Abstract

Iron(III) competes with trace metals for binding sites on organic ligands. We used X-ray absorption fine structure (EXAFS) spectroscopy to determine the binding mode and oxidation state of iron in solutions initially containing only iron(I I I) and fulvic acid at pHs 2 and 4. EXAFS spectra were recorded at different times after sample preparation. Iron was octahedrally configured with inner-sphere Fe-O interactions at 1.98-2.10 A, depending on the oxidation state of iron. Iron(III) formed complexes with fulvic acid within 15 min. Iron(III) was reduced to iron(II) with time at pH 2, whereas no significant reduction occurred at pH4. No signs of dimeric/trimeric hydrolysis products were found in any of the solution samples (<0.45 mu m). However, the isolated precipitate of the pH 2 sample (>0.45 mu m) showed Fe center dot center dot center dot Fe distances, indicating the presence of tightly packed iron(III) trimers and/or clusters of corner-sharing octahedra. It is suggested that the binding mode of iron(Ill) to fulvic acid at low pH may be phase-dependent: in solution mononuclear complexes predominate, whereas in the solid phase hydrolyzed polynuclear iron(III) complexes form, even at very low pH values. The observed pH dependence of iron(III) reduction was consistent with expected results based on thermodynamic calculations for model ligands

Published in

Environmental Science and Technology
2008, Volume: 42, number: 7, pages: 2367-2373
Publisher: AMER CHEMICAL SOC

SLU Authors

• Van Schaik, Joris

  • Department of Soil Sciences, Swedish University of Agricultural Sciences
    

• Persson, Ingmar

  • Department of Molecular Sciences, Swedish University of Agricultural Sciences
    

• Berggren Kleja, Dan

  • Department of Soil Sciences, Swedish University of Agricultural Sciences
    

• Gustafsson, Jon-Petter

  • Royal Institute of Technology (KTH)

UKÄ Subject classification

Environmental Sciences related to Agriculture and Land-use


Publication Identifiers

DOI: https://doi.org/10.1021/es072092z

Permanent link to this page (URI)

https://res.slu.se/id/publ/21129