title: Formation of layered Fe(II)-Al(III)-hydroxides during reaction of Fe(II) with aluminum oxide.
abstract: The reactivity of aqueous Fe(II) with aluminum oxide in anoxic solutions was investigated with batch kinetic experiments combined with Fe K edge X-ray absorption spectroscopy measurements to characterize Fe(II) sorption products. Formation of Fe(II)-Al(III)-layered double hydroxides with an octahedral sheet structure similar to nikischerite (NaFe(II)(6) Al(3)(SO(4))(2)(OH)(18) (H(2)O)(12)) was observed within a few hours during sorption at pH 7.5 and aqueous Fe(II) concentrations of 1-3 mM. These Fe(II) phases are composed of brucite-like Fe(II)(OH)(2) sheets with partial substitution of Al(III) for Fe(II), charge balanced by anions coordinated along the basal planes. Their fast rate of formation suggests that these previously unrecognized Fe(II) phases, which are structurally and compositionally similar to green rust, may be an important sink of Fe(II) in suboxic and anoxic geochemical environments, and impact the fate of structurally compatible trace metals, such as Co(II), Ni(II), and Zn(II), as well as redox-reactive species including Cr(VI) and U(VI). Further studies are required to assess the thermodynamics, formation kinetics, and stability of these Fe(II) minerals under field conditions.
authors.affiliation: Rutgers University, Department of Earth & Environmental Sciences, 101 Warren Street, Newark, New Jersey 07102, USA. elzinga@andromeda.rutgers.edu
authors.forename: Evert J
authors.initials: EJ
authors.lastname: Elzinga
mesh_terms: D000327:Adsorption; D000536:Aluminum Hydroxide / Q000138:chemical synthesis*; D000537:Aluminum Oxide / Q000737:chemistry*; D005296:Ferrous Compounds / Q000138:chemical synthesis*; D007700:Kinetics; D056928:X-Ray Absorption Spectroscopy
chemical_list: D005296:Ferrous Compounds; D000536:Aluminum Hydroxide; D000537:Aluminum Oxide