Electronic Theses and Dissertations (Masters)
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Item 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.PTitanium 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.Item 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.Item Development and Application of activated carbons from Avocado waste: Resource recovery for sustainable applications(University of the Witwatersrand, Johannesburg, 2023) Mohale, Lehlohonolo; Mulopo, JeanThis 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.Item Design, construction and testing of a lab-scale membrane distillation bioreactor for water purification(University of the Witwatersrand, Johannesburg, 2024) Patel, Kavisha; Sheridan, CraigThe 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.Item 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, NgonidzasheImpact 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.Item Simulation of a Wet Flue Gas Desulphurization (WFGD) plant in support of continuous grid supply of electricity and compliance to SO2 emission limits(University of the Witwatersrand, Johannesburg, 2024) Lekhuleni , Tsholofelo Bernice; Mulopo, JeanThe wet flue gas desulphurization plant is susceptible to attrition and corrosion due to the corrosive nature of its operation. It is crucial to prevent plant downtime at any cost, as a plant failure in the WFGD could disrupt electricity supplies to the national grid. Plant failures can be avoided by using models to optimize plant operations and assure higher system performance. In this work, the Aspen simulation was used to forecast the following parameters for a wet flue gas desulphurization process: • Lowest limestone concentration or quality as absorber feed, • Highest volume of gas that can be treated, • Maximum sulphur content that could be treated in the absorber tower. Various reactions such as limestone dissolution, SO2 absorption and crystallization were simulated in Aspen. An equilibrium relation was established where the SO2/SO3 relationship in the absorber reaction could be used to predict the lowest concentration of limestone slurry and the highest volumetric flowrate that could be treated in the absorber. The pH drops in the absorber and the formation of gypsum (CaSO4) also supported the findings of the equilibrium relationship. The lowest limestone concentration limit is 16% compared to a design base of 31%. The maximum volumetric flowrate is in the range of 4,0-4.5 x 106 m3/h. The maximum sulphur content that could be treated is 1.6% S on a mass basis compared to a design base of 0.9%. However, the maximum sulphur was reduced to 1.41 % due to the limestone control dosing valve which can only supply 90000 kg/h instead of the maximum requirement of 94315 kg/h. The equilibrium relations, pH, and gypsum production can all be used to establish safe operating regimes for the WFGD plant.Item Physico-chemical properties and treatment of scale formation in dust scrubber discharge lines at a PGM Smelter in South Africa(University of the Witwatersrand, Johannesburg, 2024) Fungene, Thandiwe; Ndlovu, SehliseloSeveral technologies in the field of flue-gas desulphurization (FGD) have been created to address the issue of sulphur dioxide (SO2) emission from gas streams. Among these, wet scrubbing, particularly the use of lime/ limestone (Ca(OH)2/ CaCO3) scrubbing, stands out as the primary method for reducing SO2 emissions from power plants. These methods are simple and cost-effective, making them suitable for various industrial facilities that emit SO2, including refineries and smelters. In Ca(OH)2 or CaCO3 scrubbing systems, calcium (Ca) compounds are introduced in the form of slurries into the scrubber liquid. However, this process leads to the undesired creation of solid Ca salts. Consequently, the solubility of Ca salts in the slurry restricts the efficiency of wet scrubbing techniques containing Ca. If the ion concentration in the water exceeds the solubility limit of Ca salts like calcium sulphate (CaSO4), it can result in the development of supersaturated CaSO4, which may lead to scale accumulation or deposition in the scrubber. This scaling issue, in turn, requires frequent plant shutdowns to open and remove scale from pipelines. The aim of this research is to propose a process for the prevention of hard water scale or its removal in FGD systems, particularly scrubbers commonly utilized in PGM smelters. To accomplish this goal, analyses were conducted to both physically and chemically characterize the scale or deposit, as well as all the feed materials within and around the variable throat scrubber (VTS) system at a local PGM smelter. By leveraging the physical and chemical properties of these materials, this study explores the application of traditional chemical "water softening" techniques like ion exchange and precipitation, as well as an emerging physical method known as magnetic water treatment (MWT), to combat scale formation in scrubbers. The water samples obtained from the Sibanye-Stillwater scrubbing circuit were characterized by extremely high levels of Ca and magnesium (Mg) hardness (1000—8000 mg/L CaCO3) and high levels of total dissolved solids (TDS) (3000—9000 mg/L). Both a strong acid cation exchange resin (SAC) and weak acid cation exchange resin (WAC) were employed in the treatment process. The WAC resin, commonly used for high TDS solutions, displayed better removal of Ca and Mg compared to SAC, effectively bringing the total hardness levels down to 120—180 mg/L CaCO3. Chemical precipitation using a lime and soda ash pre-treatment step prior to cation exchange resulted in residual hardness levels of 0—120 mg/L as CaCO3. Physico-chemical properties and treatment of scale formation in dust-scrubber discharge lines at a PGM smelter in South Africa Thandiwe Fungene VI The use of MWT remains a topic of debate as a non-chemical option for water softening due to concerns about its scientific validity. This research aims to investigate the potential of a magnetic field to reduce hard water scaling. Several factors, including pH, dissolved oxygen (DO), electrical conductivity (EC), calcium ion concentration ([Ca2+]), and scaling potential, were compared between treated and untreated water. The treated water displayed notable changes in these factors. Most significantly, the precipitation in treated water indicated a shift from calcite to aragonite formation, essentially inhibiting the overall scaling potential. These findings are substantiated by a mechanistic theory based on a comprehensive review of successful applications in the existing literature. This study holds significance in questioning the sustainability of chemical-based water treatment methods and explores the feasibility of non-chemical alternatives.Item 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.Item 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, KevinGlobally 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.Item 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, VusumuziThis 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.
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