GEOC 48 |
| Montmorillonite, a clay mineral ubiquitous in terrestrial weathering environments, plays an important role in the performance of clay barriers for solid waste containment. Montmorillonite dissolution kinetics, transition metal adsorption and edge-to-face aggregation are controlled by the net proton surface charge of montmorillonite, carried mainly by montmorillonite edge surfaces. A broad range of values of the point of zero net proton charge (pznpc) of montmorillonite has been reported. We introduce a montmorillonite acid-base titration model that accounts explicitly for the existence of a net proton surface charge prior to the beginning of the titration. Our model includes a modified Gouy-Chapman description of the spillover of electrostatic potential from basal onto edge surfaces and ab initio estimates of edge site reactivity. The model successfully predicts the influence of montmorillonite pretreatment on reported titration curves, and shows that reported pznpc values are unlikely to correspond to the true pznpc of montmorillonite. |
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General Poster Session
7:00 PM-9:00 PM, Sunday, 10 September 2006 Moscone Center -- Hall D, Poster
Division of Geochemistry |