3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item A comparison of conventional and unconventional reductants through characterization and reactivity tests on solid state chromite reduction for application in the South Africa ferrochrome industry(2018) Chiwoko, AaronReductants form a significant portion of the production costs during ferroalloys processing. Consequently, the need arises to cut costs and drive profitability through raw materials optimization, viz, reductants. Unconventional reductants are expected to have a high reactivity and fixed carbon content, but their current availabilities are low. Innovation together with substitution has become a necessity to ensure sustainability and competitiveness of processing operations. The main objective of this research was to study and compare the reactivity of commonly used reductants and that of readily available, new sustainable carbon materials as potential reductants for the reduction of natural chromite at steady state. The selected reductants comprise of conventional Reductants A (Market Coke), B and B1 (Trial Market Cokes), C (Industrial Char) and unconventional Reductant D (Charcoal). This investigation was undertaken by initially characterizing the reductants with the use of advanced analytical techniques including proximate, ultimate, particle size distribution and petrography and then to determine the merits and demerits of each in typical ferrochrome processes. This was followed by reactivity tests in the solid state at temperatures ranging from 1100oC, 1200oC, 1300oC to 1400oC and over a 4 hour period. A thermo-gravimetric analysing (TGA) furnace was used with tests undertaken under inert atmosphere in order to determine the practical performance and application of each reductant. Data collected from a series of TGA furnace campaigns was utilised to determine the reactivity of the selected reductants. Analytical methods of chemical speciation, XRD and SEM-EDS were applied to confirm the extent of chromite reduction. The outcome of this research project indicated that the best reductants according to overall mass loss were D (122.03%), C (112.97%), A (91.61%), B (90.51%) and B1 (80.72%), consecutively in reducing order. Whilst the unconventional Reductant D was shown to be most reactive and having the highest mass loss at test temperatures 1100oC -1300oC, all conventional reductants performed better than the unconventional reductant at 1400oC. At this temperature, Reductant B had the highest mass loss of 51.5% followed by Reductants A (47.7%), B1 (44.1%), C (40.5%) and lastly D with 31.7%. Only Reductants D and C in most instances reached saturation within the test period (4 hours). Substantial reduction of Cr2O3 and FeO occurred (%DOR for FeO, 72.03% and Cr2O3, 67.96 %) as shown by the analysis of chemical phases present. This had the iron-chrome and chrome-iron phases dominating. It is hoped that the outcomes of this research will establish the relevancy of new unconventional reductants as benchmarked against the current reductant products used in ferrochrome processing. Finally, this study has developed a procedure for the ranking of reductant reactivity.Item Investigating alternative voltammetric methodologies to study complex formation(2017) Ndlovu, Mapule PrudenceMetal complexes have a wide range of applications in fields such as medicinal, industrial, environmental and so on. Determining the formations constants for metal complexes is thus essential to gather information on complexes. Conventional methods used to study complexation include spectroscopic methods and the use of voltammetric techniques such as direct current polarography using a mercury drop electrode. In this work alternative voltammetric methods to study complex formation are investigated. Bismuth complexes have important medicinal applications but not much is known about them because of the difficulties in studying them due to extensive bismuth hydrolysis and precipitation of hydrolysis products from very low pHs. The aim of this work was to investigate whether using low concentrations of bismuth (10-6 M) would prevent precipitation in nitrate solutions as predicted in literature. Differential pulse anodic stripping voltammetry (DPASV) was the technique of choice because of its low detection limit, even though it has not been widely used in complex formation studies before. The study revealed that electrochemical response for Bi3+ was not fully reversible using this technique. Additionally, even at the low concentration precipitation was observed in the acidic region (investigated via pH titration) and was suspected to be the formation of BiONO3 species. The second alternative method investigated was the use of mercury film electrodes to replace the use of the toxic mercury drop electrodes which are being phased out worldwide. This work looked at using in situ and ex situ plated films, where the in situ measurements proved more reproducible. A number of challenges were encountered, such as film degradation, peak splitting and ligand adsorption to the film electrode. Nonetheless, formation constants of lead-glycine complexes were determined under different experimental conditions and these were found to be reasonably compared to the literature values.Item Studies on hemin and cobalt corrinoids in aqueous solution(2015-01-13) Campbell, Vivien Mary