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Title: Reduction And Immobilization Of Hexavalent Chromium By Microbially Reduced Fe-bearing Clay Minerals

Abstract

Hexavalent chromium (Cr6+) is a major contaminant in the environment. As a redox-sensitive element, the fate and toxicity of chromium is controlled by reduction-oxidation (redox) reactions. Previous research has shown the ability of structural Fe(II) in naturally present and chemically reduced clay minerals to reduce Cr6+ to Cr(III) as a way of immobilization and detoxification. However, it is still poorly known whether or not structural Fe(II) in biologically reduced clay minerals exhibits a similar reactivity and if so, what the kinetics and mechanisms of Cr6+ reduction are. The objective of this study was to determine the kinetics and possible mechanisms of Cr6+ reduction by structural Fe(II) in microbially reduced clay minerals and the nature of reduced Cr(III). Structural Fe(III) in nontronite (NAu-2), montmorillonite (SWy-2), chlorite (CCa-2), and clay-rich sediments from the Ringold Formation of the Hanford site of Washington State, USA was first bioreduced to Fe(II) by an iron-reducing bacterium Geobacter sulfurreducens with acetate as the sole electron donor and anthraquinone-2,6-disulfate (AQDS) as electron shuttle in synthetic groundwater (pH 7). Biogenic Fe(II) was then used to reduce aqueous Cr6+ at three different temperatures, 10°, 20°, and 30°C, in order to determine the temperature dependence of the redox reaction between Cr6+more » and clay-Fe(II). The results showed that nontronite and montmorillonite were most effective in reducing aqueous Cr6+ at all three temperatures. In contrast, most Fe(II) in chlorite was not reactive towards Cr6+ reduction at 10°C, though at 30°C there was some reduction. For all the clay minerals, the ratio of total Fe(II) oxidized to Cr6+ reduced was close to the expected stoichiometric value of 3. Characterization of the Cr-clay reaction product with scanning electron microscopy with focused ion beam and transmission electron microscopy with electron energy loss spectroscopy revealed that reduced chromium was possibly in the form of sub-nanometer Cr2O3 in association with residual clay minerals as micro-aggregates. This textural association was expected to minimize the chance of Cr(III) reoxidation upon exposure to oxidants. These results are important for our understanding of how various clay minerals may be used to reductively immobilize the heavy metal contaminant Cr in the environment.« less

Authors:
; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
Sponsoring Org.:
USDOE
OSTI Identifier:
1134509
Report Number(s):
PNNL-SA-101775
44687; KP1704020
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Journal Name:
Geochimica et Cosmochimica Acta, 133:186-203
Additional Journal Information:
Journal Name: Geochimica et Cosmochimica Acta, 133:186-203
Country of Publication:
United States
Language:
English
Subject:
Environmental Molecular Sciences Laboratory

Citation Formats

Bishop, Michael E., Glasser, Paul, Dong, Hailiang, Arey, Bruce W., and Kovarik, Libor. Reduction And Immobilization Of Hexavalent Chromium By Microbially Reduced Fe-bearing Clay Minerals. United States: N. p., 2014. Web. doi:10.1016/j.gca.2014.02.040.
Bishop, Michael E., Glasser, Paul, Dong, Hailiang, Arey, Bruce W., & Kovarik, Libor. Reduction And Immobilization Of Hexavalent Chromium By Microbially Reduced Fe-bearing Clay Minerals. United States. https://doi.org/10.1016/j.gca.2014.02.040
Bishop, Michael E., Glasser, Paul, Dong, Hailiang, Arey, Bruce W., and Kovarik, Libor. 2014. "Reduction And Immobilization Of Hexavalent Chromium By Microbially Reduced Fe-bearing Clay Minerals". United States. https://doi.org/10.1016/j.gca.2014.02.040.
@article{osti_1134509,
title = {Reduction And Immobilization Of Hexavalent Chromium By Microbially Reduced Fe-bearing Clay Minerals},
author = {Bishop, Michael E. and Glasser, Paul and Dong, Hailiang and Arey, Bruce W. and Kovarik, Libor},
abstractNote = {Hexavalent chromium (Cr6+) is a major contaminant in the environment. As a redox-sensitive element, the fate and toxicity of chromium is controlled by reduction-oxidation (redox) reactions. Previous research has shown the ability of structural Fe(II) in naturally present and chemically reduced clay minerals to reduce Cr6+ to Cr(III) as a way of immobilization and detoxification. However, it is still poorly known whether or not structural Fe(II) in biologically reduced clay minerals exhibits a similar reactivity and if so, what the kinetics and mechanisms of Cr6+ reduction are. The objective of this study was to determine the kinetics and possible mechanisms of Cr6+ reduction by structural Fe(II) in microbially reduced clay minerals and the nature of reduced Cr(III). Structural Fe(III) in nontronite (NAu-2), montmorillonite (SWy-2), chlorite (CCa-2), and clay-rich sediments from the Ringold Formation of the Hanford site of Washington State, USA was first bioreduced to Fe(II) by an iron-reducing bacterium Geobacter sulfurreducens with acetate as the sole electron donor and anthraquinone-2,6-disulfate (AQDS) as electron shuttle in synthetic groundwater (pH 7). Biogenic Fe(II) was then used to reduce aqueous Cr6+ at three different temperatures, 10°, 20°, and 30°C, in order to determine the temperature dependence of the redox reaction between Cr6+ and clay-Fe(II). The results showed that nontronite and montmorillonite were most effective in reducing aqueous Cr6+ at all three temperatures. In contrast, most Fe(II) in chlorite was not reactive towards Cr6+ reduction at 10°C, though at 30°C there was some reduction. For all the clay minerals, the ratio of total Fe(II) oxidized to Cr6+ reduced was close to the expected stoichiometric value of 3. Characterization of the Cr-clay reaction product with scanning electron microscopy with focused ion beam and transmission electron microscopy with electron energy loss spectroscopy revealed that reduced chromium was possibly in the form of sub-nanometer Cr2O3 in association with residual clay minerals as micro-aggregates. This textural association was expected to minimize the chance of Cr(III) reoxidation upon exposure to oxidants. These results are important for our understanding of how various clay minerals may be used to reductively immobilize the heavy metal contaminant Cr in the environment.},
doi = {10.1016/j.gca.2014.02.040},
url = {https://www.osti.gov/biblio/1134509}, journal = {Geochimica et Cosmochimica Acta, 133:186-203},
number = ,
volume = ,
place = {United States},
year = {Thu May 15 00:00:00 EDT 2014},
month = {Thu May 15 00:00:00 EDT 2014}
}