GEOC 149 |
| Ian C. Bourg1, Garrison Sposito1, and Alain C. M. Bourg2. (1) Department of Civil and Environmental Engineering, University of California, 631 Davis Hall #1710, (temporary address: Hearst Field Annex B), Berkeley, CA 94720-1710, (2) Environmental Geochemistry (LHGE), Earth Sciences Department, University of Pau, IPRA, BP 1155, 64013 Pau Cedex, France |
| The absence of a point of zero salt effect (pzse) for montmorillonite has been attributed to either 1) a spillover of electrostatic potential from the basal planes onto the crystal edges, or 2) a small number of cation-exchange sites with a high affinity for protons. We built a surface complexation model of proton adsorption to montmorillonite edge surfaces. Aluminol and silanol site densities were taken from structural estimates, and the edge surface area was estimated from particle dimensions. Surface acidity constants were derived from titrations of pure Al- and Si-oxides. A novel method accounted for the unknown initial net surface proton charge. The model successfully reproduced experimental montmorillonite titration data. The lack of a pzse was predicted to occur from the co-existence of aluminol and silanol sites on the same surface. It may thus also occur in other mixed oxides, independently of the existence of a permanent structural charge. |
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Interfacial Phenomena: Linking Atomistic and Macroscopic Properties
8:05 AM-11:30 AM, Wednesday, March 31, 2004 Marriott -- Marquis NW, Oral
Division of Geochemistry |