title: Modeling the Acid-Base Properties of Montmorillonite Edge Surfaces.
abstract: The surface reactivity of clay minerals remains challenging to characterize because of a duality of adsorption surfaces and mechanisms that does not exist in the case of simple oxide surfaces: edge surfaces of clay minerals have a variable proton surface charge arising from hydroxyl functional groups, whereas basal surfaces have a permanent negative charge arising from isomorphic substitutions. Hence, the relationship between surface charge and surface potential on edge surfaces cannot be described using the Gouy-Chapman relation, because of a spillover of negative electrostatic potential from the basal surface onto the edge surface. While surface complexation models can be modified to account for these features, a predictive fit of experimental data was not possible until recently, because of uncertainty regarding the densities and intrinsic pKavalues of edge functional groups. Here, we reexamine this problem in light of new knowledge on intrinsic pKavalues obtained over the past decade using ab initio molecular dynamics simulations, and we propose a new formalism to describe edge functional groups. Our simulation results yield reasonable predictions of the best available experimental acid-base titration data.
authors.affiliation: UMR 7327 Institut des Sciences de la Terre d'Orléans, Université d'Orléans-CNRS/INSU-BRGM , 45071 Orléans, France.|Earth and Environmental Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.|BRGM, French Geological Survey, 45100 Orléans, France.
authors.forename: Christophe
authors.identifier: 0000-0003-2379-431X
authors.initials: C
authors.lastname: Tournassat
authors.affiliation: Earth and Environmental Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: James A
authors.initials: JA
authors.lastname: Davis
authors.affiliation: BRGM, French Geological Survey, 45100 Orléans, France.
authors.forename: Christophe
authors.initials: C
authors.lastname: Chiaberge
authors.affiliation: BRGM, French Geological Survey, 45100 Orléans, France.
authors.forename: Sylvain
authors.initials: S
authors.lastname: Grangeon
authors.affiliation: Department of Civil and Environmental Engineering and Princeton Environmental Institute, Princeton University , Princeton, New Jersey 08544, United States.
authors.forename: Ian C
authors.initials: IC
authors.lastname: Bourg
mesh_terms: D000327:Adsorption; D001546:Bentonite; D017665:Hydroxyl Radical; D008903:Minerals; D013499:Surface Properties
chemical_list: D008903:Minerals; D001546:Bentonite; D017665:Hydroxyl Radical