Formation of ferric oxides from aqueous solutions: A polyhedral approach by X-ray absorption spectroscopy. I. Hydrolysis and formation of ferric gels

Journal Article · Wed Mar 01 00:00:00 EST 1989 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(89)90001-X· OSTI ID:5023361

Combes, J M; Manceau, A; Calas, G ^[1]; Bottero, J Y ^[2]

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1. Universites Paris (France)
2. Centre de Recherche sur la Valorisation des Minerais, Vandoeuvre (France)

X-ray absorption spectroscopy (XAS) was used to follow the evolution of local structural environments around ferric ions during the formation of ferric hydrous oxide gels from 1 M chloride and 0.1 M nitrate solutions. Fe K-XANES and EXAFS confirm that ferric ions remain 6-fold coordinated during this evolution. With increasing OH availability in the solution, Cl{sup {minus}} anions tend gradually to be exchanged for (O, OH, OH{sub 2}) ligands. Below OH/Fe = 1, no structural order is detected beyond the first coordination sphere. Above this ratio, two Fe-Fe distances at 3.05 {angstrom} and 3.44 {angstrom} are observed and correspond to the presence of edge- and vertex-sharing Fe-octahedra. XAS results show that ferric gels and highly polymerized aqueous species are short-range ordered. The main contribution to disorder in the gels arises from the small size of coherently scattering domains also responsible for their X-ray amorphous character. From the initial to the final stage of hydrolysis, particles possess a nearly spherical shape with a minimum average diameter ranging from 10-30 {angstrom} for polymers formed from chloride and nitrate solutions. As polymerization proceeds, the local order extends to several tens of angstroms and the particle structures becomes progressively closer to that of akaganeite ({beta}-FeOOH) or goethite ({alpha}-FeOOH). This local structure is distinct from that of the lepidocrocite ({gamma}-FeOOH)-like structure of ferric gels precipitated after oxidation of divalent Fe solutions. The growth of the crystalline Fe-oxyhydroxides from gels takes place by the progressive long-range ordering in the ferric polymers without modifying the short-range order around Fe.

• OSTI ID: 5023361
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Vol. 53:3; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
IRON COMPLEXES
INTERATOMIC DISTANCES
STRUCTURAL CHEMICAL ANALYSIS
X-RAY SPECTROSCOPY
IRON OXIDES
HYDROLYSIS
ABSORPTION SPECTROSCOPY
AQUEOUS SOLUTIONS
GEOCHEMISTRY
IRON CHLORIDES
IRON IONS
LIGANDS
MOLECULAR STRUCTURE
POLYMERIZATION
CHALCOGENIDES
CHARGED PARTICLES
CHEMICAL REACTIONS
CHEMISTRY
CHLORIDES
CHLORINE COMPOUNDS
COMPLEXES
DECOMPOSITION
DISPERSIONS
DISTANCE
HALIDES
HALOGEN COMPOUNDS
IONS
IRON COMPOUNDS
LYSIS
MIXTURES
OXIDES
OXYGEN COMPOUNDS
SOLUTIONS
SOLVOLYSIS
SPECTROSCOPY
TRANSITION ELEMENT COMPLEXES
TRANSITION ELEMENT COMPOUNDS
580000* - Geosciences