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Iron speciation in soft-water lakes and soils as determined by EXAFS spectroscopy and geochemical modelling
KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Geochemistry and Ecotechnology.
Department of Soil Science, North Carolina State University.
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2013 (English)In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 0016-1258, Vol. 105, 172-186 p.Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
2013. Vol. 105, 172-186 p.
Keyword [en]
Ultrafiltration, natural organic matter, ferrozine method, anion-exchange column, colloids, ferrihydrite
National Category
URN: urn:nbn:se:kth:diva-94536DOI: 10.1016/j.gca.2012.11.035ISI: 000315194800011ScopusID: 2-s2.0-84872550254OAI: diva2:525932
Swedish Research Council, 2007-4468Knut and Alice Wallenberg Foundation

QC 20130215. Updated from manuscript to article in journal.

Available from: 2012-05-11 Created: 2012-05-09 Last updated: 2013-03-25Bibliographically approved
In thesis
1. Iron and aluminium speciation in Swedish freshwaters: Implications for geochemical modelling
Open this publication in new window or tab >>Iron and aluminium speciation in Swedish freshwaters: Implications for geochemical modelling
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Speciation governs transport and toxicity of trace metals and is important to monitor in natural waters. Geochemical models that predict speciation are valuable tools for monitoring. They can be used for risk assessments and future scenarios such as termination of liming. However, there are often large uncertainties concerning the speciation of iron and aluminium in the models, due to the complicated chemistry of these metals. Both are important in governing the speciation of other metals, due to (i) their capacity to form minerals onto which metals can adsorb and (ii) their ability to compete for binding sites to natural organic matter (NOM). Aluminium is also potentially toxic and is therefore closely monitored in acidified freshwaters. In this study different phases of iron in Swedish lakes were characterised. This required a good method for preconcentrating the iron colloids. A new method was developed in this thesis that uses an anion-exchange column to isolate the iron colloids prior to characterisation with extended X-ray absorption fine structure (EXAFS) spectroscopy. Iron was present as ferrihydrite in particles but was also strongly monomerically complexed to NOM in two Swedish lakes. Based on the results an internally consistent process-based geochemical equilibrium model was presented for Swedish freshwaters. The model was validated for pH (= 9 400) and inorganic monomeric aluminium (Ali) (n = 3 400). The model could simulate pH and Ali simultaneously, and be used for scenario modelling. In this thesis, modelling scenarios for decreases and complete termination of liming are presented for the 3 000 limed Swedish lakes. The results suggest that liming can be terminated in 30 % of the Swedish lakes and decreased in many other lakes.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. xiv, 51 p.
Trita-LWR. PHD, ISSN 1650-8602 ; 1065
Geochemical equilibrium modelling, pH, adsorption to ferrihydrite, metal-NOM complexation, liming, EXAFS spectroscopy
National Category
urn:nbn:se:kth:diva-94528 (URN)978-91-7501-373-2 (ISBN)
Public defence
2012-10-05, V1, Teknikringen 76 1 tr, KTH, Stockholm, 10:00 (English)
Swedish Research Council, 2007-4468

QC 20120919

Available from: 2012-05-11 Created: 2012-05-09 Last updated: 2012-09-19Bibliographically approved

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