Rates and Mechanism of Fe(II) Oxidation at Nanomolar Total Iron Concentrations

D. Whitney King, Heather A. Lounsbury, Frank J. Millero

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Abstract

A fully automated luminol-based chemiluminescence system has been developed for rapid analysis of Fe(II) at natural levels. Using this system, the rates of Fe(II) oxidation in 0.7 M NaCI have been measured for nanomolar concentrations of Fe(II) over the pH range 7.0-8.3. When the production and decomposition of H2O2 in the system were considered, measured rates at these levels were in excellent agreement with a model based on previously reported rate constants determined using micromolar levels of Fe(II). These results show that O2- and OH* intermediates produced as a result of Fe(II) oxidation remain effective as Fe(II) oxidants in these controlled conditions. The chemical model for Fe(II) oxidation also allows prediction of steady-state H2O2 and O2- concentrations that result from the oxidation of micromolar levels of Fe(II). The concentration of both species increases exponentially with increasing pH. At pH 8.2, the predicted H2O2 and O2- concentrations are 220 and 2.3 nM, respectively. The predicted H2O2 concentrations are in excellent agreement with laboratory measurements. These results suggest that significant concentrations of H2O2 and O2- should be present at the oxic-anoxic interface of marine environments where micromolar levels of Fe(II) are in contact with dissolved oxygen.

Original languageEnglish (US)
Pages (from-to)818-824
Number of pages7
JournalEnvironmental Science and Technology
Volume29
Issue number3
DOIs
StatePublished - Mar 1995

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ASJC Scopus subject areas

  • Chemistry(all)
  • Environmental Chemistry

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