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Digitized by Kansas Correctional Industries

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The aim of this work was to determine whether a mechanism exists for bacterial oxidation of covellite (CuS) other than that involving cyclic reduction and oxidation of soluble iron, and to describe any such mechanism.It was thought likely that mechanisms of bacterial attack on CuS would also apply to other metal sulphides. High purity covellite was synthesized by the thermal reaction of sulphur and copper. Thiobacillus cultures were obtained from other workers and from the natural environment, and enriched for sulphide oxidizing capability. Oxygen consumption was monitored polarographically. Soluble copper, sulphate and total iron were assayed by Atomic Absorption Spectrophotometry while ferrous ion was determind spectrophotometrically as a complex with orthophenanthroline. By rapid specific inhibition of biological activity during sulphide oxidation, the contribution of bacteria to the stoichiometry of oxidation was determined. At pH 2.5 the product of either biological (Thiobaccillus ferrooxidans) or non-biological oxidation was CuSO4, the biological rate exceeding the non-biological rate about a hundredfold. At pH 4.5 T.thioparus was incapable of oxidizing CuS itself but catalysed attack by oxygen (about fivefold) by oxidizing a sulphur passivation film which formed by reaction of CuS with oxygen. The nett result was again CuSO4 production. At pH 2.5 three strains of T. ferrooxidans oxidized CuS itself without the aid of ferric ion; a fourth strain (BJR-V-1) was completely dependent on ferric ion or dissolved oxygen to oxidize CuS to sulphur. In situations where dissolved oxygen initiated the oxidation of CuS, the oxidation rate was approximately first order with respect to dissolved oxygen, while zero order kinetics were observed when other mechanisms predominated. In dilution experiments designed to demonstrate the dependence of sulphide oxidation (to sulphate) on physical contact between bacteria and mineral surfaces, no dependence was observed. It was concluded that water soluble intermediate were involved in CuS oxidation by T. ferrooxidans and in sulphur transport to the cells of T. ferrooxidans and T. thioparus. Arguments were advanced suggesting that the intermediates were inorganic and the concentration of intermediates was estimated from experimental results and the theory if diffusion. The process of CuS passivation was studied; consumption of oxygen and acid, and production of cupric ion and sulphate were measured, the results indicating that passivation resulted from the accumulation of approximately 30 micromole of elemental sulphur per square metre of CuS. Oxygen consumed during depassivation by thiobacilli supported this conclusion. Assuming an even distribution of sulphur over the surface, the film was calculated to be one or two atoms thick. From consideration of the results of this study it was proposed that polythionates may be involved both in CuS oxidation by bacteria and in transport of sulphur into bacterial cells. The role of iron was investigated. Chemically synthesized ferric ion was less effective in CuS oxidation than was ferric ion produced by T. ferrooxidans strain BJR-V-1 through oxidation of ferrous ion. The half saturation ferrous ion concentration with respect to oxidation by each of the T. ferrooxidans strains was approximately 10-5 molar, in contrast to values of 10-2 molar reported by others. Further ferrous oxidation kinetic experiments with strain BJR-V-1 indicated that the major substrate for the rate limiting reaction in ferrous oxidation was a ferrous phosphate complex; a sulphate complex also played a part.

Typescript (photocopy) / v, 151 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Organic Chemistry, 1982

"October 2002" / Includes bibliographical references (leaves 180-191) / v, 191 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Chemistry, 2003

Graduation date: 2000

Graduation date: 1997

Most paved roads in the United States are surfaced with asphalt. These asphalt pavements suffer from fatigue cracking and thermal cracking, aggravated by the oxidation and hardening of asphalt. This negative impact of asphalt oxidation on pavement performance has not been considered adequately in pavement design. Part of the reason is that the process of asphalt oxidation in pavement is not well understood. This work focused on understanding the asphalt oxidation kinetics and on developing pavement oxidation model that predicts asphalt oxidation and hardening in pavement under environmental conditions. A number of asphalts were studied in laboratory condition. Based on kinetics data, a fast-rate ? constant-rate asphalt oxidation kinetics model was developed to describe the early nonlinear fast-rate aging period and the later constant-rate period of asphalt oxidation. Furthermore, reaction kinetics parameters for the fast-rate and constant-rate reactions were empirically correlated, leading to a simplified model. And the experimental effort and time to obtain these kinetics parameters were significantly reduced. Furthermore, to investigate the mechanism of asphalt oxidation, two antioxidants were studied on their effectiveness. Asphalt oxidation was not significantly affected. It was found that evaluation of antioxidant effectiveness based on viscosity only is not reliable. The asphalt oxidation kinetics model was incorporated into the pavement oxidation model that predicts asphalt oxidation in pavement. The pavement oxidation model mimics the oxidation process of asphalt in real mixture at pavement temperatures. A new parameter, diffusion depth, defined the oxygen diffusion region in the mastic. A field calibration factor accounted for the factors not considered in the model such as the effect of small aggregate particles on oxygen diffusion. Carbonyl area and viscosity of binders recovered from field cores of three pavements in Texas were measured and were used for model calibration and validation. Results demonstrated that the proposed model estimates carbonyl growth over time in pavement, layer-by-layer, quite well. Finally, this work can be useful for incorporating asphalt oxidation into a pavement design method that can predict pavement performance with time and for making strategic decisions such as optimal time for maintenance treatments.