The uranium price decline has negatively impacted on the uranium mining industry. This decline in price requires that uranium metallurgical processes be made to operate more efficiently. Some key parameters that influence the dissolution and kinetics of leaching uraninite (one of the main minerals from which uranium can be extracted) are pH, oxidationreduction potential and iron concentration. A good understanding of the effect these parameters have on the leach kinetics would lead to an efficient operation of metallurgical processes. The objective of this work was therefore to investigate the effects of these key drivers on leach kinetics of Rӧssing Uranium ore. Added to this, was an attempt to come up with a mathematical model which can successfully replicate the leach kinetics. A series of laboratory leach experiments were performed on Rӧssing ore where the pH, oxidationreduction potential and total iron were varied, one at a time, to establish the effects they have on the leach kinetics and on the uranium extraction. Analysis of the data collected from this study showed that the leach kinetics are more dependent on the oxidation-reduction potential, followed by the iron concentration and least affected by the pH. It was further shown that oxidation-reduction potential is a function of total iron. An integral method was used to analyse the kinetic data. A literature study reveals that uraninite dissolution follows first order kinetics, but of interest in these results was that the uranium dissolution was found to closely follow the second order. Further research is recommended to look at ascertaining these results. Two models were developed, one using regression and the other by curve fitting method. Both models could fit the experimental data well enough. / Dissertation (MSc)--University of Pretoria, 2016. / Materials Science and Metallurgical Engineering / MSc / Unrestricted

<p> This thesis describes the ionic strength and ion binding effects on the oxidation reduction properties of cytochrome c and its lysine modified derivatives.</p> <p> Cytochrome c has been modified in two different ways: a complete modification of all lysine residues and specific modification of one lysine residue. Some properties of the modified derivatives are described.</p> <p> Ion binding properties of cytochrome c and its lysine modified derivatives were studied by measuring the apparent equilibrium constant of the reaction between the ferri- form of the protein and potassium ferrocyanide. It was found that unmodified cytochrome c binds one cation (K+, Na+) per molecule, and binding is much stronger to the reduced form of the protein. Binding of cations is not changed upon modification of the lysine residues. For binding of the chloride, there are two binding sites on the cytochrome c molecule, and the binding is much stronger to the oxidized form of the protein. It was shown that upon the modification of the lysine residues in either way the binding of chloride was considerably changed. It was concluded that one of these two binding sites for chloride on cytochrome c involves lysine residue, probably the residue number 13.</p> / Thesis / Master of Science (MSc)

The oxidation of 1,1-dimethylhydrazine by bromine has been studied using a coulometric method of bromine generation, and a dual intermediate system of bromide and cupric ions in solution. The system allowed over-generation of bromine and back-titration by cupric ion. The results of the investigation showed that the mechanism of oxidation is not fixed, but is a function of the concentration of bromine in the solution at any time. Additional studies have been recommended, whereby the mechanisms of the reactions may be determined.

No description available.

The kinetics for the reaction of the oxidation of acetaldehyde by chromic acid in aqueous medium has been studied in an attempt to extend the present knowledge of oxidation by chromic acid. In particular, these experiments were undertaken in order to see if there are any similarities between this reaction and the oxidation of isopropyl alcohol in aqueous medium, which other investigators have studied. The main runs were carried out at 25°, at an ionic strength of 0.3. The reaction was followed by the decrease in chromic acid concentration as determined with the Beckman Spectrophotometer. In all of the runs, the concentrations of acetaldehyde and H⁺ were in excess of the chromic acid concentrations. It was found that the oxidation of acetaldehyde is first order in acetaldehyde and first order in HCrO₄⁻, (but not strictly first order in total chromic acid). The reaction is roughly second order in H⁺. Mn⁺² has an inhibitory effect upon the rate, as has been found in the isopropyl alcohol oxidation. Because of the similarity in kinetic behavior between acetaldehyde and isopropyl alcohol, the mechanisms are probably very similar. This mechanism for acetaldehyde oxidation has been discussed in some detail. / Master of Science

The purpose of thIs investigation was to determine whether correlation exists between the O-R potential and the biochemical oxygen demand of settled sewage. The source of the samples was the effluent end of the primary clarifier at the V.P.I. Sewage Disposal Plant. The investigation consisted essentially of performing the standard biochemical oxygen demand determination and the oxidation-reduction potential determination on similar sewage samples. The data obtained were statistically analyzed and graphically presented. The standard deviation was ascertained and a ninety percent confidence limit was established. The final results based on statistical methods of analysis show that no valid correlation exists between O-R potential and B.O.D. of settled sewage. / Master of Science

The making and breaking of O-O bonds has implications ranging from artificial photosynthesis and water oxidation to the use of O₂ as a selective, green oxidant for transformations of small molecules. Oxidative generation of O₂ from coupling of two H₂O molecules remains challenging, and well defined systems that catalytically evolve O₂ are exceedingly rare. Recent theoretical studies have invoked metal oxyl radicals (L[subscript n]M=O*) containing a singly occupied M-O π-type orbital as precursors to O-O bond forming events in both biological and synthetic water oxidation catalysts. However, the lack of stable metal oxyl complexes makes it difficult to explore and understand this hypothesis. The activation of dioxygen (breaking of O-O bonds) to produce terminal metal oxos also remains a challenge. There is an inherent kinetic barrier to the spin-forbidden reactions of triplet dioxygen, and features that engender selective O₂ reduction are not easily transferable from system to system. The primary thrust of this thesis work has been to elaborate new methods to generate well-defined metal oxyl radicals for studies of their reactions in radical bond-forming reactions similar to the radical coupling hypothesis of water oxidation. A library of >20 5- and 6-coordinate high-valent oxorhenium complexes containing redox-inert and redox-active ligands has been prepared. The complexes containing redox-active ligands have shown the ability for ligand-mediated radical coupling reactions. Mechanistic studies of bimetallic O₂ homolysis (the microscopic reverse of water oxidation) and nitroxyl radical deoxygenation at five-coordinate oxorhenium(V) reveal that, in both net 2e⁻ reactions, coupling to a redox-active ligand lowers the kinetic barrier to the reaction by facilitating formation and stabilization of 1e⁻ oxidized intermediates. Coordinatively unsaturated high-valent oxorhenium complexes containing redox-active ligands direct bond-forming reactions towards the metal center. This is undesirable towards the goal of forming O-O bonds. To address this problem coordinatively saturated Re(V) and Re(VII) complexes were prepared. Oxidation of these species by chemical oxidants allowed for the isolation of "masked" oxyl species. These complexes showed reactivity towards Si and trityl radicals to produce new Si-O and C-O bonds, whereas their closed-shell congeners were inert. We have successfully developed a method for the preparation and isolation of "masked" oxyl radicals and shown their utility in ligand-mediated radical coupling reactions.

Background: Physically injured elder adults present challenges in the emergent injury phase. Oxidative stress contributes to cellular deterioration, resulting in decreases in physiological reserve. Imbalance of oxidative stress pathways lead to damage and drive the aging process and frailty. Goals of this study were to determine if a new plasma biomarker of oxidative stress is related to: 1) oxidation reduction status in patients who have experienced traumatic injury as well as healthy community dwellers, 2) outcomes of patients who have experienced trauma, 3) frailty measured by established frailty scales in healthy community dwellers. Methods: Prospective study included 1) trauma patients ≥65 admitted to Level I trauma center 2) age, gender matched healthy, community-dwelling participants. Plasma samples tested in duplicate for capacity oxidative reductive potential (cORP, μC; antioxidant reserve), and static oxidative reductive potential (sORP, mV; the current state of oxidative stress). Frailty assessments were performed in healthy participants using established frailty scales. ORP measurements were analyzed using correlation analyses. Univariate analysis analyzed cORP and sORP for differences by the variables gender, age, smoking, diabetes, statin use, vitamin use and any alcohol use in both the injured and healthy populations. Results: 186 subjects included in study (N=93 for both groups). Trauma groups's cORP values were significantly lower in patients with diabetes (p<0.05) and patients that smoked (p<0.01). Similarly the healthy group's cORP was significantly lower for those who smoked and those with diabetes (p<0.05). Non-vitamin use in the healthy group was related to lower cORP values (p<0.05). Trauma patients who smoked and those with diabetes exhibited higher sORP values (p<0.05). In the healthy group, sORP did not differ when considering the variables. No12significant differences were found based on gender, statin or alcohol use for either group. Significant correlation was found for both sORP and cORP with CSHA Clinical Frailty Scale in the healthy group. Conclusion: Findings suggest that the variables of smoking and diabetes are contributory to frailty trajectory. Data suggest the capacity to tolerate oxidative stress, measured by cORP, is lower in aged individuals that smoke or are diabetic and contributes to frailty as a result of oxidative damage.

No description available.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy