Study of Ion Exclusion Using Artificial Reference Samples for Rocks

Matti Valkiainen, Hannu Aalto, Jarmo Lehikoinen, Markus Olin

    Research output: Chapter in Book/Report/Conference proceedingConference article in proceedingsScientific

    2 Citations (Scopus)

    Abstract

    Matrix diffusion in rocks has been extensively studied experimentally with various methods including tracer experiments. Comparing the rock-capacity factors (α) for Cl-36 to corresponding values for H-3, an anion-exclusion tendency has been observed in many cases. This study uses a well-characterized reference material: porous silica (Geltech Inc.), with pore diameters of 2.5, 5, 7.5 and 20 nanometers. The equilibration-leaching method and tracers H-3 (H-3) and Cl-36 (Cl−) were used to determine the capacity factors of the samples in three molarities of NaCl solution: 0.0026, 0.01 and 0. 1 mol/liter. The ratio αcl/αH-3 gives the anion exclusion for each solution/pore diameter combination. A clear anion-exclusion tendency was seen both as a function of the decreasing pore diameter and liquid molarity.
    The modeling was based on the assumption that the silica surface acts as a proton donor according to SiOH = SiO− + H+. The pore dimensions are also included in the calculations. In the case of the silica samples, good agreement was found when comparing the experimental and calculated values of chloride exclusion. This suggests that the surface complexation model for matrix diffusion can explain the observed exclusion phenomena in rocks although the parameters needed for the application of the model are difficult to obtain in the case of rocks.
    Original languageEnglish
    Title of host publicationScientific basis for nuclear waste management XXII. Materials Research Society symposium proceedings
    EditorsJ.H. Lee, D.J. Wronkiewwicz
    Place of PublicationPittsburgh
    PublisherMaterials Research Society
    Pages641-646
    ISBN (Print)1-55899-462-9
    DOIs
    Publication statusPublished - 1999
    MoE publication typeB3 Non-refereed article in conference proceedings
    Event1998 MRS Fall Meeting: Symposium on Microstructural Processes in Irradiated Materials - Boston, United States
    Duration: 30 Nov 19982 Dec 1998

    Publication series

    SeriesMaterials Research Society Symposia Proceedings
    Volume556
    ISSN0272-9172

    Conference

    Conference1998 MRS Fall Meeting
    CountryUnited States
    CityBoston
    Period30/11/982/12/98

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