Abstract

The complexation of iron(III) to soil organic matter is important for the binding of trace metals in natural environments because of competition effects. In this study, we used extended X-ray absorption fine structure (EXAFS) spectroscopy to characterize the binding mode for iron(III) in two soil samples from organic mor layers, one of which was also treated with iron(III). In most cases the EXAFS spectra had three significant contributions, inner-core Fe-O/N interactions at about 2.02(2) A, Fe-C interactions in the second scattering shell at 3.00(4) A, and a mean Fe-Fe distance at 3.37(3) A. One untreated sample showed features typical for iron (hydr)oxides; however, after treatment of iron(III) the EXAFS spectrum was dominated by organically complexed iron. The presence of a Fe-Fe distance in all samples showed that the major part of the organically complexed iron was hydrolyzed, most likely in a mixture of complexes with an inner core of (O5Fe)(2)O and (O5Fe)(3)O. These results were used to constrain a model for metal-humic complexation, the Stockholm Humic Model (SHM). The model was able to describe iron(III) binding very well at low pH considering only one dimeric iron(III)-humic complex. The competition effect on trace metals was also well described

Keywords

iron(III); EXAFS; mor layer; organic matter; modeling

Published in

Environmental Science and Technology
2007, Volume: 41, number: 4, pages: 1232-1237
Publisher: AMER CHEMICAL SOC

SLU Authors

• Gustafsson, Jon-Petter

  • 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
    

• Van Schaik, Joris

  • Department of Soil Sciences, Swedish University of Agricultural Sciences
    

UKÄ Subject classification

Environmental Sciences related to Agriculture and Land-use


Publication identifier

DOI: https://doi.org/10.1021/es0615730

Permanent link to this page (URI)

https://res.slu.se/id/publ/13633