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Title: Electron transfer and atom exchange between aqueous Fe(II) and structural Fe(III) in clays. Role in U and Hg(II) transformations

Abstract

During this project, we investigated Fe electron transfer and atom exchange between aqueous Fe(II) and structural Fe(III) in clay minerals. We used selective chemical extractions, enriched Fe isotope tracer experiments, computational molecular modeling, and Mössbauer spectroscopy. Our findings indicate that structural Fe(III) in clay minerals is reduced by aqueous Fe(II) and that electron transfer occurs when Fe(II) is sorbed to either basal planes and edge OH-groups of clay mineral. Findings from highly enriched isotope experiments suggest that up to 30 % of the Fe atoms in the structure of some clay minerals exhanges with aqueous Fe(II). First principles calculations using a small polaron hopping approach suggest surprisingly fast electron mobility at room temperature in a nontronite clay mineral and are consistent with temperature dependent Mössbauer data Fast electron mobility suggests that electrons may be able to conduct through the mineral fast enough to enable exchange of Fe between the aqueous phase and clay mineral structure. over the time periods we observed. Our findings suggest that Fe in clay minerals is not as stable as previously thought.

Authors:
 [1]
  1. Univ. of Iowa, Iowa City, IA (United States)
Publication Date:
Research Org.:
Univ. of Iowa, Iowa City, IA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
OSTI Identifier:
1323384
Report Number(s):
Scherer
DOE Contract Number:
SC0006692
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; clay minerals; iron; electron transfer

Citation Formats

Scherer, Michelle. Electron transfer and atom exchange between aqueous Fe(II) and structural Fe(III) in clays. Role in U and Hg(II) transformations. United States: N. p., 2016. Web. doi:10.2172/1323384.
Scherer, Michelle. Electron transfer and atom exchange between aqueous Fe(II) and structural Fe(III) in clays. Role in U and Hg(II) transformations. United States. doi:10.2172/1323384.
Scherer, Michelle. Wed . "Electron transfer and atom exchange between aqueous Fe(II) and structural Fe(III) in clays. Role in U and Hg(II) transformations". United States. doi:10.2172/1323384. https://www.osti.gov/servlets/purl/1323384.
@article{osti_1323384,
title = {Electron transfer and atom exchange between aqueous Fe(II) and structural Fe(III) in clays. Role in U and Hg(II) transformations},
author = {Scherer, Michelle},
abstractNote = {During this project, we investigated Fe electron transfer and atom exchange between aqueous Fe(II) and structural Fe(III) in clay minerals. We used selective chemical extractions, enriched Fe isotope tracer experiments, computational molecular modeling, and Mössbauer spectroscopy. Our findings indicate that structural Fe(III) in clay minerals is reduced by aqueous Fe(II) and that electron transfer occurs when Fe(II) is sorbed to either basal planes and edge OH-groups of clay mineral. Findings from highly enriched isotope experiments suggest that up to 30 % of the Fe atoms in the structure of some clay minerals exhanges with aqueous Fe(II). First principles calculations using a small polaron hopping approach suggest surprisingly fast electron mobility at room temperature in a nontronite clay mineral and are consistent with temperature dependent Mössbauer data Fast electron mobility suggests that electrons may be able to conduct through the mineral fast enough to enable exchange of Fe between the aqueous phase and clay mineral structure. over the time periods we observed. Our findings suggest that Fe in clay minerals is not as stable as previously thought.},
doi = {10.2172/1323384},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Wed Aug 31 00:00:00 EDT 2016},
month = {Wed Aug 31 00:00:00 EDT 2016}
}

Technical Report:

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  • 'The objectives of the project remain the same as those stated in the original proposal. Specifically, to determine microbiological and geochemical controls on carbonate mineral precipitation reactions that are caused by bacterial reduction of Fe(III)-oxides, and identify contributions of these processes to solid phase capture of strontium and other metal/radionuclide contaminants. The project on microbial mineral transformations at the Fe(II)/Fe(III) redox boundary for the solid phase capture of strontium is progressing well. Thus far, the authors have been able to demonstrate that: pH and DIC concentrations increase during microbial reduction of HFO in batch culture experiments with G. metallireducens lastingmore » 30 days with high concentrations of strontium (1.0 \265m) and calcium (10 \265m) do not inhibit microbial HFO reduction, the extent of change in pH and DIC concentrations brings about supersaturation with respect to carbonate minerals including siderite (FeCO{sub 3}), strontianite (SrCO{sub 3}), and calcite/aragonite (CaCO{sub 3}); in addition, precipitation of siderite has been documented in cultures of HFO reducing bacteria significant amounts of strontium and calcium (40 to 50% of the total initial concentration) sorb to particulate solids (i.e., HFO and bacteria cells)-in batch culture experiments l sorption of strontium to HFO conforms with Langmuir single site sorption models derived from corresponding mass action and mass balance relationships anticipated from thermodynamic equilibrium considerations the sorption behavior of strontium with S. alga is more complex and seems to involve two sets of reactive surface sites on the bacterial cells; a high affinity site of low total sorption capacity, and a low affinity site with high sorption capacity the total strontium sorption capacities of S. alga and HFO are comparable the observed solid phase partioning of strontium in the culture experiments is in excellent agreement with sorption characteristics measured with HFO and S. alga.'« less
  • 'The Research objectives of this report are to determine microbiological and geochemical controls on carbonate mineral preciptation reactions, and identify contributions of these processes to the solid phase capture of strontium and other metal/radionuclide contaminants. The study is relevant to the development of new clean-up strategies for DOE sites where strontium and other metal/radionuclides exist as ubiquitous and often mobile contaminants. The work summarized in this report encompasses two years of a three-year project investigating the use of bacteria to concentrate and immobilize strontium, as well as other metal/radionuclide, contaminants. Major accomplishments to date include completion of metal sorption studiesmore » with bacteria and hydrous ferric oxides (HFO), assessment of the impact of strontium on bacterial Fe(III)-reduction, induction of carbonate mineral precipitation and solid phase capture of strontium under Fe(III)-reducing conditions, and discovery of a procedure to attain rapid high-level concentration of strontium in microbiologically produced calcite.'« less
  • The migration of {sup 90}Sr in groundwater is a significant environmental concern at former nuclear weapons production sites in the US and abroad. Although retardation of {sup 90}Sr transport relative to mean groundwater velocity is known to occur in contaminated aquifers, Sr{sup 2+} does not sorb as strongly to iron oxides and other mineral phases as do other metal-radionuclides contaminants. Thus, some potential exists for extensive {sup 90}Sr migration from sources of contamination. Chemical or biological processes capable of retarding or immobilizing Sr{sup 2+} in groundwater environments are of interest from the standpoint of understanding controls on subsurface Sr{sup 2+}more » migration. In addition, it may be possible to exploit such processes for remediation of subsurface Sr contamination. In this study the authors examined the potential for the solid phase sorption and incorporation of Sr{sup 2+} into carbonate minerals formed during microbial Fe(III) oxide reduction as a first step toward evaluating whether this process could be used to promote retardation of {sup 90}Sr migrations in anaerobic subsurface environments. The demonstration of Sr{sup 2+} capture in carbonate mineral phases formed during bacterial HFO reduction and urea hydrolysis suggests that microbial carbonate mineral formation could contribute to Sr{sup 2+} retardation in groundwater environments. This process may also provide a mechanism for subsurface remediation of Sr{sup 2+} and other divalent metal contaminants that form insoluble carbonate precipitates.« less