Tracking Initial Fe(II)-Driven Ferrihydrite Transformations: A Mössbauer Spectroscopy and Isotope Investigation

Drew Latta; Kevin M. Rosso; Michelle M. Scherer

doi:10.1021/acsearthspacechem.2c00291

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Tracking Initial Fe(II)-Driven Ferrihydrite Transformations: A Mössbauer Spectroscopy and Isotope Investigation

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Tracking Initial Fe(II)-Driven Ferrihydrite Transformations: A Mössbauer Spectroscopy and Isotope Investigation

Drew Latta, Kevin M. Rosso and Michelle M. Scherer

ACS earth and space chemistry, Vol.7(10), pp.1814-1824

10/19/2023

DOI: 10.1021/acsearthspacechem.2c00291

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Abstract

Transformation of nanocrystalline ferrihydrite to more stable microcrystalline Fe(III) oxides is rapidly accelerated under reducing conditions with aqueous Fe(II) present. While the major steps of Fe(II)-catalyzed ferrihydrite transformation are known, processes in the initial phase that lead to nucleation and the growth of product minerals remain unclear. To track ferrihydrite–Fe(II) interactions during this initial phase, we used Fe isotopes, Mössbauer spectroscopy, and extractions to monitor the structural, magnetic, and isotope composition changes of ferrihydrite within ∼30 min of Fe(II) exposure. We observed rapid isotope mixing between aqueous Fe(II) and ferrihydrite during this initial lag phase. Our findings from Mössbauer spectroscopy indicate that a more magnetically ordered Fe(III) phase initially forms that is distinct from ferrihydrite and bulk crystalline transformation products. The signature of this phase is consistent with the early stage emergence of lepidocrocite-like lamellae observed in previous transmission electron microscopy studies. Its signature is furthermore removed by xylenol extraction of Fe(III), the same approach used to identify a chemically labile form of Fe(III) resulting from Fe(II) contact that is correlated to the ultimate emergence of crystalline product phases detectable by X-ray diffraction. Our work indicates that the mineralogical changes in the initial lag phase of Fh transformation initiated by Fe(II)–Fh electron transfer are critical to understanding ferrihydrite behavior in soils and sediments, particularly with regard to metal uptake and release.

Fe(II)−Fe(III) interfacial electron transfer

ferrihydrite transformation

recrystallization

dissolution−reprecipitation

induction period

lag phase

labile Fe(III)

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Details

Title: Subtitle: Tracking Initial Fe(II)-Driven Ferrihydrite Transformations: A Mössbauer Spectroscopy and Isotope Investigation
Creators: Drew Latta - University of Iowa, IIHR--Hydroscience and Engineering
Kevin M. Rosso - Pacific Northwest National Laboratory
Michelle M. Scherer - University of Iowa, Civil and Environmental Engineering
Resource Type: Journal article
Publication Details: ACS earth and space chemistry, Vol.7(10), pp.1814-1824
DOI: 10.1021/acsearthspacechem.2c00291
ISSN: 2472-3452
eISSN: 2472-3452
Publisher: American Chemical Society
Grant note: DOI: 10.13039/100008893, name: University of Iowa, award: FWP 56674; DOI: 10.13039/100011661, name: Pacific Northwest National Laboratory
Comment: This article is part of the Environmental Redox Processes and Contaminant and Nutrient Dynamics special issue.
Language: English
Electronic publication date: 09/28/2023
Date published: 10/19/2023
Academic Unit: Civil and Environmental Engineering; IIHR--Hydroscience and Engineering
Record Identifier: 9984472857402771

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