3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Remediation of acid mine drainage utilizing sugar cane bagasse and basic oxygen furnace slag(2019) Dusterwald, Jarad HadleyIn this study a combination of basic oxygen furnace (BOF) slag and sugar cane bagasse (SCB) were assessed for their potential to remediate acid mine drainage (AMD). SCB was also individually assessed to determine its remedial potential. Small-scale laboratory experiments were carried out to determine the effectiveness of this combination of BOF slag and SCB in removing sulfate and iron and raising the pH. In the small-scale laboratory experiments, four different configurations were used: the first configuration was packed with SCB in the first column and SCB in the second column, the second configuration was packed with SCB in the first column and BOF slag in the second column, the third configuration was packed with a mixture of SCB and BOF slag in the first and second columns and the fourth configuration was packed with BOF slag in the first column and SCB in the second column. The results that followed indicated that there is a potential for SCB and BOF slag to treat AMD. These experiments occurred for two different residence times; a low residence time which was approximately 35.5 hours ± 5.5 and a high residence time which was approximately 78.5 hours ± 7.5. The removal of iron and sulfate as well as the increase in pH showed that all the configurations achieved some form of remediation. The highest percentage of sulfate removed in all the configurations was 86%, the highest percentage of iron removed was 99.99% and the highest pH value at the outlet was 12.82; all of these maxima were achieved for the higher residence times, indicating the impact that residence time has on these particular systems. A one-way analysis of variance (ANOVA) within each of the configurations, and variance between the configurations was performed on the resulting data using the built-in function in Excel; this was done within the 95% confidence interval. These tests indicated that there was a statistical significance, when it came to raising the pH and removing iron between the columns that had no BOF slag and the columns that did, and by interpreting the graphs in the results section, it can be seen that it was the BOF slag that was responsible for the higher rise in the pH and for most columns the higher removal of iron. Initially indications appear to be optimal for configuration D (the first column containing BOF slag and the second column containing SCB) being the most suited to treat AMD, however when the residence times were taken into account and the results found in Section 4 and ANOVA were interpreted more thoroughly, it gave an indication that configuration B (the first column containing SCB and the second column containing BOF slag) is the most suited to treating AMD. Configuration B has a high removal percentage of sulfate of 67% and maintains a removal of sulfate for over 55% for a longer period of time than configuration D. The start of breakthrough for configuration B took longer than that of any other configurations and as such the replacement of the remediating substances would not be as frequent. The results show that these materials are able to treat synthetic AMD. They also show that the interoperating of BOF slag and SCB is better than the configuration containing only SCB. Results also indicate that higher residence times are more suited to treating AMD in removing a higher percentage of iron, sulfate and raising the pH. The results also indicate that configuration B is the most suited to treat AMD.Item Gas phase extraction of vanaium from spent vanadium catalyst and tantalum from tantalum oxide(2017) Olehile, Obakeng DanielGas phase extraction of metals using volatile organic reagents can be applied to metal bearing sources such as metal oxides, iron ore fines and fly ash. The process has the potential of having a smaller environmental impact compared with conventional extraction processes and the possibility also exists to recover and recycle the extractant. The research was directed to extend the application of gas phase extraction to two new metal systems, namely spent vanadium catalysts and a synthetic low grade tantalum oxide “ore”. A literature review revealed that acetylacetone, trifluoro-acetylacetone and hexafluoro-acetylacetone were suitable extractants for vanadium and tantalum in a gas phase process. Due to safety considerations the fluorinated acetylacetone derivatives were not applied in the process and acetylacetone was the only extractant under investigation. The influence of the process parameters, temperature, particle size, acetylacetone flowrate and bed weight of the solid, on the extraction extent was studied for each system. The sulphuric acid spent catalyst contained 49.03 mg vanadium/ g catalyst and the process was capable of extracting up to 60.3% of vanadium after contacting 15 g of catalyst (particle size +250μm to -500μm) with 7 mL/min of acetylacetone at a reaction temperature of 190 °C after 7 hours. It was also found that the reaction temperature, acetylacetone flowrate, and the interaction effects between particle size, ligand flowrate and catalyst bed loading, had a significant influence on the extraction degree of vanadium at 95% confidence level. Furthermore, a kinetic analysis revealed that the gas phase extraction was either mixed controlled or diffusion controlled. The preliminary tantalum extraction study conducted here shows that gas phase extraction can be successfully applied to a synthetic tantalum oxide-silica sand mixture. The highest tantalum extraction of 93.4% was achieved at 150 °C after 5 hours of extraction at an acetylacetone flowrate of 7 mL/min for a 15 g bed (2 wt% Ta2O5). The solid-gas reaction between tantalum oxide and acetylacetone fluidised bed reactor were significantly influenced by the joint interaction effect of tantalum oxide concentration, acetylacetone flowrate and bed weight of the synthetic tantalum oxide mixture at 95% confidence level. The kinetic study showed that the gas phase extraction reaction of tantalum was governed by diffusion.Item Simulation of multiple closed loop milling circuits(2015-07-02) Rabins, RichardItem Optimizing the operating conditions of gold elution and electrowinning for Tau Lekoa stream at Kopanang gold plant(2008-06-25T08:25:30Z) Lunga, Alfred LodiThe final gold product of Tau Lekoa mine has a low fineness. This is caused by high concentration of bases metals in the reefs. Some of these base metals together with gold are leached with cyanide and are loaded into carbon. If not adequately controlled, they may elute with gold and contaminate the final product in the electrowinning process. Based on the understanding of the kinetics of the elution, four parameters, namely temperature, flow rate, free caustic soda concentration and cyanide strength, were evaluated first for the elution process. Experimental runs on the plant scale did prove that the first three parameters are the predominant parameters that maintain base metals in the carbon during the elution and therefore assist in the improvement of the fineness of the final product. Recommendations were made to change the operating conditions and the fineness of the gold did improve from 80% to 84 %. In addition, a thermodynamic model that took to consideration the competition of gold and nickel was developed for the electrowinning process. This model showed that the deposition of gold and nickel during the electrowinning was dependant of their concentrations and temperature. The single pass efficiencies and the deposition rates were also tracked during the experimental. Based on the finding on the reduction of electrowinning time, the fineness of the final product was improved from 84% to 85%. As the refining cost depends on the fineness of gold, the improved fineness means that the gold content in the bullion is increased and the impurities are decreased, therefore, the refining cost will decrease as lower penalty costs are charged for the treatment of the bullion with high fineness. The recommendations of the changes have been implemented permanently and these did show permanent improvement of the fineness.