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Published on: May 26, 2016
Fe(II)-Catalyzed Ligand-Controlled Dissolution of Iron(hydr)oxides
Jagannath Biswakarma1,2, Kyounglim Kang3, Susan C Borowski1
1Eawag , Swiss Federal Institute of Aquatic Science and Technology , CH-8600 Dübendorf , Switzerland.
Trace amounts of iron(II) significantly accelerate iron(III) mineral dissolution at neutral pH, a process crucial for environmental iron cycling. This effect is linked to electron transfer mechanisms, particularly under anoxic or sunlit conditions.
Area of Science:
- Environmental chemistry
- Geochemistry
- Mineralogy
Background:
- Dissolution of iron(III) (Fe(III)) minerals is vital in various environmental settings.
- Previous research indicated Fe(II) enhances dissolution at acidic pH, but its role at neutral pH remained unclear.
Purpose of the Study:
- To investigate the catalytic effect of Fe(II) on Fe(III) mineral dissolution at circumneutral pH (6-7).
- To elucidate the mechanisms behind Fe(II)-catalyzed dissolution using lepidocrocite and ethylenediaminetetraacetate (EDTA).
Main Methods:
- Utilized infrared spectroscopy and 57Fe isotope exchange experiments.
- Investigated lepidocrocite dissolution with EDTA under varying Fe(II) concentrations and conditions (anoxic, aerobic, UV light).
Main Results:
- Fe(II) addition (0.2-10 μM) accelerated lepidocrocite dissolution rates by factors of 7-31 at pH 6-7.
- Similar acceleration was observed with UV light exposure.
- The catalytic effect persisted under anoxic conditions but diminished with oxygen or phenanthroline addition.
- Isotope exchange and spectroscopy suggested electron transfer and altered surface complexation.
Conclusions:
- Fe(II) acts as a catalyst for Fe(III) mineral dissolution at circumneutral pH, primarily through electron transfer mechanisms.
- This catalytic effect is significant in anoxic and sunlit environments, impacting iron biogeochemical cycles.
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