Yul Roh

Microbial Synthesis and the Characterization of Metal-Substituted Magnetites

The use of bacteria as a novel biotechnology to facilitate the production of nanoparticles is in its infancy. We describe a bacterially mediated electrochemical process in which metal (Co, Cr, or Ni)-substituted magnetite powders were synthesized by iron(III)-reducing bacteria under anaerobic conditions. Amorphous Fe(III) oxyhydroxides plus soluble metal species (Co, Cr, Ni) comprise the electron acceptor and hydrogen or simple organics comprise the electron donor. The microbial processes produced copious amount of nm-sized, metal-substituted magnetite crystals. Chemical analysis and X-ray powder diffraction analysis showed that metals such as Co, Cr, and Ni were substituted into biologically facilitated magnetites. These results suggest that the bacteria may be viewed as a nonspecific source of electrons at a potential that can be calculated or surmised based on the underlying thermodynamics. Microbially facilitated synthesis of the metal-substituted magnetites at near ambient temperatures may expand the possible use of the specialized ferromagnetic particles.

Biogeochemical and environmental factors in Fe biomineralization: Magnetite and siderite formation

The formation of siderite and magnetite by Fe(III)-reducing bacteria may play an important role in C and Fe geochemistry in subsurface and ocean sediments. The objective of this study was to identify environmental factors that control the formation of siderite (FeCO3) and magnetite (Fe3O4) by Fe(III)-reducing bacteria. Psychrotolerant (<20°C), mesophilic (20–35°C) and thermophilic (>45°C) Fe(III)-reducing bacteria were used to examine the reduction of a poorly crystalline iron oxide, akaganeite (β-FeOOH), without a soluble electron shuttle, anthraquinone disulfuonate (AQDS), in the presence of N2, N2-CO2(80:20, V:V), H2 and H2-CO2 (80:20, V:V) headspace gases as well as in

Physicochemical and Mineralogical Characterization of Uranium-Contaminated Soils

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Geochemical reactions and dynamics during titration of a contaminated groundwater with high uranium, aluminum, and calcium

HCO3−-buffered medium (30–210 mM) under a N2 atmosphere. Iron biomineralization was also examined under different growth conditions such as salinity, pH, incubation time, incubation temperature and electron donors. Magnetite formation was dominant under a N2 and a H2 atmosphere. Siderite formation was dominant under a H2-CO2 atmosphere. A mixture of magnetite and siderite was formed in the presence of a N2-CO2 headspace. Akaganeite was reduced and transformed to siderite and magnetite in a

Biomineralization of a poorly crystalline Fe(III) oxide, akaganeite, by an anaerobic Fe(III)-reducing bacterium (Shewanella alga) isolated from marine environment

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Iron reduction by a psychrotolerant Fe(III)-reducing bacterium isolated from ocean sediment

HCO3−-buffered medium (>120 mM) with lactate as an electron donor in the presence of a N2 atmosphere. Biogeochemical and environmental factors controlling the phases of the secondary mineral suite include medium pH, salinity, electron donors, atmospheric composition and incubation time. These results indicate that microbial Fe(III) reduction may play an important role in Fe and C biogeochemistry as well as C sequestration in natural environments.

Formation of magnetite and iron-rich carbonates by thermophilic iron-reducing bacteria

Physicochemical and mineralogical properties of the contaminants should be taken into account to decide a remediation strategy for a given radionuclide because development and optimization of soil remedial technologies are based on physicochemical and mineralogical separation techniques. The objectives of this study are to (1) demonstrate how a priori physicochemical and mineralogical characterization of soil contaminants can direct the development of remediation strategies and their performance evaluation for soil treatments and (2) understand the nature of uranium contamination and its association with the soil matrix by chemical extractions. This study examined two U-contaminated sites (K311 and K1300) at the DOE K-25 site, presently located at East Tennessee Technology Park, Oak Ridge, Tennessee. Uranium concentrations of the soils ranged from 1499 to 216,413 Bq kg−1 at both sites. Scanning electron microscopy with backscattered electron spectroscopy and X-ray diffraction analysis showed that the dominant U phases are U oxides (schoepite), U-Ca-silicate (uranophane) and U silicate (coffinite) from the K311 site soils, whereas U-Ca-oxide and U-Ca-phosphate dominate in the K1300 site soils. Sodium carbonate/bicarbonate leaching was effective on the K1300 site soils, whereas citric acid leaching is effective on the K311 site soils. Sequential leaching showed that the majority of the uranium in the contaminated soils was contained in carbonate minerals (45%) and iron oxides (40%). Conventional leaching showed that citric acid treatment was most effective on the K311 site soils, whereas the sodium carbonate/ bicarbonate treatment was most effective on the K1300 site soils.

Biogeochemical Remediation of Cr(VI)-Contaminated Groundwater using MMPH-0 (Enterobacter aerogenes)

This study investigated possible geochemical reactions during titration of a contaminated groundwater with a low pH but high concentrations of aluminum, calcium, magnesium, manganese, and trace contaminant metals/radionuclides such as uranium, technetium, nickel, and cobalt. Both Na-carbonate and hydroxide were used as titrants, and a geochemical equilibrium reaction path model was employed to predict aqueous species and mineral precipitation during titration. Although the model appeared to be adequate to describe the concentration profiles of some metal cations, solution pH, and mineral precipitates, it failed to describe the concentrations of U during titration and its precipitation. Most U (as uranyl, UO22+) as well as Tc (as pertechnetate, TcO4−) were found to be sorbed and coprecipitated with amorphous Al and Fe oxyhydroxides at pH below ∼5.5, but slow desorption or dissolution of U and Tc occurred at higher pH values when Na2CO3 was used as the titrant. In general, the precipitation of major cationic species followed the order of Fe(OH)3 and/or FeCo0.1(OH)3.2, Al4(OH)10SO4, MnCO3, CaCO3, conversion of Al4(OH)10SO4 to Al(OH)3,am, Mn(OH)2, Mg(OH)2, MgCO3, and Ca(OH)2. The formation of mixed or double hydroxide phases of Ni and Co with Al and Fe oxyhydroxides was thought to be responsible for the removal of Ni and Co in solution. Results of this study indicate that, although the hydrolysis and precipitation of a single cation are known, complex reactions such as sorption/desorption, coprecipitation of mixed mineral phases, and their dissolution could occur simultaneously. These processes as well as the kinetic constraints must be considered in the design of the remediation strategies and modeling to better predict the activities of various metal species and solid precipitates during pre- and post-groundwater treatment practices.

Review: Magnetite Synthesis using NanoFermentation

Formation of Fe(II)-containing mineral through microbial processes may play an important role in iron and carbon geochemistry in subsurface environments. Fe(III)-reducing bacteria form Fe(II)-containing minerals such as siderite, magnetive, vivianite, and green rust using iron oxides. A psychrotolerant Fe(III)-reducing bacterium,Shewanella alga (PV-4), was used to examine the reduction and biomineralization of a poorly crystalline iron oxide, akaganeite (β-FeOOH), in the absence of a soluble electron shuttle, anthraquinone disulphonate (AQDS), under different atmospheric compositions as well as in HCO3− buffered medium (30 to 210 mM). Iron biomineralization was also examined under different growth conditions such as incubation time, electron donors, and electron acceptors. The Fe(III)-reducing bacterium, PV-4, reduced akaganeite, Fe(III)-citrate, and Co(III)-EDTA using lactate or H2 as an electron donor. The iron biomineralization of Fe(III) oxide, akaganeite—as it undergos reduction by an iron reducing bacterium—is a complex process influenced by biogeochemical factors including microorganisms, bicarbonate buffer concentration, atmospheric composition, electron donors/acceptors, incubation time, and Eh/pH. From this research we found that microorganisms do participate in the formation of diverse iron minerals and that microbial iron biomineralization may affect Fe and C biogeochemistry in subsurface environments.

Biogeochemical dynamics in zero-valent iron columns : Implications for permeable reactive barriers

Although psychophiles, which live in cold conditions (<20°C), are very common amongst a wide variety of habitats, studies of Fe(III) reduction and mineral formation by the microbes are rare. A psychorotolerant Fe(III)-reducing bacterium (W3-6-1,Shewanella baltica) isolated form ocean sediments were used to study iron reduction and mineral formation under various growth conditions. The psychorotolerant bacterium was able to use lactate, formate, and hydrogen as electron donors to reduce iron at temperatures between 0°C and 37°C. The W3-6-1 was also capable of reducing a toxic Co(III)-EDTA as the sole electron acceptor. The atmosphere and chemical conditions exhibited strong influence on the mineral types in an anaerobic culture. Magnetite formation was dominant under N2 and H2 atmospheres. Siderite formation was dominant under an H2−CO2 (20∶80) atmosphere. A mixture of magnetite and siderite was formed under an N2−CO2 (80∶20) atmosphere. This study indicates that microbial Fe(III) reduction may play important roles in iron and carbon fate in cold natural environments on a geological time scale.