Faculty of Engineering and the Built Environment (ETDs)
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Item Hydrometallurgical extraction of metals from secondary resources using various reagents(University of the Witwatersrand, Johannesburg, 2024-04) Teimouri, Samaneh; Billing, Caren; Potgieter, HermanThe advancement and widespread applications of metals in the modern world have led to a growing demand which outstrips their supply. This has resulted in a vital need for recovering precious and critical metals from waste materials, known as secondary resources. Recovering precious, critical and heavy metals not only improves the circularity of metals, but also minimises the deleterious effects of waste materials on the environment. To achieve this crucial aim, research in this thesis focuses on improving gold (Au) yield by finding different ways for pretreatment to break down pyrite, the predominant sulfidic mineral that encapsulates gold in mine tailings. In addition, the research focuses on extracting critical metals such as indium (In) and gallium (Ga) from industrial waste, in this case electric arc furnace dust (EAFD). The results achieved in this research are presented in five publications as explained in brief below: The dissolution of pyrite – the predominant host mineral encapsulating gold – to improve gold extraction from mine tailings was studied in a nitric acid (HNO3) solution. The study showed that when the concentration of HNO3 is above 2 M, it acts as a powerful acid and oxidant to break down the pyrite structure, while simultaneously exposing the enclosed gold through oxidative dissolution. The conducted experiments confirmed that within 2 h, 3 M HNO3 effectively dissolved 95% of FeS2 to release the remaining gold in pyrite at 75 °C. The kinetics of pyrite dissolution was also examined in the temperature range of 25 to 85 °C. The results indicated that the mixed controlled model (1/3Ln (1–X)+[(1–X)–1/3–1)] = k.t, where X is the fractional conversion, k the apparent reaction rate constant, and t leaching time) describing the interfacial transfer and diffusion was governing the kinetics of pyrite dissolution in nitric acid. The activation energy required at low temperatures (25-45 °C) was 145.2 kJ/mol and it reduced at higher temperatures (55-85 °C) to 44.3 kJ/mol. Therefore, nitric acid pretreatment is an effective method for mine tailings containing pyrite with enclosed gold. Nitric acid can be recovered in an eco-friendly manner by capturing the emission of NOx gases from the nitric acid decomposition and can be economically attractive when regenerating the starting acid/oxidant (see publication: “The Kinetics of Pyrite Dissolution in Nitric Acid Solution”). To gain insight into the dissolution of minerals encapsulating gold, such as pyrite and chalcopyrite, an electrochemical study was conducted in nitric acid media using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). CV scans were measured to identify the oxidation-reduction peaks for pyrite and chalcopyrite. Based on the corresponding CV scans and visual observations, anodic and cathodic reactions for oxidised and reduced species were deduced for each identified peak which occurs at a specific potential. An EIS study was then conducted at the particular oxidative potentials, to gain further indications on the relevant reactions, hence providing supporting evidence of the dissolution mechanism. The EIS study at low potential (i.e. 0.5 V vs Ag/AgCl (3 M KCl) reference electrode) showed that the dissolution reaction was controlled by a diffusion process due to the accumulation of certain species, i.e. Fe(OH)3 and S0, on the pyrite electrode, and Cu1-xFe1-yS2-z, CuS2, and S0 in the case of chalcopyrite. This was confirmed in the EIS curve through the appearance of the linear Warburg diffusion effect. Increasing the potential beyond 0.7 V leads to reactions at which the previously formed species covering the surface of the electrodes and causing a diffusion barrier, oxidised further converting them to soluble species. This was reinforced by the omission of Warburg-like effects in the EIS data (see publication: “A comparision of the Electrochemical Oxidative Dissolution of Pyrite and Chalcopyrite in Diluted Nitric Acid Solution”). Due to environmental awareness, neoteric eco-friendly solvents like ionic liquids (ILs) and deep eutectic solvents (DESs), which can be used as alternatives to conventional leaching reagents for recovering metals, are gaining increasing attention among researchers. Hence, a new hydrometallurgical method using ILs to extract Zn, In, and Ga, along with Fe as a common impurity from EAFD, that was spiked with 5% of both In and Ga, was examined. EAFD is a valuable metal containing waste generated in significant amounts during the process of steelmaking from iron scrap material in an electric arc furnace. With critical metal recovery as the main goal, two ILs: [Bmim+HSO4–] and [Bmim+Cl–], were studied in conjunction with three oxidants Fe2(SO4)3, KMnO4, and H2O2, to determine which IL and oxidant combination performs best for extracting the target metals. Following the initial tests, the influence of parameters such as the IL concentration, oxidant concentration, solid-to-liquid ratio (S/L), time, and temperature were optimised to achieve the maximum extraction of the target metals. Results from a series of experiments found the optimum condition to be; 50 ml 30% v/v [Bmim+HSO4-], 1 g of Fe2(SO4)3 oxidant (2%), S/L ratio of 1/20, at 85 °C for 240 min leaching time, resulting in extractions of 92.7% Zn, 80.2% Fe, 97.4% In, and 17.03% Ga. The dissolution kinetics of the studied metals over a temperature range of 55–85 °C was diffusion-controlled (see publication: “A New Hydrometallurgical Process for Metal Extraction from Electric Arc Furnace Dust Using Ionic Liquids”). Environmental and safety concerns about traditional methods for gold extraction, and the potential volume of enclosed gold in mine tailings in sulfidic minerals (i.e. pyrite), were the motivations to find effective, efficient and ecologically benign ways to break down the pyrite structure to expose the locked gold to improve its extraction. Hence, the feasibility of the dissolution of pyrite was studied in a deep eutectic solvent (DES) as a novel solvent. DESs are an analogue of ILs, which are gaining increasing attention as a potential solvent with eco-friendly features. Therefore, the viability of pyrite dissolution in a DES containing choline chloride – a quaternary ammonium salt [(CH3)3NCH2CH2OH]+Cl−] – and ethylene glycol [HO-CH2-CH2-OH], named ethaline, was examined both theoretically through density functional theory (DFT) calculations and experimentally. DFT calculations determined whether Cl– and/or [C2H4O2] 2−, the two ligands provided by ethaline, can make the most probable and stable complex with Fe2+ and/or Fe3+. To do so, the reaction Gibbs free energies (-G) for possible complexes that Cl– and [C2H4O2] 2− can form with Fe were calculated. In addition, the energy gaps between the highest occupied molecular orbital and the lowest unoccupied molecular orbital (HOMO-LUMO gap) were considered. Among the proposed complexes, the tetrahedral complex [Fe(C2H4O2)2]−, with Fe3+ chelation taking place through the O-donors of the ligand [C2H4O2]2−, ad the lowest -G (–71.4 eV) indicating the simultaneous formation of the complex, as well as the largest HOMO LUMO gap (1.3 eV) specifying the most stable complex. For experimental evaluation, the effect of the pH of the ethaline solvent mixed with hydrogen peroxide (H2O2) oxidant, and the different S/L ratios on Fe extraction (indicating pyrite dissolution) were examined. The results show that a pH of 8 provides the desired condition at which ethylene glycol is deprotonated to [C2H4O2]2−, was the favorable ligand for Fe complexation. It was found that the S/L ratio of 1/20 was optimal and achieved 23.7% Fe extraction. The theoretical and experimental work correlated in indicating [C2H4O2]2 − as the favourable ligand. However, the ethaline solvent as the leaching solution did not achieve adequate Fe extraction, as it did not succeed in properly breaking down pyrite to expose the locked gold (see publication: “The Feasibility of Pyrite Dissolution in a Deep Eutectic Solvent Ethaline: Experimental and Theoretical Study”). DFT modelling was also applied to theoretically calculate the possibility of the extraction of In and Ga, in the IL medium. To investigate this aim, three imidazolium-based ILs, namely [Bmim+HSO4–], [Bmim+Cl–], and [Bmim+NO3–] were selected for DFT calculations. They all have the same cationic part [Bmim+], but different anionic parts, i.e. [SO42–], [Cl–], and [NO3–], which are similar to the most commonly used mineral acids H2SO4, HCl, and HNO3, respectively. The -G for different complexes were calculated to determine which of the available ligands, i.e. sulfate (SO42–), chloride (Cl–), and nitrate (NO3–), provided by each IL most likely form the most stable complex with In and Ga. The obtained values for -G confirm that IL [Bmim+HSO4–], owing to the [SO42–] O-donor ligand, resulted in the dimer complexes of [In2(SO4)3] and [Ga2(SO4)3] having the lowest G and the largest HOMO-LUMO gap, indicating the most probable and stable complexes (see publication: “Indium and Gallium Extraction Using Ionic liquids: Experimental and Theoretical Study”)Item “Artful Sustainability” Inquiry into Urban Waste and Public Space Practices: a Case Study of Riverside View Mega City, Johannesburg(University of the Witwatersrand, Johannesburg, 2024) Mantshoane, Trevor; Charlton, SarahThe UN-Habitat (2021a, p. 29) has been spearheading efforts at ensuring that “placemaking institutionalizes the role of art and culture to achieve a lasting sense of place for [communities]” as per the SDG 11 agenda. Place-making foregrounds the central role of communities in ensuring quality and liveable public spaces often through arts-led interventions. To date, little research exists on how this global place-making agenda is faring at the neighbourhood level. Even less studied are the arts and cultural (ecosystem) services of public space and the impact of waste on people’s ability to benefit from these services. Against the global place-making agenda, this research artistically interrogates the eco-cultural dimensions of sustainability issues of waste and public spaces. It does this through a case study of Riverside View Mega City, Johannesburg (South Africa) This qualitative research study uses a case study strategy and draws on a range of practices broadly associated with the arts-based and practice- based methods. The study utilises a set of methodological tools like drawings, written and photo diaries to gain a window into the resident participants’ embodied experiences of waste and public space. In all, the research finds that waste malpractices have a disruptive impact on the residents’ ability to benefit from the eco-cultural services of public spaces in Riverside View Mega City. Consequently, public spaces are generally perceived and experienced negatively, although this is not uniform across all sections of the settlement. Moreover, efforts at institutionalising the arts and culture through place-making interventions remain ambiguous with little apparent relevance to the everyday sustainability issue of waste and public spaces.Item Evaluating the state’s response to flooding disasters: the case of deelpan village emergency housing(University of the Witwatersrand, Johannesburg, 2024) Rirhandzu, ChumaOver the past few years, South Africa has been struggling with managing flooding episodes. From a housing point of view, one then worries about the living conditions of the poor people who do not have the necessary resources to recover from the effects of the disaster, like the people of Deelpan Village in the North West province. To obtain data for this research, I analysed secondary data in relation to disaster management, housing, and planning accessed from government websites. I also conducted a total of 18 semi-structured interviews with the officials and community representatives who were actively involved in the Deelpan Village emergency housing project. This study revealed that the people of Deelpan preferred permanent housing structures over temporary solutions; hence, the Temporary Residential Units have not been provided. The study concluded that the Deelpan residents rejected TRUs for permanent structures due to fear of state failure. Three years after the 2021 flooding, no housing support has been provided by the state, indicating a lack of resources to handle disasters.Item Sacred Landscapes Under Siege: "Resolving disputes over mining claims on sacred landscapes in Musina through the legal lens of a Land Court"(University of the Witwatersrand, Johannesburg, 2024) Mamabolo, MokgadiThe proposed site for this dissertation is situated in Musina in the Vhembe District, close to the Limpopo River, which forms the border between South Africa and Zimbabwe. This area is well-known for its varied topography, which includes bushveld and savannah, as well as important natural and cultural landmarks like the esteemed Mapungubwe National Park. Historically, Musina has been successful in trade, farming, and mining which have served as the main pillars of the economy. The town is well-known for having an abundance of mineral resources, including copper, iron ore, and coal, which have made investments and created jobs that have greatly boosted the local economy. The Save Mapungubwe Coalition has been having concerns about “the possible dangerous precedent set by the lack of clarity of the offset created by this agreement. The offset agreement is an important tool for ensuring that (Coal of Africa) CoAL restores all of the ecosystems that have been depleted as a result of their mining activities” (Melissa, 2014). They emphasise the danger mining operations have on archaeological sites and the ecological balance of the Vhembe Region. This dissertation aims to unpack the historical dimensions of eco-centric architecture, particularly focusing on the nuanced relationship between indigenous African mining practices and the surrounding landscapes. It seeks to shed light on the intricate balance between culture, spirituality, heritage, and the extractive mining industry. By examining the temporality of mining and the transient nature of the miner’s experience by looking at lungs as the metaphor of the temporality of breathing. Through a critical analysis of guiding principles employed in eco-centric architecture, this dissertation aims to explore the potential significance of what a building means in a landscape where biodiversity, culture, spirituality, heritage, and mining coexist. This dissertation will address post-mining landscapes through land reparation and restitution, the idea of Land Reparation and Restitution in this dissertation aims to extend beyond environmental rewilding, restoration by studying the legal framework of mining in South Africa and integrating social justice, heritage, and ecological sustainability strategies. The historian Pulido states: “Not merely about returning land to those who were displaced but also about restoring the relationship between people and the land that sustains them” (Pulido, 2018). The land court symbolizes transformation, reconciliation and justice for the environment, biodiversity, and human life. In the context of Musina, this thesis will explore ways of reparation can be conceptualised and executed given the interconnectedness histories of mining, colonization, and indigenous land use in Musina. The land Court will not only solve mining issues in Musina, but it will be advocating for land mining disputes around South Africa. It is influenced by concerns raised by the Save Mapungubwe Coalition regarding the proposed Industrial Park by the Special Economic Zone (SEZ), South Africa’s landscapes are not only resourced but hold so much history, archaeological elements hence preserving these sacred landscape, historical mining site and indigenous knowledges are very important. Lynn Meskell explains that “Archives of cultural and spiritual heritage that reflect centuries of human-environment interaction” are important (Meskell, 2019). An area such as Musina, where we find a national archelogical site, the Mapungubwe Abstract Cultural landscape being approximately 7km from the Vele Colliery, has a coal mine is an indication a historical precedent that the coexistence of mining and scared site is not sustainable. “The Save Mapungubwe Coalition is made up of a diverse range of groups, with expertise in everything from conservation to water and even heritage resources.” (“Mapungubwe Watch - Wits University,” n.d.) Ultimately, it aims to address questions regarding the role of the landscape in addressing the challenges left behind by coal mining and, in turn, how we can embark on the journey of healing the scars inflicted on these environments through ecologically sound restoration efforts, all while honouring the cultural heritage inherent in the site. Through the legal lens, how can we reimagine a land court that advocates for sacred landscapes, community including the mine workers’ lives?Item Cultivating Terraformation - Propagating agronomic empowerment through agricultural waste transformation in the farming corridor of Ofcolaco, Limpopo(University of the Witwatersrand, Johannesburg, 2024) Mc Dougall, Kayla KateCultivating Terraformation is an exploration into the intertwined lives of the farm, the farmer and the farm worker. In the remote farming corridor of Ofcolaco, Limpopo, where history’s shadows still linger, a community is beginning to reawaken. The thesis traces the deep colonial roots of land once taken and now in the slow, tender process of being restored to those from whom it was seized. In these lands, a vision unfolds — a vision of uniting the farm, farmer, and farm worker to stand as a beacon of renewal and progression. The core of the research centres around the complex dynamics between the emerging black farmer and the generational white farmer. These two figures, bound by the same land but divided by history, represent both the obstacles and opportunities for transformation. As these farmers adapt to life in post-apartheid South Africa the tensions, alliances, and possibilities become the forefront of change. The goal is the harmonization of the relationship between farm, farmer, and farm worker. The objective is to break the sector's cycle of inequality through the creation of a new beacon in agriculture that unites and uplifts. This new sector aims to connect the land, those who own it, and those who work it, and join in on a journey of mutual development and empowerment. Central to this vision is the concept of material activism to unite all three entities of the agricultural sector. This approach redefines not only what the land and its people can produce but how it can sustain’ the environment and uplift its people. Through this alchemy, the study seeks to shape a post- apartheid farming industry that is more than a place -— it is a symbol that guides the agricultural sector toward a shared future. The aspirational endeavour seeks to offer the research as a blueprint for a reimagined agricultural landscape in South Africa. By addressing historical divides and present environmental challenges the systematic change strives to heal old wounds and cultivate new growth. The vision is a future where the scared land of our nation becomes a canvas of renewal, painting a picture of unity and resilience where the scars of the past are transformed into a tapestry of hope and harmonyItem Wasteland/ WetlandRewilding Water Systems in the Post- Mining Landscape in the Nigel Region(2024) Moll, Georgia StephanieThe Witwatersrand region, renowned for its historical mining activities, grapples with environmental degradation, particularly in its water systems. Mining operations have left a legacy of pollution through practices such as the disposal of mine waste in tailings located on or nearby rivers and wetlands, driven by convenience and insufficient regulation1 . This creates significant threats to the natural ecology and biodiversity of the region, such as acid mine drainage, which continues to impact water quality and ecosystem health long after mining activities have ceased, leading to the destruction of aquatic ecosystems, habitats, and breeding zones. Despite these challenges, research suggests that wetlands hold the key to addressing these challenges. Wetlands can be used to naturally filter wastewater, which can contain sediments and pollutants, improving water quality. They are also crucial in nutrient cycling, processing elements like nitrogen and phosphorus which are commonly found in mine runoff2 . The potential for wetlands to act as natural decontaminators highlights their importance in ecological repair and water security for the region. In areas where natural wetlands have been significantly damaged, constructed wetlands present a viable solution. These engineered systems can be strategically placed within damaged waterscapes to treat contaminated water through natural filtration. My thesis proposes an expansion of constructed wetlands into a multifunctional building typology designed to filter water as it flows through the structure. By incorporating various filtration processes and different types of constructed wetlands within the building, this concept aims to provide a pilot design that can be scaled and adapted for implementation in other contaminated sites throughout the region. The proposed building will serve multiple roles in filtration, showcasing a scalable solution for water decontamination and ecological restoration. By establishing this model, the project seeks to improve water security, restore ecological balance, and provide a blueprint for similar initiatives in other regions affected by mining- related environmental degradation. Through this research, I will research the potential for wetlands—both natural and constructed—to serve as a foundation of environmental remediation and sustainability in the Witwatersrand region