Thesis (Ph. D.)--Columbia University, 1942. / Vita. Bibliography: p. 35-37.

Thesis (Ph. D.)--Princeton University, 1927.

Thesis (M.S.)--University of Wisconsin--Madison, 1970. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (M.S.)--University of Wisconsin--Madison, 1968. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (M.Eng)(Metallurgical)--University of Pretoria, 2006. / Includes summary. Includes bibliographical references.

Floating sulphur biofilms are observed as surface layers in numerous aquatic sulphide-rich environments, and apparently play an important role in the cycling of sulphur in its various oxidation states. In addition to the conversion of sulphide to sulphur and/or sulphate species, it has been suspected that subsequent reduction back to sulphide may occur within the floating sulphur biofi1m in organic-rich environments. The use of sulphur biofilms for the harvesting of elemental sulphur from wastewater treatment systems has also been suggested. There is, however, little documented information in the literature on the structure of floating sulphur biofilms, or the microbial species responsible for their occurrence. In this study, floating sulphur biofilms were generated in a continuous flow baflle reactor and their structure was examined using scanning electron microscopy. It was found that they occur as layered structures with morphologically distinct bacterial forms present in different layers of the biofilm. The biofilpl structure was also found to be dynamic, with structural changes observed as feed conditions were altered. An enriched culture derived from the biofi1m demonstrated rates of sulphide oxidation comparable to values reported in the literature for liquid culture systems. The microbiology of the biofi1m was studied using traditional plate culture techniques and analysis ofrRNA genes. Identification of plate culture isolates as representatives of the biofi1m community proved to be limited, leading to a PeR-based cloning approach. The majority of the organisms present in the sulphur biofi1m were classified as species in the genus ~eudomonas, and a number of other bacterial species whose sulphide oxidising capacity has been noted previously. Surprisingly, only 2% of the clone library consisted of Thiobacillus spp., and no sulphate reducing bacteria were identified in the biofilm at all. These results indicate that in organic sulphide-rich environments facultative chemolithoheterotrophic bacterial forms predominate in floating sulphur biofilms, and that the complete biological cycling of sulphur may not occur in these systems.

The mechanism of polysulphide formation by γ-radiation of aqueous sodium sulphide (Na₂S) solutions was investigated. The roles of solvated electron (ēaq ) and hydroxyl radicals (•OH), as primary products of water radiolysis, were studied in a systematic manner by using N₂O as ēaq and 2-propanol as •OH scavengers. Polysulphide formation in Na₂S solutions was found to be initiated by the oxidizing intermediate, the •OH radical. The scavenger experiments were supplemented by other studies on effects of solute concentration, dose at a single dose rate, pH, oxygen and hydrogen sulphide (H₂S) saturation. Rates of polysulphide formation increased according to presence of N₂O and H₂S, Na₂S concentration, irradiation dose and were highest at pH 7.0. In these experiments, highest polysulphide yield, 14 g/l, was obtained in the 80 g/l aq Na₂S-H₂S system at pH 12.7 and exposed for 20 Mrad dosage. The effect of oxygen was to increase radiation yield for lower dose ranges. At higher doses, however, G-values fluctuated markedly. / Forestry, Faculty of / Graduate

Electrochemical methods and small scale flotation tests were used to study the effects of sulphur dioxide and potassium amyl xanthate on the floatabilities of pentlandite, chalcopyrite and nickeliferous pyrrhotite, at pH 5.5. Mixed potentials of all three mineral systems were positive to the dixanthogen/xanthate redox couple, even in the presence of aqueous SO₂. Thus the existence of dixanthogen is thermodynamically favoured in all these systems. The tests also indicated that adsorption of xanthate by: (i) chalcopyrite is enhanced by SO₂; (ii) pentlandite is impaired by SO₂; (iii) pyrrhotite is unaffected by SO₂; Anodic polarization curves, determined on mineral electrodes, suggested that, in xanthated systems, the collector (probably dixanthogen) forms a film on the electrodes. This film inhibits the continued electron transfer reactions on the surface. The protective character of the film is higher for chalcopyrite (increased by SO₂), than for pentlandite (decreased by SO₂), than for pyrrhotite (unaffected by SO₂). Cathodic polarization curves indicated that the cathodic process, on pentlandite and pyrrhotite electrodes, is controlled by oxygen reduction. The reduction of oxidized species on the surface is suggested as the controlling mechanism on chalcopyrite electrodes. Small scale flotation tests showed that the presence of SO₂ increases an already very high,recovery of chalcopyrite; decreases a high recovery of pentlandite, and decreases further a very low recovery of pyrrhotite. / Applied Science, Faculty of / Mining Engineering, Keevil Institute of / Graduate

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