Reduction and Reoxidation of Nontronite: Extent of Reduction and Reaction Rates

Komadel, Peter; Lear, Paul R.; Stucki, Joseph W.

doi:10.1346/ccmn.1990.0380212

Cited by 106 publications

(91 citation statements)

References 13 publications

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“…Consequently, the central doublet (illite associated and surface associated Fe 3+ ) increased. It is generally accepted that the oxidation of structural Fe(II) in phyllosilicates is recalcitrant to oxidation by O2 in air; thus, it can be assumed that only the surface adsorbed Fe(II) was oxidized (21). Under this assumption, the peak area of the side doublet for the reoxidized sample and that of the central doublet for the bioreduced sample should be characteristic of Fe(II) and Fe(III) in illite, respectively.…”

Section: Resultsmentioning

confidence: 99%

Microbial Reduction of Structural Fe(III) in Illite and Goethite

Dong

Kukkadapu

Fredrickson

et al. 2003

Environ. Sci. Technol.

134

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Microbial reduction of Fe(III) in illite was studied to evaluate the possibility of microbial utilization of Fe(III) in sedimentary clays and to determine the effects of bioreduction on clay composition and structure. A subsurface bacterium (Shewanella putrefaciens CN32) and illite separates (<0.2 µm) from St. Peter Formation sandstone in Ogle County, IL, were used in laboratory experiments. Illite suspensions buffered at pH 7 with bicarbonate were inoculated with CN32 and provided with H 2 as an electron donor. In selected treatments, anthraquinone-2,6-disulfonate (AQDS), was included as an electron shuttle to facilitate the bioreduction. 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 Mo ¨ssbauer spectroscopy and scanning and transmission electron microscopy (SEM and TEM). The characterization of the starting illite material revealed that it contained a minor component of goethite (R-FeOOH) in addition to fibrous illite. The starting material (both goethite and illite) contained 6% (w/ w) total Fe, and 82% of the total Fe was Fe(III). Approximately 30% of total Fe was associated with goethite. At the end of a 30-day incubation, residual goethite and illite remained. The extent of reduction was much greater in the presence of AQDS (25%) than in its absence (0%). Modeling of Mo ¨ssbauer spectra of the bioreduced material indicated that both goethite and illite were reduced but to a different extent. Additionally, TEM evidence suggested that there was a dramatic change in illite morphology upon bioreduction from fibrous needles to plates. The ability of bacteria to utilize Fe(III) in illite has important implications for microbial functions and survival mechanisms, as well as many geological processes, in the subsurface.

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Section: Resultsmentioning

confidence: 99%

Microbial Reduction of Structural Fe(III) in Illite and Goethite

Dong

Kukkadapu

Fredrickson

et al. 2003

Environ. Sci. Technol.

134

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“…Reduced gels were prepared by suspending 100 mg of stock clay in 30 ml of citrate-bicarbonate buffer solution (Stucki et al, 1984a), adding 100 nag of sodium dithionite (Na2S204) salt, and heating at 70~ under an inert atmosphere in an open-system reaction vessel for 2 hr (Komadel et aL, 1990), bringing the clay to about 50% reduction. The clay thus reduced was then washed by centrifugation to a solute concentration of about 10 -4 N, and the suspension was placed in a pressure cell described by Stucki et al (1984b) under 10 kPa N 2 gas pressure.…”

Section: Methodsmentioning

confidence: 99%

“…The deep bluegreen color, which arises from a near maximum in the Fe(II)-Fe(III) intervalence electron transfer transitions (Lear and Stucki, 1987;Komadel et al, 1990), clearly indicates that the reduced sample maintained a significant reduced state (~50%) during this stage of sample preparation.…”

Section: Methodsmentioning

confidence: 99%

“…The small difference could be due to the fact that the actual Fe(II) content in the reduced sample was not measured in these experiments, but the value assumed in Eq. (3) is only an estimate based on the reduction time used (Komadel et al, 1990). The maximum theoretical b length for a completely reduced sample is 9.323 ~, so if the actual level of reduction is > 50%, agreement between theory and experiment would be even better.…”

Section: Stacking Order In the A-b Planementioning

confidence: 99%

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Effects of Iron Oxidation State on the Texture and Structural Order of Na-Nontronite Gels

Stucki

1991

Clays and clay miner.

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--Aqueous gels of unaltered (oxidized) and chemically reduced ferrnginous smectite (SWa-1 from the Source Clays Repository of The Clay Minerals Society) were characterized by transmission electron microscopy, electron diffraction, and energy-dispersive X-ray fluorescence to establish details regarding their texture, inter-layer and inter-particle arrangements, and chemical composition. Micrographs revealed that the reduction of structural Fe(III) to Fe(II) caused a consolidation of smectite particles from an extensive network of smaU crystals (1-6 layers thick) to distinct particles of limited size in the a-b direction and about 20-40 layers thick. The interlayer distances in the reduced sample appeared to be more uniform than in the oxidized sample, but both exhibited spacings of about 12.6 A. Chemical analysis showed no qualitative differences as a result of oxidation state. Electron diffraction patterns displayed marked differences. The pattern of the oxidized sample consisted of homogeneous rings, indicating that the stacking order in the a-b plane was turbostratic or disordered, whereas the reduced pattern exhibited much more order as evidenced by distinct spots amid low-intensity rings, suggesting that inter-layer attractive forces were stronger if Fe(II) was present in the clay crystal.

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“…The redox state of the clay and knowledge of how to control or exploit it are of great importance to agriculture, industry, and the environment because of their profound effects on many physical-chemical properties of the clay Lear and Stucki, 1989;Komadel et al, 1990;Khaled and Stucki, 1991;Stucki and Tessier, 1991).…”

Section: Introductionmentioning

confidence: 99%

Reduction of Structural Iron in Ferruginous Smectite by Free Radicals

Gan

1992

Clays and clay miner.

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Abstract--The oxidation state of structural iron greatly influences the physical-chemical properties of clay minerals, a phenomenon that may have significant implications for pollutant fate in the environment, for agricultural productivity, and for industrial uses of clays. Knowledge of redox mechanisms is fundamental to understanding the underlying basis for iron's effects on clays. Past studies revealed that the extent of Fe reduction varied depending on the reducing agent used, but this variation may not have been a simple function of the reduction potential of the reducing agent. The objective of this study was to identify the relationship between the Fe reduction mechanism and free radical activity in the reducing agent. Several reducing agents and their mixtures with the Na-saturated, 0.5 to 2 #m size fraction of ferruginous smectite (SWa-1) were analyzed by electron spin resonance (ESR) spectroscopy to determine the presence of unpaired electrons or free radicals. Only NazS204 exhibited paramagnetic free-radical behavior with a signal at about g = 2.011, which was attributed to the sulphoxylate (SO2-.) free radical. The free radical was labile in aqueous solution, and the ability of NazSzO4 solution to reduce structural Fe in the smectite decreased with age of the solution and paralleled the disappearance of the free radical signal in the ESR spectrum. The paramagnetic species was preserved and enhanced ifNa2SzO4 was added to the clay suspension, indicating that either the clay surface stabilized the SO2 9 radical or the additional unpaired electrons were produced in the clay structure.

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Reduction and Reoxidation of Nontronite: Extent of Reduction and Reaction Rates

Cited by 106 publications

References 13 publications

Microbial Reduction of Structural Fe(III) in Illite and Goethite

Microbial Reduction of Structural Fe(III) in Illite and Goethite

Effects of Iron Oxidation State on the Texture and Structural Order of Na-Nontronite Gels

Reduction of Structural Iron in Ferruginous Smectite by Free Radicals

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