The importance of edge-site complexation reactions to metal cation adsorption by layer silicates

Conference · Fri Dec 31 04:00:00 EST 1993

OSTI ID:143135

Zachara, J M; McKinley, J P ^[1]

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1. Pacific Northwest Laboratory, Richland, WA (United States)

Layer lattice silicates are ubiquitous mineral components of geologic materials. They adsorb metal cations and influence metal ion concentrations and migration velocities in soil solutions and groundwater. Layer lattice silicates contain multiple surface sites, including fixed and two variable charge sites (i.e., SiOH and AlOH), that react with protons and metal cations. This presentation will evaluate the contributions of these different sites to metal cation adsorption by 1:1 and 2:1 layer silicates using sorption data for Co., Cd, and U on kaolinite and smectite. The pH, ionic strength, and electrolyte cation (Na and Ca) were varied in these experiments to selectively suppress or promote surface complexation reactions with different sites. The different metal cations vary in their aqueous speciation and affinity for hydroxylated edge sites, and show different pH dependent sorption behavior. Multiple site surface complexation models have been applied to the experimental data to evaluate the regions of pH and ionic strength over which ion exchange and edge complexation reactions are important, and to test the implications of different edge structures and reactions on the layer silicates. Adsorption data for the metal cations on layer silicates extracted from subsurface material will be used to demonstrate that variations in particle morphology and chemical composition pose challenges to the modelling of sorption reactions on natural materials.

• OSTI ID: 143135
• Report Number(s): CONF-930304--
• Country of Publication: United States
• Language: English

Related Subjects

40 CHEMISTRY
54 ENVIRONMENTAL SCIENCES
58 GEOSCIENCES
ADSORPTION
CADMIUM COMPLEXES
CATIONS
COBALT COMPLEXES
GEOCHEMISTRY
PH VALUE
SILICATE MINERALS
SORPTIVE PROPERTIES
URANIUM COMPLEXES