AVS 49th International Symposium
    Electrochemistry and Fluid-Solid Interfaces Monday Sessions
       Session EC+SS-MoA

Invited Paper EC+SS-MoA4
A New View of Ion Adsorption at Mineral-Fluid Interfaces with Synchrotron X-Ray Scattering

Monday, November 4, 2002, 3:00 pm, Room C-104

Session: Liquid-Solid Interfaces & Nanoscale Electrochemistry
Presenter: P. Fenter, Argonne National Laboratory
Authors: P. Fenter, Argonne National Laboratory
Z. Zhang, Northwestern University
M.L. Schlegel, Commissariat a l'Energie Atomique, France
C.Y. Park, Argonne National Laboratory
L. Cheng, Argonne National Laboratory
K.L. Nagy, University of Colorado at Boulder
D.J. Wesolowski, Oak Ridge National Laboratory
M. Machesky, Illinois State Water Survey
M.J. Bedzyk, Northwestern University
N.C. Sturchio, University of Illinois at Chicago
Correspondent: Click to Email
Ion adsorption at mineral-water interfaces is a key component of the electrical double-layer, a classic problem in surface science, and is fundamental for understanding the mobility of elements in the environment. We describe direct in-situ measurements of the systematic trends in ion adsorption near rutile- and muscovite-water interfaces using synchrotron X-ray scattering techniques (X-ray standing waves and X-ray reflectivity). These minerals represent two extremes in terms of location and origin of surface charge. The surface charge on rutile, an oxide, is determined by surface protonation reactions and is located above the mineral surface. In contrast, the surface charge of muscovite, a phyllosilicate, is determined by the permanent negative charge due to isomorphic lattice substitution below the mineral surface. The location of Zn@super 2+@, Sr@super 2+@ and Y@super 3+@ ions were fully triangulated at the rutile(110)-water interface revealing unexpected differences in their adsorption geometries. Separate measurements were made of K@super +@, Cs@super +@, Ca@super 2+@, Ba@super 2+@ and Zn@super 2+@ ion heights with respect to the muscovite(001)-water interface. Systematic trends in adsorption behavior will be discussed in the context of classical pictures of ion-mineral interactions (e.g., inner sphere vs. outer-sphere complexes) and by contrasting the different ion adsorption behavior at the rutile and muscovite surfaces. Research sponsored by the U.S. Department of Energy, Office of Basic Energy Science: Division of Chemical Sciences, Geosciences and Biosciences.