Neutron Diffraction Studies of α‐FeOOH

Szytuła, A.; Burewicz, Andrzej; Dimitrijević, Ž.; Kraśnicki, S.; Rżany, H.; Todorović, Jelena; Wanic, A.; Wolski, W.

doi:10.1002/pssb.19680260205

Cited by 187 publications

(109 citation statements)

References 10 publications

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“…In agreement with experimental results, 19,20 we find an AFM ground state with local spin moments of the Fe ions alternating along the cell b-axis. The optimized cell parameters and atomic coordinates agree to within 1 % and 0.3 %, respectively, with the experimental values (Tables I and II).…”

Section: A Bulk Goethitesupporting

confidence: 90%

“…Goethite crystallises with an orthorhombic unit cell, with symmetry usually described by the space group Pbnm, 19 though the orthorhombic group Pnma may be used equivalently. 20 The unit cell contains four FeOOH formula units, with ionic positions given by ±(x, y, 1 4 ) and ±( − y, 3 4 ). The structure of goethite may is antiferromagnetic, with local magnetic moments on the Fe ions alternating along the cell b-axis, and with the moments aligned parallel to the cell c-axis.…”

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confidence: 99%

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Density functional theory study of Fe(II) adsorption and oxidation on goethite surfaces

2009

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We study the interactions between Fe(II) aqua-complexes and surfaces of goethite (α-FeOOH) by means of density-functional theory calculations including the so-called Hubbard U correction to the exchange-correlation functional. Using a thermodynamic approach, we find that (110) and (021) surfaces in contact with aqueous solutions are almost equally stable, despite the evident needle-like shape of goethite crystals indicating substantially different reactivity of the two faces. We thus suggest that crystal anisotropy may result from different growth rates due to virtually barrier-less adsorption of hydrated ions on the (021) but not on the (110) surface. No clear evidence is found for spontaneous electron transfer from an adsorbed Fe(II) hex-aqua complex to a defect-free goethite substrate. Crystal defects are thus inferred to play an important role in assisting such electron transfer processes observed in a recent experimental study. Finally, goethite surfaces are observed to enhance the partial oxidation of adsorbed aqueous Fe(II) upon reaction with molecular oxygen.We propose that this catalytic oxidation effect arises from donation of electronic charge from the bulk oxide to the oxidizing agent through shared hydroxyl ligands anchoring the Fe(II) complexes on the surface.PACS numbers: 71.15.Mb

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Section: A Bulk Goethitesupporting

confidence: 90%

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confidence: 99%

Density functional theory study of Fe(II) adsorption and oxidation on goethite surfaces

2009

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“…6B) arise from variations in amplitude among overlapping shells of second-neighbor Fe atoms. The EXAFS interatomic distances for two of the three Fe± Fe shells in DP-011 and synthetic goethite are contracted relative to crystalline goethite distances calculated from XRD (Szytula et al, 1968; Table 7). In addition, values for the Debye±Waller factor (s 2 ) are increased for these two Fe shells relative to the closer Fe±Fe shell at 3.03 A Ê .…”

Section: Weathering Products: Chemistry and Mineralogymentioning

confidence: 99%

“…e Interatomic distances represented as distance from a central Fe atom. Jarosite calculated from XRD data reported by Menchetti and Sabelli (1976); geothite calculated from neutron diraction data by Szytula et al (1968). phases (Van Geen et al, 1994;Bargar, personal communication). The disorder seen with EXAFS is therefore on the local atomic scale and may be related to small particle size (<1 mm by SEM for synthetic goethite, and mean 0.1 mm for sample DP-011, Table 6) but is not due to the presence of signi®cant amounts (>5%) of another Fe phase.…”

Section: Arsenic In Goethite-rich Weathering Crustsmentioning

confidence: 99%

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

Savage

Tingle

O’Day

et al. 2000

Applied Geochemistry

377

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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“…o = 5.70 (Brown 1981); D2Fem.o = 1.76; B = 0.37 (Brown and Altermatt 1985). Fe-O and Fe-OH bond valences in eeFeOOH were calculated by using these constants and the bond lengths determined by Szytula et al (1968). Note in Figure 4 that the valence sum of Fe in bulk octahedra is equal to its formal charge (+3).…”

Section: Prepeak Intensity Enhancement In Ferrihydritementioning

confidence: 99%

Surface Structural Model for Ferrihydrite

Manceau

Gates

1997

Clays and clay miner.

136

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Abstract--A structural model for the geometry of Fe(III) octahe-dra near the surface of finely divided ferrihydrite was elaborated based on the bond-valence theory and by considering the interaction of water molecules in the 2 nearest hydration spheres. In contrast to bulk Fe atoms, which are bonded to bridging oxo (O) and hydroxo (OH) ligands, surface Fe atoms are also octahedrally coordinated to HzO ligands forming the 1st hydration shell ((H20)0. In the wet state, external water molecules of the 2nd hydration shell ((H20)n) are singly H-bonded to (H20) 1, while they are doubly coordinated in the dry state. Accordingly, wet ferrihydrite contains twice as many sorbed water molecules as dry ferrihydrite, and the structural difference due to the 2nd hydration shell accounts quantatively for the 15% increase of ferrihydrite weight experimentally measured in moist atmosphere. The interaction of surface Fe atoms with their 2 nearest hydration spheres modifies the geometry of surface Fe octahedra as compared to bulk octahedra, and idealized Fe-OH and Fe-H20 bond lengths in the wet and dry state were evaluated by the bond-valence theory. Our structural model provides a sound crystal-chemical basis to describe many apparent incongruities of Fe X-ray absorption near edge structure (K-XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopic data that have led to differing interpretations of the coordination environment of Fe in ferrihydrite by various investigators.

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Neutron Diffraction Studies of α‐FeOOH

Cited by 187 publications

References 10 publications

Density functional theory study of Fe(II) adsorption and oxidation on goethite surfaces

Density functional theory study of Fe(II) adsorption and oxidation on goethite surfaces

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

Surface Structural Model for Ferrihydrite

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