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Reverse Monte Carlo Simulations of EXAFS Spectra: Application to the Sorption of Gold on Iron Oxy-Hydroxides

Journal Article · · Phys.Scripta T115:923,2005
OSTI ID:894128
;
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:
Stanford Linear Accelerator Center (SLAC)
Sponsoring Organization:
USDOE
DOE Contract Number:
AC02-76SF00515
OSTI ID:
894128
Report Number(s):
SLAC-REPRINT-2005-314
Journal Information:
Phys.Scripta T115:923,2005, Journal Name: Phys.Scripta T115:923,2005
Country of Publication:
United States
Language:
English

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Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
ABSORPTION
ABSORPTION SPECTRA
CATIONS
COORDINATION NUMBER
DEBYE-WALLER FACTOR
DISTRIBUTION FUNCTIONS
FINE STRUCTURE
GOETHITE
GOLD
INTERFACES
IRON
MONTE CARLO METHOD
Other
OTHER
SORPTION
SORPTIVE PROPERTIES
SPECTRA
WATER
X-RAY SPECTRA