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Thompson A., Tishchenko V., Meile C., Scherer M., Pasakarni T.,
Aqueous ferrous iron (Fe2+) 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 aqueous Fe2+
(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 0.5 M and 7 M
HCl extractions targeting surface-adsorbed and bulk-soil Fe,
respectively.In 28 days, the aqueous and bulk pools both
moved ~7% toward the isotopic equilibrium (57/54Fe=1.33). The
aqueous and surface Fe initially exchanged atoms fast (~100
mmol kg-1 d-1) decreasing to a near constant rate of 1 mmol kg-
1 d-1 that was close to the 0.74 mmol kg-1
d-1 exchange-rate between the surface and bulk pools. Removing the effect of
intial Fe2+(aq) adsorption using a process-based numerical
model, we calculate final sorption-corrected 57/54Fe ratios of
5.56±0.05 and 0.43±0.03 in the aqueous and bulk pools,
respectively. . Based on Mössbauer spectroscopy, we show that
the 57Fe label re-crystallizes as short-range-ordered
Our work suggests Fe atom exchange occurs in FeIII-oxyhydroxides.
natural environments at rates fast enough to impact ecological
processes, but slow enough that changes in redox conditions
will likely occur before complete Fe mineral turnover.
Thompson A., Tishchenko V., Meile C., Scherer M., Pasakarni T. (2014): Fe2+ catalyzed iron atom exchange and re-crystallization in soils from the Luquillo Critical Zone Observatory . Goldschmidt2014.
This Paper/Book acknowledges NSF CZO grant support.