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EXAFS study on the reactions between iron and fulvic acid in acid aqueous solutions
KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Geochemistry and Ecotechnology.ORCID iD: 0000-0001-8771-7941
2008 (English)In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 42, no 7, 2367-2373 p.Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
2008. Vol. 42, no 7, 2367-2373 p.
Keyword [en]
ray-absorption spectroscopy, body distribution-functions, natural, organic-matter, humic substances, condensed matter, redox properties, ionic-strength, fresh-waters, reduction, binding
URN: urn:nbn:se:kth:diva-17416DOI: 10.1021/es072092zISI: 000254492800027ScopusID: 2-s2.0-41649094655OAI: diva2:335460
QC 20100525Available from: 2010-08-05 Created: 2010-08-05Bibliographically approved

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