skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Surface chemistry of ferrihydrite: Part 1. EXAFS studies of the geometry of coprecipitated and adsorbed arsenate

Abstract

Arsenate adsorbs on ferrihydrite surfaces mainly as an inner-sphere bidentate (bridging) complex sharing apical oxygens of two adjacent edge-sharing Fe oxyhydroxyl octahedra. Monodentate complexes are also observed and account for about 30% of all As-Fe correlations. Monodentate arsenate comparable to the bidentate concentration is observed only on ADS (adsorbed) samples with the lowest total arsenate. In these samples, monodentate/bidentate ratio decreases with increasing total arsenate. Arsenate adsorbs on the crystalline FeOOH surface mainly as an inner-sphere bidentate complex. The geometry is similar to that on ferrihydrite and is consistent with no surface contraction or expansion of the FeOOH surface layers. Monodentate complexes were observed only for the lowest arsenate concentrations on goethite. The adsorption of arsenate on goethite is consistent with past studies of phosphate adsorption. Compared with arsenate complexes on crystalline FeOOH, the arsenate complexes are more structurally disordered on the ferrihydrite surface, probably due to inherent ferrihydrite disorder and variations in polymer structure. Aging affects all ferrihydrite samples by allowing increased Fe-O-Fe polymerization to occur. The trends in number of linkages and interatomic distances suggest a progression toward goethite-like order in the ADS and pure ferrihydrite samples. The observed saturation limits for arsenate adsorption along with other evidencemore » suggest that coprecipitated samples near saturation have structures consisting of discrete mono- or dioctahedral Fe polymer chains with minimal crosslinking. The ADS samples have crosslinked dioctahedral chains possibly of goethite-like structure. The arsenate complex in all cases has essentially identical As-O distances as As(V) coordinated by water molecules in aqueous solution. The observations reported are inconsistent with precipitation of an As-Fe surface phase, or with solid solution formation. 50 refs., 18 figs., 3 tabs.« less

Authors:
 [1]; ; ;  [2]
  1. Stanford Univ., CA (United States)
  2. Geological Survey, Menlo Park, CA (United States)
Publication Date:
OSTI Identifier:
7369118
DOE Contract Number:  
AC03-82ER13000
Resource Type:
Journal Article
Journal Name:
Geochimica et Cosmochimica Acta; (United States)
Additional Journal Information:
Journal Volume: 57:10; Journal ID: ISSN 0016-7037
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ARSENATES; ADSORPTION; IRON OXIDES; CHEMICAL REACTIONS; SURFACE PROPERTIES; GOETHITE; MOLECULAR STRUCTURE; X-RAY SPECTROSCOPY; ARSENIC COMPOUNDS; CHALCOGENIDES; IRON COMPOUNDS; MINERALS; OXIDE MINERALS; OXIDES; OXYGEN COMPOUNDS; SORPTION; SPECTROSCOPY; TRANSITION ELEMENT COMPOUNDS; 400201* - Chemical & Physicochemical Properties; 400102 - Chemical & Spectral Procedures

Citation Formats

Waychunas, G A, Rea, B A, Fuller, C C, and Davis, J A. Surface chemistry of ferrihydrite: Part 1. EXAFS studies of the geometry of coprecipitated and adsorbed arsenate. United States: N. p., 1993. Web. doi:10.1016/0016-7037(93)90567-G.
Waychunas, G A, Rea, B A, Fuller, C C, & Davis, J A. Surface chemistry of ferrihydrite: Part 1. EXAFS studies of the geometry of coprecipitated and adsorbed arsenate. United States. doi:10.1016/0016-7037(93)90567-G.
Waychunas, G A, Rea, B A, Fuller, C C, and Davis, J A. Sat . "Surface chemistry of ferrihydrite: Part 1. EXAFS studies of the geometry of coprecipitated and adsorbed arsenate". United States. doi:10.1016/0016-7037(93)90567-G.
@article{osti_7369118,
title = {Surface chemistry of ferrihydrite: Part 1. EXAFS studies of the geometry of coprecipitated and adsorbed arsenate},
author = {Waychunas, G A and Rea, B A and Fuller, C C and Davis, J A},
abstractNote = {Arsenate adsorbs on ferrihydrite surfaces mainly as an inner-sphere bidentate (bridging) complex sharing apical oxygens of two adjacent edge-sharing Fe oxyhydroxyl octahedra. Monodentate complexes are also observed and account for about 30% of all As-Fe correlations. Monodentate arsenate comparable to the bidentate concentration is observed only on ADS (adsorbed) samples with the lowest total arsenate. In these samples, monodentate/bidentate ratio decreases with increasing total arsenate. Arsenate adsorbs on the crystalline FeOOH surface mainly as an inner-sphere bidentate complex. The geometry is similar to that on ferrihydrite and is consistent with no surface contraction or expansion of the FeOOH surface layers. Monodentate complexes were observed only for the lowest arsenate concentrations on goethite. The adsorption of arsenate on goethite is consistent with past studies of phosphate adsorption. Compared with arsenate complexes on crystalline FeOOH, the arsenate complexes are more structurally disordered on the ferrihydrite surface, probably due to inherent ferrihydrite disorder and variations in polymer structure. Aging affects all ferrihydrite samples by allowing increased Fe-O-Fe polymerization to occur. The trends in number of linkages and interatomic distances suggest a progression toward goethite-like order in the ADS and pure ferrihydrite samples. The observed saturation limits for arsenate adsorption along with other evidence suggest that coprecipitated samples near saturation have structures consisting of discrete mono- or dioctahedral Fe polymer chains with minimal crosslinking. The ADS samples have crosslinked dioctahedral chains possibly of goethite-like structure. The arsenate complex in all cases has essentially identical As-O distances as As(V) coordinated by water molecules in aqueous solution. The observations reported are inconsistent with precipitation of an As-Fe surface phase, or with solid solution formation. 50 refs., 18 figs., 3 tabs.},
doi = {10.1016/0016-7037(93)90567-G},
journal = {Geochimica et Cosmochimica Acta; (United States)},
issn = {0016-7037},
number = ,
volume = 57:10,
place = {United States},
year = {1993},
month = {5}
}