Molecular controls on kaolinite surface charge

Journal Article · Sun Nov 10 04:00:00 EST 1996 · Journal of Colloid and Interface Science

DOI:https://doi.org/10.1006/jcis.1996.0557· OSTI ID:404601

Brady, P V; Cygan, R T; Nagy, K L ^[1]

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1. Sandia National Labs., Albuquerque, NM (United States). Geochemistry Dept.

pH-dependent, multisite, surface charge on kaolinite can be explained by proton donor-acceptor reactions occurring simultaneously on Si and Al sites exposed on basal planes and edges. Si site Broensted acidity at the kaolinite-solution interface differs minimally from that of pure SiO{sub 2}, whereas Al site acidity increases appreciably over that of pure Al{sub 2}O{sub 3}. Increasing temperature decreases the pK values of Al and Si proton-exchange sites. Calculated site densities indicate either an elevated participation of edges or substantial contribution from basal planes in the development of surface charge. Independent evidence from scanning force microscopy points to a higher percentage of edge surface area due to thicker particles and basal surface steps than previously assumed. Thus, no basal plane participation is required to explain the site densities determined from proton adsorption isotherms. Molecular modeling of the proton-relaxed kaolinite structure has been used to establish the elevated acidity of edge Al sites and to independently confirm the crystal-chemical controls on surface reactivity.

• OSTI ID: 404601
• Journal Information: Journal of Colloid and Interface Science, Journal Name: Journal of Colloid and Interface Science Journal Issue: 2 Vol. 183; ISSN 0021-9797; ISSN JCISA5
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
ENVIRONMENTAL TRANSPORT
GEOCHEMISTRY
GROUND WATER
KAOLINITE
MOLECULAR MODELS
PH VALUE
SOILS
SURFACE POTENTIAL