Thesis (Ph. D.), Oregon Graduate Institute of Science & Technology, 1995.

Thesis (MTech (Chemical Engineering))--Cape Peninsula University of Technology, 2016. / 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.

La corrosion des aciers dans le béton armé conduit à la formation de produits de corrosion (PdC) qui, outre les pertes de section, génère des contraintes mécaniques à l’interface acier/béton qui mènent, à terme, à la fissuration du béton. Le diagnostic de ce type de dégradation est souvent difficile et limite l’évaluation de l’aptitude au service de l’ouvrage, la prédiction de l’évolution des dégradations et le choix adapté d’une méthode de réparation. L’objectif de cette étude est de préciser et de quantifier les relations entre les dégradations internes dues à la corrosion de l’armature (formation de PdC et fissuration du béton) et les dégradations externes (fissuration du béton).Un programme expérimental a été défini pour appréhender ces mécanismes de dégradations. La corrosion des armatures des corps d'épreuve en béton armé confectionnés dans le cadre de cette étude a été générée de manière artificielle et accélérée en présence d'ions chlorure sous un courant imposé en considérant trois densités de courant (50,100 et 200 µA/cm²) et différentes durées.Les caractérisations électrochimiques avant et après corrosion accélérée ont permis de démontrer le passage de la corrosion passive à active des armatures dans le béton à l'échelle macroscopique. L'analyse au MEB des PdC créés à l’interface acier/béton (échelle microscopique) a montré une hétérogénéité importante de ces PdC autour de l'armature, en termes de répartition et d'épaisseurs (entre 0 et 1584 µm). Cette hétérogénéité peut s'expliquer par l'évolution des zones anodiques et cathodiques étant donné la dissymétrie géométrique des corps d’épreuve, les conditions de l'essai accéléré qui engendrent des environnements différents (gradients d'humidité, d'ions chlorure et d'oxygène) et la nature du matériau béton (granulats, porosité).La fissuration interne (orientation, ouverture et longueur de fissures) et externe (ouverture maximale de fissure) du béton d’enrobage induite par la formation des PdC a été analysée. Les faciès de fissuration internes sont constitués d’une à cinq fissures réparties en trois groupes. Les premier et second groupes rassemblent les fissures horizontales et les fissures verticales progressant des côtés de plus petit enrobage. Le troisième groupe est formé des fissures obliques situées du côté opposé aux fissures horizontales. Les ouvertures de fissures internes sont comprises entre 0,1 et 0,4 mm et leurs longueurs entre 1 et 3 cm. Les ouvertures de fissures externes maximales, localisées sur les faces du faible enrobage, varient entre 0,1 et 0,7 mm.L’effort maximum appliqué durant les essais d’arrachement diminue en fonction du taux de corrosion, mais ces taux se sont révélés trop faibles pour influencer la loi de l’interface acier/béton. Le mécanisme prépondérant de rupture observé est l’éclatement du béton d’enrobage qui est resté inchangé avec le niveau de corrosion.Un scénario de « cause à effet » entre la corrosion de l’armature et la dégradation mécanique du béton a été proposé en prenant en compte l'ensemble des résultats.A partir des nombreuses données expérimentales acquises, deux modèles ont été élaborés. Un premier modèle a été développé pour expliquer l’initiation et le développement de la corrosion des aciers. Les résultats numériques permettent de déterminer l’instant d’amorçage de la corrosion selon la densité de courant.Une deuxième modélisation qui a pour objectif d’analyser le comportement mécanique du béton armé corrodé a été mise en place. Les résultats ont montré que la seule prise en compte des épaisseurs de PdC (donnée d'entrée expérimentale) n'était pas suffisante pour obtenir un résultat numérique en adéquation avec le faciès de fissuration interne obtenu expérimentalement. Dans une seconde étape, la prise en compte de nouvelles répartitions des épaisseurs des PdC a permis d'améliorer la concordance entre les résultats numériques et expérimentaux / Corrosion of steel in reinforced concrete generates iron oxides which induce tensile stresses at the steel/concrete interface leading to the concrete cover cracking and loss of reinforcing bar cross-section. The evaluation of such pathology remains difficult and consequently limits the assessment of the structure serviceability, the knowledge on the degradation evolution, and the choice of a suitable repair method. The aim of this study is to correlate internal degradations (corrosion products formation and concrete cracking) induced by steel corrosion to external degradations (concrete cracking).The experimental program aims to determine these degradation mechanisms. The accelerated corrosion tests are carried out on reinforced concrete specimens in the presence of chloride ions by applying a constant current using three current densities (50,100 and 200 µA/cm²) during different exposure periods.Electrochemical properties of reinforced concrete specimens are determined before and after the accelerated corrosion tests. The quantitative evaluation of the corrosion products at the steel/concrete interface based on SEM observations (microscopic scale) demonstrates an important heterogeneity in the distribution and thicknesses (between 0 and 1584 µm). This heterogeneity can be explained by the evolution of anodic and cathodic zones due to different factors such as the non symmetric geometry of the specimens, the accelerated corrosion test environment (moisture, chloride ions and oxygen gradients), and the characteristics of concrete (aggregates, porosity).The internal (angular position, width, and length of cracks) and external crack patterns (maximum crack width) induced by the formation of corrosion products are analyzed. One to five internal cracks are identified in the internal crack patterns and they are classified in three groups. The first and second groups contain horizontal and vertical cracks which propagate in the direction of the shortest concrete cover. The third group is constituted of oblique cracks which are located in the opposite side of the horizontal cracks. The widths of the internal cracks range between 0.1 to 0.4 mm and their lengths between 1 to 3 cm. The maximum external crack widths are between 0.1 to 0.7 mm and are located on the shortest cover sides of the specimens.The maximum effort applied during the pull-out tests decreases with increasing levels of corrosion. However, the corrosion levels reach during the tests are too low to affect the steel/concrete interface behavior. The failure mode identified during the testing is concrete splitting failure regardless the corrosion level. A cause/effect scenario is proposed between steel corrosion and the mechanical induced degradation considering all experimental results.Based on experimental results, two models are proposed. The first one is developed to explain corrosion initiation and propagation. This model is able to determine the corrosion initiation time for each current density.The second model analyses the concrete cover mechanical behavior. The numerical results show that taking into account only the thickness of corrosion products (as an experimental input) does not generate a numerical cracking pattern similar to the experimental one. Then, complementary calculations considering a different distribution of the corrosion product’s thicknesses allow enhancing the agreement between experimental and numerical results

The fundamental cause of low temperature breakdown (reduction disintegration) is reduction of hematite to magnetite, resulting in a volume expansion and stress relief through the formation of cracks. Serious reduction disintegration causes poor gas permeability, high flue dust production and scaffolding, poor gas distribution, higher fuel consumption and lower productivity. Northern Cape iron ore generally performs well when tested for reduction disintegration properties both for blast furnaces and Corex; nevertheless, significant breakdown is experienced when used in the Corex process (at Saldanha Steel). This study was hence conducted to determine the effects of the following on reduction disintegration:<ul><li> different ore types (from Northern Cape) </li> <li> initial particle size</li><li> temperature range</li><li> reduction gas composition</li></ul> Although disintegration is clearly triggered by reduction, no direct correlation could be established between the percentage reduction and the percentage fines generated. The results indicated that the presence of gangue minerals alone does not cause fractures to form, but does influence the direction and intensity of fractures to some extent. In many cases cracks form randomly, with no specific preference for either gangue minerals or iron oxides. For most of the samples, an incubation period was observed before the first cracks formed. No crack propagation was observed after initial cracking. This study indicates that the degree of reduction disintegration depends mostly on furnace conditions. Reduction disintegration increased with higher hydrogen percentages (>5%), higher temperatures (in the 500ºC-700ºC range) and longer exposure. Disintegration of the samples decreased at temperatures higher than 750°C. For particles smaller than 16 mm an inverse relationship was found between the average particle size and the percentage of fines generated, in line with the observation that most of the disintegration is due to spalling from particle edges rather than particles breaking into smaller clumps. The results indicate that it is important to manage the temperature in the top of the blast furnace and the COREX shaft, and the time spent at temperatures below 750°C, to minimize the amount of fines generated. / Thesis (PhD)--University of Pretoria, 2010. / Materials Science and Metallurgical Engineering / unrestricted

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. / 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.

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A unique Raman spectroscopic investigation combining a number of different techniques has been conducted in situ on the composition of the passive film on iron, both during its growth in 0.05 M NaOH by potentiodynamic polarization and during localized breakdown by pitting after addition of 0.05 M NaCl. There are differing theories for the mechanism of pit initiation and formation in the passive film on iron, and while these are in part due to different environmental factors, they are also influenced by differing theories for the nature of the passive film. The detailed information obtained in this study corroborate the two layer model for the passive film on iron, with γ-Fe2O3 forming the inner layer and the outer layer consisting of δ-FeOOH, α-FeOOH, γ-FeOOH, other components such as Fe(OH)2 and other intermediates. In the passive region of anodic polarization the film became increasingly hydrated with increasing anodic potential and with increased cycles became amorphous, comparing well with the Hydrated Polymeric Oxide model. Pre-resonance enhancement of the Raman bands of iron oxides and particularly iron oxy-hydroxides was afforded by excitation at 636.4 nm, and particularly at low wavenumbers. The use of Multivariate Curve Resolution with Alternating Least Squares (MCR-ALS) enabled determination of the relative amounts of the iron oxide and oxy-hydroxide components from the complex spectra recorded during potentiodynamic polarization. The amount of water incorporated in the passive film under the same conditions was also monitored in situ at similar potentials using excitation at 514.5 nm. Addition of chloride ions resulted in an increase in hydration and a change of the composition of the passive film to comprise mainly β-FeOOH and Green complex with some γ-Fe2O3 and γ-FeOOH. At the pitting potential significant changes in the composition occurred along with reduction in hydration, so that re-passivation could no longer be maintained at the same rate as dissolution by the chloride ions, enabling stable pitting. These observations indicate that water plays a protective role in the passive film and reinforce the mechanisms for pit initiation based on the De-passivation–Re-passivation theory and Chemical Dissolution theory.

<p> The study of free iron oxides in soils has for many years been an important area of research in the soil science. The development of many standard procedures over the years has free iron oxides. This study presents a systematic review of {a) the development of chemical processes and iron deposits in the podzolic group of soils, a major Canadian soil group in which free iron oxides deposits are found; {b) a review of the theory and experimental data behind some of the most widely accepted procedures of iron extraction; (c) a systematic review of four of the major methods of free iron extraction through experimental and statistical analysis employing soil samples from Thor Lake, N.W.T. The results of this study show that the most useful method for free iron oxide extraction is one that is independent of complexing variables such as pH, C.E.C., temperature and time.<p> / Thesis / Bachelor of Arts (BA)

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