Structure and mechanisms of formation of iron oxide hydroxide (chloride) polymers

Abstract

Iron oxyhydroxide, especially in its so-called "amorphous" form, plays a key role in the retention and migration of organic and inorganic compounds in soils and aquatic media. The local structure of these "amorphous" species can be directly investigated using synchrotron-based X-ray absorption spectroscopy. In order to study the nucleation mechanisms, FeC13 solutions were hydrolyzed by NaOH and the precursors obtained at different molar ratios (0 I r = (NaOH)/Fe I 2.7) were studied by EXAFS. For r 1 1.5, Fe polymers formed at equilibrium are hexacoordinated and their local structure is the same as 8-FeOOH. For r = 1.5, the spectra obtained at different aging times show that the starting nuclei are dimers with edge-sharing octahedra. From t -50 min, trimers with edge and corner-sharing octahedra are detected in solution. After 1 h, 8-Fe00H-like polycations, formed by the coalescence of the trimers, can be observed. These polymers are extremely stable because C1-ions are still incorporated in the structure and are easily displaced by OH-.

Highlighting the wide variability in arsenic speciation in wetlands: A new insight into the control of the behavior of arsenic

“…The spectra for the 5-3 µm, 3-0.2 µm and 0.2 µm-30 kDa fractions displayed a Fe-Fe 1 distance of 3.03-3.09 Å, which is characteristic of edge-sharing FeO 6 octahedra (Manceau and Combes, 1988;Manceau and Drits, 1993). A second Fe-Fe 2 distance of 3.38-3.49 Å was determined in all of the fractions, specific to double corner-sharing (Manceau and Combes, 1988;Combes et al, 1989;Waychunas et al, 1993;Bottero et al, 1994). In order to accurately model the spectra of the three smallest fractions, a Fe-C distance was added in the fit with 3.8 C at 2.95 …”

Electron transfer at the mineral/water interface: Selenium reduction by ferrous iron sorbed on clay

“…The slope is close to the theoretical -3.0 value, which has been derived for aqueous and sorbed Fe(II)/FeOOH(s) (see for example Silvester et al, 2005). Therefore the measured redox potential appears to be governed by the (Bottero et al, 1994).…”

Comparison of the Adsorption ofo-Phthalate on Boehmite (γ-AlOOH), Aged γ-Al2O3, and Goethite (α-FeOOH)

“…Aqueous Fe(III)-chloride complexes have been identified, and stability constants for these species have been reported (39). Furthermore, chloride ions have been shown to have a great effect on the hydrolysis of Fe(III) and the precipitation of hydroxide phases (40). At least in the goethite system, therefore, inner-sphere chloro complexes might also be of significance and contribute to the competition with phthalate.…”