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Title: Effects of in situ biostimulation on iron mineral speciation in a sub-surface soil

Authors:
; ; ;
Publication Date:
Research Org.:
Subsurface Biogeochemical Research (SBR)
Sponsoring Org.:
USDOE Office of Science (SC), Biological and Environmental Research (BER)
OSTI Identifier:
1154211
Resource Type:
Journal Article
Resource Relation:
Journal Name: Geochimica et Cosmochimica Acta; Journal Volume: 71; Journal Issue: 4
Country of Publication:
United States
Language:
English

Citation Formats

Joseph W.,Stucki, Kangwon,Lee, Bernard A.,Goodman, and Joel E.,Kostka. Effects of in situ biostimulation on iron mineral speciation in a sub-surface soil. United States: N. p., 2007. Web. doi:10.1016/j.gca.2006.11.023.
Joseph W.,Stucki, Kangwon,Lee, Bernard A.,Goodman, & Joel E.,Kostka. Effects of in situ biostimulation on iron mineral speciation in a sub-surface soil. United States. doi:10.1016/j.gca.2006.11.023.
Joseph W.,Stucki, Kangwon,Lee, Bernard A.,Goodman, and Joel E.,Kostka. Thu . "Effects of in situ biostimulation on iron mineral speciation in a sub-surface soil". United States. doi:10.1016/j.gca.2006.11.023.
@article{osti_1154211,
title = {Effects of in situ biostimulation on iron mineral speciation in a sub-surface soil},
author = {Joseph W.,Stucki and Kangwon,Lee and Bernard A.,Goodman and Joel E.,Kostka},
abstractNote = {},
doi = {10.1016/j.gca.2006.11.023},
journal = {Geochimica et Cosmochimica Acta},
number = 4,
volume = 71,
place = {United States},
year = {Thu Feb 01 00:00:00 EST 2007},
month = {Thu Feb 01 00:00:00 EST 2007}
}
  • The success of sequestration-based remediation strategies will depend on detailed information, including the predominant U species present as sources before biostimulation and the products produced during and after in situ biostimulation. We used X-ray absorption spectroscopy to determine the valence state and chemical speciation of U in sediment samples collected at a variety of depths through the contaminant plume at the Field Research Center at Oak Ridge, TN, before and after approximately 400 days of in situ biostimulation, as well as in duplicate bioreduced sediments after 363 days of resting conditions. The results indicate that U(VI) in subsurface sediments wasmore » partially reduced to 10-40% U(IV) during biostimulation. After biostimulation, U was no longer bound to carbon ligands and was adsorbed to Fe/Mn minerals. Reduction of U(VI) to U(IV) continued in sediment samples stored under anaerobic condition at <4 C for 12 months, with the fraction of U(IV) in sediments more than doubling and U concentrations in the aqueous phase decreasing from 0.5-0.74 to <0.1 {micro}M. A shift of uranyl species from uranyl bound to phosphorus ligands to uranyl bound to carbon ligands and the formation of nanoparticulate uraninite occurred in the sediment samples during storage.« less
  • The success of sequestration-based remediation strategies will depend on detailed information, including the predominant U species present as sources before biostimulation and the products produced during and after in situ biostimulation. We used X-ray absorption spectroscopy to determine the valence state and chemical speciation of U in sediment samples collected at a variety of depths through the contaminant plume at the Field Research Center at Oak Ridge, TN, before and after approximately 400 days of in situ biostimulation, as well as in duplicate bioreduced sediments after 363 days of resting conditions. The results indicate that U(VI) in subsurface sediments wasmore » partially reduced to 10-40% U(IV) during biostimulation. After biostimulation, U was no longer bound to carbon ligands and was adsorbed to Fe/Mn minerals. Reduction of U(VI) to U(IV) continued in sediment samples stored under anaerobic condition at <4 C for 12 months, with the fraction of U(IV) in sediments more than doubling and U concentrations in the aqueous phase decreasing from 0.5-0.74 to <0.1 {micro}M. A shift of uranyl species from uranyl bound to phosphorus ligands to uranyl bound to carbon ligands and the formation of nanoparticulate uraninite occurred in the sediment samples during storage.« less
  • Dissimilatory metal reducing bacteria (DMRB) can influence geochemical processes that affect the speciation and mobility of metallic contaminants within natural environments. Most investigations into the effect of DMRB on sediment geochemistry utilize various synthetic oxides as the FeIII source (e.g., ferrihydrite, goethite, hematite). These synthetic materials do not represent the mineralogical composition of natural systems, and do not account for the effect of sediment mineral composition on microbially mediated processes. Our experiments with a DMRB (Shewanella putrefaciens 200) and a divalent metal (ZnII) indicate that, while complexity in sediment mineral composition may not strongly impact the degree of “microbial ironmore » reducibility,” it does alter the geochemical consequences of such microbial activity. The ferrihydrite and clay mineral content are key factors. Microbial reduction of a synthetic blend of goethite and ferrihydrite (VHSA-G) carrying previously adsorbed ZnII increased both [ZnII-aq] and the proportion of adsorbed ZnII that is insoluble in 0.5 M HCl. Microbial reduction of FeIII in similarly treated iron-bearing clayey sediment (Fe-K-Q) and hematite sand, which contained minimal amounts of ferrihydrite, had no similar effect. Addition of ferrihydrite increased the effect of microbial FeIII reduction on ZnII association with a 0.5 M HCl insoluble phase in all sediment treatments, but the effect was inconsequential in the Fe-K-Q. Zinc k-edge X-ray absorption spectroscopy (XAS) data indicate that microbial FeIII reduction altered ZnII bonding in fundamentally different ways for VHSA-G and Fe-K-Q. In VHSA-G, ZnO6 octahedra were present in both sterile and reduced samples; with a slightly increased average Zn-O coordination number and a slightly higher degree of long-range order in the reduced sample. This result may be consistent with enhanced ZnII substitution within goethite in the microbially reduced sample, though these data do not show the large increase in the degree of Zn-O-metal interactions expected to accompany this change. In Fe-K-Q, microbial FeIII reduction transforms Zn-O polyhedra from octahedral to tetrahedral coordination and leads to the formation of a ZnCl2 moiety and an increased degree of multiple scattering. This study indicates that, while many sedimentary iron minerals are easily reduced by DMRB, the effects of microbial FeIII reduction on trace metal geochemistry are dependent on sediment mineral composition.« less
  • Dissimilatory metal reducing bacteria (DMRB) can influence geochemical processes that subsequently affect the speciation the speciation and lability of metallic contaminants within natural environments. Most investigations into the effect of DMRB on sediment geochemistry utilize various synthetic oxides as the FeIII source (e.g. ferrihydrite, goethite, hematite, hydrous ferric oxide), providing for well-controlled experiments. However, these materials do not necessarily emulate the actual mineralogical composition of natural systems, nor do they account for the effect of sediment mineralogy on microbial activity and/or microbially induced geochemical processes. Our experiments with a divalent metal (ZnII) indicate that, while sediment mineralogy may have littlemore » effect on the net rate of microbial iron reduction, it does impact the resultant speciation of reduced iron and sediment associated transition metals. These data demonstrate that microbial reduction of synthetic goethite carrying previously sorbed ZnII increased both [ZnII-aq] and the proportion of sorbed ZnII that is insoluble in 0.5 M HCl. Microbial reduction of FeIII in similarly treated iron-bearing clayey sediment (Fe-clay) and hematite sand had no similar effect. Moessbauer spectroscopy data indicate that small amounts of ferrihydrite present in the synthetic VHSA goethite are preferentially consumed during FeIII reduction, a process that may result from FeII-driven conversion of ferrihydrite to goethite. Microbial reduction of Fe-clay did not permanently alter iron speciation within the Fe-clay. Zinc k-edge XAS data collected for ZnII previously sorbed to VHSA goethite and Fe-clay indicate that microbial FeIII reduction altered ZnII bonding in fundamentally different ways for VHSA goethite and Fe-clay. In VHSA goethite, XANES data indicate ZnO6 octahedra in both sterile and reduced samples. EXAFS data indicate a slightly increased average Zn-O coordination number and a slightly higher degree of long range order in the reduced sample. This result may be consistent with enhanced ZnII substitution within goethite in the microbially reduced sample, though these data do not show the large increase in the degree of Zn-O-metal interactions expected to accompany this change. In Fe-clay, XANES data indicate that microbial FeIII reduction transforms Zn-O polyhedra from octahedral to tetrahedral coordination and leads to an increased degree of multiple scattering. EXAFS data indicate formation of a ZnCl2 moiety that may also incorporate some Zn-O bonds in the microbially reduced sample. These data indicate that, while many sedimentary iron minerals are easily reduced by DMRB, the geochemical effects of microbial FeIII reduction are highly dependent on sediment iron speciation. Thus, one must consider the effects of sediment mineralogy when investigating the effect of microbial processes on trace metal geochemistry.« less
  • We report results from an extensive study on the speciation of zinc (Zn) and its relation to the mobility and bioavailablity of this element in a smelter contaminated soil and an in situ remediated area of this soil 12 yr after the application of cyclonic ash and compost. Emphasis was placed on the role of neoformed precipitates in controlling Zn speciation, mobility and bioavailability under different environmental conditions. Twelve years after remediation, the pH of the treated and non-treated soil differed by only 0.5 pH unit. Using state-of-the-art electron and X-ray microscopies in combination with micro-focused extended X-ray absorption finemore » structure ({micro}-EXAFS) spectroscopy, no major differences in Zn speciation were found between samples of the treated and non-treated soil. In both soils, 30% to 50% of Zn was present in smelter related minerals (willemite, hemimorphite or gahnite), while 50% to 70% of Zn was incorporated into newly formed Zn precipitates. Contrary to the non-treated soil, the treated soil did not contain gahnite or sphalerite; it is possible that these minerals were dissolved under the higher pH conditions at the time of treatment. Desorption experiments, using a stirred flow technique with a 0.1 mol/L CaCl{sub 2} (pH 6.5) and a HNO{sub 3} (pH 4.0) solution were employed to determine the exchangeable Zn fraction and the Zn fraction which will be mobilized under more extreme weathering conditions, respectively. No significant differences were found in desorption behavior between the treated vs. non-treated soil. Bioavailability tests, using the R. metallidurans AE1433 biosensor showed that {approx}8% of total Zn was bioavailable in both the treated and non-treated soils. It was concluded that the incorporation of Zn into newly formed precipitates in both the treated and non treated soils leads to a significant natural attenuation of the exchangeable/bioavailable Zn fraction at near neutral pH conditions. At lower pHs, conditions not favorable to the formation of Zn precipitates, the pool of Zn associated with the secondary Zn precipitates is potentially more bioavailable.« less