Download or read book Fe III Reduction in Clay Minerals and Its Application to Technetium Immobilization written by Deb Prasad Jaisi and published by . This book was released on 2007 with total page 308 pages. Available in PDF, EPUB and Kindle. Book excerpt: The iron redox biogeochemistry, especially in clay minerals, is poorly understood. As a result, applicability of this redox reaction or the products to environmental problems such as remediation of metal contaminants is largely unexplored. This dissertation, therefore, seeks to develop a fundamental understanding of bacterial Fe(III) reduction in clay minerals and reactivity of resulting Fe(II) in reducing and immobilizing technetium (99Tc). The first subproject involves research on iron biogeochemistry in different clay minerals [nontronite (NAu-1, NAu-2), Muloorina illite (Mu-Il) and chlorite (CCa-2)]. The results reveal that the extent of Fe(III) reduction depends on the difference in the crystal structure, layer charge and Fe(III) content. Among different Fe(III) species, Fe(III) in the tetrahedral site is the most reducible and that in the cis-octahedral sites the least. Fe(II) produced from Fe(III) reduction speciates into four chemical environments in clay minerals: aqueous, structural, complexed to amphoteric surface sites and at exchangeable sites. The Fe(II) sorbed both to cell and mineral surfaces exerts a strong inhibitory effect for further Fe(III) reduction. The interplay of these factors can be modeled by considering the reactive surface site concentration, surface saturation, Fe(II) production and its surface inhibition. The second subproject involves the use of Fe(II), produced from microbial and chemical reduction of Fe(III) in nontronite, for the long-term immobilization of technetium, a significant contaminant in several U.S. DOE sites. The Fe(II) at different chemical environments in reduced nontronite (NAu-2) is found to reduce Tc(VII) into Tc(IV) with the following order of decreasing relative reactivity: Fe(II) at surface complexation sites” Fe(II) at exchangeable sites> Fe(II) at structural sites. EXAFS results suggest that ~70% of Tc(IV) is surface precipitated and the rest forms surface complex with NAu-2. Because the reduced Tc(IV) is associated with clay particle aggregates, it is very recalcitrant to reoxidation in the presence of thermodynamically more favorable electron acceptors/oxidants such as oxygen, nitrate, Fe(III) and Mn(III/IV) oxides. Since the clay aggregates are relatively stable and are less likely perturbed by any transient changes in the aquifer geo-, hydro- and biochemistry, these findings may provide an important step toward the long term immobilization of Tc.

Download or read book Microbial Reduction of Fe III in Multiple Clay Minerals by Shewanella Putrefaciens and Reactivity of Bioreduced Clay Minerals Toward Tc VII Immobilization written by Michael Edward Bishop and published by . This book was released on 2010 with total page 57 pages. Available in PDF, EPUB and Kindle. Book excerpt: The reactivity of clay minerals toward technetium immobilization utilizing a suite of clay minerals ranging from smectite-illite including montmorillonite, nontronite, rectorite, mixed layered I-S (70:30), and illite, with chlorite (ripidolite), and palygorskite common in nature. The clay minerals were characterized utilizing multiple techniques. Fe-Oxides were removed prior to bioreduction using a modified dithionite-citrate-bicarbonate method. Fe (II) in the bioreduced clay minerals is used to reduce Tc(VII) to Tc (IV) in PIPES buffer. In the S:I series, the smectite end member was most effective in reducing Tc (VII) and the illite member the least effective, parallel to the extent and rate of Fe(III) bioreduction of these minerals. For all the clay minerals, the ratio of oxidized Fe(II) to reduced Tc(VII) was ~3.5±0.5. These kinetic results are important for our understanding of how various clay minerals may be used to immobilize heavy metal Tc at DOE contaminated sites.

Download or read book Radioactive Elements Advances in Research and Application 2012 Edition written by and published by ScholarlyEditions. This book was released on 2012-12-26 with total page 209 pages. Available in PDF, EPUB and Kindle. Book excerpt: Radioactive Elements—Advances in Research and Application: 2012 Edition is a ScholarlyEditions™ eBook that delivers timely, authoritative, and comprehensive information about Radioactive Elements. The editors have built Radioactive Elements—Advances in Research and Application: 2012 Edition on the vast information databases of ScholarlyNews.™ You can expect the information about Radioactive Elements in this eBook to be deeper than what you can access anywhere else, as well as consistently reliable, authoritative, informed, and relevant. The content of Radioactive Elements—Advances in Research and Application: 2012 Edition has been produced by the world’s leading scientists, engineers, analysts, research institutions, and companies. All of the content is from peer-reviewed sources, and all of it is written, assembled, and edited by the editors at ScholarlyEditions™ and available exclusively from us. You now have a source you can cite with authority, confidence, and credibility. More information is available at http://www.ScholarlyEditions.com/.

Download or read book Mineral Formation by Microorganisms written by Aydin Berenjian and published by Springer Nature. This book was released on 2022-05-07 with total page 388 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book explains how microorganisms play a pivotal role in the formation of biominerals, including carbonates, silicate minerals and oxides. As readers will learn, these minerals may be produced either intracellularly or extracellularly in order to sustain microbial life. Experienced scientists from the field show that some of these biominerals can be produced in an active form, which involves direct enzymatic intervention to form precipitates. In addition, passive mineral formation can be mediated by the presence of dead cells. Readers from Microbiology and Biochemistry will appreciate the thorough coverage on various types of microbial mineral formation and their roles in microbial domains. Furthermore, they will benefit from the authors’ first-hand knowledge regarding common techniques for studying biomineral-producing microorganisms, factors affecting biomineralization, and the use of this process in biotechnological applications.

Download or read book Effects of Redox Cyclings of Iron in Nontronite on Reduction of Technetium written by Junjie Yang and published by . This book was released on 2010 with total page 30 pages. Available in PDF, EPUB and Kindle. Book excerpt: In situ technetium-99 (99Tc) immobilization by Fe(II) associated with clay minerals has been studied and is a potential cost-effective method for Tc remediation at the United States Department of Energy (DOE) sites. Redox cycles are ubiquitous in natural environments, but their effect on Tc reduction and immobilization has not been investigated to date. The objective of this project was therefore to study how multiple cycles of reduction-reoxidation of Fe-containing clay mineral, nontronite, affected its reactivity toward Tc (VII) reduction. Iron-enriched nontronite NAu-2 was used as a model clay mineral. NAu-2 suspension was first bioreduced by Shewanella putrefaciens CN32, which consequently was oxidized by either air or an Fe(II)-oxidizing bacterium Desulfitobacterium frappieri G2. Three cycles of reduction-oxidation were conducted and bioreduced NAu-2 samples from each cycle was collected and used for Tc(VII) reduction. With each redox cycle, an increasing amount of Fe became redox insensitive and accounted for successively lower extent of Fe(III) bioreduction and reoxidation. However, each redox cycle introduced structural alterations and resulted in a small fraction of reductive dissolution. The released Fe(II) from the dissolution was likely adsorbed onto NAu-2 surface sites and more reactive than the majority of biogenic Fe(II) in the nontronite structure. This redistribution of Fe(II) among different sites as a result of redox cycle was responsible for a two-step Fe(II) reoxidation kinetics: rapid reoxidation in the beginning followed by a slow and steady reoxidation over longer time duration. The highly reactive, surface-adsorbed Fe(II) could also account for successively higher initial rate of Fe(II) reoxidation and subsequent Fe(III) reduction with the increased number of cycles. The changes of Fe(II) speciation with Fe redox cycling could also account for the two-step Tc(VII) reduction kinetics. The rapid Tc(VII) reduction rate in the first few hrs may be attributed to a small fraction of highly reactive Fe(II) from NAu-2 surface sites, and more steady Tc(VII) reduction over longer term may be contributed by structural Fe(II). The long term Tc reduction capacity decreased as NAu-2 went through redox cycles, suggesting that nontronite became progressively inactive. These results suggest that Fe redox cycling in the NAu-2 structure plays a significant role in controlling Fe(III) bioreduction/reoxidation kinetics and the reactivity of biogenic Fe(II) toward Tc(VII) reduction. These results are important for our understanding of clay mineral-Tc interaction kinetics for the purpose of heavy metal remediation at DOE contaminated sites.

Download or read book Surface and Interface Chemistry of Clay Minerals written by Robert Schoonheydt and published by Elsevier. This book was released on 2018-11-05 with total page 428 pages. Available in PDF, EPUB and Kindle. Book excerpt: Surface and Interface Chemistry of Clay Minerals, Volume 9, delivers a fundamental understanding of the surface and interface chemistry of clay minerals, thus serving as a valuable resource for researchers active in the fields of materials chemistry and sustainable chemistry. Clay minerals, with surfaces ranging from hydrophilic, to hydrophobic, are widely studied and used as adsorbents. Adsorption can occur at the edges and surfaces of clay mineral layers and particles, and in the interlayer region. This diversity in properties and the possibility to tune the surface properties of clay minerals to match the properties of adsorbed molecules is the basis for study. This book requires a fundamental understanding of the surface and interface chemistry of clay minerals, and of the interaction between adsorbate and adsorbent. It is an essential resource for clay scientists, geologists, chemists, physicists, material scientists, researchers, and students. - Presents scientists and engineers with a resource they can rely on for their own research and work involving clay minerals - Includes an in-depth look at ion exchange, adsorption of inorganic and organic molecules, including polymers and proteins, and catalysis occurring at the surfaces of clay minerals - Includes materials chemistry of clay minerals with chiral clay minerals, optical materials and functional films

Download or read book Spectroscopic Evidence for Interfacial Fe II Fe III Electron Transfer in Clay Minerals written by and published by . This book was released on 2010 with total page 122 pages. Available in PDF, EPUB and Kindle. Book excerpt: Although interfacial electron transfer has been shown to occur for sorbed Fe(II) and Fe-oxides, it is unclear if a similar reaction occurs between sorbed Fe(II) and Fe(III)-bearing clay minerals. Here, we use the isotope specificity of 57Fe Mössbauer spectroscopy to demonstrate electron transfer between sorbed Fe(II) and structural Fe(III) in a nontronite clay mineral (NAu-2). Appearance of an Fe(II) doublet in the NAu-2 spectra after reaction with aqueous 56Fe(II) (56Fe is transparent in Mössbauer spectra) provided evidence for reduction of structural Fe(III). Mössbauer spectra using enriched 57Fe(II) reveal that Fe(II) is oxidized upon sorption to NAu-2, and the oxidation product of this reaction is a ferric oxide with spectral parameters similar to lepidocrocite. The reduction of structural Fe(III) by Fe(II) induces electron delocalization in the clay structure, which we observe by variable-temperature Mössbauer spectra and macroscopic color change indicative of Fe(II)-Fe(III) pairs. The extent of structural Fe(III) reduction in NAu-2 is equal to the amount of Fe(II) sorbed until approximately 15% reduction, after which point reduction is no longer concomitant with the amount of sorbed Fe(II).

Download or read book Iron in Soils and Clay Minerals written by J.W. Stucki and published by Springer. This book was released on 1988 with total page 924 pages. Available in PDF, EPUB and Kindle. Book excerpt: Proceedings of the NATO Advanced Study Institute, Bad Windsheim, Germany, July 1-13, 1985

Download or read book Oxidation reduction Mechanisms in Iron bearing Phyllosilicates written by J. W. Stucki and published by . This book was released on 1993 with total page 12 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Biogeochemical Coupling of Fe and Tc Speciation in Subsurface Sediments written by Steve M. Heald and published by . This book was released on 2006 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The overall project has been investigating the reactivity of pertechnetate [Tc(VII)] with Fe(II) forms in model mineral and mineral-microbe systems, and with sediments from the Oak Ridge FRC and the Hanford site. Past project results with Hanford and Oak Ridge sediments have been published in Fredrickson et al., (2004) and Kukkadapu et al., (2006). This poster summarizes a series of model system experiments that investigates whether microbes or biogenic Fe(II) were more important in the reduction of Tc(VII) in an anoxic suspension of ferrihydrite, Shewanella oneidensis MR-1, Tc(VII), and electron donor. Ferrihydrite is used to represent a bioavailable Fe(III) oxide present in small amounts in Oak Ridge and Hanford sediments. In order to address this overall goal, Tc(VII) reduction rates and redox products were studied in less complex systems where individual abiotic and biotic reactions were isolated for rigorous characterization. The specific objectives of the individual experiments in the series were as follows: (1) Identify the rates and products of the reaction of Tc(VII) with aqueous Fe(II) at circumneutral pH values (homogeneous reduction). (2) Identify the rates and products of the reaction of Tc(VII) with surface complexed Fe(II) on goethite and hematite in the circumneutral pH range (heterogeneous reduction). (3) Identify the rates and products of the reaction of Tc(VII) with MR-1 under anoxic conditions individually with hydrogen and lactate as electron donors (biologic reduction). (4) Use insights from the above experiments to determine which of the three above, potentially parallel reactions determine the final speciation of Tc in a mixture of ferrihydrite, respiring MR-1, and Tc(VII).

Download or read book The Reduction of Structural Iron in Feruginous Smectite Via the Amino Acid Cysteine written by Keith David Morrison and published by . This book was released on 2010 with total page 142 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Comprehensive Biotechnology written by and published by Newnes. This book was released on 2011-08-26 with total page 5304 pages. Available in PDF, EPUB and Kindle. Book excerpt: The second edition of Comprehensive Biotechnology, Six Volume Set continues the tradition of the first inclusive work on this dynamic field with up-to-date and essential entries on the principles and practice of biotechnology. The integration of the latest relevant science and industry practice with fundamental biotechnology concepts is presented with entries from internationally recognized world leaders in their given fields. With two volumes covering basic fundamentals, and four volumes of applications, from environmental biotechnology and safety to medical biotechnology and healthcare, this work serves the needs of newcomers as well as established experts combining the latest relevant science and industry practice in a manageable format. It is a multi-authored work, written by experts and vetted by a prestigious advisory board and group of volume editors who are biotechnology innovators and educators with international influence. All six volumes are published at the same time, not as a series; this is not a conventional encyclopedia but a symbiotic integration of brief articles on established topics and longer chapters on new emerging areas. Hyperlinks provide sources of extensive additional related information; material authored and edited by world-renown experts in all aspects of the broad multidisciplinary field of biotechnology Scope and nature of the work are vetted by a prestigious International Advisory Board including three Nobel laureates Each article carries a glossary and a professional summary of the authors indicating their appropriate credentials An extensive index for the entire publication gives a complete list of the many topics treated in the increasingly expanding field

Download or read book An Electron optical Investigation of Soil Clay Minerals and Soil Stabilizing Agent Reactions written by P. Michael Terlecky and published by . This book was released on 1975 with total page 44 pages. Available in PDF, EPUB and Kindle. Book excerpt: Characterization of reference clay mineral standards was accomplished by use of the scanning electron microscope (SEM), X-ray diffraction, and energy dispersive X-ray analysis. Experiments were conducted to determine the reactions between these clay minerals and lime which was used as a soil stabilizing agent. Examination of clay minerals visually by use of the SEM offers a partial examination of the irreactivity with soil stabilizing agents. Both surface area and surface roughness increase while there is an apparent decrease in the crystallinity of the clay minerals examined in the following order; Kaolinite group, Illite group, and Montmorillonite group. Reactions were studied of several soil clay minerals with various proportions of Ca(OH)2 and both with and without contact with the air. The major product of the reactions is calcite with smaller amounts of the material 3CaO . Al2O3 . CaCO3 . LlH2O. Scanning electron microscopy of the reacted materials shows a rough, 'corroded' surface on the clays as well as the formation of small single crystals of calcite and Ca(OH)2. Experimental studies showed that the problems of swelling soils can be alleviated by a double application Ca(OH)2 under proper moisture conditions. (Author).

Download or read book Electron Transfer and Atom Exchange Between Aqueous Fe II and Structural Fe III in Clays Role in U and Hg II Transformations written by and published by . This book was released on 2016 with total page 14 pages. Available in PDF, EPUB and Kindle. Book excerpt: During this project, we investigated Fe electron transfer and atom exchange between aqueous Fe(II) and structural Fe(III) in clay minerals. We used selective chemical extractions, enriched Fe isotope tracer experiments, computational molecular modeling, and Mössbauer spectroscopy. Our findings indicate that structural Fe(III) in clay minerals is reduced by aqueous Fe(II) and that electron transfer occurs when Fe(II) is sorbed to either basal planes and edge OH-groups of clay mineral. Findings from highly enriched isotope experiments suggest that up to 30 % of the Fe atoms in the structure of some clay minerals exhanges with aqueous Fe(II). First principles calculations using a small polaron hopping approach suggest surprisingly fast electron mobility at room temperature in a nontronite clay mineral and are consistent with temperature dependent Mössbauer data Fast electron mobility suggests that electrons may be able to conduct through the mineral fast enough to enable exchange of Fe between the aqueous phase and clay mineral structure. over the time periods we observed. Our findings suggest that Fe in clay minerals is not as stable as previously thought.

Download or read book Program and Abstracts for Clay Minerals Society Annual Meeting written by Clay Minerals Society. Annual Meeting and published by . This book was released on with total page 192 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Iron Reduction and Radionuclide Immobilization written by and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Our research focused on (1) microbial reduction of Fe(III) and U(VI) individually, and concomitantly in natural sediments, (2) Fe(III) oxide surface chemistry, specifically with respect to reactions with Fe(II)and U(VI), (3) the influence of humic substances on Fe(III) and U(VI) bioreduction, and on U(VI) complexation, and (4) the development of reaction-based reactive transport biogeochemical models to numerically simulate our experimental results. We have continued our investigations on microbial reduction of Fe(III) oxides. Modeling our earlier experimental results required assumption of a hydrated surface for hematite, more reactive than predicted based on theoretical solubility (Burgos et al. 2002). Subsequent studies with Shewanella putrefaciens and Geobacter sulfurreducens confirmed the rates of Fe(III) bioreduction depend on oxide surface area rather than oxide thermodynamic properties (Roden,2003a, b;2004; Burgos et al,2003). We examined the potential for bioreduction of U(VI) by Geobacter sulfurreducens in the presence of synthetic Fe(III) oxides and natural Fe(III) oxide-containing solids (Jeon et al,2004a, b) in which more than 95% of added U(VI) was sorbed to mineral surfaces. The results showed a significant portion of solid-associated U(VI) was resistant to both enzymatic and abiotic (Fe(II)-driven) reduction, but the rate and extent of bioreduction of U(VI) was increased due to the addition of anthraquinone-2,6-disulfonate (AQDS). We conducted long-term semicontinuous culture and column experiments on coupled Fe(III) oxide/U(VI) reduction. These experiments were conducted with natural subsurface sediment from the Oyster site in Virginia, whose Fe content and microbial reducibility are comparable to ORNL FRC sediments (Jeon et al, 2004b). The results conclusively demonstrated the potential for sustained removal of U(VI) from solution via DMRB activity in excess of the U(VI) sorption capacity of the natural mineral assemblages. Jang (2004) demonstrated that the hydrated surface of nano-particles of hematite (prepared according to well-cited recipes and confirmed to be 100% hematite by Mossbauer spectroscopy and XRD) exhibited the solubility of hydrous ferric oxide (HFO). Jang (2004) also demonstrated that the sorptive reactivity of hematite and HFO were identical except for different specific surface area and pHzpc, and that the reduction of U(VI) by sorbed Fe(II) in the presence of the two phases was also similar in spite of theoretical predictions of large differences in Nernst potential. These results are consistent with the modeling of hematite bioreduction experiments where the thermodynamic potential of hematite had to be adjusted to represent a more disordered surface phase in order to accurately model bioreduction kinetics (Burgos et al, 2002, 2003). We have demonstrated that humic substances enhance solid-phase Fe(III) bioreduction via both electron shuttling and Fe(II) complexation(Royer et al, 2002a, b). We have found that humic substances were shown to inhibit the bioreduction of dissolved U(VI) and that soluble humic-U(IV) complexes were likely formed (Burgos et al, 2004). Kirkham (2004) measured and modeled complexation of U(VI) by humic substances as a function of pH, pCO2, U(VI) concentration, and humic concentration, and demonstrated that humic substances can complex U(VI) even at neutral pH values and in the presence of high (ca. 30 mM) carbonate concentrations. Jang(2004) measured the abiotic reduction of U(VI) by Fe(II) sorbed to Fe(III) oxides in the presence/absence of humic substances and demonstrated that humic substances inhibited the heterogeneous reduction of U(VI). We have recently developed, validated, and documented a series of diagonalized reaction-based reactive transport computer models (HYDROGEOCHEM; Yeh et al,2004a, b). We demonstrated that parallel kinetic reactions could be modeled if separate experiments are used to independently measure each contributing kinetic reaction (Burgos et al, 2003). We have demonstrated the use of a reaction-based reactive transport model (HYDROGEOCHEM) for the simulation of biological iron reduction in natural sediment columns (Burgos and Yeh, unpublished results). Finally, we have developed a preliminary reaction-based model of coupled Fe(III) oxide/U(VI) reduction that has been employed in numerical simulations of U(VI) bioreduction in bench-scale (Roden, 2003d) and field-scale (Roden and Scheibe, 2003;Roden, 2003c) systems.

Download or read book Cementitious Materials for Nuclear Waste Immobilization written by Rehab O. Abdel Rahman and published by John Wiley & Sons. This book was released on 2014-08-28 with total page 245 pages. Available in PDF, EPUB and Kindle. Book excerpt: Cementitious materials are an essential part in any radioactive waste disposal facility. Conditioning processes such as cementation are used to convert waste into a stable solid form that is insoluble and will prevent dispersion to the surrounding environment. It is incredibly important to understand the long-term behavior of these materials. This book summarises approaches and current practices in use of cementitious materials for nuclear waste immobilisation. It gives a unique description of the most important aspects of cements as nuclear waste forms: starting with a description of wastes, analyzing the cementitious systems used for immobilization and describing the technologies used, and ending with analysis of cementitious waste forms and their long term behavior in an envisaged disposal environment. Extensive research has been devoted to study the feasibility of using cement or cement based materials in immobilizing and solidifying different radioactive wastes. However, these research results are scattered. This work provides the reader with both the science and technology of the immobilization process, and the cementitious materials used to immobilize nuclear waste. It summarizes current knowledge in the field, and highlights important areas that need more investigation. The chapters include: Introduction, Portland cement, Alternative cements, Cement characterization and testing, Radioactive waste cementation, Waste cementation technology, Cementitious wasteform durability and performance assessment.