Aquatic Geochemistry

, Volume 14, Issue 4, pp 337–358 | Cite as

The Chemical Speciation of Fe(III) in Freshwaters

  • Stephen Lofts
  • Edward Tipping
  • John Hamilton-Taylor
Original Paper


Dialysis and chemical speciation modelling have been used to calculate activities of Fe3+ for a range of UK surface waters of varying chemistry (pH 4.3–8.0; dissolved organic carbon 1.7–40.3 mg l−1) at 283 K. The resulting activities were regressed against pH to give the empirical model: \( \log \,a_{{{\text{Fe}}^{3 + } }} = 2.93\left( { \pm 0.40} \right) - 2.70\left( { \pm 0.06} \right) \cdot {\text{pH}} \). Predicted Fe3+ activities are consistent with a solid–solution equilibrium with hydrous ferric oxide, consistent with some previous studies on Fe(III) solubility in the laboratory. However, as has also sometimes been observed in the laboratory, the slope of the solubility equation is lower than the theoretical value of 3. The empirical model was used to predict concentrations of Fe in dialysates and ultrafiltrates of globally distributed surface and soil/groundwaters. The predictions were improved greatly by the incorporation of a temperature correction for \( a_{{{\text{Fe}}^{{ 3 + }} }} \), consistent with the temperature dependence of previously reported hydrous ferric oxide solubility. The empirical model, incorporating temperature effects, may be used to make generic predictions of the ratio of free and complexed Fe(III) to dissolved organic matter in freshwaters. Comparison of such ratios with observed Fe:dissolved organic matter ratios allows an assessment to be made of the amounts of Fe present as Fe(II) or colloidal Fe(III), where no separate measurements have been made.


Iron Speciation Solubility Freshwater Dialysis Ultrafiltration 



We thank David Abel and Sarah Thacker for help with sampling and Sarah Thacker, Colin Vincent, David Wilson, Gillian Ainsworth and Alan Lawlor for chemical analysis. This work was funded by the Natural Environment Research Council (Grant reference NER/B/S/2002/00513). We thank an anonymous reviewer for comments that led to the improvement of this article.

Supplementary material

10498_2008_9040_MOESM1_ESM.xls (16 kb)
Data 1 Major water chemistry parameters at sampling sites (XLS 17 kb)
10498_2008_9040_MOESM2_ESM.xls (14 kb)
Data 2 Concentrations of Fe, organic C and Al in 3.5 kDa dialysates (XLS 15 kb)
10498_2008_9040_MOESM3_ESM.xls (14 kb)
Data 3 Concentrations of Fe, organic C and Al in 10 Da dialysates (XLS 15 kb)
10498_2008_9040_MOESM4_ESM.xls (15 kb)
Data 4 Concentrations of Fe, organic C and Al in 15 kDa dialysates (XLS 15 kb)
10498_2008_9040_MOESM5_ESM.xls (39 kb)
Data 5 Generic predicted ratios of Fe(III):Dom for pH 3.0 to 9.0 (XLS 39 kb)


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Copyright information

© Springer Science+Business Media B.V. 2008

Authors and Affiliations

  • Stephen Lofts
    • 1
  • Edward Tipping
    • 1
  • John Hamilton-Taylor
    • 2
  1. 1.Centre for Ecology and HydrologyLancaster Environment CentreLancasterUK
  2. 2.Department of Environmental ScienceLancaster UniversityLancasterUK

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