title: Does As(III) interact with Fe(II), Fe(III) and organic matter through ternary complexes?
abstract: Up until now, only a small number of studies have been dedicated to the binding processes of As(III) with organic matter (OM) via ionic Fe(III) bridges; none was interested in Fe (II). Complexation isotherms were carried out with As(III), Fe(II) or Fe(III) and Leonardite humic acid (HA). Although PHREEQC/Model VI, implemented with OM thiol groups, reproduced the experimental datasets with Fe(III), the poor fit between the experimental and modeled Fe(II) data suggested another binding mechanism for As(III) to OM. PHREEQC/Model VI was modified to take various possible As(III)-Fe(II)-OM ternary complex conformations into account. The complexation of As(III) as a mononuclear bidentate complex to a bidentate Fe(II)-HA complex was evidenced. However, the model needed to be improved since the distribution of the bidentate sites appeared to be unrealistic with regards to the published XAS data. In the presence of Fe(III), As(III) was bound to thiol groups which are more competitive with regards to the low density of formed Fe(III)-HA complexes. Based on the new data and previously published results, we propose a general scheme describing the various As(III)-Fe-MO complexes that are able to form in Fe and OM-rich waters.
authors.affiliation: Géosciences Rennes UMR 6118, Université Rennes 1, CNRS, 35042 Rennes cedex, France. Electronic address: charlotte.catrouillet@univ-rennes1.fr.
authors.forename: Charlotte
authors.initials: C
authors.lastname: Catrouillet
authors.affiliation: Géosciences Rennes UMR 6118, Université Rennes 1, CNRS, 35042 Rennes cedex, France.
authors.forename: Mélanie
authors.initials: M
authors.lastname: Davranche
authors.affiliation: Géosciences Rennes UMR 6118, Université Rennes 1, CNRS, 35042 Rennes cedex, France.
authors.forename: Aline
authors.initials: A
authors.lastname: Dia
authors.affiliation: Géosciences Rennes UMR 6118, Université Rennes 1, CNRS, 35042 Rennes cedex, France.
authors.forename: Martine
authors.initials: M
authors.lastname: Bouhnik-Le Coz
authors.affiliation: Géosciences Rennes UMR 6118, Université Rennes 1, CNRS, 35042 Rennes cedex, France.
authors.forename: Edwige
authors.initials: E
authors.lastname: Demangeat
authors.affiliation: Géosciences Rennes UMR 6118, Université Rennes 1, CNRS, 35042 Rennes cedex, France.
authors.forename: Gérard
authors.initials: G
authors.lastname: Gruau
keywords: Arsenic(III); Binding; Humic substances; Iron(II, III); PHREEPLOT; PHREEQC–Model VI; Sorption; Ternary complex