https://etd.cput.ac.za/handle/20.500.11838/858 2026-04-15T13:13:19Z 2026-04-15T13:13:19Z Griffiths, Clive Vinee O’niell https://etd.cput.ac.za/handle/20.500.11838/4333 2026-02-11T10:24:28Z 2025-01-01T00:00:00Z

Title: The extraction of platinum group metals from catalytic converters: non conventional solvents and pressure effects Authors: Griffiths, Clive Vinee O’niell Abstract: Secondary sources of precious metals, such as catalytic converters, contain up to 200 times higher concentrations of platinum group metals (PGMs) compared to natural ores, making them increasingly important for sustainable metal recovery. Catalytic converters contain platinum, palladium, and rhodium in approximate ratios of 4:4:1, with market values in the ratio of 1:1:4, respectively. Current recovery methods using conventional organic solvents achieve high recoveries for platinum and palladium but significantly lower yields for rhodium, while also posing environmental, health, and safety concerns. Deep eutectic solvents (DES) have emerged as environmentally benign alternatives to conventional organic solvents for metal extraction. However, their high viscosity limits mass transfer efficiency, reducing extraction kinetics and overall recovery yields. This study investigates, for the first time, the combination of DES with supercritical CO₂ (sCO₂) to overcome viscosity limitations and enhance PGM recovery from spent catalytic converters. Conductor-like Screening Model for Real Solvents (COSMO-RS) identified choline chloride and oxalic acid as the optimal hydrogen bond acceptor (HBA) and hydrogen bond donor (HBD) pair for DES formulation. Extraction experiments were conducted using both water bath and pressure-assisted processes with compressed CO₂. The effect of water addition on DES viscosity and the influence of compressed CO₂ on extraction efficiency were systematically investigated. The combined DES-sCO₂ approach achieved unprecedented recovery yields from the solid residue: 86.5% for platinum, 84.7% for palladium, and above 77% for rhodium. This represents the first time such high rhodium recovery has been achieved using compressed CO₂-assisted extraction. However, a significant challenge was identified in the poor absorption of metals into the DES phase, with only 17.8%, 17.3%, and 20.5% absorption for platinum, palladium, and rhodium, respectively. This work demonstrates that while DES-sCO₂ systems can effectively leach PGMs from catalytic converter matrices, future research must focus on optimizing metal-DES complex formation to improve absorption efficiency. The findings provide a foundation for developing more sustainable PGM recovery processes and highlight the potential of pressure-assisted extraction using environmentally benign solvents. Description: Thesis (MEng (Chemical Engineering))--Cape Peninsula University of Technology, 2025

2025-01-01T00:00:00Z Swami, Kevin Nzuzi https://etd.cput.ac.za/handle/20.500.11838/4221 2025-05-21T09:51:30Z 2024-01-01T00:00:00Z

Title: Iron precipitation kinetics during microbial ferrous-ion oxidation Authors: Swami, Kevin Nzuzi Abstract: The formation of ferric-ion precipitates, such as jarosite, has been extensively documented during the bioleaching process. These precipitates serve as pathways for unwanted iron to escape from the system in various processes. However, a significant accumulation over an extended period can hinder reaction kinetics and reduce the overall efficiency of bioleaching. Therefore, this study sought to investigate the kinetics of the ferric-ion precipitates that are formed through bacterial oxidation. Experiments were conducted using a mixed mesophilic culture in shake flasks, with temperatures set at 30, 35, and 40 °C in a shaking incubator maintained at a constant pH of 1.7. The experiments lasted 14 days, with an agitating speed of 120 rpm. Upon analysing the quantification results, the maximum quantity of ferric-ion solid precipitates that developed was 2.48 grams at a temperature of 40 °C. Additionally, the data indicated that ferric-ion precipitation began 24 hours into the process. The precipitates generated were characterized by dense, light ochreous yellow residues. The patterns created by the X-ray powder diffraction (XRD) of these crystals were identified as potassium jarosite (K-jarosite), with its chemical formula being [KFe3(SO4)2(OH)6]. The scanning electron microscopy (SEM) analysis of their shape showed clusters of spherical, oval, and/or rectangular, powdery particles, all without clear, sharp edges. The Fourier transform infrared (FTIR) spectra of these crystals revealed the vibrational frequencies of SO42−, H2O, OH, and Fe–O in the jarosite. Furthermore, the thermogravimetric analysis (TGA) tests indicated the loss of hydroxyl groups from K-jarosite and the complete decomposition of yavapaiite when heated. The formation of ferric precipitates occurred according to first-order kinetics. The estimated activation energy was 117.2 kJ/mol with a frequency factor (K) of 2.94 X 1020 mmol Fe3+.h-1, indicating that the process was endothermic, with an average [Fe3+] of threshold 1.22 g/L. The thermodynamic parameters obtained were entropy (ΔS) = 0.25 kJ/mol K, Gibbs free energy (ΔG) = 43.89, 42.64, and 41.39 kJ/mol at 30, 35, and 40 °C, respectively, and Enthalpy (ΔH) = 120 kJ/mol. These values suggest that the formation of ferric precipitates was non-spontaneous and required a considerable amount of energy to proceed towards spontaneity. This study revealed that the generation of iron precipitation during microbial ferrous-ion oxidation by mesophilic consortia follows first-order kinetics. This process is endothermic and non-spontaneous, necessitating energy to transition to a spontaneous state. The findings could provide valuable insights for biohydrometallurgical processes aimed at managing and controlling jarosite formation and accumulation, thereby minimizing metal losses. Description: Thesis (MEng (Chemical Engineering))--Cape Peninsula University of Technology, 2024

2024-01-01T00:00:00Z Tshowa, Patrick Kaja https://etd.cput.ac.za/handle/20.500.11838/4186 2025-05-22T11:30:27Z 2024-01-01T00:00:00Z

Title: Design and optimisation of domestic-scale thermoacoustic refrigerator Authors: Tshowa, Patrick Kaja Abstract: This research study aimed to evaluate the performance of a standing wave thermoacoustic refrigerator and optimise the stack length and position for a single stack material. Thermoacoustic refrigerator (TAR) generally has a low coefficient of performance (COP). This has negatively impacted its development. There has been research to improve its COP, which has mostly focused on optimising the system. Numerical and experimental have been used to optimise various components of TAR. This research study combined the experimental work and numerical modelling of the standing wave TAR. Thirty experiments were conducted over three months. The experiments were done for three stack positions of 30 mm, 40 mm, and 50 mm. At each stack position, stacks of lengths of 25 mm, 35 mm, 45 mm, 55 mm, and 65 mm. In addition, numerical modelling of TAR performance was done for the three positions, with the five stack lengths for each position. The numerical modelling was done using the commercial Multiphysics software. The experiments and numerical modelling were followed by optimisation. The optimisation of the experimental data identified the optimal stack configuration as a stack position of 55 mm and a stack length of 25 mm, achieving a COP of 0.33. The optimal configuration yielded ΔT=8°C, COP=0.33, TC=25.1°C and QC=0.0532 W. On the other hand, the optimisation of numerical modelling data identified the optimal stack configuration as a stack position of 30 mm and a stack length of 25 mm, achieving a COP of 1.27. The optimal configuration yielded ΔT=8.5 K and COP=0.33. The experimental work and numerical modelling agreed regarding stack length. They both indicated an optimal stack length of 25 mm, suggesting that short stack lengths are good for a high COP while maintaining other performance metrics within acceptable ranges. The experimental work and numerical modelling differed in the optimal stack position. As a result, this study could not uncover the influence of stack position as far as optimising for a high COP is concerned. Description: Thesis (MEng (Chemical Engineering))--Cape Peninsula University of Technology, 2024

2024-01-01T00:00:00Z Kaskote, Ephraim Vundikanwa https://etd.cput.ac.za/handle/20.500.11838/4185 2025-02-07T06:20:06Z 2024-01-01T00:00:00Z

Title: Assessment of nanobubble aeration performance in treating poultry slaughterhouse wastewater Authors: Kaskote, Ephraim Vundikanwa Abstract: Due to their simplicity and effectiveness, biological treatment methods, including aerobic and anaerobic processes, are widely used for treating medium to high-strength wastewater, such as poultry slaughterhouse wastewater (PSW). Conventional aeration methods, although effective in removing organics and nutrients from wastewater, have drawbacks such as high sludge production, substantial energy consumption, and low oxygen transfer efficiency. To overcome these challenges, technologies such as nanobubble (NB) technology have been developed to enhance aerobic processes by optimising aeration methods and gas diffusion. NBs, with diameters less than 200 nm, have emerged as a promising alternative due to their ability to enhance the efficiency of aeration and reduce sludge production. NBs possess unique properties that contribute to physical, chemical, and biological processes in water and wastewater treatment. This research investigates the performance of NB technology in the application and enhancement of aerobic treatment of PSW. Three NB aeration methods were evaluated: air- NBs, ozone-NBs, and air-NBs combined with Ecoflush enzymes. These methods were tested for their effectiveness in removing chemical oxygen demand (COD), total suspended solids (TSS), ammonia (NH3-N), total nitrogen, and fats, oils, and grease (FOG) over a period of 6 h. Air-NB and ozone-NB aeration methods demonstrated high efficiency in COD removal, achieving over 80% removal within just 2 h of treatment. In contrast, NBs combined with Ecoflush enzymes exhibited initially lower COD removal rates (20%) in the first 4 h but ultimately achieved 86.8% removal of COD and 99.5% removal of FOG after 6 h of aeration. TSS removal efficiency remained consistent across all aeration methods after 4 h, with the ozone-NB method showing the highest removal efficiency. Ammonia removal was most effective when using NBs combined with Ecoflush enzymes, reaching 99% removal after 6 h of treatment. Both the ozone-NBs and NBs combined with Ecoflush enzymes showed high FOG removal capabilities. These findings highlight that nanobubbles can significantly enhance mass transfer in wastewater treatment processes, providing an effective method for improving the degradation of pollutants in PSW. Description: Thesis (MEng (Chemical Engineering))--Cape Peninsula University of Technology, 2024

2024-01-01T00:00:00Z