Download or read book FINAL REPORT Biogeochemistry of Uranium Under Reducing and Re oxidizing Conditions written by James Amonette and published by . This book was released on 2005 with total page 190 pages. Available in PDF, EPUB and Kindle. Book excerpt: Our understanding of subsurface microbiology is hindered by the inaccessibility of this environment, particularly when the hydrogeologic medium is contaminated with toxic substances. Research in our labs indicated that the composition of the growth medium (e.g., bicarbonate complexation of U(VI)) and the underlying mineral phase (e.g., hematite) significantly affects the rate and extent of U(VI) reduction and immobilization through a variety of effects. Our research was aimed at elucidating those effects to a much greater extent, while exploring the potential for U(IV) reoxidation and subsequent re-mobilization, which also appears to depend on the mineral phases present in the system. In situ coupons with a variety of mineral phases were placed in monitoring wells at the NABIR FRC. These coupons showed that the mineral phase composition significantly affected the resulting attached phase microbial community. Our comparative use of both batch and open flow reactors (more representative of field conditions) indicates that hydrodynamics and continual influx of substrate and contaminants can also yield significantly different results than those obtained with closed serum bottles. To this end, the following overall experimental hypothesis tested was the following: On a mineral surface under anaerobic conditions, accumulations of secondary inorganic precipitates are controlled by a) the bacteria associated with the mineral surface, b) the electron acceptors available for anaerobic bacterial respiration, and c) local hydrodynamics and pH buffers govern micro- and meso-scale interaction of U in the presence of electron donors and acceptors, and nutrients.
Download or read book FINAL REPORT Biogeochemistry of Uranium Under Reducing and Re oxidizing Conditions written by and published by . This book was released on 2005 with total page 190 pages. Available in PDF, EPUB and Kindle. Book excerpt: Our understanding of subsurface microbiology is hindered by the inaccessibility of this environment, particularly when the hydrogeologic medium is contaminated with toxic substances. Research in our labs indicated that the composition of the growth medium (e.g., bicarbonate complexation of U(VI)) and the underlying mineral phase (e.g., hematite) significantly affects the rate and extent of U(VI) reduction and immobilization through a variety of effects. Our research was aimed at elucidating those effects to a much greater extent, while exploring the potential for U(IV) reoxidation and subsequent re-mobilization, which also appears to depend on the mineral phases present in the system. In situ coupons with a variety of mineral phases were placed in monitoring wells at the NABIR FRC. These coupons showed that the mineral phase composition significantly affected the resulting attached phase microbial community. Our comparative use of both batch and open flow reactors (more representative of field conditions) indicates that hydrodynamics and continual influx of substrate and contaminants can also yield significantly different results than those obtained with closed serum bottles. To this end, the following overall experimental hypothesis tested was the following: On a mineral surface under anaerobic conditions, accumulations of secondary inorganic precipitates are controlled by a) the bacteria associated with the mineral surface, b) the electron acceptors available for anaerobic bacterial respiration, and c) local hydrodynamics and pH buffers govern micro- and meso-scale interaction of U in the presence of electron donors and acceptors, and nutrients.
Download or read book Final Report Phase II Biogeochemistry of Uranium Under Reducing and Re oxidizing Conditions written by and published by . This book was released on 2006 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Our understanding of subsurface microbiology is hindered by the inaccessibility of this environment, particularly when the hydrogeologic medium is contaminated with toxic substances. Past research in our labs indicated that the composition of the growth medium (e.g., bicarbonate complexation of U(VI)) and the underlying mineral phase (e.g., hematite) significantly affects the rate and extent of U(VI) reduction and immobilization through a variety of effects. Our research was aimed at elucidating those effects to a much greater extent, while exploring the potential for U(IV) reoxidation and subsequent re-mobilization, which also appears to depend on the mineral phases present in the system. The project reported on here was an extension ($20,575) of the prior (much larger) project. This report is focused only on the work completed during the extension period. Further information on the larger impacts of our research, including 28 publications, can be found in the final report for the following projects: 1) Biogeochemistry of Uranium Under Reducing and Re-oxidizing Conditions: An Integrated Laboratory and Field Study Grant # DE-FG03-01ER63270, and 2) Acceptable Endpoints for Metals and Radionuclides: Quantifying the Stability of Uranium and Lead Immobilized Under Sulfate Reducing Conditions Grant # DE-FG03-98ER62630/A001 In this Phase II project, the toxic effects of uranium(VI) were studied using Desulfovibrio desulfuricans G20 in a medium containing bicarbonate or 1, 4-piperazinediethane sulfonic acid disodium salt monohydrate (PIPES) buffer (each at 30 mM, pH 7). The toxicity of uranium(VI) was dependent on the medium buffer and was observed in terms of longer lag times and in some cases, no measurable growth. The minimum inhibiting concentration (MIC) was 140 M U(VI) in PIPES buffered medium. This is 36 times lower than previously reported for D. desulfuricans. These results suggest that U(VI) toxicity and the detoxification mechanisms of G20 depend greatly on the chemical forms of U(VI) present and the buffer present in a system. Phase II of this project was supported at a cost of $20,575 with most funds expended to support Rajesh Sani salary and benefits. Results have been published in a peer reviewed journal article.
Download or read book Uranium in Plants and the Environment written by Dharmendra K. Gupta and published by Springer. This book was released on 2019-04-25 with total page 253 pages. Available in PDF, EPUB and Kindle. Book excerpt: In recent years, radioactive contamination in the environment by uranium (U) and its daughters has caused increasing concerns globally. This book provides recent developments and comprehensive knowledge to the researchers and academicians who are working on uranium contaminated areas worldwide. This book covers topics ranging from the beginning of the nuclear age until today, including historical views and epidemiological studies. Modelling practices and evaluation of radiological and chemical impact of uranium on man and the environment are included. Also covered are analytical methods used for the determination of uranium in geo/bio environments. Some chapters explore factors which influence uranium speciation and in consequence plant uptake/translocation. Last but not least, several chapters provide approaches and practices for remediation of uranium contaminated areas.
Download or read book Coupling of the Biogeochemical Cycles of Uranium and Manganese written by Zimeng Wang and published by . This book was released on 2013 with total page 264 pages. Available in PDF, EPUB and Kindle. Book excerpt: Organic electron donor stimulated microbial reduction of U(VI) to U(IV) has been proposed as a strategy for the in situ immobilization of uranium contamination in the subsurface. The success of the bioremediation of uranium relies on the stability of the reduced U(IV) species (e.g., UO2) with respect to reoxidation and/or remobilization under groundwater conditions. Manganese is present at appreciable concentrations at several uranium-contaminated sites, and the redox cycling of manganese may significantly impact uranium's fate and transport. The biogeochemical coupling of uranium and manganese involves multiple interaction pathways that occur in the aqueous phase as well as at solid-water interfaces. A mechanistic and quantitative understanding of these processes is needed to establish input parameters for reactive transport models and to enable decision-making for remediation strategies. Coupling of the biogeochemical cycles of uranium and manganese involves various interfacial reactions that occur between UO2 and Mn species of various oxidation states (+IV, +III and +II). This study investigated the physical and chemical factors controlling the interactions between uraninite (UO2) and manganese oxide (MnO2), which are both poorly soluble minerals. A multi-chamber reactor with a permeable membrane was used to simulate a barrier for direct contact of the two solids. The results suggested that an effective redox reaction between UO2 and MnO2 requires physical contact. Continuously-stirred tank reactors (CSTRs) were used to evaluate the dissolution rates of UO2. MnO2 dramatically promoted UO2 dissolution, but the degree of promotion leveled off once the MnO2:UO2 ratio exceeded a critical value. The fate of uranium and manganese after the reaction was investigated by chemical extraction and X-ray absorption spectroscopy (XAS). Substantial amounts of U(VI) and Mn(II) were retained on MnO2 surfaces, and the fate of Mn products may involve Mn(III) phases. A conceptual model was proposed to describe the oxidation of UO2 by MnO2, which is potentially applicable to other environmental redox processes involving two poorly soluble minerals. Although MnO2 can oxidize UO2, the U(VI) produced may not be readily released into the aqueous phase due to its strong adsorption to MnO2. This study integrated batch experiments of U(VI) adsorption to synthetic and biogenic MnO2, surface complexation modeling (SCM), and molecular-scale characterization of adsorbed U(VI) with extended X-ray absorption fine structure (EXAFS) spectroscopy. The surface complexation model incorporated the surface complexes that are consistent with EXAFS analysis, and it could successfully simulate adsorption results over a broad range of pH and dissolved inorganic carbon concentrations. The description of bidentate surface complexes, which are widely observed for contaminant adsorption to metal oxides including the U(VI)-MnO2 system, is a subject with considerable confusion in the literature. Consequently, a critical review was prepared that discussed the theoretical and practical aspects of mass action expressions for bidentate surface complexation reactions. Suggestions were provided for handling bidentate reactions and publishing results without ambiguity or confusion. The effects of soluble Mn species (+III and +II oxidation states) on UO2 dissolution were also investigated. Soluble Mn(III) species were recently identified as important intermediates in Mn biogeochemical cycling. This study evaluated the kinetics of oxidative UO2 dissolution by soluble Mn(III) stabilized by pyrophosphate (PP) and desferrioxamine B (DFOB). The Mn(III)-PP complex was a potent oxidant that induced rapid UO2 dissolution at a rate higher than by a comparable concentration of dissolved O2. However, the Mn(III)-DFOB complex was not able to induce oxidative dissolution of UO2. The potency of Mn(III) with respect to oxidizing UO2 was governed by the identity of the ligand and water chemistry parameters that affect the speciation of the Mn(III). The effect of soluble Mn(II) was more complicated than that of non-redox-active divalent cations (e.g., Ca and Zn). Under anoxic conditions, Mn(II) inhibited UO2 dissolution, which may be attributed to both Mn(II) adsorption to the UO2 surface and precipitation of MnCO3, both of which could decrease the exposure of U(IV) surface sites. In contrast to the anoxic conditions, Mn(II) promoted UO2 dissolution under oxidizing condition. The promotional effect was likely due to Mn redox cycling in which oxidized forms of Mn species were (re)generated as oxidants of UO2 that were more potent than O2. The observed effects of soluble Mn(II, III) species on UO2 dissolution highlighted the need to consider Mn redox intermediates in facilitating electron transfer processes in subsurface biogeochemical cycles.
Download or read book Report of Investigations written by and published by . This book was released on 1970 with total page 490 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Final Report on Recovery of Uranium from Shales written by and published by . This book was released on 1956 with total page 372 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Recovery of Uranium from Saline Solutions by Biological Slimes written by B. B. Ewing and published by . This book was released on 1955 with total page 36 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Water resources Investigations Report written by and published by . This book was released on 1995 with total page 546 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book MESOSCALE BIOTRANSFORMATIONS OF URANIUM IN SEDIMENTS AND SOILS Program Element written by Terry Hazen and published by . This book was released on 2006 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In-situ bioreduction is being considered as a remediation strategy for uranium (U) contaminated sediments because of its potentially low cost, and because short-term studies support its feasibility. However, any in-situ approach for immobilizing U will require assurance of either permanent fixation, or of very low release rates into the biosphere. Our long-term laboratory studies have shown that reoxidation of bioreduced UO{sub 2} can occur even under reducing (methanogenic) conditions sustained by continuous infusion of lactate. The biogeochemical processes underlying this finding need to be understood. Our current research is designed to identify mechanisms responsible for anaerobic U oxidation, and identify effects of key factors controlling long-term stability of bioreduced U. These include: (1) effects of organic carbon (OC) concentrations and supply rates on stability of bioreduced U, (2) influences of pH on U(IV)/U(VI) redox equilibrium, (3) the roles of Fe- and Mn-oxides as potential U oxidants in sediments, and (4) the role of microorganisms in U reoxidation. Findings from some of these studies are summarized here.
Download or read book Biogeochemistry of Uranium Reduction and Reoxidation written by Benjaporn Boonchayaanant and published by . This book was released on 2009 with total page 156 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Biogeochemistry Biophysics Radiobiology and Technical Challenges of Deep Subsurface Research written by Geoffrey Battle Smith and published by Frontiers Media SA. This book was released on 2021-07-02 with total page 141 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Reoxidation of Bioreduced Uranium Under Reducing Conditions written by and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Uranium mining and processing for nuclear weapons and fuel have left thousands of sites with toxic levels of this actinide in soil and ground water. An emerging strategy for remediating such environments involves using organic carbon to promote microbially-mediated reduction and precipitation of insoluble U(IV) minerals. Although previous U bioreduction studies have shown promising results, they were of short duration (up to a few months). Our longer-term (20 months) laboratory study using historically contaminated sediment has alarmingly shown that microbial reduction of U was transient even under reducing (methanogenic) conditions. Uranium was reductively immobilized during the first 100 days, but later (150 to 600 days) reoxidized and mobilized, although a microbial community capable of reducing U(VI) remained through the end of the experiment. The formation of Ca2UO2(CO3)3 complexes (caused by the elevated carbonate concentration from microbial respiration and presence of calcium) drove the U(IV)/U(VI) reduction potential to much more reducing conditions. Fe(III) and Mn(IV) were found to be likely terminal electron acceptors (TEAs) for U reoxidation. Thus, U remediation by organic carbon based reductive precipitation is not sustainable in calcareous, neutral to alkaline soils and ground waters.
Download or read book Reoxidation of Bioreduced Uranium Under Reducing Conditions written by Terry Hazen and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Stimulation of U(VI) bioreduction is becoming an attractive in-situ method for stabilizing U in contaminated sediments. After reduction of U(VI) is completed in sediments, how stable is bioreduced U(IV) upon exposure to oxidizing groundwaters?
Download or read book Final Report written by and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: One strategy to remediate U contamination in the subsurface is the immobilization of U via injection of an electron donor, e.g., acetate, which leads to stimulation of the bioreduction of U(VI), the more mobile form of U, to U(IV), the less mobile form. This process is inevitably accompanied by the sequential reductive dissolution of Mn and Fe oxides and often continuing into sulfate-reducing conditions. When these reducing zones, which accumulate U(IV), experience oxidizing conditions, reduced Fe and Mn can be reoxidized forming Fe and Mn oxides that, along with O2, can impact the stability of U(IV). The focus of our project has been to investigate (i) the effects of Mn(II) on the dissolution of UO2 under both reducing and oxidizing conditions, (ii) the oxidative dissolution of UO2 by soluble Mn(III), (iii) the fate of U once it is oxidized by MnO2 in both laboratory and field settings, and (iv) the effects of groundwater constituents on the coupled Mn(II)/U(IV) oxidation process. Additionally, studies of the interaction of Se, found at the DOE site at Rifle, CO, and Mn cycling were initiated to understand if observed seasonal fluctuations of Se and Mn are directly linked and whether any such linkages can affect the stability of U(IV).
Download or read book Reduction and Re oxidation of Soils During and After Uranium Bioremediation Implications for Long Term Uraninite Stability and Bioremediation Scheme Implementation written by John Zachara and published by . This book was released on 2006 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This research focuses on the conditions and rates under which uranium will be remobilized via oxidation after it has been reduced and precipitated biologically, and what factors can contribute to increasing its long-term stability in groundwater after the injection of an electron donor has been discontinued.
Download or read book Mesoscale Biotransformations of Uranium written by Terry C. Hazen and published by . This book was released on 2006 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Bioreduction of U in contaminated sediments is an attractive strategy because of its low cost, and because of short-term studies supporting its feasibility. However, any in-situ immobilization approach for U will require assurance of either permanent fixation, or of very low release rates into the biosphere. Our previous long-term (2 years) laboratory experiments have shown that organic carbon (OC) based U(VI) bioreduction to UO2 can be transient even under sustained reducing (methanogenic) conditions. The biogeochemical processes underlying this finding urgently need to be understood. The current research is designed to identify mechanisms responsible for anaerobic U oxidation, and identify conditions that will support long-term stability of bioreduced U. We are investigating: (1) effects of OC concentration and supply rate on remobilization of bioreduced U, (2) the roles of Fe- and Mn-oxides as potential U oxidants in sediments, and (3) the role of microorganisms in U reoxidation, and (4) influences of pH on U(IV)/U(VI) redox equilibrium.
