title: Fe(II) sorption on a synthetic montmorillonite. A combined macroscopic and spectroscopic study.
abstract: Extended X-ray absorption fine structure (EXAFS) and Mössbauer spectroscopy combined with macroscopic sorption experiments were employed to investigate the sorption mechanism of Fe(II) on an iron-free synthetic montmorillonite (Na-IFM). Batch sorption experiments were performed to measure the Fe(II) uptake on Na-IFM at trace concentrations as a function of pH and as a function of sorbate concentration at pH 6.2 and 6.7 under anoxic conditions (O2 < 0.1 ppm). A two-site protolysis nonelectrostatic surface complexation and cation exchange sorption model was used to quantitatively describe the uptake of Fe(II) on Na-IFM. Two types of clay surface binding sites were required to model the Fe(II) sorption, the so-called strong (≡S(S)OH) and weak (≡S(W)OH) sites. EXAFS data show spectroscopic differences between Fe sorbed at low and medium absorber concentrations that were chosen to be characteristic for sorption on strong and weak sites, respectively. Data analysis indicates that Fe is located in the continuity of the octahedral sheet at trans-symmetric sites. Mössbauer spectroscopy measurements confirmed that iron sorbed on the weak edge sites is predominantly present as Fe(II), whereas a significant part of surface-bound Fe(III) was produced on the strong sites (∼12% vs ∼37% Fe(III) species to total sorbed Fe).
authors.affiliation: Laboratory for Waste Management, Paul Scherrer Institut, Villigen PSI, Switzerland. daniela.soltermann@psi.ch
authors.forename: Daniela
authors.initials: D
authors.lastname: Soltermann
authors.forename: Maria Marques
authors.initials: MM
authors.lastname: Fernandes
authors.forename: Bart
authors.initials: B
authors.lastname: Baeyens
authors.forename: Rainer
authors.initials: R
authors.lastname: Dähn
authors.forename: Jocelyne
authors.initials: J
authors.lastname: Miehé-Brendlé
authors.forename: Bernhard
authors.initials: B
authors.lastname: Wehrli
authors.forename: Michael H
authors.initials: MH
authors.lastname: Bradbury
mesh_terms: D000327:Adsorption; D001546:Bentonite / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000737:chemistry*; D008956:Models, Chemical; D015204:Spectroscopy, Mossbauer; D056928:X-Ray Absorption Spectroscopy
chemical_list: D001546:Bentonite; D007501:Iron