Reverse Monte Carlo Simulations of EXAFS Spectra: Application to the Sorption of Gold on Iron Oxy-Hydroxides
The sorption of Au at the goethite-water interface is studied. In order to better understand sorption models for cations on mineral surfaces, reverse Monte-Carlo (RMC) simulations were used to analyze EXAFS spectra. A starting model is constructed based on the (110) mineral surface separated by a layer of water molecules. Some of metal cations at the mineral-water interface are replaced by absorbed gold cations. All atomic positions are allowed to vary on both the mineral surface and in the water layer during the RMC simulations. Partial pair distribution functions and corresponding EXAFS spectra are computed and refined by a Metropolis algorithm. The final RMC model matches most EXAFS features (including short- and medium-range environments). The usual EXAFS parameters (coordination number, coordination distance and Debye-Waller factor and higher moments) are retrieved from the partial pair distribution functions by moment analysis. In case of Au at the goethite-water interface four Au-O coordinations are found at an average distance of 1.99 {angstrom} with a second moment of 0.0013 {angstrom}{sup 2}. Two iron next-nearest neighbors show a broad distribution between 3.2 and 3.8 {angstrom} with an average coordination distance of 3.49 {angstrom}, a coordination number of 3 and a second moment of 0.013 {angstrom}{sup 2}. The results of the RMC simulations are compared with results of conventional EXAFS analysis methods.
- Research Organization:
- SLAC National Accelerator Lab., Menlo Park, CA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC02-76SF00515
- OSTI ID:
- 894128
- Report Number(s):
- SLAC-REPRINT-2005-314; TRN: US200702%%98
- Journal Information:
- Phys.Scripta T115:923,2005, Conference: Proceedings 12th International Conference on X-ray Absorption Fine Structure (XAFS XII) 115:923,2005
- Country of Publication:
- United States
- Language:
- English
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