Hostname: page-component-745bb68f8f-lrblm Total loading time: 0 Render date: 2025-02-10T07:41:54.943Z Has data issue: false hasContentIssue false
  • English
  • Français

Surface Precipitation in the Co(II)/Al2O3 Sorption System

Published online by Cambridge University Press:  10 February 2011

S. N. Towle ,
J. R. Bargar ,
P. Persson ,
G. E. Brown Jr.  and
G. A. Parks
S. N. Towle
Affiliation:
Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305-2115 Department of Materials Science and Engineering, Stanford Univeristy, Stanford, CA 94305
J. R. Bargar
Affiliation:
Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305-2115
P. Persson
Affiliation:
University of Umeå, Department of Inorganic Chemistry, Umeå, Sweden
G. E. Brown Jr.
Affiliation:
Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305-2115 Stanford Synchrotron Radiation Laboratory, P.O. Box 4349, M.S. 99, Stanford, CA 94309-0210
G. A. Parks
Affiliation:
Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305-2115
Get access

Abstract

Surface precipitation is a critically important process in many systems of scientific and technological importance, such as modeling the segregation of contaminants from aqueous to solid phases in groundwater and the dispersion of active phases on catalyst supports. XAFS and TEM studies of Co(II) sorbed on Al2O3 indicate clearly that surface precipitates have formed from solutions that are undersaturated with respect to any known bulk solid Co-bearing phase. These studies indicate that the structure of the precipitates is similar to that of Co(OH)2(s), but it is disordered and has a high concentration (about 30%) of Co vacancies. Using the FEFF 6.011 multiple-scattering code, we have been able to model the XANES spectrum of the precipitate phase by making small modifications to the structure of Co(OH)2(s). The formation of this precipitate phase is consistent with the coprecipitation of Co(II) with Al(III) derived from dissolution of the substrate, forming a double hydroxide. The existence of a phase that is less soluble than the Al(OH)3 and Co(OH)2 endmembers was proved by forming a colloidal coprecipitate from a mixture of Al(III) and Co(II) aqueous solutions, at the same pH and concentration as in the sorption samples; this material was shown to have Co-XAFS similar to that of the sorption samples. We conclude, therefore, that the surface precipitation observed in the Co(II)/Al2O3 system is due to the the formation of a ternary hydroxide of Al and Co. Successful quantitative models of metal-ion transport in groundwater should include the possibility of forming ternary and higher order precipitates that include ions derived from sparingly soluble solids. For the impregnation of catalysts, the process of surface coprecipitation will make it more difficult to produce a well dispersed precursor material.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 432: Symposium S – Aqueous Chemistry and Geochemistry of Oxides , 1996 , 237
Copyright
Copyright © Materials Research Society 1997

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

1. Zabinsky, S., Rehr, J., Ankudinov, A., Albers, R., Eller, M., Phys. Rev. B 52, 1995, p. 2995.Google Scholar
2. Chisholm-Brause, C. J., O'Day, P. A., Brown, G. E. Jr., Parks, G. A., Nature 348, 1990, p. 528.Google Scholar
3. Farley, K. J., Dzombak, D. A., Morel, F. M., J.Coll. Interf Sci. 106, 1985, p. 226.Google Scholar
4. Benjamin, M. M., Env. Sci. Tech. 17, 1983, p. 686.Google Scholar
5. George, G. N.,, “EXAFSPAK.” Stanford Synchrotron Radiation Laboratory, 1993.Google Scholar
6. Paces, T., M.S. Thesis, Stanford University, 1968.Google Scholar
7. Feitknecht, W., Hartmann, L., Chimia 8, 1954, p. 95.Google Scholar
8. O'Day, P. A., Rehr, J. J., Zabinsky, S. I., Brown, G. E. Jr., J.Am. Chem. Soc. 116, 1994, p. 2938.Google Scholar
9. Taylor, R. M., Clay Minerals 19, 1984, p. 591–603.Google Scholar
10. Caillerie, J.-B. d'Espinose de la, Kermarec, M., Clause, O.,J. Am. Chemi. Soc. 117, 1995, 11471–11481.Google Scholar
11. Scheidegger, A. M., Lamble, G. M., Sparks, D. L., Env. Sci. Tech. 30, 1996, p. 548–554 Google Scholar