GEOC 172 |
| John R. Bargar, Stanford Synchrotron Radiation Laboratory, 2575 Sand Hill Road, MS 69, Menlo Park, CA 94025, James D. Kubicki, Department of Geosciences, Pennsylvania State University, 308 Deike Bldg, University Park, PA 16802, Rebecca Reitmeyer, Stanford Linear Accelerator Center, 2575 Sand Hill Rd, Menlo Park, CA 94025, and J. A. Davis, Water Resources Division, U.S. Geological Survey, 345 Middelfield Rd, Menlo Park, CA 94025. |
| The speciation of carbonate adsorbed to hematite in air-equilibrated aqueous solutions has been studied using ATR-FTIR spectroscopy over a range of pH conditions, at 0.1 M NaCl and in the absence of ionic strength control, and in H2O and D2O solutions to permit a multi-species analysis. Two major species coexist at near-neutral pH and low ionic strength. One of the complexes is relatively sensitive to ionic strength, being displaced at 0.1 M NaCl, whereas the other is not. DFT/MO vibrational frequency calculations suggest these two major species to be (a) an outer-sphere carbonate species closely associated with the surface, and (b) a monodentate binuclear carbonate surface complex. The putative outer-sphere complex appears to reside in the structured vicinal water layers at the interface. The putative outer-sphere complex as well as the inner-sphere complex are likely to be of significance in controlling the surface charge behavior of Fe-oxides in ground water. |
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Vibrational Spectroscopy in the Earth and Environmental Sciences
8:00 AM-11:40 AM, Thursday, April 1, 2004 Marriott -- Marquis NE, Oral
Division of Geochemistry |