Wide angle X-ray scattering (WAXS) study of “two-line” ferrihydrite structure: Effect of arsenate sorption and counterion variation and comparison with EXAFS results

Waychunas, Glenn A.; Fuller, Christopher C.; Rea, Brigid A.; Davis, James A.

doi:10.1016/0016-7037(96)89830-9

Cited by 180 publications

(141 citation statements)

References 30 publications

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“…3 for arsenate (Waychunas et al, 1993;Waychunas et al, 1996;Sun and Doner, 1996;Fendorf et al, 1997) and selenite (Hayes et al, 1987) correspond with the spectroscopically found structures for pH values and surface coverages comparable to the ones used in our experiments. The structure of sulfate adsorbed onto hematite was studied recently by Hug (1997) with in situ ATR-FTIR.…”

Section: Modelingsupporting

confidence: 87%

The relationship between molecular structure and ion adsorption on variable charge minerals

Rietra¹,

Hiemstra²,

Riemsdijk³

1999

Geochimica et Cosmochimica Acta

130

164

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Section: Modelingsupporting

confidence: 87%

The relationship between molecular structure and ion adsorption on variable charge minerals

Rietra¹,

Hiemstra²,

Riemsdijk³

1999

Geochimica et Cosmochimica Acta

130

164

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“…The best ®t for the DP-011 spectrum shows two As±Fe shells at 3.23 and 3.47 A Ê (Table 7). These distances are similar, but not identical, to those found for laboratory samples of As sorbed to ferrihydrite, goethite (a-FeOOH), and akaganeite (b-FeOOH) reported by Waychunas et al (1993Waychunas et al ( , 1996 and Foster et al (1998). The present Fe± As distances are 0.07 and 0.18 A Ê shorter than the two As±Fe shells reported by Waychunas et al (1993) for arsenate sorbed on crystalline goethite, but are closer (0.07 and 0.03 A Ê shorter) to those reported by Foster et al (1998).…”

Section: Arsenic In Goethite-rich Weathering Crustssupporting

confidence: 79%

Arsenic speciation in pyrite and secondary weathering phases, Mother Lode Gold District, Tuolumne County, California

Savage

Tingle

O’Day

et al. 2000

Applied Geochemistry

381

126

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Arsenian pyrite, formed during Cretaceous gold mineralization, is the primary source of As along the Melones fault zone in the southern Mother Lode Gold District of California. Mine tailings and associated weathering products from partially submerged inactive gold mines at Don Pedro Reservoir, on the Tuolumne River, contain H20±1300 ppm As. The highest concentrations are in weathering crusts from the Clio mine and nearby outcrops which contain goethite or jarosite. As is concentrated up to 2150 ppm in the ®ne-grained (<63 mm) fraction of these Fe-rich weathering products.Individual pyrite grains in albite-chlorite schists of the Clio mine tailings contain an average of 1.2 wt.% As. Pyrite grains are coarsely zoned, with local As concentrations ranging from H0 to 5 wt.%. Electron microprobe, transmission electron microscope, and extended X-ray absorption ®ne-structure spectroscopy (EXAFS) analyses indicate that As substitutes for S in pyrite and is not present as inclusions of arsenopyrite or other As-bearing phases. Comparison with simulated EXAFS spectra demonstrates that As atoms are locally clustered in the pyrite lattice and that the unit cell of arsenian pyrite is expanded by H2.6% relative to pure pyrite. During weathering, clustered substitution of As into pyrite may be responsible for accelerating oxidation, hydrolysis, and dissolution of arsenian pyrite relative to pure pyrite in weathered tailings. Arsenic K-edge EXAFS analysis of the ®ne-grained Ferich weathering products are consistent with corner-sharing between As(V) tetrahedra and Fe(III)-octahedra. Determinations of nearest-neighbor distances and atomic identities, generated from least-squares ®tting algorithms to spectral data, indicate that arsenate tetrahedra are sorbed on goethite mineral surfaces but substitute for SO 4 in jarosite. Erosional transport of As-bearing goethite and jarosite to Don Pedro Reservoir increases the potential for As mobility and bioavailability by desorption or dissolution. Both the substrate minerals and dissolved As species are expected to respond to seasonal changes in lake chemistry caused by thermal strati®cation and turnover within the monomictic Don Pedro Reservoir. Arsenic is predicted to be most bioavailable and toxic in the reservoir's summer hypolimnion. 7

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“…To our knowledge, transformations among the forms of ferrihydrite with varying numbers of peaks have not been demonstrated. Despite an early suggestion that 36% of the iron in 6LFh is in tetrahedral coordination (Eggleton and Fitzpatrick, 1988), synchrotron techniques have shown that essentially all of the iron in the interiors of 6LFh crystals is octahedrally coordinated (e.g., Combes et al, 1989Combes et al, , 1990Manceau and Drits, 1993;Zhao et al, 1993;Shinoda et al, 1994;Waychunas et al, 1996). Intermediate-range structures involving possible corner-, edge-, and face-sharing between octahedra remain subjects of active investigation (Combes et al, 1989(Combes et al, , 1990Waychunas et al, 1993Waychunas et al, , 1996Manceau and Drits, 1993;Shinoda et al, 1994) as do coordination environments of iron atoms at crystal surfaces (Zhao et al, 1994;Manceau and Gates, 1997).…”

confidence: 99%

Transmission Electron Microscopy of Synthetic 2- and 6-Line Ferrihydrite

Janney

Cowley

Buseck

2000

Clays and clay miner.

206

161

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Abstraet~High-resolution transmission electron microscopy (HRTEM), selected-area electron diffraction (SAED), annular dark-field scanning transmission electron microscope (STEM) images, and electron nanodiffraction were used to examine structures of synthetic 2-and 6-line ferrihydrite specimens. 086, 0.093, 0.107, 0.112, 0.119, 0.125, and 0.135 nm are visible in strongly exposed SAED patterns. Small quantities of hematite, magnetite or maghemite, and an acicular material tentatively identified as goethite were observed in the 6-line ferrihydrite, but these quantities do not contribute significantly to the overall diffracted intensity from the sample.

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Wide angle X-ray scattering (WAXS) study of “two-line” ferrihydrite structure: Effect of arsenate sorption and counterion variation and comparison with EXAFS results

Cited by 180 publications

References 30 publications

The relationship between molecular structure and ion adsorption on variable charge minerals

The relationship between molecular structure and ion adsorption on variable charge minerals

Arsenic speciation in pyrite and secondary weathering phases, Mother Lode Gold District, Tuolumne County, California

Transmission Electron Microscopy of Synthetic 2- and 6-Line Ferrihydrite

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