4. Electronic Theses and Dissertations (ETDs) - Faculties submissions
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Item Surface water dependencies and activity patterns of mammalian herbivores in South Africa(University of the Witwatersrand, Johannesburg, 2024-10) Padayachy, Janiel; Hetem, Robyn; Strauss, Willem Maartin; Venter, JanAn increase in aridity in Africa may make water availability more variable, thus understanding how animals respond to these conditions is important for future wildlife management and conservation. However, mammalian herbivores with varying water requirements may respond differently to changes in water availability and predation. Using camera trap data, I analysed the spatial distribution relative to surface water sources and the 24-hour activity of 16 mammalian herbivores across 10 sites in South Africa. As expected, water dependent herbivores were generally closer to water, but only at sites where lions were absent. Herbivores with low water requirements were more nocturnal, potentially reducing water required to cool themselves evaporatively when active during the heat of the day. But that nocturnal activity was reduced when lions were present, likely reducing predation risk, increasing water requirements to dissipate heat and forcing herbivores to remain close to water. Nocturnal activity increased with body size in mixed-feeders and grazers, but decreased with body size in browsers, potentially reflecting more time spent foraging by large browsers. Using a novel approach of multistate diel occupancy models I showed that herbivores were generally active during both the day and night, and that the presence of lions impacted occupancy of preferred prey species (blue wildebeest, gemsbok and zebra). Diel occupancy of water-dependent prey (blue wildebeest) was influenced by an interaction between lion presence and distance to water sources. Thus environmental factors as well as physiological and morphological features affected the timing of activity and spatial distribution of several mammalian herbivore species in South African wildlife areas, which should be considered for future research and management of these species.Item Flood Susceptibility Modeling in the uMhlatuzana River Catchment using Computer Vision-Based Deep Learning Techniques(University of the Witwatersrand, Johannesburg, 2024-10) Chirindza, Jonas; Ajoodha, Ritesh; Knight, JasperIn this study, covolutional neural networks (CNN) models are employed for flood susceptibility modeling in the uMhalatuzana River catchment in KwaZulu-Natal, South Africa. The CNN models, including 1D-CNN, 2D-CNN, and 3D-CNN, pro-vide a detailed assessment of flood vulnerability in the region. The models use di- verse spatial information, such as topography, land use, and hydrological features, to estimate the likelihood of flooding in different areas of the catchment. The flood susceptibility maps within the uMhalatuzana River catchment, classified into five risk zones namely, ‘very low’, ‘low’, ‘moderate’, ‘high’ and ‘very high’ susceptibility zone, serve as proactive instruments for risk mitigation and disaster management. The 1D-CNN model displays strong overall performance in flood susceptibility modeling, evident in key metrics such as accuracy, precision, recall, area under curve (AUC) score, and F1-score. The results suggest that the model effectively captures patterns in the input data, emphasizing its potential for flood susceptibility modeling. Moreover, the 2D-CNN model outperforms the 1D-CNN, achieving higher values when evaluated using various performance metrics. Finally, the 3D-CNN model outperformed both the 1D-CNN and 2D-CNN, emphasizing its predictive abilities in flood susceptibility modelling. The flood susceptibility maps produced by the 1D-CNN model, shows that most of the study area exhibits very low flood susceptibility (96.4%), with localized areas of higher susceptibility, particularly in the very high-risk category (2.53%). The 2D CNN model demonstrates a more diverse risk distribution, with a substantial portion having very low susceptibility (74.19%) and significant areas of higher risk, notably in the very high-risk category (10.93%). The 3D-CNN model emphasizes a spatial pattern where a large portion has very low susceptibility (84.10%), but with a concentration of high and very high-risk areas, comprising 12.34% of the total area. Finally, the consistent identification of higher risk susceptibility areas enhances the robustness of the assessments. The models’ high accuracy and detailed risk assessments provide valuable tools for decision-makers, urban planners, and emergency response teams in the uMhalatuzana River catchment. The precision of the models facilitates informed strategies for flood risk management, including targeted interventions such as improved drainage systems and early warning systems.Item Improving Iterative Soft Decision Decoding of Reed Solomon Codes Using Deep Learning(University of the Witwatersrand, Johannesburg, 2024) Nkiwane, Kimberly NtokozoTelecommunications in the current information age is increasingly dependent on efficient transmission of data through a noisy channel. Therefore, utilizing For- ward Error Correction (FEC) in the development of decoding algorithms is an active area of research. This dissertation work focuses on exploiting deep learn- ing techniques and error correction techniques to improve iterative soft decision decoding of Reed Solomon codes (RS). The parity check matrix of RS codes is characterized by a dense structure. This directly affects the exchange of soft information during the iterative decoding process. Therefore, to counter this issue, a bit-level implementation is utilized with the proposed decoding approach. Furthermore, additional techniques to add sparsity to the parity check matrix are presented in this research work. The proposed method for adding sparsity leverages the cyclical properties of RS codes to add low rate rows to the parity check matrix. This sparse implementation aids with the exchange of soft information during the message passing stage of the proposed iterative decoding process. The implementation of deep learning techniques to improve iterative soft decision decoders are also presented in this dissertation. The proposed approach makes adjustments to the Neural Belief Propagation (NBP) algorithm for RS codes. The proposed NBP utilizes the sparse implementation presented in this research to improve exchange of soft information. This in turn leads to gains in error correction performance without further adding complexity which is one of the main advantages of incorporating neural networks in the iterative decoding process. Additionally, this dissertation proposes a Graph Neural Network (GNN) imple- mentation for iterative soft decision decoding of RS codes. The approach employs the GNN architecture to construct a fully connected graph. This graph represents a message passing algorithm based on the Tanner graph, with trainable weights assigned to the graph nodes. This implementation improves the error correction performance of the proposed iterative soft decision decoder while reducing the number of iterations required to decode the received vector.Item A linear vibration isolator integrating a non-linear energy sink (nes)(University of the Witwatersrand, Johannesburg, 2024) Waite, Clinton; Li, KuinianThis report investigates the integration of traditional linear vibration isolators with non-linear energy sinks (NES) to enhance vibration control in structures subjected to dynamic loading. Structures often respond to dynamic loads—such as machinery vibrations, seismic activity, and environmental factors—by vibrating at their natural frequencies, potentially leading to resonance and structural failure. Vibration isolation and damping systems, such as linear isolators and NES, mitigate these effects. Linear isolators are effective at higher frequencies but have limited performance at lower frequencies, while NES systems offer broader frequency- range effectiveness. This study explores the effectiveness of combining these systems to optimize vibration control. Through simulation of both simple and complex setups, the research compares the vibration response of traditional linear isolators, NES-integrated isolators, and NES systems combined with additional damping elements. Key findings demonstrate that integrating NES with linear isolators significantly reduces peak transmissibility and improves vibration reduction under harmonic and seismic loading. However, the integration's effectiveness varies depending on system configuration and specific loading conditions, highlighting the need for further optimization. The study also presents a parametric analysis for designing vibration control systems tailored to diverse applications, offering valuable insights for engineering practice in reducing structural vibrations.Item Emerging Contractor Development through the Provision of Low-cost Housing in the Eastern Cape(University of the Witwatersrand, Johannesburg, 2024) Joseph, Shati; Fitchett, AnneThe construction industry is an economic stimulant and enabler of growth particularly in developing nations such as South Africa. The industry’s low entry barriers and the nature of work being labour-intensive attract emerging contractors. These contractors create jobs, upskill the community and transfer wealth to the previously marginalised. However, studies have shown that despite these several benefits, emerging contractors are prone to fail. Therefore, this research investigated the challenges facing emerging contractors and in addition, examined the low-cost housing programme. The positivism paradigm was adopted because of the nature of the research questions, its efficiency in the collection of voluminous data, and its perceived credibility by the policymakers. The collated data from 66 out of 173 contractors on the Eastern Cape Department of Human Settlements database were statistically analysed. The findings showed that most of emerging contractors are typically owned by a black male with a tertiary education, employ less than 20 employees, are capable of work worth less than R20 million and do not have a background in construction. The findings presented that the government was the primary employer of emerging contractors while some rely on subcontracting. Several contractors reported that they spent between 30 to 60 per cent of the contract value on materials. The start-up funds for emerging contractors are largely from family’s savings due to limited access to low- interest loans. During operation, the contractors heavily depend on monthly payment certificates to meet their expenses hence the importance of promptly settling these certificates. Emerging contractors receive training, it is largely from unaccredited mentors, which limits the upskilling of these contractors and leads to poor performance. The study then proposed possible initiatives that can employed for a progressive developmental programme based on the findings.Item The Informal Waste Sector in the City of Ekurhuleni(University of the Witwatersrand, Johannesburg, 2024) Nyirenda, Irene N. Inan; Fitchett, AnneIn South Africa, landfilling has traditionally been the primary method for dealing with general municipal solid waste. However, in recent years, there has been a shift in focus towards promoting a circular economy, which has brought about a change in waste management practices. The focus is now on minimising waste generation and reducing the waste stream rather than simply disposing of it. This approach aligns with South African National Waste Management Strategy 2020, which encourages such practices. The study focused on City of Ekurhuleni and the opportunities that exist in the formalisation of the informal waste sector with particular focus on landfill waste pickers and by analysing the amount of waste disposed of at the landfill site over a six (6) year period and comparing it to the percentage of materials that informal waste pickers recovered and reclaimed, the study provided valuable insights. This study utilised a mixed-method design that involved collecting and analysing both quantitative and qualitative data through desktop surveys, face- to-face interviews, and questionnaires. The practice of informal recycling at landfill sites encounters numerous environmental and health hazards for those who reclaim materials, because the waste is not sorted before disposal. The municipality lacks adequate resources for waste reduction initiatives, regulatory framework and capacity, educational campaigns, and enforcements, unlike those carried out by private companies or organisations. The study highlighted that some of the key inconsistencies in the interpretation of informal sector activities and their integration thereof in the context of the municipal regulatory framework are vague and unsupported.Item Heavy metal contamination and its spatial distribution from mining wastesin receiving environments of Mazowe District, Zimbabwe(University of the Witwatersrand, Johannesburg, 2024) Charema, Josiah; Taigbenu, Akpofure; Newete, SolomonThe purpose of this study was to investigate heavy metal contamination and its spatial distribution from mining wastes (especially artisanal/informal mining) and the impact of agriculture on heavy metal pollution in receiving environments of the Mazowe district, Zimbabwe. Agriculture and mining have considerably contributed to heavy metal and nutrient concentration into the world’s freshwater systems. This study aimed to improve the understanding of the contribution of agriculture and informal mining to heavy metal and nutrients pollution of Mazowe River. Also, the research aimed to establish the contribution of sulphates and phosphorous on heavy metal mobility in agricultural and mining areas. The research was conducted in Mazowe District in Mashonaland Central Province of Zimbabwe. Collection of the samples was carried out at five locations along Mazowe River, from its outlet at Mazowe dam to about 25 km downstream. The samples were preserved using WHO approved preservation methods and transported to a licensed laboratory in Harare for testing and analysis of heavy metals (Hg, Pb, Cr and Cd), extractable sulphates and phosphorus at Zim Labs laboratory, in Harare - Zimbabwe. Heavy metal analysis was done using the flame Atomic Absorption Spectrometer after wet digestion. The results indicated an average concentration of heavy metals in the river sediments ranging from 0.01mg/kg (Hg) to 26.68 mg/kg (Pb) during the wet season. During the dry season the levels of Hg, Pb, Cr and Cd were less than 0.01mg/kg. There were low detectable levels of heavy metals in the water samples for both wet and dry seasons. Significant differences in mean levels of phosphates and extractable sulphate pollutants were observed in the wet and dry season. The average phosphorus levels detected in the sediment samples during the wet season was 14.93mg/kg which was 93.7% higher than that of water samples which was at an average of 0.94 mg/l. The sampling points were small due to budget constraints and limited access to some areas because of property rights’ issues and national key points along Mazowe River. Thus, it would imperatively be unjustified to generalise the effects of the research outcome to other locations within Mazowe River Catchment or locations along Mazowe River downstream from the study area, without considering other land use patterns. The results showed that the presence of heavy metals in the sediment samples of Mazowe River could be highly attributed to informal mining along the river while extractable sulphates and phosphorous in both water and sediment samples could be attributed to agricultural activities. These findings may assist the environmental management and mining authorities to regulate the activities of artisanal mining to combat heavy metal contamination of rivers from mining activitiesItem Extraction of Alumina from South African calcined clays(University of the Witwatersrand, Johannesburg, 2024) Maria, Matome BatsalelwangThe growing need for high-purity alumina (HPA) is driven by its critical importance in sophisticated batteries and electronic applications. Typically produced from high- purity aluminum (Al) metal using the alkoxide method, HPA production is closely linked to the Bayer process, which relies on Al metal derived from alumina (Al2O3) extracted from bauxite ores. However, the scarcity of alumina-rich bauxite reserves has prompted interest in alternative local sources of alumina including kaolinitic clays, which are abundant and widespread. Although the Bayer process is not appropriate for treating kaolinitic clays owing to their high silica content, efforts have been made to explore alkaline and acidic processing methods for alumina extraction. In particular, the HCl acid leaching process has been extensively studied as a viable acidic processing route. South Africa possesses abundant kaolinitic clays despite the lack of bauxite reserves, making it necessary to investigate the potential for alumina extraction via HCl processing. This study investigated the dissolution of aluminum and iron species from thermally activated clay in a hydrochloric acid solution, emphasizing the selectivity of aluminum extraction over iron impurities. Furthermore, the effect of different calcination and acid leaching conditions on the dissolution of aluminum and impurity species in a hydrochloric acid solution was investigated. Three different kaolinitic clays sourced from South Africa, namely ball (BL), flint (FL), and fire (F) clays, were analyzed to ascertain their chemical and mineralogical properties. It was observed that the raw BL and FL clays utilized in this study shared similar mineralogical compositions, whereas the F clay contained additional clay minerals such as carbonates and smectite. However, mineralogical analysis revealed that BL and FL clays were predominantly rich in kaolinite (82.4% and 91.1%, respectively), whereas raw F clay exhibited a lower kaolinite content (16.5%) and a higher amount of quartz (44.7%). The calcination of kaolinitic clay was performed at temperature range of 600 to 800 °C (interval of 50 °C) for a period of 8 hours. Infrared spectroscopy and X-ray diffraction were employed to confirm the structural and mineralogical changes, iii revealing the transformation of kaolinite into amorphous metakaolinite. The research revealed that calcination temperature significantly influenced alumina extraction, with varying effects on iron content. The calcination temperatures necessary for the complete dehydroxylation of kaolinite into amorphous metakaolinite were uniform across all samples of raw BL, FL, and F clays at 600°C. At this temperature, BL clay demonstrated an Al extraction 79.4%, FL clay showed a recovery of 78.4%, and F clay exhibited an Al extraction of 36.7%. However, although the Al extraction from F clay increased with an increase in calcination temperature, it did not exceed 50 %. Conversely, an increase in the thermal decomposition temperature was accompanied by a decline in the amount of Al extracted from calcined BL clay. The incorporation of iron oxide species in calcined BL clay resulted in the formation of insoluble aluminum spinels at higher temperatures, particularly starting from 700°C until 800 °C. This process led to a decrease in the acid solubilities of both aluminum and iron. Interestingly, the extraction of aluminum from calcined FL clay exhibited a fluctuating pattern: it decreased at 650°C and 750°C but increased at 700°C (69.5%) and 800°C (71.8%). Both calcined BL and FL clays at 600°C demonstrated high aluminum extraction, although accompanied by high iron content (67.8% and 66%, respectively), whereas calcined FL clay at 800°C offered high aluminum extraction with moderate iron content (40.2%). In comparison with BL clay, the lower amount of iron oxides in FL clay did not present a clear trend for the formation of spinels. Statistical analysis showed that leaching time had a significant impact on aluminum extraction of BL clay. Meanwhile, the acid concentration (pertaining only to FL clay), leaching temperature, solid/liquid ratio, and leaching time and solid/liquid ratio interaction significantly affected aluminum extraction for FL and F clays. A higher iron content has ramifications in HPA production for subsequent processing of the leachate solution. However, the reduced energy requirement for achieving complete dehydroxylation, which is essential for aluminum dissolution, presents a significant advantage for aluminum recovery from both BL and FL clays. The choice between BL and FL clays would depend on either a lower energy requirement in the pre-treatment stage with the associated higher cost of processing leachate containing elevated iron content, or a higher energy demand in the iv pretreatment phase with a lower cost linked to processing leachate with moderate iron content. Notably, for FL clay, there was flexibility in assessing the three calcination temperatures that yielded high aluminum dissolution. The findings of this study hold considerable importance for utilizing South African kaolinitic clays as a cost-effective, locally sourced alumina resource for HPA production.Item Extraction of gold from tailings using environmentally friendly reagents(University of the Witwatersrand, Johannesburg, 2024) Khuduwe, Marema JackThe depletion of high-grade gold ores, the high production costs associated with mining at lower depths, and the high demand for gold have caused the mining industry to search for alternative sources of gold. Additionally, the conventional cyanidation process raises health and environmental concerns. The treatment of waste generated by the cyanidation process to reduce the residual cyanide content before disposal also incurs additional costs. Therefore, this study focuses on the extraction of gold from tailings using environmentally benign reagents such as 1-butyl-3-methyl-imidazolium hydrogen sulfate (BmimHSO4) ionic liquid (IL), ethaline (mixture of choline chloride and ethylene glycol) deep eutectic solvent (DES), and thiosulfate. The gold tailings used in this work were obtained from DRD Gold Ergo Mining (Pty) Ltd operations in the Witwatersrand Basin, South Africa. Mineralogical analysis by X-ray diffraction (XRD) showed that the tailings material consisted of quartz (72.13%), muscovite (7.49%), chlorite (2.65%), pyrophyllite (1.50%), clinochlore (1.30%), and other trace minerals. The gold association by mineral liberation analysis (MLA) employing the Sparse Phase Liberation-Dual Zoom (SPL-DZ) method indicated that all the gold was locked in the iron oxide (FeO) matrix. Gold grade analysis by fire assay analysis (FAA) showed that the tailings had a head grade of 0.32 g/t Au. The leaching of the gold tailings was carried out by employing the use of the design of experiments (DOE) method to identify factors that significantly influence the gold extraction process. The central composite design (CCD) technique in conjunction with response surface methodology (RSM) was used to optimize the identified significant factors to obtain optimum conditions for optimal gold extraction. The effect of particle size and the co-dissolution of Ag, Cu, Fe, and Ni with Au was investigated. Furthermore, the recovery of Au by activated carbon (AC) from leach solutions of the investigated reagents was also investigated The results from the IL studies indicated that the reagent concentration had a positive and significant influence on the gold extraction process, suggesting that to achieve optimal gold extraction, IL concentration must be kept at a high level. The interaction of temperature, concentration, and pulp density also significantly influenced the gold extraction process in the IL solution. The theoretical optimum conditions established from the statistically-based optimization model were 75 C leaching temperature, 1.0 M (25% aqueous BmimHSO4 Extraction of gold from tailings using environmentally friendly reagents Marema J Khuduwe 4 mixture ) IL concentration, and 10 %w/v pulp density, giving a maximum Au extraction of 45.3%. This low Au extraction is attributed to the inefficiency of ILs in dissolving metals from their solid oxide form, thus unable to liberate the gold for dissolution locked in the metal iron oxide. On the other hand, leaching studies focusing on the use of DES found that pulp density and leaching time had a significant and positive influence on the gold extraction process. This suggests that to achieve maximum gold extraction, pulp density and leaching time must be kept at high levels. The optimum conditions were found to be 30 %w/v pulp density and 7 hrs leaching time. A maximum Au extraction of 76.4% was achieved. This high gold extraction is attributed to the high FeO destruction observed in the study, suggesting that the gold was liberated and amenable to leaching. Lastly, thiosulfate leaching studies identified temperature, time, pulp density, the interaction of temperature and concentration, the interaction of concentration and pulp density, and the interaction of temperature and time as the parameters significantly influencing gold extraction. A maximum Au extraction of 47% was achieved. This low gold extraction is attributed to the low efficiency of thiosulfate in dissolving metal iron oxide and the reagent consumption through silica dissolution, thus reducing the amount of thiosulfate available for gold dissolution. The results of the effect of tailings particle size results revealed that the IL leaching of bulk tailings (-300 m, P80 = 75 m) gave Au extraction of 21.9% while the leaching of smaller particle size tailings (-38 m) increased Au extraction to 45.3%. The high gold extraction at smaller particle sizes is attributed to the large surface area available for interaction with the leaching agent and the presence of a thin boundary, thus resulting in improved leaching efficiency. On the other hand, DES leaching of bulk tailings resulted in Au extraction of 71.9% and the leaching of smaller particle size tailings gave 76.4% Au extraction, indicating that reduction in particle size did not have a significant impact on gold dissolution. Lastly, thiosulfate leaching of bulk tailings gave a maximum Au extraction of 24% and the leaching of smaller particle size tailings resulted in an increased Au extraction of 47%, indicating that a reduction in particle size in this system had a significant effect. The study indicated that DES was more efficient in the dissolution of gold tailings compared to the use of IL and thiosulfate. Furthermore, DES gave higher Au extraction (71.6%) compared to cyanide solutions which gave Au extraction of 46.9%. However, cyanide gave a higher Au extraction compared to IL (21.9%) and thiosulfate (24%). These results indicate that ethaline DES is more efficient compared to 1-butyl-3-methyl-imidazolium hydrogen sulfate IL Extraction of gold from tailings using environmentally friendly reagents Marema J Khuduwe 5 and thiosulfate, and thus can be used in the processing of this kind of tailings as an alternative to cyanide. Moreover, the reagents dissolved more gold compared to other metals in the tailings except for IL which dissolved more Cu (50.4%) and Ni (61.9%) compared to Au (45.3%). Finally, the recovery of gold from the leach solution of the investigated reagents using activated carbon (AC) was found to be possible with the maximum Au adsorption of 84.6% achievable from IL leach solution in 2 hours at AC amount of 60 g/l and 4 hours at AC amount of 120 g/l. The maximum Au adsorption of 75% was achieved from DES leach solution in 4 hours at an AC amount of 120 g/l. The highest Au adsorption of 46.4% was achieved from thiosulfate leach solution in 6 hours. The recovery of Au by AC from leach solutions of IL and DES was high, however, they are not comparable to the 99% gold recovery by AC from cyanide solutions in the industry. This indicates that the recovery of gold from these solutions by alternative adsorbents should form a basis for further investigation.Item Quantification of benefits of digitalisation of process data of a craft distillery(University of the Witwatersrand, Johannesburg, 2024) Kankenga, Daniel Pembe; Higginson, AntonyCraft breweries and distilleries are frequently not digitalised, making them susceptible to regular production losses. Despite this, benefits of investing in digitalising process are often not easily measurable. The purpose of this research study is to develop a comprehensive framework to quantify the benefits of digitalising process data within the brewing process of a craft distillery. The study was based on historical data from Primal Spirit Distillery, located in Johannesburg, South Africa. The data underwent validation through the application of data visualisation techniques as well as a comprehensive statistical analysis. Mass balance calculations were conducted for the mash tun and fermentation processes, as well as an overall mass balance assessment to compare potential alcohol content with actual alcohol produced. Statistical tools, such as correlation analysis and the student t-test, were used to interpret the data and identify opportunities for digitalisation to enhance productivity. The study concluded with an economic analysis, assessing the financial implications and profitability of digitalising process data in the distillery. The conclusion of the research study highlighted the significant potential for improving productivity in craft distilleries and breweries through the digitalisation of process data. The developed framework proved effective in quantifying these benefits, encompassing steps such as historical data collection, visualisation, mass balance, statistical analysis, intervention planning, and economic feasibility assessment. The analysis revealed considerable sugar loss during mashing, with an average of 16.45%. Fermentation resulted in alcohol levels within the acceptable range in only 53.66% of instances, with an average alcohol deviation of 32.29%. The distillery, on average, operated at 67.71% of its potential alcohol production capacity. Correlation analysis and t-tests identified key variables requiring careful monitoring to reduce deviations and enhance productivity. While there are more economical alternatives, the optimal solution involves the use of affordable storage platform for process data, process control instrumentation devices, such as sensors and flow meters. The economic study indicates that a R 200,000 investment to digitalise the distillery's process data could boost productivity by 30%. The investment would be fully recovered in 4 months, with a 25.43% profit gain within 5 months. However, actual profitability may range between 10 to 20% due to potential unforeseen circumstances during production.