title: Porosity investigation of compacted bentonite using XRD profile modeling.
abstract: Many countries intend to use compacted bentonite as a barrier in their deep geological repositories for nuclear waste. In order to describe and predict hydraulic conductivity or radionuclide transport through the bentonite barrier, fundamental understanding of the microstructure of compacted bentonite is needed. This study examined the interlayer swelling and overall microstructure of Wyoming Bentonite MX-80 and the corresponding homo-ionic Na(+) and Ca(2+) forms, using XRD with samples saturated under confined swelling conditions and free swelling conditions. For the samples saturated under confined conditions, the interparticle, or so-called free or external porosity was estimated by comparing the experimental interlayer distances obtained from one-dimensional XRD profile fitting against the maximum interlayer distances possible for the corresponding water content. The results showed that interlayer porosity dominated total porosity, irrespective of water content, and that the interparticle porosity was lower than previously reported in the literature. At compactions relevant for the saturated bentonite barrier (1.4-1.8 g/cm(3)), the interparticle porosity was estimated to ≤3%.
authors.affiliation: KTH School of Chemical Science and Engineering, Nuclear Chemistry, Royal Institute of Technology, SE-100 44 Stockholm, Sweden. holmboe@kth.se
authors.forename: Michael
authors.initials: M
authors.lastname: Holmboe
authors.forename: Susanna
authors.initials: S
authors.lastname: Wold
authors.forename: Mats
authors.initials: M
authors.lastname: Jonsson
mesh_terms: D001546:Bentonite / Q000737:chemistry*; D008962:Models, Theoretical; D016062:Porosity; D011848:Radioactive Pollutants / Q000737:chemistry*; D011850:Radioactive Waste; D018505:Waste Management / Q000379:methods*; D014959:Wyoming; D014961:X-Ray Diffraction
chemical_list: D011848:Radioactive Pollutants; D011850:Radioactive Waste; D001546:Bentonite