title: In situ redox flexibility of FeII-III Oxyhydroxycarbonate green rust and fougerite.
abstract: Bacterial activity is commonly thought to be directly responsible for denitrification in soils and groundwater. However, nitrate reduction in low organic sediments occurs abiotically by FeII ions within the fougerite mineral (IMA 2003-057), giving the bluish-green color of gleysols. Fougerite, the mineral counterpart of FeII-III oxyhydroxycarbonate, FeII6(1-x)FeIII6xO12H2(7-3x)CO3, provides a unique in situ redox flexibility, which can adapt x = {[FeIII]/[Fetotal]} between 1/3 and 2/3 as shown using Mössbauer spectroscopy. Chemical potential and Eh-pH diagrams for this system were determined from electrode potential monitored during deprotonation of hydroxycarbonate FeII4FeIII2(OH)12CO3 to assess the possibility of reducing pollutants in the field. Bioreduction of ferric oxyhydroxides in anoxic groundwater yields dissolved FeII, whereas HCO3- anions produced from organic matter are incorporated into fougerite layered double oxyhydroxide structure. Thus, fougerite is the solid-state redox mediator acting as electron shuttle that helps bacterial activity for reducing nitrate by coupling dissimilatory FeIII reduction and oxidation of FeII with reduction of NO3-. It is proposed that this system could be used in the remediation of soils and nitrified waters.
authors.affiliation: Laboratoire de Chimie Physique et Microbiologie pour l'Environnement, UMR 7564 CNRS- Université Henri Poincaré-Nancy 1, France.
authors.forename: Christian
authors.initials: C
authors.lastname: Ruby
authors.forename: Chandan
authors.initials: C
authors.lastname: Upadhyay
authors.forename: Antoine
authors.initials: A
authors.lastname: Géhin
authors.forename: Georges
authors.initials: G
authors.lastname: Ona-Nguema
authors.forename: Jean-Marie R
authors.initials: JM
authors.lastname: Génin
mesh_terms: D001639:Bicarbonates / Q000737:chemistry*; D001711:Biotransformation; D005290:Ferric Compounds / Q000737:chemistry*; D005296:Ferrous Compounds / Q000737:chemistry*; D007501:Iron; D058085:Iron Compounds / Q000737:chemistry*; D008903:Minerals; D008956:Models, Chemical; D009566:Nitrates / Q000737:chemistry; D010084:Oxidation-Reduction; D010087:Oxides / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000737:chemistry
chemical_list: D001639:Bicarbonates; D005290:Ferric Compounds; D005296:Ferrous Compounds; D058085:Iron Compounds; D008903:Minerals; D009566:Nitrates; D010087:Oxides; D014874:Water Pollutants, Chemical; C517972:fougerite; D007501:Iron