Abstract of Thesis (Ph. D.)--University of Michigan, 1935. / Cover title. Bibliography: p. 20-21.

Thesis (MTech: Chemical Engineering))--Cape Peninsula University of Technology, 2012 / The microbial ferrous-iron oxidation process plays a significant role in bioleaching, providing ferric-iron (Fe3+) − a strong oxidising agent for the dissolution of most sulphide minerals. An extensive literature review has shown that several studies have been carried out on microbial ferrous-iron oxidation, mostly in stirred tank reactors and in conditions close to optimum. However, limited studies have been carried out on this subject in the context of heap bioleach situation. Despite the fact a packed column system may be used to represent heap bioleaching, most of the studies on microbial ferrous-iron oxidation in such systems were carried out under flooded/fluidised conditions which do not adequately represent solution flow dynamics in a heap system. The microbial ferrous-iron oxidation kinetics of Leptospirillum ferriphilum were studied at substrate loading rates of 0.17 – 0.5 g.L-1h -1 (dilution rates 0.033 – 0.1 h-1). The study was conducted in a packed column with a view to investigating the kinetics in a system which simulates the solution flow dynamics of a typical heap bioleach operation. Glass marbles, 15 mm in diameter, were used as reactor packing. The microbial oxidation kinetics were investigated in a continuous mode at the desired loading rates. The pH of the bioreactor was maintained at pH 1.45 ± 0.05 and the aeration at 15 mL.s-1. Both Monod and Hansford models were used to describe the biooxidation kinetics.

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.

This thesis describes a new Laser-Assisted Spray Pyrolysis technique developed to grow nanoparticle coatings with controllable particle sizes. In this method, droplets of a precursor formed by a nebulizer are injected into a growth chamber using SF6 carrier gas. An experimental study and a computational model to investigate the particle size dependence on various growth parameters have been carried out. The results show that heating of 1.5and#61549;m droplets of metalorganic precursor in a carrier gas using a CO2 laser resulted in the formation of TiC and Fe3O4 particles with diameters in the range of 50-60nm. Also the results show that by reducing the concentration of the metal organic precursor the diameter of the deposited particles can be reduced.

Thesis (Ph. D.)--School of Civil and Environmental Engineering, Georgia Institute of Technology, 2005. Directed by Ching-Hua Huang. / Wine, Paul, Committee Member ; Pavlostathis, Spyros, Committee Member ; Mulholland, James, Committee Member ; Yiacoumi, Sotira, Committee Member ; Huang, Ching-Hua, Committee Chair. Includes bibliographical references.

Thesis submitted in fulfilment of the requirements for the degree of Masters of Technology: Chemical Engineering in the Faculty of Engineering Cape Peninsula University of Technology, South Africa Supervisor: Prof TV Ojumu Cape Town Campus September 2013 / Jarosite formation is regarded as undesirable in the bioleaching processes as it depletes ferric reagent; a critical reagent for the oxidation of most sulphide minerals, from bioleach solution. It creates kinetic barriers and clogs on mineral surfaces, thereby retarding leach rates of most minerals. However, jarosite has also been shown to serve as support for the attachment of bioleaching microbes, facilitating a high ferric-iron generation rate. In this study, a series of experiments on microbial ferrous-iron oxidation by a mesophilic microbe were carried out in a novel packed-column bioreactor with a view to investigating the potential use of solution pH to manage jarosite accumulation in the bioreactor. The kinetics of the oxidation was also investigated to establish base case data for the novel bioreactor. The bioreactor was packed with glass balls 15 mm in diameter. The experiments were conducted at a constant temperature of 38.6 °C, residence time of 18 hrs, airflow rate of 20 mL.s-1 and at desired solution pHs (1.3, 1.5 and 1.7). The results showed that the amount of jarosite accumulation is proportional to the operating solution pH and also to the duration of operation of the bioreactor. Jarosite precipitate of 4.95, 5.89 and 7.08 g.L-1 were obtained after 10 days of continuous operation at solution pH of 1.3, 1.5 and 1.7 respectively, while after 15 days the precipitate concentration increased to 5.50, 7.90 and 9.98 g.L-1respectively. The results also showed that a 33% and 52% reduction in jarosite accumulation could be achieved by a gradual decrease of the bioreactor solution pH after being continuously operated for 10 days from pH 1.7 to 1.5 and pH 1.7 to 1.3, respectively, for an additional five days of continuous operation. The results of the ferrous-iron biooxidation kinetics investigated at pH 1.3 show a maximum ferrous oxidation rate ( max 2 Fe r ) of 6.85 mmol.L-1.h-1 and apparent affinity kinetics constants (   2 Fe K , 2 Fe K ) of 0.001 mmol Fe2+.L-1 and 0.006 (dimensionless) using Hansford and Monod equations, respectively. Although a direct relationship exists between jarosite formation and solution pH, the results of this study may be relevant in bioleach heaps, or at least in column bioreactors, to manage and control jarosite accumulation, thereby improving leach kinetics of sulphide minerals.

Thesis submitted in fulfilment of the requirements for the degree of Masters of Technology: Chemical Engineering in the Faculty of Engineering Cape Peninsula University of Technology, South Africa, 2013 / Jarosite formation is regarded as undesirable in the bioleaching processes as it depletes ferric reagent; a critical reagent for the oxidation of most sulphide minerals, from bioleach solution. It creates kinetic barriers and clogs on mineral surfaces, thereby retarding leach rates of most minerals. However, jarosite has also been shown to serve as support for the attachment of bioleaching microbes, facilitating a high ferric-iron generation rate. In this study, a series of experiments on microbial ferrous-iron oxidation by a mesophilic microbe were carried out in a novel packed-column bioreactor with a view to investigating the potential use of solution pH to manage jarosite accumulation in the bioreactor. The kinetics of the oxidation was also investigated to establish base case data for the novel bioreactor. The bioreactor was packed with glass balls 15 mm in diameter. The experiments were conducted at a constant temperature of 38.6 °C, residence time of 18 hrs, airflow rate of 20 mL.s-1 and at desired solution pHs (1.3, 1.5 and 1.7). The results showed that the amount of jarosite accumulation is proportional to the operating solution pH and also to the duration of operation of the bioreactor. Jarosite precipitate of 4.95, 5.89 and 7.08 g.L-1 were obtained after 10 days of continuous operation at solution pH of 1.3, 1.5 and 1.7 respectively, while after 15 days the precipitate concentration increased to 5.50, 7.90 and 9.98 g.L-1respectively. The results also showed that a 33% and 52% reduction in jarosite accumulation could be achieved by a gradual decrease of the bioreactor solution pH after being continuously operated for 10 days from pH 1.7 to 1.5 and pH 1.7 to 1.3, respectively, for an additional five days of continuous operation. The results of the ferrous-iron biooxidation kinetics investigated at pH 1.3 show a maximum ferrous oxidation rate ( max 2 Fe r ) of 6.85 mmol.L-1.h-1 and apparent affinity kinetics constants (   2 Fe K , 2 Fe K ) of 0.001 mmol Fe2+.L-1 and 0.006 (dimensionless) using Hansford and Monod equations, respectively. Although a direct relationship exists between jarosite formation and solution pH, the results of this study may be relevant in bioleach heaps, or at least in column bioreactors, to manage and control jarosite accumulation, thereby improving leach kinetics of sulphide minerals.

When a permanent magnet is considered for an application, the quantity that quantifies the usability of that material is the magnetic energy product (BH)max. In today’s world, rare earth transition metal permanent magnets like Nd-Fe-B, Sm-Co possesses the maximum magnetic energy product. But still for the industrial application, the ferrite permanent magnets are the primary choice over these rare transition metal magnets. Thus, in the present context, the magnetic energy product of the low cost ferrite system makes it unsuitable for the high magnetic energy application. In this regard, exchange spring magnets which combine the magnetization of the soft phase and coercivity of the hard magnetic phases become important in enhancing the magnetic energy product of the system. In this thesis, the exchange spring behaviour is reported for the first time in hard/soft oxide nanocomposites by microstructural tailoring of hard Barium Ferrite and soft Nickel Zinc Ferrite particles. We have analyzed the magnetization reversal and its correlation with the coercivity mechanism in the Ni0.8Zn0.2Fe2O4/BaFe12O19 exchange spring systems. Using this exchange spring concept, we could enhance the magnetic energy product in Iron Oxide/ Barium Calcium Ferrite nanocomposites compared to the bare hard ferrite by ~13%. The presence of the exchange interaction in this nanocomposite is confirmed by the Henkel plot. Moreover, a detailed Reitveld study, magnetization loop and corresponding variation of the magnetic energy product, Henkel plot analysis and First Order Reversal Curve analysis are performed on nanocomposites of hard Strontium Ferrite and soft Cobalt Ferrite. We have proved the exchange spring behaviour in this composite. In addition, we could successfully tailor the magnetization behaviour of the soft Cobalt Ferrite- hard Strontium Ferrite nanocomposite from non exchange spring behaviour to exchange spring behaviour, by tuning the size of the soft Cobalt Ferrite in the Cobalt Ferrite/Strontium Ferrite nanocomposite. The relative strength of the interaction governing the magnetization process in the composites has been studied using Henkel plot and First Order Reversal Curve method. The FORC method has been utilized to understand the magnetization reversal behaviour as well as the extent of the irreversible magnetization present in both the nanocomposites, having smaller and larger particle size of the Cobalt Ferrite. It has been found that for the all the studied composites, the pinning is the dominant process for magnetization reversal. The detailed structural analysis using thin film XRD, angle dependent magnetic hysteresis and remanent coercivity measurement, coercivity mechanism by micromagnetic analysis and First Order Reversal Curve analysis are performed for thin films of Strontium Ferrite which are grown on c-plane alumina using Pulsed Laser Deposition (PLD) at two different oxygen partial pressures. The magnetic easy directions of both the films lie in the out of plane direction where as the in plane direction corresponds to the magnetic hard direction. Depending on the oxygen partial pressure during deposition, the magnetization reversal changes from S-W type reversal to Kondorsky kind of reversal. Thus, the growth parameter for the Strontium Ferrite single layer which will be used further as a hard layer for realizing oxide exchange spring in oxide multilayer, is optimized. The details of the magnetic and structural properties are analyzed for Nickel Zinc Ferrite thin film grown on (100) MgAl2O4. We have obtained an epitaxial growth of Nickel Zinc Ferrite by tuning the growth parameters of PLD deposition. The ferromagnetic resonance and the angle dependent hysteresis loop suggest that, the magnetic easy direction for the soft Nickel Zinc Ferrite lie in the film plane whereas the out of plane direction is the magnetic hard direction. Using the growth condition of respective Nickel Zinc Ferrite and Strontium Ferrite, we have realized the exchange spring behaviour for the first time in the trilayer structure of SrFe12O19 (20 nm)/Ni0.8Zn0.2Fe2O4(20 nm)/ SrFe12O19 (20 nm) grown on c-plane alumina (Al2O3) using PLD. The FORC distribution for this trilayer structure shows the single switching behaviour, corresponding to the exchange spring behaviour. The reversible ridge measurement shows that the reversible and the irreversible part of the magnetizations are not coupled with each other.

Metal oxide-facilitated transformation is likely an important degradation pathway of antibacterial agents at soil-water interfaces. Phenolic disinfectants (triclosan and chlorophene), fluoroquinolones (FQs), and aromatic N-oxides are of particular concern due to their widespread usage, potential toxicity and frequent detection in the environment. Results of the present study show that the above antibacterial agents are highly susceptible to metal oxide-facilitated oxidation. The interfacial reactions exhibit complex reaction kinetics, which are affected by solution pH, the presence of co-solutes, surface properties of metal oxides, and structural characteristics of antibacterial agents. Adsorption of the antibacterial agents to Mn and Fe oxide surfaces generally proceeds faster than oxidation reactions of these compounds by Mn and Fe oxides, especially in the case of Fe oxides. Reaction intermediates and end products are identified by GC/MS, LC/MS and/or FTIR. Structurally-related model compounds are examined to facilitate reaction site and mechanism elucidation. On the basis of experimental results and literature, reaction schemes are proposed. In general, the antibacterial agent is adsorbed to the oxide surface, forming a precursor complex. Electrons are transferred within the precursor complex from the antibacterial agent to the oxide, followed by releasing of the radical intermediates which undergo further reactions to generate oxidation products. The precursor complex formation and electron transfer are likely rate-limiting. For triclosan, phenoxy radicals are critical intermediates to form oxidation products through three pathways (i.e., radical coupling, further oxidation of the radical, and breakdown of an ether bond within the radical). The first two pathways are also operative in the oxidation of chlorophene. For FQs, oxidation generates radical intermediates that are most likely centered on the inner N in the piperazine ring. The radical intermediates then undergo three major pathways (i.e., radical coupling, N-dealkylation, and hydroxylation) to yield a variety of products. For aromatic N-oxides, a N-oxide radical intermediate is generated upon oxidation by MnO2, followed by the loss of oxygen from the N-oxide moiety and the formation of a hydroxyl group at the C-atom adjacent to the N-oxide moiety. Overall, a fundamental understanding of the reaction mechanisms between three classes of antibacterial agents and metal oxides has been obtained.

M.Tech. (Department of Chemical Engineering, Faculty of Engineering and Technology), Vaal University of Technology / Corrosion responses of some carbon steels, stainless steel and copper alloys in the presence of a culture of bacteria (referred to as SRB-Sulphate-reducing bacteria) found in industrial heat exchangers, was studied to recommend best alloys under this service condition, with techno-economic consideration. Water from cooling towers in three plants in a petrochemical processing complex were analysed for SRB presence. Two of the water samples showed positive indication of SRB presence. The mixed cultures obtained from plant one were grown in prepared media and incubated at 35 °C for 18 days. Potentiodynamic polarisation studies in anaerobic conditions were done on the selected alloys in aqueous media with and without the grown SRB. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) were then used to study the corrosion morphology and corrosion products formation. The voltamograms show higher icorr for alloys under the SRB compared to the control media, indicating the SRB indeed increased the corrosion rates. The surface analysis showed pitting on steel alloy ASTM A106-B. Localised attack to the grain boundaries on a selective area, was seen on ASTM A516-70 dislodging the grains, and intergranular corrosion was seen throughout the exposed area of ASTM A179. Copper alloys showed pitting on ASTM B111 grade C71500 (70-30), and denickelification on ASTM B111 grade C70600 (90-10), and is a good alternative material for use apart from carbon steel alloys, recording a low corrosion rate of 0.05 mm/year. The EDS analysis supported the findings showing higher weight percent of iron and sulphur on surface of the alloys after exposure to the SRB media. This implies that the presence of the sulphur ion indeed increased the corrosion rate. ASTM A516-70 carbon steel was chosen as a suitable alternative material to the stainless steel in this environment. The Tafel plot recorded a corrosion rate of 1.08 mm/year for ASTM A516-70 when exposed to SRB media.