Fe2+ catalyzed iron atom exchange and recrystallization-LCZO


Fe2+ catalyzed iron atom exchange and re-crystallization in soils from the Luquillo Critical Zone Observatory

10e: Room 304, Wednesday @ 09:45 - 10:00

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.

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