GEOC 25 |
| Although much progress has been made using spectroscopic data and multi-site complexation models to understand sorption of dissolved species to mineral surfaces, few studies have examined changes with time. We used 19F MAS-NMR to study fluoride substitution for hydroxyl bridges (µ2-OH) and terminal water (η-OH2) groups at the surface of monodispersed gibbsite at pH 5. We find that at low loadings sorption is mostly at the terminal sites, as evidenced in the 19F-MAS NMR peak at -142 ppm. A peak attributed to bridging fluorides, at -128 ppm increases with increased loadings. These peak assignments were confirmed by 19F{27Al} TRAPDOR experiments. Suspensions aged for long periods, however, appear to contain primarily bridging F configuration. These results are consistent with migration of fluoride from terminal to bridging sites over time, which has also been observed for F- sorption on the GaAl12 cation. |
|
Physical Chemistry of Soil and Aquifer Systems: A Symposium in Honor of Garrison Sposito
1:30 PM-5:10 PM, Sunday, 10 September 2006 Moscone Center -- Room 256, Oral
Division of Geochemistry |