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Article Dans Une Revue Chemical Geology Année : 2014

Geochemical modeling of Fe(II) binding to humic and fulvic acids

Charlotte Catrouillet
Mélanie Davranche
Aline Dia
Martine Bouhnik-Le Coz
Remi Marsac
Olivier Pourret
Gérard Gruau

Résumé

The complexation of Fe(II)with organic matter (OM)and especiallywith humic acids (HAs) remains poorly characterized in the literature. In this study, batch experiments were conducted on a pH range varying from 1.95 to 9.90 to study HA-mediated Fe(II) binding. The results showed that high amounts of Fe(II) are complexed with HAdepending on the pH. Experimental datawere used to determine a new set of binding parameters by coupling PHREEPLOT and PHREEQC-Model VI. The new binding parameters (log KMA = 2.19 ± 0.16, log KMB= 4.46± 0.47 and ΔLK2=3.90 ± 1.30) were validated using the LFER (linear free energy relationship) method and published adsorption data between Fe(II) and Suwannee River fulvic acid (SRFA) (Rose andWaite, 2003). Theywere then put in PHREEQC-Model VI to determine the distribution of Fe(II) onto HA functional groups. It was shown that Fe(II) forms mainly bidentate complexes, some tridentate complexes and only a few monodentate complexes with HA. Moreover, Fe(II) is mainly adsorbed onto carboxylic groups at acidic and neutral pH, whereas carboxy-phenolic and phenolic groups play a major role at basic pH. The major species adsorbed onto HA functional groups is Fe2+; Fe(OH)+ appears at basic pH (frompH 8.13 to 9.9). The occurrence of OMand the resulting HA-mediated binding of Fe(II) can therefore influence Fe(II) speciation and bioavailability in peatlands and wetlands, where seasonal anaerobic conditions prevail. Furthermore, the formation of a cationic bridge and/or the dissolution of Fe(III)-(oxy)hydroxides by the formation of Fe(II)-OM complexes can influence the speciation of other trace metals and contaminants such as As.
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insu-00965127 , version 1 (24-03-2014)

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Charlotte Catrouillet, Mélanie Davranche, Aline Dia, Martine Bouhnik-Le Coz, Remi Marsac, et al.. Geochemical modeling of Fe(II) binding to humic and fulvic acids. Chemical Geology, 2014, 372, pp.109-118. ⟨10.1016/j.chemgeo.2014.02.019⟩. ⟨insu-00965127⟩
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