Journal article
Fe2+ catalyzed iron atom exchange and re-crystallization in a tropical soil
Geochimica et cosmochimica acta, Vol.148, pp.191-202
01/01/2015
DOI: 10.1016/j.gca.2014.09.018
Abstract
Aqueous ferrous iron (Fe2+(aq)) is known to transfer electrons and exchange structural positions with solid-phase ferric (FeIII) atoms in many Fe minerals. However, this process has not been demonstrated in soils or sediments. In a 28-day sterile experiment, we reacted 57Fe-enriched Fe2+(aq) (57/54Fe=5.884±0.003) with a tropical soil (natural abundance 57/54Fe=0.363±0.004) under anoxic conditions and tracked 57/54Fe in the aqueous phase and in sequential 0.5M and 7M HCl extractions targeting surface-adsorbed and bulk-soil Fe, respectively; we also analyzed the reacted soil with 57Fe Mössbauer spectroscopy. In 28days, the aqueous and bulk pools both moved ∼7% toward the isotopic equilibrium (57/54Fe=1.33). Using a kinetic model, we calculate final adsorption-corrected 57/54Fe ratios of 5.56±0.05 and 0.43±0.03 in the aqueous and bulk pools, respectively. The aqueous and surface/labile Fe initially exchanged atoms rapidly (10–80mmolkg−1d−1) decreasing to a near constant rate of 1mmolkg−1d−1 that was close to the 0.74mmolkg−1d−1 exchange-rate between the surface and bulk pools. Thus, after 28 days we calculate aqueous Fe has exchanged with 20.1mmolkg−1 of bulk Fe atoms (1.9% of total Fe) in addition to the 17.0mmolkg−1 of surface/labile Fe atoms (1.6% of total Fe), which have likely turned over several times during our experiment. Extrapolating these rates, we calculate a hypothetical whole-soil turnover time of ∼3.6yrs. Furthermore, Mössbauer spectroscopy indicates the soil-incorporated 57Fe label re-crystallized as short-range-ordered (SRO) FeIII-oxyhydroxides: our model suggests this pool could turnover in less than seven months via Fe2+-catalyzed recrystallization. Thus, we conclude Fe atom exchange can occur in soils at rates fast enough to impact ecological processes reliant on Fe minerals, but sufficiently slow that complete Fe mineral turnover is unlikely, except perhaps in permanently anoxic environments.
Details
- Title: Subtitle
- Fe2+ catalyzed iron atom exchange and re-crystallization in a tropical soil
- Creators
- Viktor Tishchenko - University of Georgia (Crop and Soil Science), United StatesChristof Meile - University of Georgia (Marine Science), United StatesMichelle M Scherer - The University of Iowa (Civil and Environmental Engineering), United StatesTimothy S Pasakarnis - The University of Iowa (Civil and Environmental Engineering), United StatesAaron Thompson - University of Georgia (Crop and Soil Science), United States
- Resource Type
- Journal article
- Publication Details
- Geochimica et cosmochimica acta, Vol.148, pp.191-202
- Publisher
- Elsevier Ltd
- DOI
- 10.1016/j.gca.2014.09.018
- ISSN
- 0016-7037
- eISSN
- 1872-9533
- Language
- English
- Date published
- 01/01/2015
- Academic Unit
- Civil and Environmental Engineering
- Record Identifier
- 9983991973202771
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