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Title: Influence of Biogenic Fe(II) on the Extent of Microbial Reduction of Fe(III) in Clay Minerals Nontronite, Illite, and Chlorite

Abstract

Microbial reduction of Fe(III) in clay minerals is an important process that affects properties of clay-rich materials and iron biogeochemical cycling in natural environments. Microbial reduction often ceases before all Fe(III) in clay minerals is exhausted. The factors causing the cessation are, however, not well understood. The objective of this study was to assess the role of biogenic Fe(II) in microbial reduction of Fe(III) in various clay minerals. Bioreduction experiments were performed in a batch system, where lactate was used as the sole electron donor, Fe(III) in clay minerals as the sole electron acceptor, and Shewanella putrefaciens CN32 as the mediator with and without an electron shuttle AQDS. Our results showed that bioreduction activity ceased within two weeks with variable extents of bioreduction of structural Fe(III) in clay minerals. When fresh CN32 cells were added to the old cultures (6 months), bioreduction resumed and extents increased. This result indicated that the previous cessation of Fe(III) bioreduction was not necessarily due to the exhaustion of bioavailable Fe(III) in the mineral structure, and suggested that the changes of cell physiology or solution chemistry, such as Fe(II) production during microbial reduction, affected the extent of bioreduction. To investigate the effect of Fe(II) productionmore » on Fe(III) bioreduction, a typical bioreduction process (consisting of lactate, clay, cells and AQDS) was separated into two steps: 1. AQDS was reduced by cells in the absence of clay but in the presence of variable Fe(II) concentrations; 2. reduction of Fe(III) in clays by biogenic AH2DS in the absence of cells. The inhibitory effect of Fe(II) on CN32 activity was confirmed. TEM analysis revealed a thick electron dense halo surrounding the cell surfaces that most likely resulted from Fe(II) sorption/precipitation. Such electron dense materials might have blocked or interfered electron transfers on cell surfaces. The inhibitory effect of Fe(II) was also observed in AH2DS reduction of clay Fe(III). The reduction extent consistently decreased with an increasing concentration of presorbed Fe(II) (onto clay surfaces) at the start of reduction experiments. The relative reduction extent (i.e., reduction extent after normalization to the reduction extent when spiked Fe(II) was zero) was similar for all clay minerals studied and showed a systematic decrease with increasing clay-sorbed Fe(II) concentration. These results suggest a similar inhibitory effect of clay-sorbed Fe(II) on the reduction extent for different clay minerals. An equilibrium thermodynamic model was established with independently estimated parameters to evaluate whether the cessation of Fe(III) reduction by AH2DS was due to the exhaustion of reaction free energy. Model-calculated reduction extents were, however, over 50% higher than experimentally measured, indicating that other factors, such as blockage of the electron transfer chain and mineralogy, restricted the reduction extent. This study also revealed that the relative reducibility of Fe(III) in different clay was as follows: nontronite > chlorite > illite. This order is qualitatively consistent with the differences in crystal chemistry of these minerals.« less

Authors:
; ;
Publication Date:
Research Org.:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org.:
USDOE
OSTI Identifier:
909233
Report Number(s):
PNNL-SA-49307
Journal ID: ISSN 0016-7037; GCACAK; 4691; KP1302000; TRN: US200722%%1046
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Geochimica et Cosmochimica Acta, 71(5):1145-1158; Journal Volume: 71; Journal Issue: 5
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; CLAYS; ILLITE; CHLORITE MINERALS; IRON COMPOUNDS; BIODEGRADATION; REDUCTION; BIOGEOCHEMISTRY; Fe(II) inhibition, microbial reduction, clay; Environmental Molecular Sciences Laboratory

Citation Formats

Jaisi, Deb P., Dong, Hailiang, and Liu, Chongxuan. Influence of Biogenic Fe(II) on the Extent of Microbial Reduction of Fe(III) in Clay Minerals Nontronite, Illite, and Chlorite. United States: N. p., 2007. Web. doi:10.1016/j.gca.2006.11.027.
Jaisi, Deb P., Dong, Hailiang, & Liu, Chongxuan. Influence of Biogenic Fe(II) on the Extent of Microbial Reduction of Fe(III) in Clay Minerals Nontronite, Illite, and Chlorite. United States. doi:10.1016/j.gca.2006.11.027.
Jaisi, Deb P., Dong, Hailiang, and Liu, Chongxuan. Thu . "Influence of Biogenic Fe(II) on the Extent of Microbial Reduction of Fe(III) in Clay Minerals Nontronite, Illite, and Chlorite". United States. doi:10.1016/j.gca.2006.11.027.
@article{osti_909233,
title = {Influence of Biogenic Fe(II) on the Extent of Microbial Reduction of Fe(III) in Clay Minerals Nontronite, Illite, and Chlorite},
author = {Jaisi, Deb P. and Dong, Hailiang and Liu, Chongxuan},
abstractNote = {Microbial reduction of Fe(III) in clay minerals is an important process that affects properties of clay-rich materials and iron biogeochemical cycling in natural environments. Microbial reduction often ceases before all Fe(III) in clay minerals is exhausted. The factors causing the cessation are, however, not well understood. The objective of this study was to assess the role of biogenic Fe(II) in microbial reduction of Fe(III) in various clay minerals. Bioreduction experiments were performed in a batch system, where lactate was used as the sole electron donor, Fe(III) in clay minerals as the sole electron acceptor, and Shewanella putrefaciens CN32 as the mediator with and without an electron shuttle AQDS. Our results showed that bioreduction activity ceased within two weeks with variable extents of bioreduction of structural Fe(III) in clay minerals. When fresh CN32 cells were added to the old cultures (6 months), bioreduction resumed and extents increased. This result indicated that the previous cessation of Fe(III) bioreduction was not necessarily due to the exhaustion of bioavailable Fe(III) in the mineral structure, and suggested that the changes of cell physiology or solution chemistry, such as Fe(II) production during microbial reduction, affected the extent of bioreduction. To investigate the effect of Fe(II) production on Fe(III) bioreduction, a typical bioreduction process (consisting of lactate, clay, cells and AQDS) was separated into two steps: 1. AQDS was reduced by cells in the absence of clay but in the presence of variable Fe(II) concentrations; 2. reduction of Fe(III) in clays by biogenic AH2DS in the absence of cells. The inhibitory effect of Fe(II) on CN32 activity was confirmed. TEM analysis revealed a thick electron dense halo surrounding the cell surfaces that most likely resulted from Fe(II) sorption/precipitation. Such electron dense materials might have blocked or interfered electron transfers on cell surfaces. The inhibitory effect of Fe(II) was also observed in AH2DS reduction of clay Fe(III). The reduction extent consistently decreased with an increasing concentration of presorbed Fe(II) (onto clay surfaces) at the start of reduction experiments. The relative reduction extent (i.e., reduction extent after normalization to the reduction extent when spiked Fe(II) was zero) was similar for all clay minerals studied and showed a systematic decrease with increasing clay-sorbed Fe(II) concentration. These results suggest a similar inhibitory effect of clay-sorbed Fe(II) on the reduction extent for different clay minerals. An equilibrium thermodynamic model was established with independently estimated parameters to evaluate whether the cessation of Fe(III) reduction by AH2DS was due to the exhaustion of reaction free energy. Model-calculated reduction extents were, however, over 50% higher than experimentally measured, indicating that other factors, such as blockage of the electron transfer chain and mineralogy, restricted the reduction extent. This study also revealed that the relative reducibility of Fe(III) in different clay was as follows: nontronite > chlorite > illite. This order is qualitatively consistent with the differences in crystal chemistry of these minerals.},
doi = {10.1016/j.gca.2006.11.027},
journal = {Geochimica et Cosmochimica Acta, 71(5):1145-1158},
number = 5,
volume = 71,
place = {United States},
year = {Thu Mar 01 00:00:00 EST 2007},
month = {Thu Mar 01 00:00:00 EST 2007}
}
  • A quantitative study was performed to understand how Fe(III) site occupancy controls Fe(III) bioreduction in nontronite by Shewanella putrefaciens CN32. NAu-1 and NAu-2 were nontronites and contained Fe(III) in different structure sites with 16% and 23% total iron (w/w), respectively, with almost all iron as Fe(III). Moessbauer spectroscopy showed that Fe(III) was present in the octahedral site in NAu-1 (with a small amount of goethite), but in both the tetrahedral and the octahedral sites in NAu-2. Moessbauer data further showed that the octahedral Fe(III) in NAu-2 existed in at least two environments- trans (M1) and cis (M2) sites. The microbialmore » Fe(III) reduction in NAu-1 and NAu-2 was studied in batch cultures at a nontronite concentration of 5mg/mL in bicarbonate buffer with lactate as the electron donor. Fe(II) production in inoculated treatments was determined by extraction with 0.5 N HCl and compared to uninoculated controls to establish the extent of biological reduction. The resulting solids were characterized by X-ray diffraction (XRD), Moessbauer spectroscopy, and transmission electron microscopy (TEM). In the presence of an electron shuttle, anthraquinone-2,6-disulfonate (AQDS), the extent of bioreduction was 11-16% for NAu-1 but 28-32% for NAu-2. The extent of reduction in the absence of AQDS was only 5-7% in NAu-1 but 14-18% in NAu-2. The reduction rate was also faster in NAu-2 than that in NAu-1. Moessbauer data of the bioreduced nontronite materials indicated that the Fe(III) reduction in NAu-1 was mostly from the presence of goethite, whereas the reduction in NAu-2 was due to the presence of the tetrahedral and trans-octahedral Fe(III) in the structure. The measured aqueous Fe(II) was negligible [< 2.5% of the total biogenic Fe(II)]. As a result of bioreduction, the average nontronite particle thickness remained nearly the same (from 2.1 to 2.5 nm) for NAu-1, but decreased significantly from 6 to 3.5 nm for NAu-2 with a concomitant change in crystal size distribution. The decrease in crystal size suggests reductive dissolution of nontronite NAu-2, which was supported by aqueous solution chemistry (i.e., aqueous Si). These data suggest that the more extensive Fe(III) bioreduction in NAu-2 was due to the presence of the tetrahedral and the trans-octahedral Fe(III), which was presumed to be more reducible. The biogenic Fe(II) was not associated with biogenic solids such as siderite or green rust or in the aqueous solution. We infer that it may be either adsorbed onto surfaces of nontronite particles/bacteria and in the structure of nontronite. Furthermore, we have demonstrated that natural nontronite clays were capable of supporting cell growth even in non-growth medium, possibly due to presence of naturally existing nutrients in the nontronite clays. These results suggest that crystal chemical environment of Fe(III) is an important determinant in controlling the rate and extent of microbial reduction of Fe(III) in nontronite.« less
  • 99Tc is formed mostly during nuclear reactions and is released into the environment during weapons testing and inadvertent waste disposal. The long half-life, high environmental mobility (as Tc(VII)O4-) and its possible uptake into the food chain cause 99Tc to be a significant environmental contaminant. In this study, we evaluated the role of Fe(II) in biologically reduced clay mineral, nontronite (NAu-2), in reducing Tc(VII)O4- to poorly soluble Tc(IV) species as a function of pH and Fe(II) concentration. The rate of Tc(VII) reduction by Fe(II) in NAu-2 was higher at neutral pH (pH 7.0) than at acidic and basic pHs when Fe(II)more » concentration was low (< 1 mmol/g). The effect of pH, however, was insignificant at higher Fe(II) concentrations. The reduction of Tc(VII) by Fe(II) associated with NAu-2 was also studied in the presence of common subsurface oxidants including iron and manganese oxides, nitrate, and oxygen, to evaluate the effect of the oxidants on the enhancement and inhibition of Tc(VII) reduction, and reoxidation of Tc(IV). Addition of iron oxides (goethite and hematite) to the Tc(VII)-NAu-2 system, where Tc(VII) reduction was ongoing, enhanced reduction of Tc(VII), apparently as a result of re-distribution of reactive Fe(II) from NAu-2 to more reactive goethite/hematite surfaces. Addition of manganese oxides stopped further Tc(VII) reduction, and in case of K+-birnessite, it reoxidized previously reduced Tc(IV). Nitrate neither enhanced reduction of Tc(VII) nor promoted reoxidation of Tc(IV). Approximately 11% of Tc(IV) was oxidized by oxygen. The rate and extent of Tc(IV) reoxidation was found to strongly depend on the nature of the oxidants and concentration of Fe(II). When the same oxidants were added to aged Tc reduction products (mainly NAu-2 and TcO2•nH2O), the extent of Tc(IV) reoxidation decreased significantly relative to fresh Tc(IV) products. Increasing NAu-2 concentration also resulted in the decreased extent of Tc(IV) reoxidation. The results were attributed to the effect of NAu-2 aggregation that effectively retained Tc(IV) in the solid and decreased its vulnerability to reoxidation. Overall, our results implied that bioreduced clay minerals could play an important role in reducing Tc(VII) and in maintaining the long-term stability of reduced Tc(IV).« less
  • {sup 99}Tc is formed mostly during nuclear reactions and is released into the environment during weapons testing and inadvertent waste disposal. The long half-life, high environmental mobility (as Tc(VII)O{sub 4}{sup -}) and its possible uptake into the food chain cause {sup 99}Tc to be a significant environmental contaminant. In this study, we evaluated the role of Fe(II) in biologically reduced clay mineral, nontronite (NAu-2), in reducing Tc(VII)O{sub 4}{sup -} to poorly soluble Tc(IV) species as a function of pH and Fe(II) concentration. The rate of Tc(VII) reduction by Fe(II) in NAu-2 was higher at neutral pH (pH 7.0) than atmore » acidic and basic pHs when Fe(II) concentration was low (< 1 mmol/g). The effect of pH, however, was insignificant at higher Fe(II) concentrations. The reduction of Tc(VII) by Fe(II) associated with NAu-2 was also studied in the presence of common subsurface oxidants including iron and manganese oxides, nitrate, and oxygen, to evaluate the effect of these oxidants on the enhancement and inhibition of Tc(VII) reduction, and reoxidation of Tc(IV). Addition of iron oxides (goethite and hematite) to the Tc(VII)-NAu-2 system, where Tc(VII) reduction was ongoing, enhanced reduction of Tc(VII), apparently as a result of re-distribution of reactive Fe(II) from NAu-2 to more reactive goethite/hematite surfaces. Addition of manganese oxides stopped further Tc(VII) reduction, and in case of K{sup +}-birnessite, it reoxidized previously reduced Tc(IV). Nitrate neither enhanced reduction of Tc(VII) nor promoted reoxidation of Tc(IV). Approximately 11% of Tc(IV) was oxidized by oxygen. The rate and extent of Tc(IV) reoxidation was found to strongly depend on the nature of the oxidants and concentration of Fe(II). When the same oxidants were added to aged Tc reduction products (mainly NAu-2 and TcO{sub 2} {center_dot} nH{sub 2}O), the extent of Tc(IV) reoxidation decreased significantly relative to fresh Tc(IV) products. Increasing NAu-2 concentration also resulted in the decreased extent of Tc(IV) reoxidation. The results were attributed to the effect of NAu-2 aggregation that effectively retained Tc(IV) in the solid and decreased its vulnerability to reoxidation. Overall, our results implied that bioreduced clay minerals could play an important role in reducing Tc(VII) and in maintaining the long-term stability of reduced Tc(IV).« less
  • Microbial reduction of structural Fe(III) in nontronite was studied in batch cultures under non-growth condition using Shewanella putrefaciens, strain CN32. The rate and extent of structural Fe(III) reduction was examined as a function of electron acceptor [Fe(III)] and bacterial concentration. Fe(II) sorptions onto nontronite and CN32 cells were independently measured and well-described by the Langmuir expression with affinity constant 2.3 and 2.25 for nontronite and cells, respectively. The Fe(II) sorption capacity of nontronite, however, decreased with increasing nontronite concentration, suggesting particulate agglomeration effect. An empirical equation for sorption capacity was derived from the sorption isotherms at different nontronite concentrations andmore » was used to calculate the 'effective' Fe(III) concentration for bioreduction. The initial rate of microbial reduction was found to be first order with respect to the 'effective' Fe(III) concentration. A kinetic biogeochemical model was assembled that incorporated the first order rate expression with respect to the ‘effective’ Fe(III) concentration, rates and extent of Fe(II) sorption to cell and nontronite surfaces, and the empirical equation for sorption capacity. The model successfully described the experimental results of microbial reduction of nontronite with variable nontronite concentrations. The microbial reduction rate, after normalized to cell concentration, however, decreased with increasing cell concentration, indicating that cell concentration did not linearly affect the reduction as commonly assumed in literature. A nonlinear, saturation-type rate expression with respect to cell concentration was needed to model bioreduction at variable cell concentration. Our results indicated that the kinetics of microbial reduction of structual Fe(III) in nontronite can be modeled after consideration of Fe(II) production and sorption, its role in inhibiting further Fe(III) reduction, and nonlinear effect of cell concentration.« less