GEOC 29 |
| That phosphate binds to goethite in a bridging-bidentate fashion is one of the fundamental precepts of soil chemistry. In this presentation, we will show that this coordination geometry is unlikely. We have measured in situ the infrared spectra of phosphate adsorbed on goethite over a broad range of pH values and surface coverages using simultaneous infrared and potentiometric titrations. We compare the spectra of the surface complexes with the protonation states of phosphate in solution and two aqueous metal-phosphate complexes. We have clear evidence from the OH and PO-stretching regions that phosphate binds to surface Fe(III) in a monodentate fashion, and the complexes are doubly, singly, or unprotonated depending on pH. Furthermore, our spectra indicate that phosphate is strongly hydrogen-bonded, probably to neighboring surface sites. We find no evidence of a bridging-bidentate structure, and our results challenge previous surface-complexation models, spectroscopic studies, quantum-mechanical results, and theories about mineral dissolution inhibition. |
|
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 |