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Research article - Peer-reviewed, 2013

Iron speciation in soft-water lakes and soils as determined by EXAFS spectroscopy and geochemical modelling

Sjöstedt, Carin; Persson, Ingmar; Hesterberg, Dean; Berggren Kleja, Dan; Gustafsson, Jon Petter


Complexation of iron by organic matter can potentially compete with toxic metals for binding sites. Iron(III) forms both monomeric and di/trimeric complexes with fulvic and humic acids, but the nature and extent of complexation with natural organic matter samples from soft-water lakes has not been extensively studied. The aim of this study was to determine the coordination of iron in complexes with organic matter in two soft-water lakes and in the surrounding Oe soil horizons. Iron K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy was performed on particles and large colloids (>0.45 μm) collected by in-line pre-filtration, and on smaller colloids isolated both on an AGMP-1 anion-exchange column and by concentration using 1000 Da ultrafiltration. The results showed that iron(III) was mainly present in monomeric complexes with organic matter, both in the lake water smaller colloids and in the soil samples. Evidence for iron(III) (hydr)oxides was found for the lake particles, in the ultrafiltration retentates, and in some of the soils. Overall, the results suggest that complexation of iron(III) to organic matter prevents hydrolysis into polymeric forms. Strong complexation of iron(III) would lead to competition with other metals for organic-matter binding sites.

Published in

Geochimica et Cosmochimica Acta
2013, volume: 105, pages: 172-186

Authors' information

Royal Institute of Technology (KTH)
Swedish University of Agricultural Sciences, Department of Chemistry
Hesterberg, Dean
North Carolina State University (NC State)
Swedish Geotechnical Institute (SGI)
Borg, Hans
Stockholm University
Gustafsson, Jon Petter (Gustafsson, Jon-Petter)
Swedish University of Agricultural Sciences, Department of Soil Sciences

Sustainable Development Goals

SDG6 Clean water and sanitation

UKÄ Subject classification

Environmental Sciences

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