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  • 1.
    André, Magnus
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Neretnieks, Ivar
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Malmström, Maria
    KTH, School of Industrial Engineering and Management (ITM), Industrial Ecology.
    Measuring sorption coefficients and BET surface areas on intact drillcore and crushed granite samples2008In: Radiochimica Acta, ISSN 0033-8230, E-ISSN 2193-3405, Vol. 96, no 9-11, p. 673-677Article in journal (Refereed)
    Abstract [en]

    In general sorption coefficients, K-d cat ion exchange capacity, CEC, and BET surface areas are measured on crushed rock samples because it is very time consuming to measure K-d and CEC on larger rock pieces as it takes a long time for the sorbing species to penetrate into and equilibrate a large sample. Also conventional sample holders for BET measurements are too small to hold a large sample. We have manufactured large sample holders for BET measurements and modified the equipment so that it is possible to measure BET surface areas on samples with 50 mm diameter and LIP to 100 mm length. Results are presented for intact pieces and compared to results on crushed material from the same drillcore. For K-d and CEC measurements we have developed a technique and equipment by which ions can be made to rapidly intrude into and equilibrate the internal surfaces of the same size samples as mentioned above. The method is based on electro-migration where the sample is placed between two vessels one with an anode and other with a cathode. The electric potential gradient drives the ions into and through the sample very much faster than molecular diffusion does. With Cs as the sorbing ion a few weeks were sufficient to equilibrate the 50 mm long sample. In previous diffusion experiments it took more than a year to equilibrate a 15 mm thick sample. A special mixing technique eliminates the development of low and high PH in the electrode compartments. K-d results from measurements on an intact drillcore are presented and comparison is made with results obtained on crushed material from the same bore core. The results from the sorption experiments are compared with the results from the BET surface area determinations in an attempt to evaluate the use of the BET surface area as a proxy for sorption behaviour.

  • 2.
    Jansson, Mats
    et al.
    KTH, Superseded Departments, Chemistry.
    Eriksen, Trygve E
    KTH, Superseded Departments, Chemistry.
    CHEMLAB - in situ diffusion experiments using radioactive tracers1998In: Radiochimica Acta, ISSN 0033-8230, E-ISSN 2193-3405, Vol. 82, p. 153-156Article in journal (Refereed)
    Abstract [en]

    In situ diffusion experiments in bentonite clay have been carried out in the probe CHEMLAB, using the radioactive tracers Co-57, Sr-85 and Cs-134. The measured diffusion profiles for the radionuclides are in good agreement with predicted profiles obtained from modelling based on apparent diffusivities and sorption coefficients obtained in laboratory experiments with corresponding clay density and ground water composition.

  • 3.
    Liu, Jinsong
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Neretnieks, Ivars
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Coupled transport/reaction modelling of copper canister corrosion aided by microbial processes2004In: Radiochimica Acta, ISSN 0033-8230, E-ISSN 2193-3405, Vol. 92, no 11-sep, p. 849-854Article in journal (Refereed)
    Abstract [en]

    Copper canister corrosion is an important issue in the concept of a nuclear fuel repository. Previous studies indicate that the oxygen-free copper canister could hold its integrity for more than 100 000 years in the repository environment. Microbial processes may reduce sulphate to sulphide and considerably increase the amount of sulphide available for corrosion. In this paper. a coupled transport/reaction model is developed to account for the transport of chemical species produced by microbial processes. The corroding agents like sulphide would come not only from the intruding groundwater, but also from the reduction of sulphate near the canister. The reaction of sulphate-reducing bacteria and the transport of sulphide in the bentonite buffer is included in the model. The local depth of copper canister corrosion is calculated by the model.

  • 4. Moll, H.
    et al.
    Reich, T.
    Hennig, C.
    Rossberg, A.
    Szabo, Zoltan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    Grenthe, I.
    Solution coordination chemistry of uranium in the binary UO22+-SO42- and the ternary UO22+-SO42--OH- system2006In: Radiochimica Acta, ISSN 0033-8230, E-ISSN 2193-3405, Vol. 88, no 11-sep, p. 559-566Article in journal (Refereed)
    Abstract [en]

    The structure and reaction dynamics in the systems UO22+-SO42- and UO22+-SO42--OH- were investigated using EXAFS and O-17-NMR spectroscopy. Uranium Lm edge EXAFS indicated a bidentate coordination mode of sulfate to uranyl. In solution, this is characterized by an U-S distance of 3.11 Angstrom. Approximately 5 oxygen atoms were observed in the equatorial plane at 2.39-2.43 Angstrom. The kinetics in the binary uranyl sulfate system can be described by four dominant exchange reactions: (1) UO22++SO(4)(2-)reversible arrow UO2SO4(k(1)), (2) U*O-2(2+)+UO(2)SO(4)reversible arrowU*O2SO4+UO22+(k(2)), (3) UO22++UO2(SO4)(2)(2-)reversible arrow 2UO(2)SO(4)(k(3)), and (4) UO2SO4+SO42-reversible arrowUO2(SO4)(2)(2-)(k(4)). These reactions have rate constants indicating that the exchange is not of the simple Eigen-Wilkins type. Ternary uranyl sulfate hydroxide species were characterized by their O-17 chemical shift and by potentiometry. There are no separate signals for the possible isomers of the ternary species indicating that they are in fast exchange with each other.

  • 5. Moll, H.
    et al.
    Reich, T.
    Szabo, Zoltan
    KTH, Superseded Departments, Chemistry.
    The hydrolysis of dioxouranium(VI) investigated using EXAFS and O-17-NMR2000In: Radiochimica Acta, ISSN 0033-8230, E-ISSN 2193-3405, Vol. 88, no 7, p. 411-415Article in journal (Refereed)
    Abstract [en]

    The structure of dioxouranium(VI) as a function of pH at different (CH3)(4)N-OH concentrations has been investigated with the aid of U L-III-edge EXAFS. Polynuclear hydroxo species were identified by an U-U interaction at 3.80(8) Angstrom at pH = 4.1. The precipitate formed at pH = 7 has a schoepite like structure. In solution at high pH [0.5 M (CH3)(4)N-OH], the EXAFS data are consistent with the formation of a monomeric four coordinated uranium(VI) hydroxide complex UO2(OH)(4)(2-) of octahedral geometry. The first shell contains two O atoms with a U=O distance of 1.83(o) Angstrom, and four O atoms were identified at a U-O distance of 2.26(5) Angstrom. In strong alkaline solutions [>1 M (CH3)(4)N)-OH],O-17-NMR spectra indicate the presence of two species, presumably UO2(OH)(4)(2-) and UO2(OH)(5)(3-), the latter in low concentration, which are in rapid equilibrium with one another at 268 K in aqueous solution.

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