bentonite is investigated with the DFT modeling in aqueous solutions at pH 7.0. It is found that a significant variation of the selectivity coefficient could be observed with the surface charge density, ionic diameter and interlayer separations. This implies that ion selectivity in compacted bentonite differs from that in dilute smectite dispersions.

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