Electronic Theses and Dissertations (Masters)

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A Life Cycle Assessment of Plastic vs Cardboard Packaging in the Fast-Moving Consumer Goods Market
(University of the Witwatersrand, Johannesburg, 2024) Rivett, Stephanie Anne; Harding, Kevin
Globally there is a movement to mitigate the need for single-use plastics as well as the utilization of plastic materials when alternative options are available. This movement comes in response to the extensive research that has demonstrated the long-term negative environmental impact that plastics pose to our existence when disposed of into landfills. A significant contributing factor to the mass of single-use plastics is the packaging industry. This study focused more specifically on the single use plastic packaging in the fast-moving consumer goods (FMCG) market which are used to shrink-wrap bottles together to be supplied into the trade such as Pick ‘n Pay and Checkers. South Africa is facing two main challenges pertaining to the FMCG market: namely the constrained supply of energy and the socio-economic pressure to reduce the environmental impact caused by unrecycled packaging waste. This research aimed to investigate the energy requirements and environmental impact of packaging configurations that included shrink-wrap plastic and cardboard cartons versus packaging configurations that utilized only cardboard cartons to ascertain which option provides the lowest possible energy requirements, and environmental impact. This study aimed to execute a cradle-to-grave life-cycle assessment (LCA) of the two different packaging configurations by utilizing the SimaPro software. The LCA was executed with respect to one reference product that is supplied into the FMCG market year-round known as Prewash Promo. Prewash Promo is a laundry pretreatment that aids in the removal of stains. The first of the two packaging configurations under analysis was the traditional packaging configuration of Prewash Promo that has always been used. This packaging configuration consisted of six bottles that were grouped into two sets of three using rubber bands. The two sets of three were then shrink-wrapped into a group of six. Two shrink-wrapped sixes were then placed into a box that was sealed using plastic packaging tape or sellotape. The second packaging configuration under analysis mitigated the use of shrink wrap plastic and associated materials (elastic bands) thus the second packaging configuration consisted of twelve bottles placed into the box that was then sealed using packaging tape. The main objective of this LCA was to ascertain the packaging material configuration that was the most energy-efficient and environmentally responsible choice to utilize in the Stephanie Anne Rivett A Life Cycle Assessment of Plastic vs Cardboard Packaging in the Fast-Moving Consumer Goods Market iv FMCG market. This LCA was conducted utilizing the data pertaining to the year 2022 and the functional unit of this study was one year’s worth of packaging used in the production of Prewash Promo. Prewash Promo was chosen as the reference product as it does not demonstrate seasonal or geographically specific use, and it was a viable option for the change in packaging configuration. A significant factor that influenced the impact of LCA results was the waste scenarios associated with the use of different materials. In this study, the exact quantities of material that were recycled versus sent to landfills could not be definitively known. It was for this reason that the published industry standard recycling rates for the year 2022 and knowledge of socioeconomic habits were used to formulate assumptions. It was assumed that the minor materials included in the packaging configurations such as packaging tape and elastic bands conformed with social habits and did not exhibit any recycling and went directly to landfill. The recycling rate of corrugated board for the year 2022 was reported to be 61.4% and the recycling rate of plastic for the year 2022 was reported to be 42.8% (Mpact Recycling, 2019a). These recycle rates were utilized to model the packaging configurations to facilitate the comparison between the two. The validity and influence of these assumptions were assessed by means of a sensitivity analysis after the main LCA was executed. The ecoinvent 3 database library available via the SimaPro software (version 9.4.0.3, 2022) and the ReCiPe Midpoint method were used to execute the impact assessment calculations. This method consisted of eighteen impact categories that assessed the impact of each of the packaging materials with respect to the impact they posed to human health, biodiversity, and resource scarcity. The full eighteen category impact assessment was condensed into five focus categories based on the target audience, the research objectives and geographical location of the study. These five focus categories were: global warming, stratospheric ozone depletion, fine particulate matter formation, freshwater ecotoxicity and water consumption. These five categories were chosen because they provide the best overview of the impact in a summarized form pertaining to factors contributing to environmental decline, changing weather conditions, reduction in air quality and the impact of freshwater resources. The LCA was first executed for each packaging configuration in isolation to ascertain the impact contributions of each of the individual factors involved in the construction of the Stephanie Anne Rivett A Life Cycle Assessment of Plastic vs Cardboard Packaging in the Fast-Moving Consumer Goods Market v packaging set-up. The analysis of each packaging configuration in isolation facilitated highlighting major contributing factors to consider replacing with alternatives or mitigating the use thereof. This assessment highlighted the drastic impact contribution that the use of electricity had on the impact score of the heat shrink-wrap plastic configuration. The full LCA comparison was then executed to compare the two packaging configurations. In each of the five focus impact categories the corrugated board only packaging configuration achieved an environmental impact score 83% lower than the heat shrink-wrap plastic packaging configuration. This drastic difference was only reduced to 79.6% when excluding long-term emissions. Upon the conclusion of the LCA comparative assessment the validity of the recycle rate assumptions for corrugated board and shrink-wrap plastic were assessed by executing sensitivity analyses. These analyses determined that the conclusion achieved at the end of the LCA comparison stage remained valid irrespective of the recycling rate of corrugated board or shrink-wrap plastic. The final objective investigated in this study was the uncertainty analysis to assess the accuracy and reliability of the data utilized in the LCA. The uncertainty analysis was executed in the SimaPro software by utilizing a Monté Carlo analysis with the ReCiPe 2016 midpoint (H) method which consisted of 1 000 fixed runs with a confidence interval of 95%. An uncertainty bar chart was generated that displays the error associated with each of the eighteen impact categories. The uncertainty analyses for both packaging configurations determined that the data for global warming, stratospheric ozone depletion, fine particulate matter formation and freshwater ecotoxicity demonstrated low error. The cardboard only configuration exhibited very low error values of between 8% and 61% as opposed to the plastic packaging configuration which exhibited errors between 16% and 214%. The water consumption data in contrast exhibited significant uncertainty for both configurations due to the difficulty in definitively determining accurate water consumption data for such extensive life cycles. Water was utilized extensively in the developmental stages of each of the materials (forestry, paper/pulp manufacturing and plastic polymer and plastic shrink manufacturing) and exhibited significant variation in volume of consumption due to high degrees of variation in plant technology and process equipment age. Stephanie Anne Rivett A Life Cycle Assessment of Plastic vs Cardboard Packaging in the Fast-Moving Consumer Goods Market vi The culmination of the results of each of the assessments executed concluded that the corrugated board only configuration is the packaging configuration that is the most environmentally friendly, and energy-efficient packaging option of the two that were considered.
A Process Systems Analysis Towards Hydrogen Pathways Optimisation
(University of the Witwatersrand, Johannesburg, 2024) Kaitano, Caroline; Majozi, Thokozani
Hydrogen is garnering increasing attention as a promising and eco-friendly energy carrier, holding the potential to address global energy and environmental challenges. The emergence of the hydrogen economy is a pivotal technological leap forward in future energy systems. Its central objective is to generate hydrogen primarily from abundant energy sources, thus mitigating our dependence on fossil fuels across industries, businesses, residences, and transportation sectors. At its core, the hydrogen economy encompasses essential facets, including the generation, dissemination, transformation, and retention of hydrogen gas and its diverse applications. Establishing efficient hydrogen production processes represents a critical stride toward the overarching global objective of constructing an economy that revolves around hydrogen as a principal energy carrier, capable of providing a substantial portion of our energy needs and services. The work in this dissertation comprehensively explores hydrogen production pathways by applying a superstructure approach, encompassing various options. A comprehensive database comprising 19 distinct hydrogen production pathways is established in this study. These pathways are subjected to a rigorous analysis, considering availability, environmental sustainability, and economic costs. The overarching goal is to discern the most feasible routes for hydrogen production. The framework devised in this research systematically narrows the initial 19 pathways to a final selection of three, achieving an impressive 84 % reduction in the search space. Among these, the pathway involving steam reforming with carbon capture at 1230 K and 10 bar emerges as the most promising option for hydrogen generation. Having identified the optimal reaction pathway, the focus of the study shifts beyond the framework towards the process design and optimisation of this specific route. After a thorough post-optimisation analysis, it is concluded that the steam reformer operates most favorably under a temperature of 908 K and a pressure of 10 bar. This optimised pathway boasts a remarkable 48 % conversion of methane, underscoring its exceptional environmental and economic advantages. iv This dissertation not only elucidates the systematic framework employed in synthesizing and evaluating the hydrogen pathways superstructure, leading to a significantly reduced search space, but also delves into the intricacies of process design and optimization for the most viable hydrogen production pathway. In doing so, it contributes valuable insights and a structured methodology to the field of hydrogen energy research, offering a blueprint for sustainable and efficient hydrogen production in the pursuit of a cleaner and more sustainable energy future.
An Investigation into the Effect of Advanced Gravity Separation on Platinum Group Metals (PGM) Flotation Concentrates
(University of the Witwatersrand, Johannesburg, 2024) Nair, Taurean Jevaldo; Sibanda, Vusumuzi
“It's the gravity that shapes the large-scale structure of the universe, even though it is the weakest of four categories of forces” - Stephen Hawking Gravity concentration has been around since the dawn of mankind, and just as man has evolved so too has gravity concentration. The earliest records involved ancient cultures (Greeks, Romans, Mayans and Egyptians) using water to selectively separate precious metals from gangue. Gravity concentration has remained an integral part of many processes involving the recovery of native or alluvial precious metals and minerals which are amenable to this process. Developments in gravity concentration technology have led to the inception of advanced gravity separation devices. These advanced gravity separators can overcome the challenges associated with conventional gravity concentration as they are able to induce a high gravitational force that is capable of recovering fine and ultrafine heavy particles as well as particles with a complex mineralogy. Decreasing feed grades and falling metal prices are placing an exorbitant amount of pressure on the PGM industry. As a price-taker, the industry is at the mercy of the prevailing market conditions. This means that the only levers the industry can use are cost cutting or optimization of the process to produce more PGMs at a better quality from the current feed source. The premise of this research project is to essentially find a way to optimize the PGM beneficiation process by the use of gravity concentration. This research specifically targeted the high-grade flotation concentrate stream of a UG2 tailings plant to understand how effective advanced gravity concentration would be in recovering PGMs, upgrading the resulting concentrate as well as rejecting chromite and gangue. PGMs are associated with base-metal sulphides and are inherently complex. This complexity is further exacerbated by the fact that PGMs are in the fine to ultrafine particle size range which makes recovery of PGMs challenging. Gravity concentration is primarily a function of particle size, density and mineralogy. Separation of gangue and chromite from PGMs is another added complication as the gangue minerals are present in higher concentration than the PGMs, have a complex mineralogy and are also found in the fine and ultrafine particle sizes. Fire Assay/ICP- ii MS, XRF, XRD and SEM all confirmed the complexity of the ore being treated. This ‘entanglement of complexity’ makes processing these ores very challenging. A lab-scale Falcon gravity concentrator with an unfluidized (ultrafine) bowl was used in the main experimental work. The optimal parameters to run the gravity concentrator for PGMs was found to be a flow rate of 3 L/min, percent solids of 13.22% and a gravitational force of 300 G’s. These parameters were then applied to a multi-stage gravity concentration process. The feed to the gravity concentrator was found to have a grade of 131.02 g/t 4E PGM. The results indicated that a recovery of 48.90% and a final concentrate grade of 292.04 g/t 4E was achieved at a mass pull of 21.90%. The chromite in the final concentrate of the Falcon gravity concentrator was found to be 1.99% which did not exceed the maximum allowable chrome in concentrate of 3.00%. This proved that gravity concentration was indeed capable of recovering complex PGMs and rejecting chromite. The optimal parameters experiments indicated repeatability, and the assay results were validated by a statistical outlier test in the Minitab Software to ensure data integrity. The particle size analysis revealed that 97.07% of the feed to the Falcon was below 75μm and 66.29% below 25μm, thus confirming that the feed material was fine to ultrafine particles. The final gravity concentrate had a D90 of 42.24μm which was finer than the D90 for the feed, this demonstrates that fine and ultrafine heavy particles were more mineralized and recoverable by the Falcon. This analysis was further reinforced by the fractional analysis which confirmed that the majority of the PGMs were found in the fine to ultrafine fraction. The experiments were repeated using a fluidized bowl in the Falcon to see what the impact of fluidizing water would be. These experiments had lower overall recoveries and mass pulls than those done with an unfluidized bowl. The concentrate grade was, however, higher than the unfluidized bowl experiments possibly due to this bowl recovering PGMs in the coarser fraction. This research provides a steppingstone to understanding the effect of advanced gravity concentration on PGM flotation concentrates and indeed on PGMs in general as well as providing an alternative unique processing option for PGMs. Ultimately advanced gravity concentration has been shown to be an uncomplicated process that can be viable in the recovery of fine and ultrafine complex PGMs. It is environmentally friendly, has low capital and operational costs and has a relatively high efficiency.
Bio-tribocorrosion behavior of low- cost titanium alloys in simulated body fluids
(University of the Witwatersrand, Johannesburg, 2023) Rundora, Nicola Ruvimbo; Bodunrin, M.O.; Merwe, Van der; Klenam, D.E.P
Titanium and its alloys are considered the gold-standard material in the manufacturing of biomedical implants. This is due to their superior mechanical properties and resistance to corrosion in comparison to the other biomaterials on the market. Titanium and its alloys are however very expensive in comparison and their application and accessibility is thus limited. Issues of toxicity as in the case of the commercial alloy (Ti-6Al-4V) have also been reported. One approach to combat these issues has been the development of new low-cost and less expensive α+β type titanium alloys through the modification of the commercial alloy composition. These efforts led to the development of the following alloys: Ti-3Fe, Ti-4.5Al-1V-3Fe, and Ti-6Al-1V-3Fe. To determine whether these alloys can be utilised for the manufacturing of biomedical implants, they have to undergo a series of screening tests. Some of those tests include wear, corrosion, and tribocorrosion tests. This is the basis of this study. Dry sliding ball-on-disk wear tests were conducted on these alloys. Ti-4.5Al-1V-3Fe and Ti-6Al-1V-3Fe had superior wear resistance to Ti-3Fe, the alloy where the full substitution of V with Fe was employed. Ti-4.5Al-1V-3Fe and Ti- 6Al-1V-3Fe alloys wear resistance was closely comparable to that of the commercial alloy, Ti- 6Al-4V. The corrosion behavior of the experimental alloys was investigated in 0.9 wt.% NaCl solution, Hanks Balanced Salt Solution, prediabetic Hanks Balanced Salt Solution, and diabetic Hanks Balanced Salt Solution. It was important to study the behavior of these alloys in a simulated diabetic environment because of the increase in the number of people living with diabetes and their increased risk of developing different bone and joint disorders. The corrosion behavior of Ti-3Fe was superior to that of the commercial alloy and the other experimental alloys in 0.9 wt.% NaCl solution and Hanks Balanced Salt Solution. In the prediabetic and diabetic Hanks Balanced Salt Solution, the experimental alloys resistance to corrosion was comparable to that of the commercial alloy with Ti-4.5Al-1V-3Fe having the best resistance to corrosion in the prediabetic solution and Ti-6Al-1V-3Fe having the best resistance to corrosion in the diabetic solution. Ti-4.5Al-1V-3Fe and Ti-6Al-1V-3Fe showed tribocorrosion resistance that was comparable to the commercial alloy in both the normal HBSS and diabetic HBSS under both open circuit potential and potentiostatic conditions. These alloys showed better tribocorrosion behavior in the normal HBSS under potentiostatic conditions compared to Ti-3Fe and the commercial alloy. In the diabetic HBSS under potentiostatic conditions, Ti-4.5Al-1V-3Fe had the best resistance to tribocorrosion. The iv | P a g e glucose addition had a slightly negative effect on the tribocorrosion behavior as the wear rates and total worn volume values in such solutions were slightly higher than in the normal solutions. Ultimately, under corrosion and tribocorrosion testing conditions, the partial substitution of V with Fe as beta stabilisers in low-cost titanium alloy designs offered superior properties over the total replacement of V with Fe.
Carbon nanotubes application for lithium-ion battery anodes
(University of the Witwatersrand, Johannesburg, 2024) Mhlanga, Nqobile; Raphulu, Mpfunzeni; Sibanda, Vusumuzi
The most commonly used anode material for lithium-ion batteries (LIBs) is graphite, however it has some shortcomings such as having a low reversible capacity and low diffusion rate which produce low-power density batteries. Thus, the purpose of this study was to examine the application of carbon nanotubes (CNTs) as an alternative LIB anode material. A bimetallic iron-cobalt catalyst supported on calcium carbonate (Fe-Co/CaCO3) was used for the synthesis of CNTs and it was prepared using the wet impregnation method. X-ray diffraction (XRD) analysis of the catalyst showed that it was highly crystalline. The specific surface area (SSA) which was determined using Brunauer-Emmett-Teller (BET) was found to be 11.3 m2/g. CNTs were prepared using the chemical vapour deposition (CVD) method at various test parameters i.e. temperature (650°C,700°C,750°C and 800°C), hydrocarbon flow rate (90 mL/min and 120 mL/min) and carbon source (acetylene and ethylene). High-resolution transmission electron microscopy (HRTEM) results for samples synthesised at 650°C and 700°C using acetylene at a flow rate of 90 mL/min (650°C-A90 and 700°C-A90) showed that CNTs which were multiwalled carbon nanotubes (MWCNTs) in nature were produced. The formation of what appeared to be non-tubular carbon and carbon nanofibers was observed when the synthesis temperature was increased from 700°C to 800°C. The average outer diameter (OD) of the tubes ranged from 20 to 89 nm. At a higher acetylene flowrate (120 mL/min), the quality of CNTs seemed to deteriorate for synthesis temperatures above 650°C. The formation of non-tubular carbon-like nanofibers was observed at synthesis temperatures above 650°C. The average OD of the tubes ranged from 22 to 81 nm. XRD analysis of all samples synthesised using acetylene showed a similar pattern with the most intense peak being that of carbon and minor peaks being of iron. The samples also contained some broad peaks which suggested that the samples contained amorphous carbon. The calculated crystallite size ranged from 3.4 to 6.4 nm for samples synthesised using acetylene at a flowrate of 90 mL/min. For samples synthesised using acetylene at a flowrate of 120 mL/min, the crystallite size ranged from 3.1 to 4.4 nm. Raman spectroscopy confirmed the successful synthesis of MWCNTs; however, the intensity ratio (ID/IG) was found to be above 0.7 for a majority of the samples which confirmed the presence of impurities in the samples. SSA studies revealed that an inversely proportional relationship existed between the SSA and the synthesis temperature. vi HRTEM results for samples synthesised at 650°C and 700°C using ethylene at a flow rate of 90 mL/min (650°C-E90 and 700°C-E90) revealed that CNTs which were MWCNTs in nature were formed. As the synthesis temperature increased from 700°C to 800°C, the formation of what appeared to be non-tubular carbon and carbon nanofibers was observed. The average OD of the tubes ranged from 21 to 84 nm. At a higher ethylene flowrate (120 mL/min), the quality of CNTs seemed to deteriorate for synthesis temperatures above 700°C. The formation of non-tubular carbon-like nanofibers was observed at synthesis temperatures above 700°C. The average OD of the tubes ranged from 11 to 79 nm. XRD analysis of all samples synthesised using ethylene showed a similar pattern with the most intense peak being that of carbon and minor peaks being of iron. However, the depicted minor peaks were broad which suggested that the samples contained amorphous carbon. The calculated crystallite size ranged from 3.7 to 5.7 nm for samples synthesised using ethylene at a flowrate of 90 mL/min. For samples synthesised using ethylene at a flowrate of 120 mL/min, the crystallite size ranged from 3.6 to 6.5 nm. Raman spectroscopy confirmed the successful synthesis of MWCNTs. SSA studies revealed that the SSA decreased with an increase in the synthesis temperature. Furthermore, to evaluate the electrochemical performance of the synthesised material, electrodes of selected samples were fabricated. Commercial graphite electrodes were also fabricated to compare the performance with the samples synthesised in this study. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used for the electrochemical measurements. The CV tests were conducted at scan rates of 5 mV/s and 10 mV/s, An increase in the CV curve area was observed as the scan rate was increased. The calculated specific capacity of the samples compared well with that of the electrode fabricated with commercial graphite which reported an average of ~197 mAh/g after four cycles at a scan rate of 5 mV/s. The average specific capacity of the electrode fabricated with CNTs sample synthesised at 650°C using ethylene at a flowrate of 120 mL/min (650°C-E120) reported the highest value of 214 mAh/g after four cycles at a scan rate of 5 mV/s. Overall the variation between the samples of the EIS data was marginal. These EIS results also compared well with that of the electrode fabricated with commercial graphite. The findings of this work suggest that MWCNT electrodes have a good application potential and with doping, they may provide better electrochemical performance than graphite as a viable anode material for LIBs.
Characterisation and surface finish evaluation of Direct Energy Deposited AlCoCrCuFeNi High Entropy Alloys
(University of the Witwatersrand, Johannesburg, 2024-01) Modikwe, Thembisile Patience; Mathe-Maleboho, Ntombi; Maledi, Nthabiseng
This study focused on the use of direct energy deposited (DED) techniques for the fabrication of AlCrCoCuFeNi high entropy alloy (HEAs) samples. HEAs have become a ground-breaking research field that provides solutions to complex problems in the aerospace industry. The industry requires improvement in the application of structural materials that are well-functioning at a low cost for example turbine blades. The fabrication of HEAs via DED commonly produces poor surface finish Ra in the range of 5 μm - 20 μm due to the layer-by-layer deposition method, as a result, it fails the industrial application requirements where the usual range of roughness tolerance required in the industry ranges from Ra is 0.8 μm < Ra < 1.6 μm thus, the need to deploy post-processing methods. This study focused on electropolishing (EP) and centrifugal barrel finishing (CBF) of AlCrCoCuFeNi-HEA samples. The polishing was performed using 80% methanol and 20% per-chloric acid solution used as the electrolyte. The samples were polished for 30 and 60 seconds in a Struers LectroPol-5 electrolytic polishing and etching device. The surface removal at 1200W for 30 sec on sample a was 50.29%, 58.65% for sample b, and 75.48% for sample c. The surface removal at 1400W for 60 sec on sample d is 63.25%, 45% for e, and 49.19% for f. The samples were polished for 7 and 14 hours in a CB320-CBF. During the period of 14 hours, a surface removal where the proportion of material removed for sample a was 55.37%, sample b was 43.13%, and sample c was 32.2% at a laser power of 1200W. After 7 hours of polishing, sample d achieved a surface removal of 86.02%, sample e achieved a surface removal of 43.18%, and sample f achieved a surface removal of 90% at a power of 1400W. Oxidation tests were conducted in static air at 1000˚C for 200h. The presence of FCC, BCC, and Fe2O3 oxide scales resulted in a noticeable increase in mass, with Fe2O3 scales being the most prevalent.
Characterization of a TW R260-60E1 Pearlite Rail Steel with a Weld Gap Size of 40 mm and 50 mm
(University of the Witwatersrand, Johannesburg, 2024) Meyiwa, Lindani; Maledi, Nthabiseng
The continuous weld rails (CWR) tracks that are joined by thermite welding (TW) method are known to experience weld failures during their service life. In avoiding or mitigating these failures, a weld gap in joining two rail ends was introduced. The purpose of the weld gap was to accommodate rail expansion during elevated temperatures. Traditionally, a weld gap of 24 mm was created between two rail ends. However, these weld joints were observed to be experiencing challenges of not being able to withstand high contact loads during service life, leading to plastic deformation and eventual failures. This study was investigating the effect on microstructural characteristics, heat-affected zone (HAZ) dimensions, mechanical properties attributes, and wear resistance behaviour of TW R260-60E1 pearlitic rail steel when the weld gap was set to 40 mm and 50 mm. The results revealed that the TW R260-60E1 pearlitic rail microstructure had no martensitic, bainitic and intergranular Widmanstätten ferritic structures. Pearlitic grain sizes and interlamellar spacing on the weld zone of the web region were measured to be 3.6 % wider on the sample with 40 mm weld gap compared to those on the sample with 50 mm weld gap. Big surface area to volume ratio and fast cooling rate had an influence on the production of finer pearlite grain sizes and interlamellar spacing within the web region for both samples. The results further showed that the HAZ width was one of the attributors to the improvement on the mechanical and wear resistance properties. HAZ width varied from 29 mm – 35 mm for sample with 40 mm weld gap, and 27 mm – 33 mm for sample with 50 mm weld gap. The HAZ width on the sample with 50 mm weld gap was narrow than the HAZ width on the sample with 40 mm weld gap. Narrow HAZ width improves microstructural characteristics, mechanical properties and wear resistance behaviour compared to the wider HAZ width. The improvement on the microstructure characterisation, mechanical properties and wear resistance behaviour are expected to extend the service life of the rail and facilitate superior rail expansion capabilities. This, in turn, is projected to diminish the probabilitiy of rail-related incidents and mitigate the risks of human fatilies associated with rail transportation
Characterizing flotation processes of Platreef PGM ores: The applicability of models based on the Weibull and γ rate constant distributions
(University of the Witwatersrand, Johannesburg, 2024) Ngema, Sithandokuhle Fortune; Safari, Mehdi; Sibanda, Vusumuzi
This dissertation delves into a comprehensive examination of the flotation behaviour of Platreef Platinum Group Metal ores, with a specific focus on the applicability of two widely used distribution models, the Weibull and Gamma distributions. The primary objective of this study was to demonstrate the effectiveness of these models in characterizing the flotation response of the ore under varying grind sizes, ranging from 80% passing 150 μm down to 38 μm, and under varying collector dosages. In this research, a series of meticulous experiments that involved the collection of samples from Platreef PGM ore were conducted. These samples were characterized based on their mineralogical composition, and their flotation behaviour across specified particle size distributions and varying collector dosages. The gathered data were then subjected to analysis using the Weibull and Gamma models. This allowed the assessment of the flotation performance of the ore and the description of the intricate flotation sub-processes involved to be possible. The parameters for both the Weibull and Gamma distributions were determined through a rigorous statistical method known as regression. This method involved fitting the experimental data to the models and iteratively adjusting the model parameters until convergence to their most accurate estimates was achieved. The results from the research reveal that both the Weibull and Gamma models demonstrate a commendable ability to describe the flotation process of Platreef PGM ores. However, the study also highlights certain limitations of these models, especially when dealing with coarser grind sizes, where the Weibull model shows a slight decrease in effectiveness. The investigation also points to the significant impact of liberation and grinding time on the accuracy of these models. These findings underscore the importance of understanding the nuances of particle interactions and liberation at different grind sizes in floatation processes. Furthermore, the effect of varying collector dosages on the performance of the models was explored. It was observed that the accuracy of the models diminishes with longer residence times, particularly when collector dosages are changed. This sensitivity to longer residence times and grind characteristics underscores the need for a holistic approach to model development. Another intriguing aspect of the study was the relationship between collector dosage and grind characteristics. It became apparent that increasing collector dosage has a more v pronounced positive effect on recoveries for both coarser and finer grinds, while the intermediate grinds exhibit a less substantial improvement. This discovery challenges the convention of a near-linear relationship between collector dosage and recovery. In conclusion, the research provides valuable insights into the complexities of the flotation process for Platreef PGM ores and underscores the significance of selecting the most appropriate distribution models based on specific ore characteristics and grind sizes. The dissertation also highlights the need for a nuanced approach to process optimization, acknowledging the interplay of factors such as liberation, grind characteristics, and collector dosage. This understanding can be applied to enhance recovery rates and efficiency in flotation processes, offering valuable contributions to the field of mineral processing and chemical engineering. Findings of this work shed light on the intricate nature of chemical processes, emphasizing the importance of a holistic approach to model development and practical applications.
Design of an Industrial Process for Enzymatic Cannabidiol Conversion
(University of the Witwatersrand, Johannesburg, 2024) Flavell, Erin Reece; Harding, Kevin; Rumbold, Karl
This work aims to model a theoretical enzymatic bioreactor and all the necessary surrounding processes required to facilitate the bioremediation of THC into CBD, to produce a CBD product with THC levels below the legal concentration limits (0.001%). The primary purpose is to explore whether further research into the potential biochemical remediation of THC into CBD would be worth pursuing in terms of both functionality and profitability within the CBD industry. Two primary process designs were modelled using SuperPro Designer, one producing a CBD isolate, and another producing a full spectrum CBD blend containing other cannabinoids beyond CBD, as well as other compounds like flavonoids and terpenes. The CBD isolate model is composed of four parts: the extraction of the crude oil (including the pre-extraction process); the upstream processing of the oil; the reaction of THC into CBD; and the downstream processing of the oil. The full spectrum CBD model is similarly structured but with a different fourth process stage (downstream processing). Cultivating one’s own cannabis was calculated to be more economical than purchasing it from a third-party supplier, and thus a drip-based irrigation system of 1.2108 hectares was used, requiring capital costs of $ 24 641.90 and a yearly cultivation cost of $ 7629.76. Both processes begin with milling to increase the surface area of the cannabis, followed by passing through two consecutive cold ethanol mixer-settler extraction units. Next, the oil-plant matter mixture passes through a plate-and-frame filtering system and then a decarboxylation oven, which will convert the cannabinoids into their neutral forms, producing CBD from CBDA and THC from THCA, and releasing CO2 as a co-product. The oil then passes into a PFR, where CLEAs catalyse the reaction of THC into CBD. Due to the theoretical nature of the as-yet-unknown enzyme, conversion was assumed to be 85 %, where 37.46 kg of the enzyme was calculated to be required per year, assuming replacement is required after seven days of operation. The possibility of either producing or purchasing the enzyme was considered, but producing the enzyme worked out more economically viable, at a yearly cost of $ 2.84. This is where the full spectrum process halts. In the isolate process, the oil is then mixed with an acetonitrile-TBME stream before entering the CPC, alongside a heptane stream. Most of the CBD passes into the heptane, which moves iv to a distillation column after exiting the CPC process, with CBD isolate emerging from the bottom stream. The acetonitrile-TBME stream exiting the CPC will contain other cannabinoids and remaining cannabis compounds and will flow into a separate distillation. The bottom stream of the distillation column provides other valuable cannabinoid isolates, forming ancillary products (CBG, CBN, and THC isolates). In the full spectrum CBD model, the oil flows directly into a series of three consecutive distillation columns upon exiting the PFR, designed to reduce the THC concentrations in the oil to acceptable levels. The CBD oil emerging from both processes must then be incorporated into an MCT carrier oil. CBD isolates were assumed to be sold for $ 39.00 per 30 ml, with each unit containing 600 mg of CBD. Full spectrum CBD oil was assumed to be sold for $ 40.00 per 30 ml, where every 30 ml contains 1500 mg of cannabis oil. Once the costs of the MCT oil were deducted from the theoretical revenue values, the net revenue values came to $ 64 089.93 per kilogram for CBD isolate and $ 26 302.64 per kilogram for the full spectrum CBD oil. Collectively, the ancillary cannabinoid products (CBG, CBN, and THC) yielded a net revenue value (less the cost of the required MCT oil) of $ 17749.48 /kg. CBD isolate was produced at a rate of 637 kg/year, at 99.47 % purity, with ancillary cannabinoid products being produced at 494 kg/year by the isolate process. The full spectrum CBD blend was produced at a rate of 656 kg/year and did not contain any solvent residues. The isolate process was found to have a gross margin of 83.86%, an ROI of 101.58%, a payback time of 0.98 years, and an NPV of $ 190 458 000. The full spectrum blend has a gross margin of 50.89%, an ROI of 21.75%, a payback time of 4.60 years, and an NPV of $ 14 199 000. Thus, the isolate process was deemed the more economically viable of the two processes. An additional CBD isolate design involving supercritical CO2 extraction was also modelled for comparison. In this variation, the cannabis buds undergo milling before passing through the supercritical CO2 extraction unit. The CO2-ethanol solvent feed enters a CO2 storage unit wherein is pressurised to achieve supercritical conditions before entering the extraction unit alongside the cannabis stream. The bottom stream from the extraction unit then passes into a plate-and-frame filtration system, which removes the plant matter from the stream; the recovered cannabis oil is then reunited with the top stream from the extraction unit. The combined oil stream then undergoes winterisation, in 24-hour cycles, before moving into a distillation column which removes any remaining solvent. The bottom stream from the column then enters the decarboxylation oven; the remainder of the process continues in the same manner as the original, cold ethanol extraction isolate process. The CO2 extraction process produced CBD isolate at a rate of 600.54 kg/year. CBD purity of 99.29 % was achieved. An economic analysis produced project indices of a gross margin of 84.07%, an ROI of 95.28%, a payback time of 1.05 years, and an NPV of $ 173 404 000. Thus, with gross margin being the sole exception, all project indices indicate the cold ethanol process being the process with greater potential profitability to produce CBD isolates. Because the isolate process proved the most profitable of the alternatives, its potential profitability when scaled up to industrial size was also assessed. The process feed rate was increased to 79 200 kg of cannabis buds per year, solvent input streams were proportionally scaled up, and several equipment units were multiplied as required. Additionally, the quantity of the enzyme required for catalysing the reaction was recalculated based on the increased plant material in the process, coming to a yearly mass of 576.25 kg, for $ 345 750. The scaled-up process produced a CBD isolate product with a purity of 99.47% and a production rate equivalent to 9800 kg per year and the ancillary cannabinoid product at a rate of 7587 kg per year. The NPV of the scaled-up process came to $ 3.99 billion and a gross margin of 99 % was achieved, with an ROI of 1340 % and a payback time of 0.07 years. Therefore, from the simulated model and the economic analyses, the production of CBD oils using THC-to-CBD bioremediation was found to be a potentially profitable, as-yet-untapped production method that would benefit from further research. It is worth noting, however, that the research is limited by its reliance on theoretical models and assumptions, which may not fully reflect real-world conditions, potentially affecting the generalisability of the findings. The lack of empirical validation and practical factors not captured by simulations, such as enzyme stability, further constrain the applicability. Future work should focus on empirical testing and exploring a wider range of parameters to improve the results' relevance and generalisability.
Design, construction and testing of a lab-scale membrane distillation bioreactor for water purification
(University of the Witwatersrand, Johannesburg, 2024) Patel, Kavisha; Sheridan, Craig
The pulp and paper industry produces a significant amount of wastewater that contains a variety of organic and inorganic contaminants. This makes it impossible to discharge untreated wastewater directly into a water source. As a result of the condition of the untreated mill effluent and strict environmental regulations, significant pressure has been placed to develop suitable technologies capable of treating and reusing this wastewater. In light of this, this study evaluated the potential of a membrane distillation bioreactor (MDBR), a technology which combines a conventional membrane bioreactor (MBR) with membrane distillation (MD) for the treatment and reuse of pulp and paper mill effluent. In this study, effluent from a paper mill was analyzed for its most significant components. The analysis identified sulphate, sodium, chloride and calcium as the main components of the feed wastewater with concentrations of 391 mg/L, 300 mg/L, 160 mg/L and 157 mg/L respectively. A high TDS of 1 394-1 566 mg/L, TSS of 496-876 mg/L and COD of 397-496 mg/L were found for the feed wastewater, typical of pulp and paper mill effluent. MDBR performance characteristics including permeate water quality, permeate flux as well as membrane fouling and membrane wetting were investigated systematically. The performance of the MDBR was also evaluated at three different operating temperatures of 45ºC, 55ºC and 65ºC. Experimental results showed that the MDBR achieved 99.4% removal of all compounds and a high salt rejection rate of 86.3%, regardless of the operation temperature. However, the MDBR was only able to achieve an organic rejection rate of 78.0%. It was found that the effects of bioreactor temperatures had strong impacts on both the permeation performance and fouling behaviour. The permeate flux dropped by 88.1% over the duration of the experimental program at the relatively low operational temperatures due to membrane fouling. SEM analysis showed a compact fouling layer on the membrane surface from the bioreactors operated at the temperatures of 55ºC and 65ºC while only a few depositions were found on the membrane from the 45ºC bioreactor. EDS results indicated that the deposits formed on the membrane surface mainly consisted of calcium. A loss in membrane hydrophobicity of 66.0% at increased temperatures was detected with contact angle measurement due to the partial wetting of the membrane. In the present study, the optimal MDBR temperature was found to be 65ºC as it showed better process performance and treatment efficiency. Overall, the MDBR in this study was effective in remediating pulp and paper mill effluent.
Development and Application of activated carbons from Avocado waste: Resource recovery for sustainable applications
(University of the Witwatersrand, Johannesburg, 2023) Mohale, Lehlohonolo; Mulopo, Jean
This research sought to produce activated carbons that could be used for hydrogen storage. The effect of hydrothermal pretreatment of the char, the effect of varying the activation ratio of KOH as the activation agent and the effect of activation temperature in producing these activated carbons were evaluated. Hydrothermal pretreatment of the char enhanced the properties of the resulting activated carbons. The best performing activated carbon was produced from the hydrochar pretreated at 200℃. It was observed that activation improved with increased activation agent concentration and activation temperature, to a point, and the best activated carbon was produced at 1:3 activation ratio and 800℃ activation temperature. This activated carbon had the highest total pore and micropore volumes of 1.45cm3/g and 1.16 cm3/g, respectively. The highest surface area of 2529.8m2/g was obtained, which is relatively higher than previously reported surface areas obtained from activated carbons created from coal or biomass. The porosity and the high surface area show well developed activated carbons that have desirable gas adsorption performance. The activated carbons had oxygen containing functional groups that aid in hydrogen sorption, the highest hydrogen sorption at 77K and 1 bar was 352 cm3/g, which supports the use of the produced activated carbons in the hydrogen economy. These activated carbons enable the circular economy. Well developed micropores were observed in the activated carbons produced through this work and their gravimetric capacity meets the DOE targets for hydrogen storage.
Development and experimental validation of an acid mine drainage prediction tool based on mineral particles
(University of the Witwatersrand, Johannesburg, 2024) Ramatsoma, Mafeni Samuel
Acid Mine Drainage (AMD) is an environmental hazard that is generated as a by-product of mining-related activities. It is an acidic metal-rich water formed when sulfide minerals react with oxygen and water. Due to different ore types at different mines, kinetic AMD models are often ‘calibrated’ with kinetic humidity tests done with the target mine site ore. However, most of these tests require several months to complete. This study aimed to investigate ways to reduce the time required to conduct kinetic humidity tests, and to develop a mineral particles-based kinetic AMD model. An Accelerated Humidity Cell (AHC) is proposed in this study. It was tested with two ore types and performed better (produced 24% more acidic-leachates) than normal humidity cells. The particles-based model was developed and tested with experimental data and gave promising results. It is recommended that the proposed model and AHC be further tested with other ore types.
Dynamic compartmentalised heat transfer modelling for systems with biological applications
(University of the Witwatersrand, Johannesburg, 2023) Xu, Lan; Moodley, Prebantha; Hildebrandt, Diane
Proper thermal management is crucial to controlling the temperature of biological systems within an optimized operating range. A biological system is comprised of a multitude of interacting facets, where a system is often disrupted as a consequence of random events such as the change in ambient temperature. In contrast the design of most human engineered chemical systems or processes may assume steady state operation and as a result is relatively straightforward to design and optimise. Yet, often steady temperature ranges are required in unsteady conditions. This sort of unsteady state system requires consideration of the dynamic changes to the conditions and are often required to be within many applications. A narrow temperature band is essential for controlling the outcomes of how biological systems’ function—thermal denaturation of biological components depend on precise control of the transport of heat. Insulin—a hormone peptide drug—is temperature sensitive and undergoes thermal fibrillation when exposed to temperatures above manufacturers' recommendations. To maintain such medication within specific temperature bands is a challenge in the face of energy intermittency from the energy crisis that South Africa is currently facing. Within this dissertation, a medical device to contain thermosensitive biological compounds is designed and modelled as a system undergoing dynamic thermal conditions. This heat transfer modelling is used as a prototyping process for designing the medical device to protect temperature sensitive medication during power outages. The simulated device, when used correctly, is able to keep medication thermally stable under 8°C during Stage 4 load shedding (7.5 hours of power outages within a 24-hour period).
Experimental heat transfer coefficients for the cooling of oil in horizontal internal forced convective transitional flow
(University of the Witwatersrand, Johannesburg, 1981) Rogers, Douglas Gordon; Van der Merwe, D.F.
Extraction of Alumina from South African calcined clays
(University of the Witwatersrand, Johannesburg, 2024) Maria, Matome Batsalelwang
The 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.
Extraction of gold from tailings using environmentally friendly reagents
(University of the Witwatersrand, Johannesburg, 2024) Khuduwe, Marema Jack
The 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.
Flammability, corrosion resistance, and environmental friendliness of coal composites produced from various coal fines
(University of the Witwatersrand, Johannesburg, 2024) Vatsha , Mhlawakhe; Bada, Samson O.
The concept of recycling carbon-containing waste into secondary raw materials is highly promising for fostering a resource-efficient and circular economy, given the increasing scarcity of natural resources and growing population. The effectiveness of coal tar modified by air- blowing technique as a binder “pitch” for coal fines in the production of structural composites is highlighted in this study. In addition, the feasibility of commercial dimethylpolysiloxane as a binder for coal carbon composite production was assessed and compared to that produced using coal tar-pitch. The two coal fines (GG1 and GS) used in this study have an ash content of 84.02% and 62.27%, respectively, and can be classified as rock. Their fixed carbon content ranges between 5.44% and 16.27%, compared to coal tar (35.23%). The coal tar has a volatile matter content of 64.50%, and with the air-blowing pretreatment, the tar was converted to pitch with a low volatile matter content of 11.27%. A pitch with the highest fixed carbon content of 87.68% and total carbon content of 96.01% was produced. Various ASTM standard test methods were used in the investigation to characterise and evaluate samples, including mineral phases and functional groups in the raw and coal composites produced. The composites were fabricated using a circular mould with a diameter of 30 mm and a 40 mm square mould. In the study, it was found that composites with a low H/C atomic ratio had low water absorption. Additionally, composites with high volatile matter content had high water absorption. However, the sample with the highest water absorption (19%) was the GG1 50/50 coal tar pitch 400-composite, which falls within the range (0-25%) for building materials. The composites with an intense O-H group had high compressive and flexural strengths ranging from 106.58 to 344.71 MPa and 48.75 to 159.30 MPa, respectively. The flammability of all composites was low. The highest flammability mass ablation rate and linear ablation rate were found to be 0.008 g/sec and 0.00983 mm/sec, respectively. In terms of the corrosion rate, the GS 80%/20% dimethylpolysiloxane coal composite had the highest corrosion rate (0.081 μmpy), which is minimal compared to some commercial ceramic tiles. The composites' environmental friendliness was determined by leaching them at various pH levels. The test was conducted by comparing the concentration of heavy toxic elements in the solution to the leachable concentration threshold for waste management standards (NEM WA Act No. 59 of 2008). All composites were environmentally friendly, meeting the moderate risk leaching concentration threshold. The composites that were produced in this study from South iii African discard coal can be used in large quantities in the environment without any danger or hazards, as demonstrated. Based on this study's overall results, repurposing South African discard coal as carbon/ceramic composites for building materials could play a role in the country's Just Transition initiatives. In addition to waste reduction, this strategy could reduce operational emissions, improve circularity, and address associated environmental risks.
Influence of copper on the corrosion and mechanical properties of Grade 4 titanium for biomedical applications
(University of the Witwatersrand, Johannesburg, 2022-12) Hadebe, Nomsombuluko Dayanda Elizabeth; Cornish, Lesley; Chown, Lesley H.; Smit, Melanie; Mwamba, Alain
This study assessed the effect of Ti2Cu and its proportions on the corrosion resistance, and compared the results to Grade 4 commercially pure titanium. The Thermo-Calc program with the TTTI3 (Ti-alloy) database was used to predict the phases. Materials Studio software was used to model the crystal structures and XRD patterns of the phases of Ti-Cu alloys. Ti-Cu samples with 0, 5, 15, 25, 33, 40, 47 and 50 wt % Cu were produced. Composition, microstructures, phases, hardness and corrosion resistance were studied in the as-cast and annealed conditions (750° and 900°C water quenched). The CP Ti samples comprised basket-weave acicular microstructures. The Ti-5Cu samples comprised lamellar (αTi) and Ti2Cu phases. The Ti-15Cu, Ti-25Cu and Ti-33Cu alloys comprised (αTi) dendrites and sparse eutectic of Ti2Cu and (αTi). The ((βTi) dendrites decomposed to (αTi) and Ti2Cu, and could not be retained due to insufficient fast quenching. The Ti-40Cu and Ti-47Cu samples had minor titanium oxide dendrites which solidified first and then Ti2Cu nucleated on them and grew as dendrites, surrounded by the Ti2Cu + TiCu eutectic. In the Ti-50Cu sample, TiCu was the true primary phase and grew as needles, and was subsequently surrounded by a coarse TiCu + Ti2Cu eutectic. No Ti3Cu phase was observed. The microstructures of the as-cast alloys agreed with the Cu-Ti phase diagram of Ansara et al. (2021) and Dyal Ukabhai et al. (2022) with the congruent formation of Ti2Cu, as well as no Ti3Cu. The addition of copper to titanium increased the hardness, while annealing decreased the hardness of the Ti-Cu alloys. Addition of copper above 5 wt % Cu and annealing decreased the corrosion resistance of the samples, but since copper ions in liquid solutions promote the antimicrobial activity, some corrosion is necessary to allow the copper ions to be available. The corrosion tests showed that the corrosion rates obtained were very low, below 0.13 mm/y, which is an acceptable corrosion rate for biomaterial applications. Ti-5Cu showed the best corrosion resistance.
Investigating operational parameters that would affect the performance of a laboratory impact crusher
(University of the Witwatersrand, Johannesburg, 2022) Ndlovu, Mangaliso Nhlakanipho; Bwalya, Mulenga; Chipise, Liberty; Chimwani, Ngonidzashe
Impact crushers are widely used in the mining and construction industries to crush and size various types of materials. However, their performance can be affected by several operational parameters, including the rotor speed, rotor position, number of rotors and relative direction of rotors. The aim of this study is to investigate the impact of these parameters through a numerical model, Discrete Element Method (DEM). A Laboratory scale impact crusher was simulated using various configurations while also making use of a range of materials with known breakage data to predict expected grinding rates in the crusher. The Discrete Element Method (DEM) algorithm is a computational approach utilized to solve complex problems that involve numerous interacting bodies. In this technique, the dissipative forces (such as normal, tangential or frictional forces) at contact points are simulated using a spring-slider-dashpot model. While the movement of particles is computed using Newton's laws of motion. During simulations, the information about contact events are captured and saved in output files, which can later be used for various purposes. The energy spectra, a record of energy involved in every contact event of one such output that is utilised to predict the breakage of particles of different materials provided their breakage characteristics are known. Using the DEM simulation various equipment configurations of a laboratory impact crusher were conducted. The results showed that the rotor speed, number of rotors, rotor direction and rotor position significantly influenced the number of impacts and energy spectrum produced by the crusher. The crusher operation configuration significantly affected the energy spectra obtained. Additionally, the comparison of the crushing characteristics of the double rotor impact crusher to those of the single rotor impact crusher revealed differences in their performance that can be attributed to their design and operating parameters. - 3 - [OFFICIAL] The findings of this study provide valuable insights into the design and operation of impact crushers, and can be used to improve their efficiency and productivity when processing a variety of materials with different operational parameters.
Investigating the effect of size, density and shape of Iron ore particles on batch jig performance
(University of the Witwatersrand, Johannesburg, 2024-02) Dzaringa Kisembo, Daniel Elvis; Woollacott, Lorenzo
The gravity separation method is one of the oldest methods of mineral beneficiation that takes advantage of the difference in the specific gravity of particles that are being separated. The separation occurs in a fluid medium, usually water, and involves floating off lighter material to leave behind denser ones. There are several types of gravity separation techniques, and they vary according to the equipment that is used for the separation or the property of the medium that is being used; the main gravity separation methods that are widely used for the beneficiation of Iron ore are Jigging and Dense Medium Separation (DMS). In this research, the jigging method is selected to investigate the concentration of an Iron ore by using a batch laboratory Jig; the jigging method was preferred for its simplicity and availability, generally Jigging has several advantages, some of which include cost effectiveness and simplicity of operation and its minimum impact on the environment. During the beneficiation of minerals using the jigging method of ore concentration, several feed material characteristics affect the efficiency, such as the particle density, size and shape. The aim of this research was to investigate the effect of these feed properties on jig performance. Tests were conducted on a Hematite ore sample using a batch jig to gain a deeper understanding of how the density, the size and shape of particles affect segregation. The iron ore samples were screened and any extremely small particles were removed, maintaining a particle size range between 2.8 and 10 mm. The results showed that particles were stratified on the basis of their specific gravity, denser particles reported toward the bottom layer of the bed and separated more efficiently. Less denser particles reported more toward the upper layer of the bed and were less efficiently separated. Coarser particles tend to report to the bottom layer of the bed and finer particles to the top product layer. Particles that were flatter and more elongated tended to end up in the bottom layer of the bed more often, while more rounded particles were not as likely to be found in the bottom layer.