Impact of microstructure on anion exclusion in compacted clay media

Christophe Tournassat (1) , Stéphane Gaboreau (1) , Jean-Charles Robinet (2) , Ian C. Bourg (3, 4) , Carl I. Steefel (3)

1 BRGM - Bureau de Recherches Géologiques et Minières (BRGM)
2 ANDRA - Agence Nationale pour la Gestion des Déchets Radioactifs
3 LBNL - Lawrence Berkeley National Laboratory [Berkeley]
4 Princeton University

The sensitivity of ion concentration distribution models to three key model assumptions, the pore-size distribution of clay media, the distance of closest approach of ions to the clay surface, and the accessibility of sub-nanometer-wide clay mineral interlayer spaces to anions, was explored by solving the Poisson-Boltzmann equation for swelling and non-swelling clay materials. Our calculations show that all three model assumptions significantly impact values predicted for the anion accessible porosity. As a consequence, macroscopic measurements of anion exclusion in clay media cannot be used to test any of the three model assumptions independently of the two others. Information gained at the nanoscale,in particular, a detailed characterization of pore size distribution, is necessary to develop accurate predictive models of the anion accessible porosity of clay media.

Mots clés: molecular dynamics; clay; illite; montmorillonite; anion exclusion; Poisson-Boltzmann; microstructure

Domaines: Géochimie

Christophe Tournassat, Stéphane Gaboreau, Jean-Charles Robinet, Ian C. Bourg, Carl I. Steefel. Impact of microstructure on anion exclusion in compacted clay media. Euroclay 2015, Clay Mineral Society, Jul 2015, Edinburgh, United Kingdom. ⟨hal-01137606⟩