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1
Yang, Xiaofang. "Interactions between iron oxides and silicates /." Luleå : Division of Chemistry, Department of Chemical Engineering and Geosciences, Luleå University of Technology, 2008. http://epubl.ltu.se/1402-1757/2008/31/.
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2
Leake, Thomas Russell. "Zinc removal using biogenic iron oxides." Pullman, Wash. : Washington State University, 2009. http://www.dissertations.wsu.edu/Thesis/Fall2009/T_Leake_120409.pdf.
Testo completoAbstract (sommario):
Thesis (M.S. in enviromental engineering)--Washington State University, December 2009.<br>Title from PDF title page (viewed on Jan. 28, 2010). "Department of Civil and Environmental Engineering." Includes bibliographical references (p. 27-31).
3
Majzlan, Juraj. "Thermodynamics of iron and aluminum oxides /." For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2002. http://uclibs.org/PID/11984.
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4
Rennert, Thilo. "Sorption of iron cyanide complexes on iron oxides and in soils." [S.l.] : [s.n.], 2002. http://deposit.ddb.de/cgi-bin/dokserv?idn=964937069.
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5
Lee, Sung Oh School of Chemical Engineering & Industrial Chemistry UNSW. "Dissolution of iron oxides by oxalic acid." Awarded by:University of New South Wales. School of Chemical Engineering & Industrial Chemistry, 2005. http://handle.unsw.edu.au/1959.4/23924.
Testo completoAbstract (sommario):
The iron content of industrial minerals can be reduced by physical and chemical processing. Chemical processing is very efficient to achieve a high degree of iron removal at minimum operating cost. Both inorganic acids and organic acids have been used for clay refining. However, due to environmental pollution and contamination of products with the SO42- and Cl-, inorganic acids should be avoided as much as possible. This research investigated the use of oxalic acid to dissolve iron oxides and the dissolution characteristics of natural iron oxides. The dissolution of iron oxides in oxalic acid was found to be very slow at temperatures ranging from 25??? to 60???, but increased rapidly at a temperature above 90oC with increasing oxalic acid concentration, whereas the pH caused the reaction rate to decrease at pH>2.5 and improved the rate from pH 1 to pH 2.5. The iron oxides such as goethite (??-FeOOH), lepidocrocite (??-FeOOH) and iron hydroxide (Fe(OH)3) can be dissolved faster at the presence of magnetite which exhibits an induction period at the initial stage and showed the bell-shaped curves for the dissolution. In titration tests, however, the increase of temperature causes an increase in solubility of the oxalate complexes, resulting in an increased stability of ionized species in solution. During the addition of NaOH, NaHC2O4???H2O was precipitated without forming Na2C2O4???H2O, but it was re-dissolved at pH>4.0. On the other hand with NH4OH, NH4HC2O4???H2O and (NH4) 2C2O4???H2O co-precipitated at pH 0.93, but also re-dissolved at over pH 2.03. The reaction temperature was found not to affect the removal of iron from the ferric oxalate complex solution using lime. Iron is removed as iron hydroxide and calcium oxalate is then precipitated during the iron removal step. The formation of Fe(OH)3 in the solution was affected by the dissociation of Ca(OH)2. The thermodynamics of sodium, ammonium and iron oxalate complexes were investigated and the standard free energy, ??Go was calculated using thermodynamic data and solubility products. The dissolution of pure hematite by oxalate was found to follow a shrinking core model of which the kinetic step of the reaction is the controlled mechanism.
6
Gonzalez, Lucena Fedora. "Mineral magnetism of synthetic microcrystalline and nanophase iron oxides and iron oxyhydroxides." Thesis, University of Ottawa (Canada), 2004. http://hdl.handle.net/10393/26646.
Testo completoAbstract (sommario):
A suite of well-characterized synthetic microcrystalline hematite samples, 2-line and 6-line ferrihydrite samples and nanohematite samples are studied through magnetization-field curves measured at room temperature. The single-domain microcrystalline hematite samples are analyzed through basic hysteresis parameters providing sample characteristics such as magnetic anisotropy information, the effect of annealing on the origin of the magnetization and the relatively constant intrinsic high field susceptibility. The application of a magnetic granulometry method on the magnetic data of the superparamagnetic nanohematite and ferrihydrite samples provides fundamental information such as the intrinsic mass magnetization and estimated particle size. Additionally, it gives insight into possible moment formation mechanisms within the superparamagnetic particles. The observed differences between the magnetic properties of the magnetically blocked and the superparamagnetic samples considered are also discussed.
7
Bertel, Douglas E. "Characterizations of Iron Sulfides and Iron Oxides Associated with Acid Mine Drainage." University of Akron / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=akron1302276664.
Testo completo
8
Ferraioli, C. Christopher. "Nanocrystals, core-shells, and nanocapsules of iron oxide." Click here for download, 2008. http://proquest.umi.com/pqdweb?did=1559855251&sid=1&Fmt=2&clientId=3260&RQT=309&VName=PQD.
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9
Mäkie, Peter. "Surface reactions of Organophosphorus compounds on Iron Oxides." Doctoral thesis, Umeå universitet, Kemiska institutionen, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-53958.
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10
Nadler, Jason Hayes. "The hydrogen reduction of iron and chromium oxides." Diss., Georgia Institute of Technology, 2003. http://hdl.handle.net/1853/19410.
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11
Al-Rawwas, Ahmed Dhofar. "A Mossbauer spectroscopy study of strontium iron oxides." Thesis, University of Liverpool, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385228.
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12
Cordray, Antoine. "Phosphorus removal characteristics on biogenic ferrous iron oxides." Pullman, Wash. : Washington State University, 2008. http://www.dissertations.wsu.edu/Thesis/Fall2008/a_cordray_111708.pdf.
Testo completoAbstract (sommario):
Thesis (M.S. in environmental engineering)--Washington State University, December 2008.<br>Title from PDF title page (viewed on Dec. 23, 2008). "Department of Civil and Environmental Engineering." Includes bibliographical references (p. 69-72).
13
Ayub, Ibrar. "Oxidation and reduction properties of iron-containing oxides." Thesis, n.p, 2001. http://ethos.bl.uk/.
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14
Menting, Victor L. "Solubility Studies of Iron(III) Oxides and Hydroxides." PDXScholar, 1994. https://pdxscholar.library.pdx.edu/open_access_etds/4853.
Testo completoAbstract (sommario):
The hydrolysis of iron(III) ions in aqueous solution forms a series of soluble hydroxide complexes with associated equilibrium constants. The solubility of iron(III) is controlled by the various soluble hydroxide complexes, and can, in theory, be calculated from the pH and equilibrium constants. Experimental verification of the calculated solubility has proven difficult due to the lack of sensitive analytical techniques and the presence of colloidal ferric hydroxide interferences. Recently, electrochemical methods for the determination of low levels of iron(III) have been developed using adsorptive cathodic stripping voltammetry which relies on the interfacial accumulation of the chelate of iron with Solochrome Violet RS on a hanging mercury drop electrode. The purpose of this investigation was to experimentally verify the calculated solubility of iron(III) in the pH 4-12 region using adsorptive cathodic stripping voltammetry. The ubiquitous nature of iron requires background levels of iron be reduced below the experimental concentrations to be determined. Attempts to lower the background levels of iron were ineffective as concentrations below about 10-8M iron could not be attained. Verification of the calculated solubility of iron(III) was unsuccessful as background concentrations of iron(III) and tr.e presence of colloidal ferric hydroxide hindered the experimental results. The dissolution of the ferric hydroxide colloids coupled with the background levels of iron resulted in the determination of experimental concentrations which exceeded theoretical values by two to four orders of magnitude.
15
Meyers, Emily. "Phosphate Cycling in the Presence of Biogenic Iron Oxides and Iron-Reducing Bacteria." Thesis, Université d'Ottawa / University of Ottawa, 2018. http://hdl.handle.net/10393/37306.
Testo completoAbstract (sommario):
Nutrient pollution from industrial activity is an environmental problem that persists in
water bodies near urban settings, and has been a primary contributor to eutrophication,
bacterial contamination, and harmful algal blooms. Biogenic iron oxides offer a
potential solution to the treatment of lakes and rivers containing high concentrations of
phosphate, the limiting nutrient in aquatic systems. Soluble ferrous iron can act as an
electron donor for iron-oxidizing bacteria, which thrive in low-oxygen environments.
This results in the formation of insoluble ferric iron minerals, ideal adsorbents for
negatively charged phosphate. Conversely, iron-reducing bacteria reduce ferric iron to
form ferrous iron, resulting in the formation of secondary minerals depending on the
chemistry of the particular environment.
This project investigates the chemical conditions at which biogenic iron oxides have the
maximum adsorptive capacity, especially with respect to organic carbon content. A
simplified model of natural biogenic iron oxides was synthesized by co-precipitating the
mineral ferrihydrite (a common iron oxide) with the polysaccharide alginate, an
analogue to bacterial exopolysaccharides. At the levels of carbon investigated, organic
matter was not found to affect the adsorptive capacity of iron oxides at the C/Fe ratios
analyzed. Similarly, organic matter did not appear to significantly influence the rate of
reduction of ferrihydrite by the iron-reducing bacterium Shewanella putrefaciens CN32.
Presence of organics did however influence rates of reduction and the mineralogy of the
post-reduction precipitates. Phosphate adsorbed to iron oxides prior to microbial
reduction greatly increased both the rate and the extent of ferric iron reduced, and also
had an impact on the secondary minerals that formed (vivianite, green rust).
An improved understanding of these conditions could contribute to a more efficient
process by which iron-oxidizing bacteria are used for large-scale industrial water
treatment.
16
Messi, C. "Nanostructured catalytic metal oxides supported over oxide supports of various nature : the iron oxide system." Doctoral thesis, Università degli Studi di Milano, 2008. http://hdl.handle.net/2434/57081.
Testo completo
17
Zaki, Aliaa. "A study of thin magnetic films of iron oxides and yttrium iron garnet." Thesis, University of Sheffield, 2018. http://etheses.whiterose.ac.uk/21664/.
Testo completoAbstract (sommario):
The structural, magnetic and magneto-optical properties of iron oxides (wustite, magnetite, Hematite and maghemite), yttrium iron garnet (YIG) and calcium doped YIG (Ca:YIG) thin films prepared by pulsed laser deposition (PLD) technique were studied. The properties of iron oxides films grown on sapphire substrate were found to be dependent on the annealing temperature of the target and the oxygen pressure (PO2) during the ablation. For example, the high annealing temperature of the target and base pressure give wustite, whereas a lower annealing temperature with same oxygen pressure and conditions give magnetite. In addition, the fraction of Fe3+ ions increases with increasing the oxygen pressure, which leads to pure maghemite at PO2 more than 100 mTorr. YIG thin films were grown on gadolinium gallium garnet (GGG) and yttrium aluminium garnet (YAG) substrates. The GGG substrate was found to cause a lower lattice strain (ɛ= 0.016%) in YIG lattice compared to YAG substrates (ɛ=1.12%). The oxygen pressure was also found to affect the magnetic and magneto optical properties of YIG thin films. For example, YIG/GGG films prepared at PO2 =400 mTorr were found to have magnetic properties close to bulk YIG with saturation magnetisation (Ms= 143 emu/cm3) and coercive field (Hc) < 1 Oe. These insights were used to prepare Ca:YIG thin films. The Ca:YIG films showed an increase in the oxygen vacancies, a decrease in Ms and high strain; with increasing the amount of doped Ca+2 ion. It also found that all the Ca:YIG/GGG films contain about 5% Fe2+ at this PO2. For example, the film that contains x=0.05 has a reduction in the magnetisation of about 18% from the pure YIG/GGG thin film. Lower PO2 led to the occurrence of Fe2+ ions in the tetrahedral sites of YIG and increased the oxygen vacancies that reduced Ms.
18
Fernández-Baca, Cristina Paola. "Investigation of the effect of phosphate on iron(ii) sorption to iron oxides." Thesis, University of Iowa, 2010. https://ir.uiowa.edu/etd/497.
Testo completoAbstract (sommario):
Iron is ubiquitous in the environment mostly as stable iron hydr(oxides) such as hematite (α-Fe2O3) and goethite (α-FeOOH). The Fe(II)-Fe(III) redox couple plays a vital role in nutrient cycling, bacteria respiration, and contaminant removal. This redox couple, however, can be affected by external influences such as anion adsorption of sulfate, oxalate, and phosphate which can influence various goethite properties including the point of zero charge. This study attempts to determine the effect of phosphate sorption to a goethite surface and its subsequent influence on Fe(II) sorption. The objectives, specifically, were to quantify phosphate sorption on a goethite surface using colorimetric methods and to use Mössbauer spectrometry to determine if electron transfer occurred after a layer of phosphate was adsorbed to the goethite surface. The hypothesis of this study is as follows: an adsorbed layer of phosphate on a goethite surface will inhibit the electron transfer between the Fe(II) and Fe(III) phases at the surface.
The results of the study showed that phosphate follows typical anion sorption as seen in previous works, where more phosphate sorbed at lower pH values. In addition, with increasing aqueous phosphate concentrations there is increasing phosphate adsorption to the goethite surface. However, phosphate sorption was not significantly affected by reaction time after 20 hours or by changes in Fe(II) concentrations. Fe(II) sorption pH edges showed characteristic cation adsorption, where more Fe(II) sorbed at higher pH values. Fe(II) sorption was not affected by the presence or absence of phosphate, but was affected by an increase in the aqueous Fe(II) concentration. With increased Fe(II) there was a pH edge shift to a higher pH, which is consistent with Ca2+ sorption results on goethite. An Fe(II) isotherm was also conducted and showed that as Fe(II) concentration increased so did Fe(II) sorption, however the isotherm appeared to be approaching a plateau where the goethite surface sites would be saturated, below this limit the surface sites where not saturated.
Mössbauer analysis was conducted on a sample by Drew Latta, spectra showed that electron transfer was still occurring despite the adsorbed phosphate layer, disproving our initial hypothesis. It is possible that a higher concentration of phosphate could inhibit electron transfer, but at 500 μM PO43- and 100 μM Fe(II), electron transfer between the adsorbed Fe(II) and bulk phase Fe(III) still occurred.
19
Handler, Robert Michael Scherer Michelle M. "Still oxides run deep studying redox transformations involving Fe and Mn oxides using selective isotope techniques /." Iowa City : University of Iowa, 2009. http://ir.uiowa.edu/etd/295.
Testo completo
20
Kumar, Arun Gurian Patrick L. "Arsenic removal effectiveness of iron oxide-based fibrous adsorbents and stability of granular iron oxide media /." Philadelphia, Pa. : Drexel University, 2008. http://hdl.handle.net/1860/2929.
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21
Taujale, Saru. "INTERACTIONS BETWEEN METAL OXIDES AND/OR NATURAL ORGANIC MATTER AND THEIR INFLUENCE ON THE OXIDATIVE REACTIVITY OF MANGANESE DIOXIDE." Diss., Temple University Libraries, 2015. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/347169.
Testo completoAbstract (sommario):
Civil Engineering<br>Ph.D.<br>Mn oxides have high redox potentials and are known to be very reactive, rendering many contaminants susceptible to degradation via oxidation. Although Mn oxides typically occur as mixtures with other metal oxides (e.g., Fe, Al, and Si oxides) and natural organic matter (NOM) in soils and aquatic environments, most studies to date have studied the reactivity of Mn oxides as a single oxide system. This study, for the first time, examined the effect of representative metal oxides (Al2O3, SiO2, TiO2, and Fe oxides) and NOM or NOM-model compounds (Aldrich humic acid (AHA), Leonardite humic acid (LHA), pyromellitic acid (PA) and alginate) on the oxidative reactivity of MnO2, as quantified by the oxidation kinetics of triclosan (a widely used phenolic antibacterial agent) as a probe compound. The study also examined the effect of soluble metal ions released from the oxide surfaces on MnO2 reactivity. In binary oxide mixtures, Al2O3 decreased the reactivity of MnO2 as a result of both heteroaggregation and complexation of soluble Al ions with MnO2. At pH 5, the surface charge of MnO2 is negative while that of Al2O3 is positive resulting in intensive heteroaggregation between the two oxides. Up to 3.15 mM of soluble Al ions were detected in the supernatant of 10 g/L of Al2O3 at pH 5.0 whereas the soluble Al concentration was 0.76 mM in the mixed Al2O3 + MnO2 system at the same pH. The lower amount of soluble Al in the latter system is the result of Al ion adsorption by MnO2. The experiments with the addition of 0.001 to 0.1 mM Al3+ to MnO2 suspension indicated the triclosan oxidation rate constant decreased from 0.24 to 0.03 h-1 due to surface complexation. Fe oxides which are also negatively charged at pH 5 inhibited the reactivity of MnO2 through heteroaggregation. The concentration of soluble Fe(III) ions ( 4 mg-TOC/L or [alginate/PA] > 10 mg/L, a lower extent of heteroaggregation was also observed due to the negatively charged surfaces for all oxides. Similar effects on aggregation and MnO2 reactivity as discussed above were observed for ternary MnO2‒Al2O3‒NOM systems. HAs, particularly at high concentrations (2.0 to 12.5 mg-C/L), alleviated the effect of soluble Al ions on MnO2 reactivity as a result of the formation of soluble Al-HA complexes. Alginate and PA, however, did not form soluble complexes with Al ions so they did not affect the effect of Al ions on MnO2 reactivity. Despite the above observations, the amount of Al ions dissolved in MnO2+Al2O3+NOM mixtures was too low, as a result of NOMs adsorption on the surface to passivate oxide dissolution, to have a major impact on MnO2 reactivity. In conclusion, this study provided, for the first time, a systematical understanding of the redox activity of MnO2 in complex model systems. With this new knowledge, the gap between single oxide systems and complex environmental systems is much narrower so that it is possible to have a more accurate prediction of the fate of contaminants in the environment.<br>Temple University--Theses
22
Lafferty, Brandon James. "Methyl arsenic adsorption and desorption behavior on iron oxides." Thesis, Texas A&M University, 2003. http://hdl.handle.net/1969.1/2264.
Testo completoAbstract (sommario):
Arsenic is a toxic element that is widely distributed throughout the earth??s crust as a result of both natural geologic processes and anthropogenic activities. In virtually all environments, methylated forms of arsenic can be found. Because of the widespread distribution and toxicity of arsenic and methyl-arsenic, their adsorption behavior on soil minerals is of great interest. Although considerable attention has been given to the behavior of inorganic arsenic on mineral surfaces, little research has been conducted regarding interactions of the methyl-arsenic forms. The objective of this study was to compare the adsorption and desorption behavior of methylarsonate (MMAsV), methylarsonous acid (MMAsIII), dimethylarsinate (DMAsV), dimethylarsinous acid (DMAsIII), arsenate (iAsV), and arsenite (iAsIII) on iron oxide minerals (goethite and ferrihydrite) by means of adsorption isotherms and adsorption envelopes. Additionally, desorption envelopes were obtained using sulfate and phosphate as competitive ligands. Arsenic was measured by FI-HG-AAS. MMAsV and iAsV were adsorbed in higher amounts than DMAsV on goethite and ferrihydrite at all pH values studied. Although MMAsV and iAsV were adsorbed quantitatively at lower concentrations on goethite and ferrihydrite, as arsenic concentration was increased MMAsV was adsorbed in slightly lower quantities than iAsV. DMAsV was not quantitatively adsorbed at any concentration on goethite or ferrihydrite. MMAsV and iAsV exhibited high adsorption affinities on both goethite and ferrihydrite at pH values below 9 and showed decreasing adsorption above this point (more rapidly for MMAsV). DMAsV was adsorbed only at pH values below 8 on ferrihydrite and below 7 on goethite. MMAsV, iAsV, and DMAsV each exhibited adsorption characteristics suggesting specific adsorption on both goethite and ferrihydrite. Increased methyl substitution resulted in increased ease of arsenic release from the iron oxide surface. MMAsIII and DMAsIII exhibited no evidence for any type of specific adsorption under the conditions studied. Phosphate was a more effective desorbing ion than sulfate, but neither desorbed all arsenic species quantitatively.
23
Tadesse, Behailu. "Iron and manganese oxides in the soil-water environment." Thesis, Brunel University, 1997. http://bura.brunel.ac.uk/handle/2438/6624.
Testo completoAbstract (sommario):
The importance of iron and manganese oxides in soil-water environments and their roles in controlling the availability and mobility of contaminants and nutrients are determined. Sorption is simulated using the synthetic iron and manganese oxides: goethite (a-FeOOH), birnessite (Na4Mn14O27.9H20a) nd magnetite (Fe304) which are analogous to natural soil components. Goethite is investigated in the three possible modes of occurrences in soil: colloidal, aggregate, and as coatings on inert materials. The adsorption of cadmium and cobalt onto goethite occurs in a narrow pH range between 6.5 and 7.5. Metal retention increased with both temperature and contact time. A tenfold decrease in ionic strength has no effect on the adsorption pH. Goethite pellets have a different pattern of adsorption due to reduction in surface area and granulation. The sorbing capacity of goethite coated sand is lower than that of the colloidal goethite but has a similar adsorption curve. The coated material is shown to have potential in industrial applications and notably in effluent treatment. Cobalt and cadmium uptake on to hydrated suspensions of birnessite occur in a pH range (3.0-8.0) with sigmoidal shapes for the percent of adsorption curves. Birnessite uptake capacity increases with increasing pH with a maximum at about 6.4 pH. The pH, contact time and the surface area of the oxide are the main factors that control the uptake. The adsorption of coloured species and organic colloids on magnetite was investigated in which magnetite is used both as an adsorbent and as magnetic material. Colour species and organic colloids adsorbed in acid pH and the adsorption decreases with increasing alkalinity. Dissolutions of the magnetite itself increases in low and high pH conditions. The results of investigations of sorption of contaminants and nutrients onto iron and manganese oxides have been applied to shed light upon the behaviour of contaminants and nutrients in soil in the light of soil resource management. The importance of a detailed understanding of contaminant and nutrient transport behaviour in soil-water systems to achieve effective environmental management is demonstrated. Although soil pollution is of major environmental concern, it is probably the least understood source of pollution in terms of both transport of contaminants and remediation. The studies carried out in this work have indicate the types of information required to permit the development of soil management and remediation protocols that will assist in technical management of issues related to soil resources. Detailed knowledge from experimental work must form the scientific basis for the development of contaminated soil assessment and management in an integrated approach.
24
Falconer, Haley Ryanne Watson. "Column filter studies phosphorus removal using biogenic iron oxides /." Pullman, Wash. : Washington State University, 2009. http://www.dissertations.wsu.edu/Thesis/Fall2009/H_Falconer_100709.pdf.
Testo completoAbstract (sommario):
Thesis (M.S. in environmental engineering)--Washington State University, December 2009.<br>Title from PDF title page (viewed on Jan. 12, 2010). "Department of Civil and Environmental Engineering." Includes bibliographical references (p. 52-53).
25
Carey, Elizabeth A. "Using plug-flow reactors to determine the role of soluble Fe(III) in the cycling of iron and sulfur in salt marsh sediments." Thesis, Available online, Georgia Institute of Technology, 2004:, 2003. http://etd.gatech.edu/theses/available/etd-03292004-141819/unrestricted/carey%5Felizabeth%5Fa%5F200312%5Fms.pdf.
Testo completo
26
Hao, Yalin. "Continuous Hydrothermal Production of Iron Oxide (Fe[subscript 2]0[subscript 3]) and Cobalt Oxide (Co[subscript 3]O[subscript 4])." Thesis, Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/11217.
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27
Kwan, Wai P. (Wai Pang) 1974. "Decomposition of hydrogen peroxide and organic compounds in the presence of iron and iron oxides." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/29585.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2003.<br>Includes bibliographical references.<br>Most advanced oxidation processes use the hydroxyl radical (OH) to treat pollutants found in wastewater and contaminated aquifers because OH reacts with numerous compounds at near diffusion-limited rates. OH can be made by reacting hydrogen peroxide (H202) with either Fe(II) (the Fenton reaction), Fe(1), or iron oxide. This dissertation investigated the factors that influence the decomposition rates of H202 and organic compounds, as well as the generation rate of -OH (VoH), in the presence of dissolved Fe(IH) and iron oxide. The Fe(III)-initiated chain reaction could be the dominant mechanism for the decomposition of H202 and organic compounds. The degradation rates of H14COOH, an OH probe, and H202 were measured in experiments at pH 4 containing either dissolved Fe(III) or ferrihydrite. Combined with the results from experiments using a radical chain terminator, we concluded that a solution chain reaction was important only in the Fe(III) system. In the ferrihydrite system the amount of dissolved Fe was insufficient to effectively propagate the chain reaction. In addition, a nonradical producing H202 loss pathway exists at the oxide surface. The oxidation rate of any dissolved organic compound can be predicted from VOH if the main sinks of -OH in the solution are known. Experiments using H14COOH and ferrihydrite, goethite, or hematite showed that VOH was proportional to the product of the concentrations of surface area and H202. Based on these results, a model was created for predicting the pseudo-first-order oxidation rate coefficients of dissolved organic compounds (korg) in systems containing iron oxide and H202. While our model successfully predicted korg in aquifer sand experiments, it yielded mixed results when compared to measurements from previously published studies.<br>(cont.) Some factors that could have caused the disagreements between model predictions and measurements were examined to refine our model. Results from experiments containing goethite, H 4COOH, and 2-Chlorophenol showed that H 4COOH detected more OH, which is produced at the oxide surface, than did 2-Chlorophenol. This was attributed to electrostatic attraction between the formate anions and the positively charged oxide surface, and could explain why our model, based on H14COOH, overpredicted the korg values of many neutral compounds.<br>by Wai P. Kwan.<br>Ph.D.
28
Man, Vincent. "The characteristics of synthetic and natural hydrous iron oxides in aqueous environments." Thesis, University of Plymouth, 1987. http://hdl.handle.net/10026.1/2188.
Testo completoAbstract (sommario):
The work in this thesis is concerned with the Green Rusts, which are bluegreen metastable Fe(II) - Fe(III) hydroxy compounds incorporating anions such as SO42-, Cl- or CO3-. These Green Rust compounds (or Fe-GR compounds to distinguish them from the aluminium Green Rusts (Al-GRs) which are isostructural Fe(II) - Al(III) hydroxy compounds) can be produced in a consistent fashion from Fe(II) solutions by the method of induced hydrolysis using Fe(III) gel at pH 7 and under anoxic conditions. A series of sulphate and chloride Fe-GR samples were synthesised, and characterised primarily by the analytical techniques of M8ssbauer spectroscopy, X-Ray diffractometry, infra-red spectroscopy, and vacuum microbalance to measure surface area using the BET N2 adsorption method. For comparison, a few samples of the analogous Al-GR compounds were also synthesised and characterised by the analytical techniques mentioned above. The results in this thesis showed that the systems producing the Fe-GR compounds were of a highly complex nature, and that the amount of precipitate formed depended crucially on the starting conditions. For the 0.1 M FeSO4 system, the GR formed was almost always accompanied by a goethite phase while, for the 0.1 M FeC12 system, pure GR material was only formed at initial Fe(II) - Fe(III) ratios (IFFRs) greater than 6. Any-differences between__the, sulphate and chloride Fe-GRs can. be attributed to the difference in anion-type. X-Ray diffraction in conjunction with electron microscopy and surface area measurements confirm-that the Fe-GRs have a pyroaurite crystal structure, with brucite-like layers formed by a matrix of Fe2+ and Fe 3+ cations and each layer bridged to the other by anions. As far as Messbauer spectroscopy is concerned, the most important diagnostic parameter is the quadrupole splitting (QS) of the Fe(II) doublet measured at 77K for the wet, fresh precipitate (i. e. frozen material). For sul phate Fe-GRs derived from 0.1 M FeSO4 the mean QS is 2.93 ± 0.05 mms-', while for the chloride Fe-GRs derived from 0.1 M FeC12 the mean QS is 2.80 ± 0.05 mms-1. Surface areas for the sulphate Fe-GRs are in the range 40-65 m2. g-1. The products of oxidation and ageing for the Fe-GRs indicate several transformation pathways, especially for the chloride Fe-GRs. Sulphate Fe-GRs converted to goethite on oxidation under both wet and dry conditions, while the chloride Fe-GRs converted to akaganeite on dry oxidation, and to lepidocrocite on wet oxidation. Under both wet and dry anoxic conditions, the chloride Fe-GRs converted to magnetite. In the case of the sulphate Fe-GRs, there was a suggestion that, under the right wet anoxic conditions, the material probably transformed into magnetite. These facts clearly demonstrate that the Fe-GRs are intermediaries in the thermodynamic transformation of Fe in the II oxidation state to Fe in the III oxidation state.
29
Teggart, Brian Joseph. "Fabrication, characterisation and magneto-optical enhancement of thin film BiGa : Dy iron garnet." Thesis, Queen's University Belfast, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287432.
Testo completo
30
Chukwuchendo, Emmanuel Chukwunonso. "Bio-oxidation of ferrous iron at low temperature conditions in a packed bed column bioreactors." Thesis, Cape Peninsula University of Technology, 2016. http://hdl.handle.net/20.500.11838/2545.
Testo completoAbstract (sommario):
Thesis (MTech (Chemical Engineering))--Cape Peninsula University of Technology, 2016.<br>The oxidation of microbial ferrous iron is an important sub-process in the bioleaching process. Several studies focussing on microbial ferrous iron oxidation have been investigated and reported in various studies. These studies were carried out using stirred tank bioreactors and shake flasks at optimum conditions. However, these studies could not describe the context of heap bioleach system. Packed column system may describe heap bioleaching, and most studies on microbial ferrous iron oxidation were performed under flooded conditions, which do not represent solution flow dynamics in a heap situation.
Biooxidation of ferrous iron oxidation kinetics of Acidiobacillus ferrooxidans was studied in a packed-bed bioreactor to investigate the kinetics in a system that mimics the solution flow dynamic of a heap bioleach operation at low-temperature conditions. This was done in a batch mode operation, with glass marble (15 mm) as reactor packing. The pH of the bioreactor was maintained at pH 1.35 ± 0.05 and aeration at 500 ml/min. Unstructured models known as Monod and Hansford were used to describe the experimental data in determining the kinetics of bio-oxidation.
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Cerkez, Elizabeth B. "Investigations of Surface Redox Chemistry on Environmentally Relevant Iron Oxides and Sulfides." Diss., Temple University Libraries, 2016. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/383744.
Testo completoAbstract (sommario):
Chemistry<br>Ph.D.<br>Important reactions in the environment often occur at the interface between a mineral surface and aqueous phase. Reactions occurring at this interface often control the uptake or release of harmful components resulting in the geochemical cycling of elements in the environment. Additionally, minerals are commonly used in the remediation of contaminated areas, where similar chemistry occurs at their interfaces. Thus, studies of the chemistry of these interfaces are essential to our understanding of complex environments. Many of these processes are controlled by electron transfer reactions between adsorbates and the mineral interface, and it is here where this research presented will concentrate. The studies in this thesis key in on redox chemistry on various environmentally relevant iron minerals, including ferrihydrite, pyrite, and amorphous iron sulfide. A large portion of this body of work is dedicated to the understanding of the surface mediated reaction between chromate (Cr(VI)) and arsenite (As(III)). Both of these species are present in the environment and are detrimental to human health. Using in- and ex-situ experiments we have monitored the coupled redox transformation of Cr(VI) and As(III) to chromite (Cr(III)) and arsenate (As(V)). Quantum mechanical modeling was used to support the experimental studies of this novel redox chemistry. The reaction was monitored in situ, using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), on the surface of the iron oxyhydroxide, ferrihydrite, at various solution pH values by following vibrational modes unique to Cr(VI), As(III), and As(V). At pH < 9 we observed an initial growth of Cr(VI) vibrational modes due to adsorption, followed by the simultaneous decrease in Cr(VI) vibrational modes and increase in As(V) vibrational modes. Ex situ analysis of the reaction products via X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) indicated that there was an increase in the percentage of reaction products as the pH decreased. Quantum mechanical calculations were completed to model the reaction of Cr(VI) and As(III) on the ferrihydrite surface by analyzing differences in geometric and electronic structural changes and thermodynamic preferences. The results indicate that Cr(VI) and As(III) adsorbed physically separated from each other is not only thermodynamically favorable but results in changes in As(III)-Fe and Cr(VI)-Fe atomic distances, towards those characteristic of As(V)-Fe and Cr(III)-Fe. Thus a mechanism where electron transport occurs through bulk states is plausible. Additionally, natural bond order analysis reveals a redistribution of electron density away from the Cr(VI) atomic center upon adsorption, indicating probable changes in Cr(VI) reduction potential. The electrochemical reduction of Cr(VI) on three surfaces, ferrihydrite, titanium dioxide, and aluminum oxides, indicate that Cr(VI) reduction potential is surface dependent, an observation that has significance for redox chemistry in the environment. The interaction of ferric, Fe(III), with iron sulfide surfaces (during and after coal mining activities) contributes to the detrimental environmental problem known as acid mine drainage (AMD). We investigated whether Fe(III) chelating siderophores could be used to suppress the oxidation of iron sulfide surfaces and the resulting AMD chemistry. The exposure of the iron sulfide, pyrite, to the siderophore, desferrioxamine B (DFOB) at initial pH values of 3, 6, and 8 under oxic conditions showed a significant decrease in the rate of dissolution of pyrite: decreases of 43.7%, 37.5% and 78.4%, respectively. An even greater decrease in pyrite oxidation was observed when DFOB was present in anoxic conditions, specifically 56.1%, 74.4% and 91.5%, at pH 3, 6 and 8, respectively. We further compared the rate of dissolution between DFOB and another siderophore, enterobactin, which is a stronger chelator of Fe(III). The presence of enterobactin suppressed pyrite oxidation more than DFOB, consistent with the contention that inhibiting the interaction of Fe(III) with pyrite will decrease the oxidation of the mineral. We also analyzed the exposure of the pyrite surface to DFOB using ATR-FTIR, to determine if any surface chelation occurs. We found that when Fe(III) is present on the pyrite surface, DFOB adsorbs to the surface via hydroxamate groups, similar to the aqueous phase spectra of DFOB-Fe(III) complex. In contrast the spectra do not exhibit hydroxamate vibrational modes when Fe(III) was not initially present on the pyrite surface and in this circumstance the spectra resembled that of aqueous phase unchelated DFOB. Taken together the results showed that siderophore inhibited pyrite oxidation by chelating Fe(III) present on the pyrite surface and in solution. Finally, the reduction of NO(g) to NH3/NH4+ with amorphous iron sulfide (FeS) was studied. The exposure of NO gas to a suspension of FeS solid resulted in the conversion of 2.3% NO(g) to the reaction product ammonia (NH3), which was found to grow over time, while the exposure of NO(g) to water (in the absence of mineral) resulted in no NH3 formation. Additionally, we completed in situ analysis of NO exposure to FeS as a function of water concentration using ATR-FTIR. The exposure of NO to an aqueous paste of FeS or a FeS film (with adsorbed H2O), resulted in the adsorption of NO to the FeS surface and the subsequent production of NH3, as indicated by N-H vibrational modes. In contrast, the removal of all water, via thermal desorption from the film, resulted in the adsorption of NO but did not show vibrational modes consistent with the formation of NH3. We conclude that the presence of H2O, as a source of protons, and a FeS surface, as a source of electrons, results in the transformation of NO to NH3 via a heterogeneous reaction. This result has important implications towards remediation of NOx gases and mechanisms of prebiotic synthesis of NH3. In summary, the research presented expands our understanding of redox reactions at mineral interfaces in the environment. The work herein aims to inform and aid in the development of remediation methods for arsenic and chromium, the formulation of methods to inhibit the production of acid mine drainage, and develop our understanding of toxic NOx gas reduction on surfaces.<br>Temple University--Theses
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Carrasco, Naraya. "Influence of surfactants on siderophore-promoted dissolution of iron oxides /." Zürich : ETH, 2007. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=17262.
Testo completo
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Jarlbring, Mathias. "Surface reactions in aqueous suspensions of fluorapatite and iron oxides /." Luleå : Luleå University of Technology, 2006. http://epubl.ltu.se/1402-1544/2006/05/index.html.
Testo completo
34
Porter, J. T. "The preparation and characterisation of iron oxides : Colloids and powders." Thesis, University of Exeter, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384726.
Testo completo
35
Church, Nathan Stewart. "Magnetic properties of iron-titanium oxides and their nanoscale intergrowths." Thesis, University of Cambridge, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609524.
Testo completo
36
Potapova, Elisaveta. "Studies on the adsorption of flotation collectors on iron oxides /." Luleå : Luleå university of technology, 2009. http://pure.ltu.se/ws/fbspretrieve/3359292.
Testo completo
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Wu, Si Hyun Goyne Keith William Lerch Robert N. "Adsorption of isoxaflutole degradates to hydrous aluminum and iron oxides." Diss., Columbia, Mo. : University of Missouri--Columbia, 2009. http://hdl.handle.net/10355/6598.
Testo completoAbstract (sommario):
Title from PDF of title page (University of Missouri--Columbia, viewed on Feb 24, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Thesis advisors: Dr. Keith W. Goyne and Dr. Robert N. Lerch. Includes bibliographical references.
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Cheng, Wei. "Fate and transport of quinolones at iron oxides/water interface." Thesis, Rennes, Ecole nationale supérieure de chimie, 2019. http://www.theses.fr/2019ENCR0058.
Testo completoAbstract (sommario):
En raison de leur utilisation accrue, de nombreux contaminants émergents, comme les antibiotiques de type quinolone sont retrouvés dans l’environnement. Leur devenir étant fortement contrôlé par leur interaction avec surfaces minérales, cette thèse a eu pour objectif de comprendre et prédire l’adsorption de quinolones sur des minéraux dans des conditions environnementales variées (pH, salinité, présence de cations et d’anions naturels, etc…) et de développer des modèles de transport réactif. Une approche innovante a alors été développée, combinant des données cinétiques et thermodynamiques, des mesures spectroscopiques in situ et de la modélisation de la complexation de surface. Cette thèse est divisée en deux sections. La première a eu pour but de déterminer les mécanismes de complexation de quinolones sur des oxydes de fer (goethite et magnétite) dans des conditions réduites et dans l’eau de mer. La stœchiométrie de la magnétite (Fe(II)/Fe(III)) s’est avéré être un facteur majeur de contrôle de l’adsorption de l’acide nalidixique (NA). Les effets compétitifs et coopératifs de différents ions présents dans l’eau de mer ont pu être prédits avec précision en réacteur fermé et en colonne (conditions de flux). La deuxième partie de la thèse s’est penchée sur les interactions entre goethite avec des ligands ubiquistes dans l’environnement, comme la matière organique naturelle (MON), et leur impact sur le transport de quinolones. L’adsorption de NA sur la goethite en présence et en l’absence de MON, ainsi que le fractionnement de la MON, ont été étudiés en colonne. Ces résultats pourraient permettre de mieux comprendre et prédire le devenir des quinolones dans l’environnement<br>Due to their extensive use, many emerging contaminants, such as quinolone antibiotics, are released to the environment. Because their environmental fate is largely controlled by their interaction with mineral surfaces, such as iron oxides, this thesis aimed to assess quinolones adsorption onto minerals under environmental relevant conditions (pH, ionic strength, presence of ubiquitous cations and anions, etc.) and develop reactive transport models. To address these issues, an innovative approach combining kinetic and thermodynamic data, in situ spectroscopic measurements and surface complexation modeling, was proposed. This thesis manuscript consists of two parts. The first part investigated the binding mechanisms of quinolones onto iron oxides (goethite and magnetite) under reducing or seawater conditions. Considerable impact of the magnetite stoichiometry (Fe(II)/Fe(III)) on its sorption capability towards nalidixic acid has been demonstrated. Competitive and synergetic effects of different seawater ions on quinolone adsorption to goethite were accurately predicted under static and water saturated flow-through conditions. The second part investigated the interactions of goethite with naturally occurring ligands such as natural organic matter (NOM) and their impacts on the mobility/transport of quinolones. Interactions of NOM and goethite and effects on the surface hydrophilicity were first investigated. Then, nalidixic acid adsorption to goethite and to NOM-covered goethite and NOM fractionation were examined under flow-through conditions. These results may have important implications for assessment and prediction of the fate of quinolones antibiotics in the environment
39
Pang, Kwan-Nang. "Origin of the permian panzhihua layered gabbroic intrusion and the hosted Fe-Ti-V oxide deposit, Sichuan Province, SW China." Click to view the E-thesis via HKUTO, 2008. http://sunzi.lib.hku.hk/hkuto/record/B39634000.
Testo completo
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Sim, Andrew Gregory Chemical Sciences & Engineering Faculty of Engineering UNSW. "Reduction-oxidation cycling of metal oxides for hydrogen production." Awarded By:University of New South Wales. Chemical Sciences & Engineering, 2010. http://handle.unsw.edu.au/1959.4/44763.
Testo completoAbstract (sommario):
A process for the production of clean hydrogen from methane based upon the sequential reduction and oxidation of metal oxides has been studied. The original process, based on iron oxide, suffers from significant disadvantages including deactivation by sintering and coke deposition. Improvement of the iron based system and identification and development of alternative metal oxides for hydrogen production has formed the basis of this study. The literature review outlines current methods for hydrogen production, followed by a review of the Steam-Iron Process as an improved and simpler method for clean hydrogen production. Thermodynamic assessment shows Fe3O4/FeO/Fe, WO3/WO2/W and SnO2/SnO/Sn to be the most prospective systems for the Steam-Metal Process. Experimental testing showed that Fe and W based systems were suitable for hydrogen production, but Sn based systems were unsuitable due to poor reducibility using methane. Attention was then focused on the addition of CeO2/ZrO2 promoters to Fe and W based systems in order to improve reactivity and prevent catalyst deactivation. CeO2/ZrO2 promoted Fe2O3 showed improved redox reactivity and increased stability, with formation of FeO. This aided in mitigation of sintering and introduced the possibility of prevention of coking, as catalysed by methane decomposition over fully reduced Fe metal. Although WO3 was found to be a suitable oxide, complete reduction to tungsten metal resulted in the formation of tungsten carbide and contamination of hydrogen produced. The formation of 31mol% [CeO2/ZrO2] / 69 mol% WO3 showed stabilised reduction using methane, allowing for redox cycling of the WO3-WO2 couple and preventing complete reduction to W metal. The use of the doped metal oxide showed the best performance of all the metal oxides tested, with clean hydrogen production over multiple redox cycles and high metal oxide stability. Further kinetic studies of both the reduction and oxidation reactions show reduction is chemical reaction controlled process (WO3/WO2.9 → WO2) with an apparent activation energy of 142 ?? 3 kJ/mol. Oxidation is also fitted to a chemically controlled process, with a reaction rate expression derived as: rH2 = [0.064 + (F x 0.00038)].e^(-108750/8.314xT).[PH2O]^(0.75) The apparent activation energy for oxidation was calculated as 109 ?? 1 kJ/mol.
41
Gonzalez, Lucena Fedora. "Mineral Magnetism of Environmental Reference Materials: Iron Oxyhydroxide Nanoparticles." Thesis, Université d'Ottawa / University of Ottawa, 2010. http://hdl.handle.net/10393/19608.
Testo completoAbstract (sommario):
Iron oxyhydroxides are ubiquitous in surface environments, playing a key role in many biogeochemical processes. Their characterization is made challenging by their nanophase nature. Magnetometry serves as a sensitive non-destructive characterization technique that can elucidate intrinsic physical properties, taking advantage of the superparamagnetic behaviour that nanoparticles may exhibit. In this work, synthetic analogues of common iron oxyhydroxide minerals (ferrihydrite, goethite, lepidocrocite, schwertmannite and akaganéite) are characterized using DC and AC magnetometry (cryogenic, room temperature), along with complementary analyses from Mössbauer spectroscopy (cryogenic, room temperature), powder X-ray diffraction and scanning electron microscopy. It was found that all of the iron oxyhydroxide mineral nanoparticles, including lepidocrocite, schwertmannite and akaganéite were superparamagnetic and therefore magnetically ordered at room temperature. Previous estimates of Néel temperatures for these three minerals are relatively low and are understood as misinterpreted magnetic blocking temperatures. This has important implications in environmental geoscience due to this mineral group’s potential as magnetic remanence carriers. Analysis of the data enabled the extraction of the intrinsic physical parameters of the nanoparticles, including magnetic sizes. The study also showed the possible effect on these parameters of crystal-chemical variations, due to elemental structural incorporation, providing a nanoscale mineralogical characterization of these iron oxyhydroxides. The analysis of the intrinsic parameters showed that all of the iron oxyhydroxide mineral nanoparticles considered here have a common magnetic moment formation mechanism associated with a random spatial distribution of
iv
uncompensated magnetic spins, and with different degrees of structural disorder and compositional stoichiometry variability, which give rise to relatively large intrinsic magnetization values. The elucidation of the magnetic nanostructure also contributes to the study of the surface region of the nanoparticles, which affects the particles’ reactivity in the environment.
42
Reeves, N. J. "Studies on the hydrolysis of iron (III) in the presence of growth modifiers." Thesis, University of Bath, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357406.
Testo completo
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Kriedemann, Brett Craig. "The critical process conditions for controlled growth of iron oxide nanoparticles synthesized using continuous hydrothermal synthesis." Thesis, Cape Peninsula University of Technology, 2014. http://hdl.handle.net/20.500.11838/920.
Testo completoAbstract (sommario):
Thesis Submitted in Fulfilment of the Requirements for the Degree
Master of Technology: Chemical Engineering
in the Faculty of Engineering
at the Cape Peninsula University of Technology
2014<br>Iron oxide nanoparticles have recently become attractive for use in gas sensing, as catalysts and have also shown promise in other fields, such as biomedicine, for targeted drug delivery and cancer treatment. Despite these growing applications, the ability to produce iron oxide and one dimensional (1D) iron oxide nanoparticles on an industrial scale has proven to be a challenge. The continuous hydrothermal synthesis, (CHS), method has been proposed as the most promising method, yet the effect of the operating parameters on particle characteristics are still widely contested in the literature. One such parameter, temperature, is still widely contested on its effect on APS.
To address this issue, a CHS pilot plant was constructed and commissioned. The inability to isolate certain parameters in CHS is a common shortcoming. Parameters such as temperature and flow rate are prime examples, as changing the temperature has several effects on the system resulting in a change in reaction rate, a change in density and a change in the reactor residence time while the flow rate is closely linked to the residence time and mixing conditions.
A 3-level Box-Behnken factorial design method was used to statistically analyze the correlations and interactions between operating parameters (temperature, concentration and flow rate) in CHS and evaluate their resulting effect on particle characteristics, with focus on morphology.
All particles were characterized by X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). Reactions in the presence of solvents or surfactants proved incapable of modifying particle morphology, although significant particle size reduction revealed that they were actively involved in particle growth and may be used as a further tool for controlling particle characteristics. The concentration was found to have the greatest effect on particle characteristics including a slight alteration of particle shape and a massive influence on the average particle size. The interactions between operating parameters were significant, especially in the case of temperature and concentration. The temperature and concentration were found to interact revealing three different trends on APS, offering a solution to conflicting reports in the literature. The temperature was also observed to interact favourably with the flow rate, presenting a method of increasing the PY and RC, with little change in APS and PSD. This knowledge will prove invaluable for the design of future experiments in CHS.
44
Zhang, Zili. "The effect of sulfur on chemical looping combustion with iron oxides." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/25534.
Testo completoAbstract (sommario):
Advancing climate change poses an increasing threat to humanity, together with the higher demand for energy around the world. New 'cleaner' technologies for the production of energy from solid fuels (coal or biomass) via thermo-chemically viable routes are required. Chemical looping combustion (CLC) is a process concept using metal oxide (oxygen carrier) for transportation of oxygen from air for electrical power generation and inherent production of a pure stream of CO2. CLC has been generally applied to gaseous fuel; however, by integrating chemical looping and gasification, the combined process shows great potential for producing H2 and power from solid fuels. Coal and biomass contain significant quantities of sulfur. Upon gasification, the sulfur is released in the form of H2S, which will be then be introduced into the iron-based chemical looping process, followed by further gasification. Iron oxides are known to form stable sulfides under reducing conditions. The performance of chemical looping using iron-based oxygen carrier could therefore be adversely affected by the introduction of H2S in a real system. The overarching aim of this thesis is to assess the effect of H2S on chemical looping combustion using iron (III) oxide in a laboratory scale spouted bed reactor. A closed-system spouted bed reactor has been designed and constructed to study the solid looping system with gaseous fuel. A model of the bed was developed, from which the bed could reasonably be assumed to be a well-mixed bubbling fluidised bed reactor at certain conditions. The reactor was used for the kinetic study of reduction of Fe2O3 to Fe3O4 with a CO/CO2 mixture under isothermal condition at the temperature range of 723K - 973K. The oxygen carrier before and after thermal cycling was characterised using SEM, mercury porosimetry, BET surface area analysis. Using a nominal particle size of Fe2O3, the rate of reduction was controlled mainly by intrinsic chemical reaction kinetics with a high effectiveness factor. The intrinsic rate constant was estimated with an activation energy of 73 kJ mol-1, which is comparable to values reported in the literature. The reactor was modified for use in the quartz internal, together with acid-washed, calcined sand (Quartz-T) to be able to significantly reduce interactions between sulfur and the inert material used in the construction of the reactor and the spouted bed. The fate of H2S in the chemical looping cycling was determined and the effect of H2S on reduction of Fe2O3 to Fe3O4 over multiple cycles was studied. There were two major mechanisms of reaction between H2S and Fe2O3 that were found to affect the rate of reduction of Fe2O3 and main sulfur product distribution: (1) production of SO2 as a main sulfur product, (2) production of FeS as a main sulfur product. The dominating mechanism was found to depend on the thermodynamic potential of S2, the thermodynamic potential of O2 (which depends on the extent of reduction), and the temperature. The effect of the H2S on the kinetics of reduction was found to be due to the structural change of Fe2O3 particles that is governed by the reaction between H2S and Fe2O3. A mathematical simulation based on a grain model under chemical reaction control was used to satisfactorily describe the relationship between rate of reduction and the extent of the reaction in the presence of sulfur.
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Benaiges-Fernandez, Robert. "Bioreduction of iron (hydr)oxides from mine tailings under marine conditions." Doctoral thesis, Universitat de Barcelona, 2021. http://hdl.handle.net/10803/673411.
Testo completoAbstract (sommario):
Mining industry faces environmental problems concerning waste management. Given the environmental issues associated with storage of mine wastes on land, one disposal option that has gained attraction is submarine tailings disposal (STD). This practice involves disposal of mine tailings under seawater through underwater pipelines. Discharged mine wastes may be geochemically altered by microbial communities that living in the seabed have an ecophysiology that is compatible with the mine tailings. These communities (e.g., Shewanella, Geobacter) would be able to reduce the structural Fe(III) of oxides and oxyhydroxides (henceforth referred to as (hydr)oxides) of iron contained in the tailings, leading to a release of Fe(II) and Trace Elements (TEs) into the marine environment.
The present study aimed at understanding the reaction of bioreduction of iron (hydr)oxides that are contained in mine tailings and assessing the environmental impact of STD. For this purpose, different samples of iron (hydr)oxides and mine tailings were reacted in batch and column experiments in the presence of Shewanella loihica, a dissimilatory iron reducing bacteria. The release of Fe(II) and TE was monitored throughout the experiments, and the surface of the reacted oxides were examined. Geochemical simulations of the experimental data were used to quantify the extent of the overall reductive dissolution reaction. Furthermore, to understand the influence of aqueous iron in the ocean’s nitrogen cycle, a series of experiments were carried out with Fe(II) released from bioreduced iron oxides in the presence of nitrite.
Results showed that Shewanella loihica bioreduces Fe(III) from the iron (hydr)oxides contained in the mine tailings under marine conditions. The dissolution process leads to a release of Fe(II) and TEs, which are harmful for the marine environment. It was deduced that the reactive surface area of the iron (hydr)oxides is a key factor in the bioreduction process as it provides available Fe(III) and available surface, on which Shewanella loihica attach for electron transferring. However, adsorption of some of released Fe(II) onto the surface leads to a decrease in the reactive surface area, which lowers the total available Fe(III), and to a transformation of the former oxide to a new biogenic phase containing Fe2+/Fe3+ (i.e. magnetite). Moreover, it was demonstrated that the Fe(II) released promotes a nitrite removal, interfering thus with the nitrogen cycle of the ocean. The nitrite removal was
characterized using chemical and isotopic analyses, which allowed a better understanding of the mechanisms controlling the Fe(II)-N interaction and an identification of the source of nitrite reduction in the sea.
From the results, it is inferred that STD can become a major environmental concern because (1) the Fe(II) released may lead to fertilization and eutrophication of disposal sites, resulting in an oxygen depletion and an expansion of the oxygen minimum zone and (2) the TEs released bioaccumulate in the environment and trophic webs, ultimately affecting human health and social economic development.<br>La indústria minera s’encara a un problema de gestió dels residus produïts. Degut als problemes mediambientals que provoca l’emmagatzematge terrestre de les cues mineres, la deposició submarina de les cues (STD) és una opció que ha guanyat interès en els darrers anys. Aquesta pràctica implica el dipòsit dels residus al fons marí mitjançant canonades submergides des de les indústries mineres. Aquestes cues es poden veure afectades geoquímicament per les poblacions microbianes que viuen en el fons marí i que poden tenir una ecofisiologia compatible amb els residus. Aquestes comunitats (per exemple, Shewanella, Geobacter) poden bioreduir el ferro fèrric dels òxids i/o hidròxids continguts en els residus miners, alliberant Fe (II) i elements traça (TE) al medi marí.
El principal objectiu d’aquest treball va ser entendre el procés de bioreducció dels òxids i hidròxids de ferro presents en els residus miners i avaluar les conseqüències mediambientals dels dipòsits de residus al fons marí.
Per dur a terme aquest propòsit, es van fer experiments de tipus batch i de columna amb diverses mostres d’òxids i hidròxids de ferro i de residus miners, les quals van reaccionar amb Shewanella loihica, un bacteri desassimilatori del ferro capaç de dur a terme la dissolució reductiva del ferro. Es va monitoritzar l’alliberament de Fe(II) i de TEs, es van observar les superfícies dels sòlids reaccionats i es va fer un model geoquímic per quantificar la bioreducció. A més a més, per tal d’entendre millor la influència del ferro en el cicle del nitrogen de l’oceà es van dur a terme uns experiments batch on el ferro bioreduït interaccionava amb nitrit.
Els resultats han demostrat que la Shewanella loihica pot bioreduir els òxids i/o hidròxids de ferro continguts en residus miners en condicions semblants a les del fons marí. Aquesta dissolució bioreductiva comporta l’alliberament de Fe(II) i de TEs que poden arribar a ser perjudicials per l’ambient. S’ha deduït que la superfície reactiva dels òxids i/o hidròxids é un factor clau en la bioreducció perquè proveeix Fe(III) per bioreduir i superfície perquè els bacteris transfereixin electrons.. Ara bé, l’adsorció de Fe(II) en la superfície comporta, per una banda, la disminució de la superfície reactiva
i del Fe(III) disponible i, per altra banda, la formació d’una nova fase mineral biogènica
que conté Fe2+/Fe3+, és a dir una transformació a magnetita
També s’ha demostrat que el Fe(II) alliberat per la bioreducció pot interferir, amb el cicles biogeoquímic del nitrogen de l’oceà. Així, el Fe(II) bioproduït desencadena l’eliminació del nitrit en el mar. Aquest procés s’ha caracteritzat utilitzant anàlisis químiques i isotòpiques. Les dades isotòpiques han servit per entendre millor els mecanismes que regulen la interacció Fe(II)-nitrogen, i per identificar l’origen de la reducció de nitrit en el medi marí.
A partir dels resultats obtinguts, es dedueix que el dipòsit de residus miners al mar (STD) és un problema mediambiental perquè (1) l’alliberament de Fe(II) pot provocar una fertilització i eutrofització dels llocs on es dipositin els residus amb una disminució de l’oxigen dissolt i una expansió de la zona mínima d’oxigen i (2) l’alliberament d’ETs pot provocar una bioacumulació d’aquests elements a les xarxes tròfiques. Tot plegat afecta no només l’equilibri d’altres cicles biogeoquímics a l’oceà sinó també la salut humana i l’economia de la societat.
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Gorshe, Dominik S. "Synthesis and thermodynamic and kinetic characterization of meta-stable iron oxides /." The Ohio State University, 1998. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487951595501567.
Testo completo
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Zurkiya, Omar. "Magnetic Resonance Molecular Imaging Using Iron Oxide Nanoparticles." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/19848.
Testo completoAbstract (sommario):
Magnetic resonance imaging (MRI) is regularly used to obtain anatomical images, greatly advancing biomedical research and clinical health care today, but its full potential in providing functional, physiological, and molecular information is only beginning to emerge. The goal of magnetic resonance molecular imaging is to utilize MRI to acquire information on the molecular level. This dissertation is focused on ways to increase the use of MRI for molecular imaging using superparamagnetic iron oxide (SPIO) nanoparticle induced MRI contrast. This work is divided into three main sections: <B>1)<I> Elucidation of the contribution of size and coating properties to magnetic nanoparticle induced proton relaxation.</I></B> To maximize contrast generated without increasing particle size, new methods to increase effects on relaxivity must be developed. Experimental data obtained on a new class of biocompatible particles are presented, along with simulated data. The effects of coating size, proton exchange, and altered diffusion are examined. Simulations are presented confirming the effect of particle coatings on clustering-induced relaxivity changes, and an experimental system demonstrating the clustering effect is presented. <B>2)<I> Development of a diffusion-dependent, off-resonance imaging protocol for magnetic nanoparticles.</I></B> This work demonstrates an alternative approach, off-resonance saturation (ORS), for generating contrast sensitive to SPIO nanoparticles. This method leads to a calculated contrast that increases with SPIO concentration. Experimental data and a mathematical model demonstrate and characterize this diffusion-dependent, off-resonance effect. Dependence on off-resonance frequency and power are also investigated. <B>3)<I> Development of a genetic MRI marker via in vivo magnetic nanoparticle synthesis.</I></B> This work seeks to provide a gene expression marker for MRI based on bacterial magnetosomes, tiny magnets produced by naturally occurring magnetotactic bacteria. Here, <I>magA</I> is expressed in a commonly used human cell line, 293FT, resulting in the production of magnetic, iron oxide nanoparticles by these cells. MRI shows these particles can be formed <I>in vivo</I> utilizing endogenous iron and can be used to visualize cells positive for <I>magA</I>. These results demonstrate <I>magA</I> alone is sufficient to produce magnetic nanoparticles and that it is an appropriate candidate for an MRI reporter gene.
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Coetsee, Theresa. "Non-isothermal reaction of iron ore-coal mixtures." Pretoria : [s.n.], 2007. http://upetd.up.ac.za/thesis/available/etd-07092008-142912/.
Testo completo
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Lei, Yun School of Chemical Engineering & Industrial Chemistry UNSW. "Novel Fe2O3-Cr2O3 catalyst for high temperature water gas shift reaction." Awarded by:University of New South Wales. School of Chemical Engineering and Industrial Chemistry, 2005. http://handle.unsw.edu.au/1959.4/23321.
Testo completoAbstract (sommario):
The thesis is focused on the study of high temperature water gas shift catalysis, the identification of new improved catalysts and the study of the kinetics and mechanism of reaction over these catalysts. Rh-promoted Fe2O3-Cr2O3 was found to offer best performance which was significantly better than unpromoted catalyst over wide temperatures range. An extensive literature survey is first reported. Guidelines to develop new WGS catalysts are developed. As a result, the activities of precious metals supported on various oxides for high temperature WGS reaction have been tested. Rh(1wt%) doped Fe2O3/Cr2O3, exhibits the highest activity for WGS over a wide temperature range. 5wt%CuO/Fe2O3-Cr2O3, 1wt%Pt/Cr2O3, 1wt%Pt/Fe2O3-Cr2O3, 1wt%Pt/U3O8, 1wt%Pt/10%U3O8-Al2O3 and 1wt%Pt/5%V2O5-TiO2 fall into the second most active catalysts group, with an improved activity compared to commercial Fe2O3-Cr2O3 catalyst. It is clear that both the support/catalyst and the promoter can affect the efficiency of the WGS, leading to the obvious inference that the reaction rate is controlled at the promoter ??? support interface. Further kinetic studies and characterisation (TPR, TPD, pulse-adsorption (reaction)) on Rh/Fe3O4/Cr2O3 have been conducted. The study, conducted under conditions without inhibition from products of both forward and backward reactions, shows that the overall reaction rate expression is described as: 2 22 ??? =0.0041exp(???4042.6 ) 0.64 0.5 ???0.024 exp(???6022.9 ) 0.46 0.73 CO CO H O CO H r PP P P T T . Kinetics studies carried out under fuel reforming gas compositions shows that reaction rate expression changed when the temperature of reaction varied. The reaction rate equations at temperatures of 573K, 623K and 673K are derived as: 573K: 2 2 2 - 2.84 10-6 0.6 0.12 - 9.08 10-7 0.09 0.52 rCO = ?? PCO PH O ?? PCO PH 623K: 2 2 2 - 1.45 10-6 0.99 0.40 - 7.12 10-7 0.11 0.73 rCO = ?? PCO PH O ?? PCO PH 673K: -6 2 2 2 - = 4.37 ?? 10 0.86 0.41 -1.83 ??10-6 0.28 0.66 rCO PCO PH O PCO PH , The apparent activation energy was 61.7??2.5 kJmol-1 . TPR, TPD, TPO characterisation studies and reoxidation of catalysts by CO2 or H2O show that the active site for high temperature WGS reaction on Rh/Fe2O3/Cr2O3 is reduced magnetite Fe3O4 which dissociatively breaks down the H2O to form H* and OH* and adsorbs CO2. The deposited metal, Rh, acts as a promoter by facilitating the uptake of hydrogen (H2) and carbon monoxide (CO), desorption of H2 (at high temperature) and CO2.
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FLORIO, DANIEL Z. de. "Analise de eletrolitos de ZrO sub(2):Y sub(2) O sub(3) + B sub(2) O sub(3) e de eletrodos de La sub(0,8) Sr sub(0,2) Co sub (0,8) Fe sub (0,2) O sub (3-delta) por espectroscopia de impedancia." reponame:Repositório Institucional do IPEN, 2003. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11130.
Testo completoAbstract (sommario):
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09305.pdf: 5404217 bytes, checksum: 19eda8ad49f8cd247304fef0fb69c1bc (MD5)<br>Tese (Doutoramento)<br>IPEN/T<br>Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP