Iron isotope fractionation during proton-promoted, ligand-controlled, and reductive dissolution of goethite

Jan G. Wiederhold, Stephan M. Kraemer, Nadya Teutsch, Paul M. Borer, Alex N. Halliday, Ruben Kretzschmar

Research output: Contribution to journalArticlepeer-review


Iron isotope fractionation during dissolution of goethite (α-FeOOH) was studied in laboratory batch experiments. Proton-promoted (HCl), ligand-controlled (oxalate dark), and reductive (oxalate light) dissolution mechanisms were compared in order to understand the behavior of iron isotopes during natural weathering reactions. Multicollector ICP-MS was used to measure iron isotope ratios of dissolved iron in solution. The influence of kinetic and equilibrium isotope fractionation during different time scales of dissolution was investigated. Proton-promoted dissolution did not cause iron isotope fractionation, concurrently demonstrating the isotopic homogeneity of the goethite substrate. In contrast, both ligand-controlled and reductive dissolution of goethite resulted in significant iron isotope fractionation. The kinetic isotope effect, which caused an enrichment of light isotopes in the early dissolved fractions, was modeled with an enrichmentfactorforthe 57Fe/54Fe ratio of -2.6‰ between reactive surface sites and solution. Later dissolved fractions of the ligand-controlled experiments exhibit a reverse trend with a depletion of light isotopes of ∼0.5‰ in solution. We interpret this as an equilibrium isotope effect between Fe(III)-oxalate complexes in solution and the goethite surface. In conclusion, different dissolution mechanisms cause diverse iron isotope fractionation effects and likely influence the iron isotope signature of natural soil and weathering environments.

Original languageEnglish
Pages (from-to)3787-3793
Number of pages7
JournalEnvironmental Science and Technology
Issue number12
StatePublished - 15 Jun 2006
Externally publishedYes

ASJC Scopus subject areas

  • General Chemistry
  • Environmental Chemistry


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