The oxidation characteristics of iron droplets and a range of binary iron alloy droplets have been investigated at 1600°C. The droplets were generated by a novel technique of melting the iron or iron-alloy, in the form of wire, in a levitation coil. The droplets were held for several minutes in hydrogen prior to releasing them into a mass transfer column separated from the levitation chamber by a thin plastic film. The oxidised droplets were quenched. The oxidising or reducing characteristics of various quenching media were investigated and silicone oil was selected as the quenchant. Pure iron and a range of iron-manganese, iron-chromium and iron-silicon alloys were investigated. Whereas the iron-manganese system showed increasing oxygen pick-up with increasing manganese content, the iron-chromium and iron-silicon systems showed an inversion in oxidation behaviour after an initial increase in oxidation rate. The oxidation characteristics of these systems have been related to the surface morphology of the droplets as revealed by Scanning Electron Microscopy and to SIMS analysis of the thin surface oxide films, and mechanisms are proposed for each system. A mathematical model has been developed which simulates the mass transfer of oxygen by forced convection to an accelerating molten iron droplet. The model generates an almost linear oxidation rate for iron, for the period of flight of the droplet and is in good agreement with the experimental work when the model is compensated for circulation within the droplet. The model predicts that temperature has a minimal effect on oxidation rate whereas droplet size is of major importance. Both of these effects were confirmed by the experimental studies. The roles of the alloying elements in relation to the characteristics of oxide films reduced in hydrogen at 1150°C have also been considered. Reduction mechanisms are postulated to account for the morphology of the reduced droplets and the final oxygen levels in the droplets.

Flux of ferrous iron (FeII) to the estuarine environment, whether from bottom sediments or via groundwater seepage, has been identified as a potentially important source of iron required for the development and sustenance of nuisance blooms of the toxic cyanobacteria Lyngbya majuscula in Moreton Bay, Queensland. However the rapid oxidation of FeII in seawater imparts importance to the resultant form of ferric iron (FeIII). Oxidation of FeII in the presence of natural organic matter (NOM) results in a mixture of FeIII-NOM complex and amorphous ferric oxides (AFO). The fate of these oxidation products has implications for the supply of iron to L. majuscula where transformations over time scales of hours are likely to be important. In this thesis the process of oxidation of FeII in seawater in the presence of NOM and the subsequent transformations of the products of oxidation are investigated. UV and visible spectroscopic techniques were used to monitor the production of organically complexed FeIII for both NOM and a model organic compound. Kinetic modelling of data facilitated the examination of key reactions, especially those involving AFO. Controls on the reactivity and aging of AFO were investigated using two different dissolution reactions to measure reactivity. Light scattering techniques were used to probe the structure of AFO and X-ray absorption spectroscopy was used to examine the coordination environment of Fe centres within AFO. Analysis of a kinetic model of iron transformations parameterised using the best available knowledge revealed large uncertainty surrounding the role of ligand classes in complex formation and dissociation and the role of AFO in both formation of oxidation products and the subsequent decay of organically complexed FeIII. Laboratory studies demonstrated that, within a wide range of initial concentrations, unstable mixtures of FeIII-NOM and AFO are produced from the oxidation of FeII in seawater containing NOM and that the organic complexes immediately commence transformation to AFO. Simulation using numerical kinetic modelling of the processes investigated indicated that AFO has a significant role in the processes of formation of oxidation products and dissociation of organically complexed FeIII. The rapid aging that AFO was recognised to undergo was successfully incorporated into the model though whether the aging was due toeither 1) increased coordination of Fe centres or 2) decreased Fe centre accessibility due to aggregation could not be ascertained from the model results. However, together with information regarding the coordination environment of the Fe centres and the particle and fractal structure of the aggregates, aggregation was considered most likely to be the factor responsible for the observed and modelled decreases in AFO reactivity.

Flux of ferrous iron (FeII) to the estuarine environment, whether from bottom sediments or via groundwater seepage, has been identified as a potentially important source of iron required for the development and sustenance of nuisance blooms of the toxic cyanobacteria Lyngbya majuscula in Moreton Bay, Queensland. However the rapid oxidation of FeII in seawater imparts importance to the resultant form of ferric iron (FeIII). Oxidation of FeII in the presence of natural organic matter (NOM) results in a mixture of FeIII-NOM complex and amorphous ferric oxides (AFO). The fate of these oxidation products has implications for the supply of iron to L. majuscula where transformations over time scales of hours are likely to be important. In this thesis the process of oxidation of FeII in seawater in the presence of NOM and the subsequent transformations of the products of oxidation are investigated. UV and visible spectroscopic techniques were used to monitor the production of organically complexed FeIII for both NOM and a model organic compound. Kinetic modelling of data facilitated the examination of key reactions, especially those involving AFO. Controls on the reactivity and aging of AFO were investigated using two different dissolution reactions to measure reactivity. Light scattering techniques were used to probe the structure of AFO and X-ray absorption spectroscopy was used to examine the coordination environment of Fe centres within AFO. Analysis of a kinetic model of iron transformations parameterised using the best available knowledge revealed large uncertainty surrounding the role of ligand classes in complex formation and dissociation and the role of AFO in both formation of oxidation products and the subsequent decay of organically complexed FeIII. Laboratory studies demonstrated that, within a wide range of initial concentrations, unstable mixtures of FeIII-NOM and AFO are produced from the oxidation of FeII in seawater containing NOM and that the organic complexes immediately commence transformation to AFO. Simulation using numerical kinetic modelling of the processes investigated indicated that AFO has a significant role in the processes of formation of oxidation products and dissociation of organically complexed FeIII. The rapid aging that AFO was recognised to undergo was successfully incorporated into the model though whether the aging was due toeither 1) increased coordination of Fe centres or 2) decreased Fe centre accessibility due to aggregation could not be ascertained from the model results. However, together with information regarding the coordination environment of the Fe centres and the particle and fractal structure of the aggregates, aggregation was considered most likely to be the factor responsible for the observed and modelled decreases in AFO reactivity.

The mobility of trace metals and radionuclides released into aquatic and terrestrial environments by mining, industrial processes, and municipal waste disposal practices is an area that deserves significant scientific, public health, and regulatory attention. Indirect microbial interaction offers one potential mechanism for immobilizing these contaminants. For example, many metals, such as uranium and chromium, are less soluble once bound as iron oxide precipitates, thus inhibiting the spread of soluble heavy metals and radionuclides within groundwater and halting them from contaminating additional areas. Microbial iron oxidation is known to contribute to the immobilization of heavy metals and radionuclides in contaminated sites. A safe, cost-effective decontamination method for these materials is the association of radionuclides with iron oxides formed via microbial pathways, thus precipitating them out of solution and providing a promising technique for in situ bioremediation. Nitrate-dependent iron-oxidizing bacteria have been shown to play an important role in the retention of soluble uranium by forming iron oxides that absorb onto soluble U(VI) particles, rendering them immobile as U(VI)-iron oxides. Dechloromonas aromatica strain RCB is a β-proteobacterium that has been cultured and extensively studied in our laboratory and is capable of reducing perchlorate and anaerobically oxidizing benzene, humic acids, and ferrous iron. In addition, a newly-isolated β-proteobacterium, Diaphorobacter sp. strain TPSY, is of interest due to its ability to anaerobically oxidize humic acids, uranium, and ferrous iron. Thus, these two strains have enormous bioremediative potential and are prime candidates for in situ bioremediation. Microarray analysis was used to identify genes induced under iron-oxidizing conditions and RNA dot blotting was used to confirm mRNA expression in D. aromatica. As a follow-up, RNA arbitrarily primed (RAP)-PCR, a method used to randomly reverse-transcribe RNA into cDNA, was also used to identify expression that might not have been observed in the microarray. Genes that were identified from both microarray and RAP-PCR experiments include several hypothetical proteins, lipoproteins, and transmembrane proteins located in major operons, as well as genes annotated as signal transduction enzymes, c-type cytochromes, and proteins involved in chemotaxis, flagellar, and pilus development. Suicide vectors were used to create deletion mutations targeting the genes of interest. Additionally, transposon mutagenesis was used in Diaphorobacter sp. TPSY to identify any potential iron-oxidizing mutants. Out of seven TPSY mutants deficient in iron oxidation, four were identified as genes that encode an inner membrane protein, a signal transduction protein, a putative lipoprotein downstream of a cytochrome c, and a regulatory DNA-binding protein. Mutants were confirmed for their inability to oxidize iron by measuring Fe(II) concentrations over time with a ferrozine assay. The identification of genes involved in microbial anaerobic nitrate-dependent iron oxidation will prove to be a valuable asset when designing and assessing bioremediative strategies.

No description available.

No description available.

abstract: Many acidic hot springs in Yellowstone National Park support microbial iron oxidation, reduction, or microbial iron redox cycling (MIRC), as determined by microcosm rate experiments. Microbial dissimilatory iron reduction (DIR) was detected in numerous systems with a pH < 4. Rates of DIR are influenced by the availability of ferric minerals and organic carbon. Microbial iron oxidation (MIO) was detected from pH 2 – 5.5. In systems with abundant Fe (II), dissolved oxygen controls the presence of MIO. Rates generally increase with increased Fe(II) concentrations, but rate constants are not significantly altered by additions of Fe(II). MIRC was detected in systems with abundant ferric mineral deposition. The rates of microbial and abiological iron oxidation were determined in a variety of cold (T= 9-12°C), circumneutral (pH = 5.5-9) environments in the Swiss Alps. Rates of MIO were measured in systems up to a pH of 7.4; only abiotic processes were detected at higher pH values. Iron oxidizing bacteria (FeOB) were responsible for 39-89% of the net oxidation rate at locations where biological iron oxidation was detected. Members of putative iron oxidizing genera, especially Gallionella, are abundant in systems where MIO was measured. Speciation calculations reveal that ferrous iron typically exists as FeCO30, FeHCO3+, FeSO40 or Fe2+ in these systems. The presence of ferrous (bi)carbonate species appear to increase abiotic iron oxidation rates relative to locations without significant concentrations. This approach, integrating geochemistry, rates, and community composition, reveals biogeochemical conditions that permit MIO, and locations where the abiotic rate is too fast for the biotic process to compete. For a reaction to provide habitability for microbes in a given environment, it must energy yield and this energy must dissipate slowly enough to remain bioavailable. Thermodynamic boundaries exist at conditions where reactions do not yield energy, and can be quantified by calculations of chemical energy. Likewise, kinetic boundaries exist at conditions where the abiotic reaction rate is so fast that reactants are not bioavailable; this boundary can be quantified by measurements biological and abiological rates. The first habitability maps were drawn, using iron oxidation as an example, by quantifying these boundaries in geochemical space. / Dissertation/Thesis / Doctoral Dissertation Geological Sciences 2017

Unusual Fe-rich mineral formations were collected from the Calvert Cliffs area of Maryland. Surficial features such as wire-like filaments and columnar “chimneys” indicated a potential biological origin for the samples. Reference samples were collected from an Fe-rich acid mine drainage site near Carbondale, IL to serve as a comparison. The Chesapeake Bay samples were subjected to X-ray diffraction analysis, Scanning Electron Microscope-Electron Dispersive Spectroscopy analysis and Next-Generation Sequencing microbial assay. Minor ferrihydrite in the surficial wires and extensive microcrystalline goethite throughout the rest of the samples indicates a relatively recent origin. The small particle size and unusual microscale morphologies of iron (oxy)hydroxides and the presence of birnessite suggest that microbial metabolism was involved in the formation of these Fe minerals. EDS data indicate a strong relationship between Fe and C, as well as between Fe and P, while a lack of inorganic phosphate and carbonate minerals also indicates biological input. Genetic analysis reveals distinct internal and external microbial communities and the most common taxon within the sample interior was a novel bacterial phylum, indicating the mineralization may be a product of previously undescribed metabolic pathways. The presence of SO4- reducing, nitrogen-reducing and Fe-oxidizing bacteria as described by NGS analysis lends support to a microbially-mediated origin. Microbially driven oxidation of Fe and minor Mn into metal hydroxides is the proposed formation mechanism.

The sandstone-hosted McArthur River Zone 4 U ore body and alteration system, located in the Athabasca Basin, are the focus of a detailed mineralogical and geochemical study aimed at reconstructing its evolution. The oxidation state of Fe in clay alteration from Zone 4 is measured using 57Fe Mössbauer spectroscopy and compared with other mineralized and barren sandstone-hosted alteration systems in the Athabasca Basin. The aim is to ascertain the role of Fe in forming U deposits and determine whether Fe oxidation state in alteration minerals can indicate proximity to mineralization. At Zone 4, early diagenetic kaolin is overprinted by zones of dravite, illite, chlorite, and late kaolinite forming around the P2 fault. Uranium mineralization occurred at ca. 1600 Ma and was triggered by mixing between oxidizing U-bearing basinal fluids and reducing basement-modified basinal fluids, the latter forming when basinal fluids interacted with basement lithologies. Early pre-ore silicification in the lower 200 metres of the Manitou Falls Formation above the ore body created favourable conditions for mineralization by focusing basinal fluids into the reduction site and enhancing ore preservation. However, it obstructed the post-ore migration of radiogenic Pb and U pathfinder elements from the deposit and limited the extent of hydrothermal sudoite alteration in the overlying strata. Sandstone-hosted alteration systems in the Athabasca Basin are commonly surrounded by an outer illite and an inner chlorite zone. Illites have high Fe3+/ƩFe ratios characteristic of formation from oxidizing basinal fluids, whereas, chlorites have lower and more varied Fe3+/ƩFe ratios, reflecting their origin from reducing, Fe2+-bearing basement-derived fluids having undergone variable mixing with oxidizing basinal fluids. Chlorites in mineralized systems where fluid-mixing occurred, such as at McArthur River Zone 4 and Maurice Bay, record higher Fe3+/ƩFe ratios than barren systems where fluid-mixing did not, such as at Wheeler River Zone K and Spring Point. The scarcity of U-bearing basinal fluids available for mixing with Fe2+-bearing basement fluids is a critical geochemical factor precluding mineralization in barren sandstone-hosted systems. The Fe3+/ƩFe ratio of chlorites has potential applications for discriminating barren and mineralized systems and as spatial vectors to ore when coupled with Pb isotope ratios. / Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2012-11-01 14:08:33.51

Neste trabalho, foi estudado a oxidação do ferro com vapor d\'água em forno elétrico, para a produção de gás hidrogênio. Partindo-se da revisão bibliográfica, escolheu-se o ferro devido suas propriedades e por apresentar um bom rendimento, além disso o ferro é um material barato e abundante. Na estudo experimental foi três experimentos diferentes. No primeiro, o ferro foi oxidado em forno elétrico em temperaturas de 600 a 1000ºC, variando a cada 100ºC, e tempo fixado em 3 horas. Na segunda série de experimento, foi fixado a temperatura em 800ºC e variou a duração do processo de oxidação de 1 a 4 horas, com variação de 1 hora. E na terceira série de experimentos foi realizado a análise termogravimétrica para avaliação da cinética química do processo de oxidação. Os resultados dos experimentos indicaram a produção de gás hidrogênio em quantidades maiores em temperatura de 1000ºC. Além disso foi possível observar que a taxa de oxidação do ferro é maior durante a primeira hora de ensaio. A estimativa de hidrogênio produzido é de 0,9549 g/min -m2 em oxidação a 1000ºC. Já nos resultados da termogravimetria foi obtido a energia de ativação de 147 kJ/mol. / In this work was studied the oxidation of iron by steam in the electric furnace to produce hydrogen. The first step was the literature review and iron oxide was chose to be oxidized, due to its characteristics and good yield. Furthermore, the iron is a cheap and abundant in the earth. In the experimental studies was conducted three different experiments. The First one, the iron was oxidized in the electric furnace in the temperature range of 600 - 1000ºC with a variation of 100ºC and the oxidation time was fixed in 3 hours. The second experiment was conducted with fixed temperature of 800ºC and varied the oxidation time, the range of time was from 1 to 4 hours with a variation of 1 hour. The third experiment was the thermogravimetric analysis to study the chemical kinetics, with three different temperature, 600, 800 and 1000ºC. The result of studies showed that a high temperature the hydrogen production increased and decreased with low temperature. Furthermore, the high oxidation rate was observed in the first hour of the experiment. The hydrogen production was estimated in 0.9549 g/min - m2 at 1000ºC. Another result was the activation energy Ea= 147 kJ/mol.