Browsing by Author "Broadhurst, Jennifer Lee"

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    Analysis of energy efficiency in South Africa's primary mineral industry: a focus on gold
    (2012) Johnston, Oliver Ross; Cohen, Brett; Broadhurst, Jennifer Lee
    Energy use is the human activity responsible for the majority of its greenhouse gas emissions. In 2010 the global energy-related emissions of carbon dioxide - the principal greenhouse gas-jumped by 5.3% from the previous year, to a record 30.4 gigatonnes (IEA 2011a). The International Energy Agency (2011) has projected that the world's primary energy demand could increase by 33% and that energy related CO2 emissions will increase by 20% to 36.4 Gt between 2010 and 2035 (IEA 2011a). South Africa is one of the most energy intensive countries in the world, measured as GHG emissions per Gross Domestic Product produced. South Africa's energy intensiveness is a result of the energy intensive nature of a number of its key industries. The mineral industry is one such industry. It plays a crucial role in South Africa's economy and is the largest industry in its primary economic sector (Chamber of Mines 2010). Energy efficiency has been identified as one of the cheapest and most effective measures to reduce energy consumption and its associated greenhouse gas emissions. The Long Term Mitigation Scenarios coordinated by the University of Cape Town's Energy Research Centre identified that South Africa's industrial sector had cumulatively the greatest potential to reduce its GHG emissions through improved energy efficiency, ahead of the commercial, residential or transport sectors(Winkler 2007). South Africa's continued reliance on unsustainable energy production, particularly coal, increases the need for maximising energy efficiency to mitigate resource consumption and the GHG emissions associated with the production and use of fossil fuel generated energy. This project aims to identify and holistically evaluate the potential opportunities that exist for the reduction of energy and climate footprints of South Africa's gold industry sub-sector, with the aim of providing guidance to both government and industry for a path towards a more energy efficient industry with lower associated GHG emissions. To this end the thesis begins with a comprehensive review of the potential drivers, barriers and opportunities for increased EE and GHG emissions mitigation for the local minerals industry.
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    Application of life cycle assessment in process design: case study on SOâ‚‚ abatement technologies in the PGM sector
    (2016) Munyongani, Veronica; Von Blottnitz, Harro; Broadhurst, Jennifer Lee
    Platinum group elements (PGEs) are increasingly being used in a variety of environmentally-related technologies such as catalysts and catalytic converters which have strong expected growth to meet environmental and technological challenges this century. The platinum industry is actively seeking to progress its commitment to sustainability principles by reducing the negative impacts of their mining and mineral processing operations. Technical innovation to improve future plant designs, as well as the development of management policies, guidelines and protocols for efficient operation of process plants has therefore become a strategic priority for the South African platinum industry. The industry has also made an effort to understand the environmental impacts of its products from mine to metal, using life cycle methods. However, very limited research has been done to investigate what environmental value could be created if strategic and design decisions in minerals processing were life cycle based, particularly in the context of PGMs. Seminal work by Stewart (1999) investigating the environmental life cycle consideration for design-related decision making in the minerals industry has not led to significant adoption. Forbes et al. (2000) analysed metal processing using LCA and were able to identify opportunities for improved environmental performance. They however did not explore how it would be incorporated into the decision making cycle. Therefore, the main objective of this research is to determine whether life cycle assessment could help inform design decision making in the minerals industry. In the years 2002-2008 several PGM-producing companies commissioned new SOâ‚‚ scrubbing technologies to meet the regulations that had been set to prevent the release of excessive amounts of sulphur dioxide from smelters in the Rustenburg area, a mining town located in the North West Province of South Africa. Using these cleanup process retrofits as case studies, this dissertation aims to determine whether the introduction of LCA as an environmental analysis tool would have provided additional value to the decision makers. The case study approach that was chosen compared and assessed the performance of SOâ‚‚ abatement technologies and the effect of efficiencies chosen on environmental performance by using life cycle assessment modelling. By doing the life cycle assessment on the different options that the companies had, it was possible to evaluate the indirect environmental impacts that could have been overlooked during the design decision making process. In addition , experts who were involved in the design processes of the SOâ‚‚ abatement retrofits were interviewed to establish: i) how the design decisions were made and ii) whether the life cycle based insights into technology performance would have been of use in the design work. The goal of the life cycle assessment was to identify whether there were design decisions that induced environmental burden shifting when platinum smelters in the Rustenburg area added SOâ‚‚ abatement technologies to their processes, which could have been avoided had the LCA perspective been taken into account. The assessments considered two key variables, namely extent of recovery and technology choice.
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    Application of mineralogy in the interpretation of laboratory scale acid rock drainage (ARD) prediction tests : a gold case study
    (2014) Dyantyi, Noluntu; Becker, Megan; Broadhurst, Jennifer Lee
    The mining and beneficiation of gold generates large tonnages of waste, with up to 99% of mined gold ore discharged as waste. The waste generated contains unoxidized sulfides that when exposed to air and water react to form acid, which results in acid rock drainage (ARD). ARD is usually associated with low pH, high sulfate content and elevated concentrations of toxic elements. The mobility of ARD affects our scarce water resources, land and aquatic species. Methods applied to treat ARD do not provide a walk-away solution and they are either expensive or difficult to maintain. The best solution to completely eradicate ARD is to prevent it from the source. However, the effectiveness of ARD prevention depends on the accuracy of predicting future drainage quality. This can be done by using ARD prediction tests, which are generally classified as either static (acid base accounting, ABA, net acid generation, NAG) or kinetic (column leach, humidity cell, biokinetic test). There is no single test capable enough to accurately predict acid generating potential. It is therefore usual practise to conduct more than one test and cross-check results to ensure that the appropriate conclusions are made. In doing so, the reliability of the tests is improved but in some cases the different test results do not correlate. Mineralogy is an analytical technique that can be used to understand the nature of the errors and to better understand the leaching behaviour of minerals in the different tests. This study uses mineralogy to analyse both static and biokinetic test results of a Witwatersrand gold sample in order to improve the understanding of behaviour of mine wastes under different ARD prediction test conditions. A run-of-mine gold sample from the Witwatersrand region in South Africa was used as a case study to explore the mineral leaching behaviour for different ARD prediction tests.
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    Characterising the acid mine drainage potential of fine coal wastes
    (2013) Kotelo, Lerato Olga; Broadhurst, Jennifer Lee; Becker, Megan; Harrison, STL; Franzidis, Jean-Paul
    Acid mine drainage (AMD) is one of the major environmental challenges facing the South African mining sector. Acid mine drainage has received significant public attention in recent years. South Africa's long mining history has led to a growing concern that coal-related AMD from these mines (both operational and defunct) will continue for centuries to come. Pyrite bearing fine waste, generated during coal preparation and beneficiation, is thought to carry a significant amount of AMD pollution risk. Coal-related AMD generation has not been afforded the same exposure as AMD generation from high sulphide minerals such as gold and copper ores. This is exacerbated by the growing concern over water quality degradation in the Mpumalanga region of South Africa. The development of integrated solutions to address the management of coal-related AMD requires an understanding of the principle causes behind coal-related AMD. To date, most of the prediction methods described in literature have been derived for the prediction of AMD in metal bearing ores. Furthermore, some of these methods are based on assumptions and do not take into consideration the various sulphur species present. Additionally, some of these methods have limited applicability to coal due to the high total organic carbon content (TOC) of the material. This research project attempts to address these short comings and uncertainties by developing a systematic and meaningful framework for the characterisation of South African coal and coal waste. The research project contributes to the knowledge of coal-related AMD with particular emphasis on the characterisation methods responsible for sulphur speciation and mineralogy for coal. The approach entails carrying out a case study assessment aimed at empirically assessing a coal tailings sample according to: particle size distribution, textural reference, mineralogical characteristics, and how the aforementioned factors influence the acid potential in coal. The approach intends to address key factors which include: identifying the sulphur bearing organic and inorganic constituents related AMD generation in coal, assessing how the mineralogy, texture and particle size distribution contribute to AMD potential in coal tailings, and then identifying suitable analytical techniques and test methods which can provide data. The combination of these key outcomes will seek to provide a systematic and meaningful framework for the characterisation of coal and coal waste streams. The characterisation methods used in this case study outlined a framework focusing on four main areas of acid mine drainage characterisation for coal wastes, these included: chemical characterisation, mineralogical characterisation, sulphur speciation and AMD prediction. This comprehensive approach employed a suite of techniques, including: petrography, quantitative x-ray diffraction (QXRD) and quantitative evaluation of minerals by scanning electron spectrometry (QEMSCAN).
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    Developing minerals beneficiation flowsheets for eco-efficiency : a systems approach
    (2010) Guma, Mondli; Von Blottnitz, Harro; Broadhurst, Jennifer Lee
    Eco-efficiency has been proposed by the World Business Council for Sustainable Development as a performance indicator framework that contributes to sustainability by assisting corporate decision makers improve the environmental performance of their operations and processes, while also extracting additional economic value. Given the emergent importance of eco-efficiency within the business community and the urgency with which environmental impacts generated by the minerals industry need to be mitigated, it becomes apparent that there is a need to assess whether eco-efficiency indicators can drive environmental sustainability performance improvement during process design within the minerals industry. This thesis aims to respond to this research need by assessing the strengths and limitations of eco-efficiency indicators as performance metrics in guiding decision making during minerals process design in the interests of environmental sustainability. The ultimate aim of this thesis is to contribute towards improved guidance for process design engineers in the selection of the appropriate tools for more environmentally sustainable design of minerals beneficiation processes.
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    Dreams come true: youth entrepreneurs in eSikhawini township, Richards Bay
    (2016) Manqoyi, Ayanda; Fuh, Divine; Broadhurst, Jennifer Lee; Franzidis, Jean-Paul
    This research project examines the emergence of youth entrepreneurs in the moments just before mining and industrial activities develop within a community. It focuses on how young people engage with the hopes and promise of opportunities engendered by the expansion of mines and industry within a particular place. Using ethnography as methodology, it looks at how young people's dreams and desires in eSikhawini, a township in the Richards Bay area within the uMhlathuze Municipality, are activated by the coming of mining activities and how they use these to create entrepreneurs. In the context of mining and industrial expansion, young people use the promise of opportunity and the pursuit of dreams and desires to create particular kinds of entrepreneurs who attempt to stabilize their lives and that of their community in the face of precarity. It argues that the interrelations emergent in the daily enterprise of creating a stable future are key resources and insurance against uncertainty that sustain "community" in the context of eSikhawini. Overall, the thesis attempts to demonstrate that by recognising and strengthening youth entrepreneurs' capacity to aspire and realise their dreams can entrepreneurship interventions and programmes foster and sustain empowering relationships amongst marginalized people living in areas affected by mining and mineral beneficiation.
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    Environmental Performance Assessment of Froth Flotation for Coal Recovery and Sulfur Removal from Ultrafine Coal Waste
    (2016) Fundikwa, Bridget; Broadhurst, Jennifer Lee; Harrison, STL
    The South African coal mining industry generates large volumes of coal ultrafine waste (< 150 microns) each year, with a significant amount being dumped in tailing slurry dams. These slurry dams have been associated with prolonged pollution and loss of valuable resources. In the two stage flotation process developed at the University of Cape Town, froth flotation is used to both recover coal (stage 1) and remove pyritic sulfur (stage 2) from ultrafine coal waste, resulting in three outputs streams: a saleable coal product, a small volume sulfide-rich stream, and a reduced volume sulfide lean tailings stream. Pre-disposal removal of sulfide sulfur and coal recovery by means of froth flotation is aimed at effectively removing the acid rock drainage (ARD) risk associated with sulfide bearing waste s and at recovering valuable resources respectively. Previous studies have demonstrated the technical feasibility of this process for a number of coal waste types on a laboratory-scale, with results indicating that it is possible to recover large quantities of useable coal whilst generating a tailings waste stream with a reduced sulfur content and negligible ARD risk. An order of magnitude financial model for a fictitious plant has also been developed, and applied to demonstrate the economic viability for s elected case studies. To date, however, studies on the environmental viability of the process have only focused on the ARD mitigating potential of the two-stage flotation process and little attention has been given to the systemic environmental implication s of the process such as the energy and reagent usage. The research study therefore aims to evaluate the environmental burdens and benefits of the two-stage flotation process, particularly from a South African context, and to compare the environmental performance to the conventional disposal of untreated coal ultrafines. Furthermore, this project aims to establish which stages along the process contribute the most to the environmental burdens of the process and how the variations of the input parameters affect the overall environmental performance of the proposed process. To this end, a life cycle inventory of inputs and outputs was compiled on the basis of the empirical results derived from a previous laboratory-scale case study conducted on a sample of an acid generating ultrafine coal waste from the Waterberg region. Experimental results from the case study, which entailed two-stage flotation (using Naflote 9858 as a coal collector and xanthate (SIBX) as a sulfide collector in stages 1 and 2), and detailed characterisation of the feed and desulfurised tailings, was supplemented with literature information and data from mass and energy balance calculations for a fictitious plant. An environmental impact analysis was subsequently conducted using a combination of Life Cycle Impact Assessment and risk-based impact assessment techniques and criteria. The impact categories selected included climate change, terrestrial acidification, fossil fuel depletion, natural land transformation, aquatic water pollution risk, drinking water quality risk, aqueous acidification, salinity and consumptive water footprint. Aquatic water pollution risk, drinking water quality risk and aqueous acidification impact indicators were calculated by summing up risk potential factors for the constituents of the final disposed waste streams. The rest of the impact categories were calculated by multiplying the inventory result with a characterisation factor developed from impact assessment models The case study results indicated that the simple mentation of the two-stage flotation process results in a notable decrease in eco-toxicity, salinity, consumptive water footprint, metal toxicity, aqueous acidification, fossil fuel depletion and natural land transformation impacts. However, the results al so indicated an increase in atmospheric related impacts (climate change and terrestrial acidification impacts), which has been attributed to the additional energy consumption associated with the two-stage flotation process and the production processes associated with the flotation reagents. Analyses of the process contributions to the individual impact categories for the two-stage flotation process revealed the climate change and terrestrial acidification impact categories to be dominated by the electricity production process and the flotation reagents production process. The sensitivity analyses revealed a higher dependence of the fossil fuel depletion impact category on the percentage coal yield than the electricity consumption of the foreground process. Furthermore the sensitivity analyses indicated a strong dependence of the climate change and terrestrial acidification impacts on the electricity consumption and the SIBX dosage in the foreground process. In the South African context, implementation the two-stage flotation process would result in a significant recovery of coal (approximately 1.2 million tonnes for every 4 million tonnes dry coal ultrafines lost per annum) and a sulfide-rich product which can be utilised for electricity production and sulfuric acid production respectively, hence promoting resource efficiency. Although higher than in the case of conventional land disposal, the energy used in the two-stage flotation process is infinitesimal compared to the energy recovered in the process through the generation of additional coal, and results in only a 0.025 % increase in the annual greenhouse gas emissions. The implementation of the two-stage flotation would also result in reduced water losses in comparison to conventional land disposal, which is beneficial in the South African context as South Africa is a water scarce region. Lastly whilst the implementation of the two-stage flotation process would result in the reduction of water related impacts associated with acidification, salinization and metal pollution, it might pose a further threat to aquatic life if the xanthate salt reagents are emitted to local water sources. The limitations of the study were mainly associated with the quality of the input and output data, the impact categories and the system boundary and scenario development. The multiple sources of information and the variations in literature of the energy input estimates were noted as a source of uncertainty. The lack of characterisation factors for some of the substances in the system as well as the exclusion of the possibility of utilization of the sulfide-lean stream were also part of the limitations associated with the study. Recommendations for future work include improving the environmental assessment by incorporating various case studies and by incorporating downstream processing as well as optimizing the two-stage flotation process by using less energy and by using less toxic flotation reagents.
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    Generalised strategy for predicting environmental characteristics of solid mineral wastes : a focus on copper
    (2007) Broadhurst, Jennifer Lee; Petrie, Jim
    The impacts associated with primary production of metallic and fossil minerals are significant, and these industry sectors are facing increasing pressure to improve environmental performance and contribute to development that is consistent with sustain ability principles. The management of large volumes of solid wastes poses a particular problem, with the potential post-closure impacts and liabilities associated with the prolonged discharge of contaminated leachate from deposits of such wastes remaining of major concern to both regulators and industry. It is only by quantitatively characterising these impacts that we can begin to focus attention backwards in the material chain to the waste generation processes themselves, and thus identify opportunities for process improvements to minimise waste formation and to render wastes environmentally benign. Whilst recognising that knowledge of the key waste properties or characteristics is an essential and integral part of quantitative environmental impact predictions, currently available data pertaining to the characteristics of solid mineral wastes are largely incomplete and inconsistent, and the mechanisms of leachate generation poorly understood. The need to improve the way in which solid mineral wastes are characterised is driven not only by the limitations in terms of current data bases and methodologies for the generation of such. There is also a requirement for a more systematic and rigorous approach, which will ensure that the necessary data and information is integrated into the early decision stages of an environmental performance assessment programme and, ultimately, project life cycle in a time and cost effective manner. It is these shortcomings and challenges that this thesis attempts to address, through the development of a generalised and systematic strategy for predicting the environmentally significant properties of solid mineral wastes on the basis of ore characteristics (waste origins) and generating processes (waste source). The conceptual approach developed within this thesis essentially entails addressing current data gaps and deficiencies through reconciliation of available empirical data with a fundamental understanding of element properties and distribution behaviour in two systematic and consecutive steps. In the first instance, solid waste characteristics are predicted from a consideration of ore type and composition (Le. waste origins), combined with knowledge of the process route from ore to waste (i.e. waste source). Due to their relevance in terms of technical and economic criteria, such as product quality and operational throughput, the behaviour of the targeted metal and major ore components in ores and beneficiation input-output streams is generally fairly well understood. Data gaps and inconsistencies pertaining to these ore components can, for the most part, be adequately addressed on the basis of meaningful generalisations and simple mass balance calculations. In contrast, available data and information relating to compositions of trace and minor co-elements are largely qualitative and inconsistent, and their deportment during the formation and subsequent beneficiation theoretical assessment of the potential distributions, properties and associations of these elements within ore deposits and across process unit operations, based on a fundamental understanding of the governing reaction mechanisms and influencing parameters. The theoretical data and information are subsequently reconciled with available empirical data to generate a comprehensive and quantitative list of potential element distribution factors which, when combined with total mass flow data, results in a first-order inventory of process input-output stream compositions. The second step of the proposed approach entails the prediction of key characteristics relating to criteria of environmental significance. In this step the solid waste constituents, identified and quantified in the first step of the methodology, are screened and ranked in accordance with their hazardous properties and availability for release to the surrounding environment in a disposal scenario. As in the case of predictions of element distributions during ore formation and beneficiation, the theoretical assessment of the potential distribution behaviour of elements from solid wastes is underpinned by a qualitative understanding of the mechanisms and parameters governing their dissolution and attenuation within a waste deposit. Potential environmental risks associated with the various solid waste constituents are subsequently estimated and compared on the basis of their total concentrations, potential environmental availability, and inherent capacity to cause harm. Three separate but inter-related case studies in the context of primary copper production present the key features of the developed approach and related tools. Such features pertain in particular to first order predictions of the chemical and mineralogical compositions of porphyry-type copper sulphide ore deposits; the subsequent distribution of ore components during concentration and smelting of the run-of-mine ores; and the waste constituents of potential environmental significance within a typical flotation tailings impoundment. Apart from addressing data gaps and inconsistencies, these case studies have also served to highlight the links in the ore formation.
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    The impact of coal mining on the environment and community quality of life: a case study investigation of the impacts and conflicts associated with coal mining in the Mpumalanga Province, South Africa
    (2018) Shongwe, Bonisile Nolwando; Broadhurst, Jennifer Lee
    Coal is South Africa's major primary energy source, and plays a significant role in supplying the chemicals and steelmaking industries. The benefits of coal production are relevant in the light of South Africa's development priorities of job creation and economic growth. Even so, primary metal production and coal-based power generation industries, through their operations and activities, pose a significant and irreversible risk to the surrounding environment. The impact on the environment further manifests on the health of local communities and on sustainable livelihoods, and frequently also presents a long-term economic burden and loss of valuable resources. Despite changes in legislation and improved social and environmental performance by the industry, there is growing concern over the impacts and conflicts associated with coal mining, with continuing claims by communities and civil society of associated health issues, cattle and livestock death, and destruction of livelihoods. However, to date, little attempt appears to have been made to support community concerns and perceptions with factual evidence and information, suggesting a lack of convergence between lay and expert knowledge. This dissertation investigates the facts, perceptions, concerns and conflicts in the mine-environment-community cause-effect chain in the context of the environmental and social impacts associated with the South African coal mining industry. More specifically this entails a detailed review of published data on academic literature, newspaper articles, popular magazines, and internet and specialist reports, with particular emphasis on the South African scenario; and semi-structured interviews with representatives from communities, civil society organisations, and independent environmental consultants. Particular focus is placed on coal mining in the Mpumalanga Province, which accounts for over 84% of South Africa's coal production. This was done with a view to developing a better understanding of the interrelationships between the coal mining industry and the local environment and society in which it operates. It is envisaged that this will ultimately serve to facilitate the development of sustainable solutions to the concerns and conflicts associated with coal mining. Historically, coal mining has had a significant impact on the environment and there is substantial evidence of a strong link between environmental pollution from mining activities and the health and well-being of humans and eco-systems in the surrounding vicinities. These impacts can be largely associated with water quality, physical and chemical land degradation, and air pollution through dust fall-out and emissions of particulate matter (PM) and toxic gases. In particular, AMD from coal mining results in significant pollution of land and water resources. The published literature provides evidence that this environmental pollution may, and often does, have an adverse effect on local eco-systems as well as on community health and livelihoods, particularly on crop and livestock farming. The findings also indicate that there has been response to these concerns by government and the industry. The government has instituted a number of legislative reforms, particularly since 2002, and has established programmes aimed at improving socio-economic challenges in mining towns. Industry has also taken steps to improve its environmental performance, in terms of waste management, mine water reclamation and post-closure rehabilitation. The literature findings were found to be largely consistent with the perceptions and concerns of communities, community support groups and consultants active in the coal-mining regions of Mpumalanga Province. The perceptions of the coal mining and processing sector were extremely negative; all participants expressed considerable concern over the environmental and social impacts. Emissions, particularly AMD and dust, from current and defunct workings and waste piles continue to be a source of water pollution, air pollution and land degradation which further have an adverse effect on aquatic life and human health as well as on livestock and crop productivity. Of particular concern in the coal-mining intensive area of Mpumalanga, is the impact of environmental pollution on maize production. With increasing public knowledge and awareness of these impacts, which can be largely attributed to the activities of the relatively large number of civil society organisations that now exist, the concerns and incidents relating to the environmental and socio-economic impacts from coal mining in the Mpumalanga area are generally well reported. The general consensus was that the concerns of communities and community-support organisations are not been taken seriously, and that government and industry are failing to alleviate the environmental degradation and human suffering in the Mpumalanga coal-mining areas. The lack of adequate response on the part of both the government and industry, and the continuing issues of environmental pollution and adverse community effects, have resulted in on-going (and possibly escalating) conflict situations in the form of community activisim, protests and litigation. This lack of response from government was, furthermore, considered as highly politicised and attributed largely to unethical arrangements between government officials and/or community leaders and mining corporations. Participants were generally of the perception that the negative aspects of coal mining outweigh any benefits and should be discontinued completely. The findings of this dissertation suggest that effective rehabilitation, consistent implementation and enforcement of the regulations designed to protect the environment and society, and stakeholder collaboration are a key requirement in terms of mitigating the environmental impacts and associated risks pertaining to human and livestock health and crop productivity. It is therefore recommended that the government address the rehabilitation of abandoned coal mines and discard dumps in the Mpumalanga Province, and establish action plans, linked to regional development plans, that are based on a comprehensive environmental monitoring programme in collaboration with other stakeholders, including communities, the mining industry and other business sectors in the region. A more detailed study on opportunities to improve the quality and availability of performance reporting by the coal industry is also recommended.
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    An integrated approach to AMD mitigation through sulfide removal from tailings
    (2010) Hesketh, Alexander H; Broadhurst, Jennifer Lee; Harrison, STL
    The formation of acid mine drainage (AMD) from the microbial oxidation of sulfides in mineral waste deposits is one of the major challenges facing the mining industry worldwide. Growing environmental awareness and subsequent changes in legislation has focused research in addressing the prevention of pollution by AMD. Current waste management approaches focus on deposition techniques to control AMD formation and on remediation. However, these approaches do not remove the risk of AMD generationand are yet to be proven effective in mitigating long-term acid generating potential. Incompliance with the principles of pollution prevention, addressing waste at its source,the aim of this work is to remove the risk of AMD generation by focusing on theremoval of sulfides from potentially acid generating tailings prior to disposal.
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    An investigation into the dissolution of pyroxene : a precursor to mineral carbonation of PGM tailings in South Africa
    (2014) Meyer, Nicole Anne; Becker, Megan; Broadhurst, Jennifer Lee; Reid, Dave
    Carbon sequestration through mineral carbonation is becoming an increasingly attractive alternative for mitigating excess COâ‚‚ in the atmosphere. Mineral carbonation is a natural process whereby COâ‚‚ is fixed to CaFeMg-silicates to form Ca-, Fe-, and Mg-carbonates. This process is thermodynamically favourable and the products are benign and stable over millions of years. Pyroxene-rich tailings generated from the processing of PGM ores in South Africa have the potential to sequester significant amounts of COâ‚‚ (~14 Mt per annum). In the indirect pH swing method, silicate minerals are initially leached at low pH and then carbonated at high pH. A previous study on these tailings highlighted the slow extraction of cations from orthopyroxene, the major Mg-host. The low reactivity of the orthopyroxene resulted in an overall low conversion of tailings to carbonates with only 30 % for Ca, 3 % for Mg and 9 % for Fe. Under similar experimental leach conditions, ~100 % dissolution of olivine and serpentine can be achieved.
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    Life cycle assessment of the production of xanthate salts and of their application for ARD mitigation
    (2015) Kunene, Makhosazane Chucky; Broadhurst, Jennifer Lee; Von Blottnitz, Harro; Dicks, Patrick.
    Xanthate salts are commonly used as collectors in the mineral processing of sulphide ores. In more recent studies, xanthate has also been used in the environmental desulphurisation flotation of sulphidic mine tailings and coal waste, with a view to mitigating acid rock drainage (ARD) risks through the pre-disposal removal of sulphide minerals. In South Africa, xanthate salts are produced by Senmin® International (Pty Ltd) via the conversion of carbon disulphide at its facility in Sasolburg. In 2010, Senmin® commissioned a new state-of-the art plant for the production of carbon disulphide using methane rather than charcoal as a carbon source. Although this process has many advantages over the old process, no attempt has been made to date to quantify the environmental benefits. Similarly, whilst the technical feasibility of using xanthate salts in the desulphurisation flotation to reduce the ARD generating potential of mine tailings has been demonstrated in a number of case studies, little attention has been given to the broader environmental implications of this tailings treatment option. The life cycle assessment (LCA) approach proves to be a valuable tool to study the environmental aspects and potential impacts throughout the life cycle of a product or process. In this study, LCA was used as a tool to assess the implications of the new carbon disulphide production process on the environmental performance of subsequent xanthate salt production, as well as the environmental consequences of using these salts in the downstream desulphurisation of base metal sulphide tailings. The objectives of the study were achieved by conducting two inter-related LCA studies: LCA of xanthate production (LCA 1) and LCA of ARD mitigation (LCA 2). These LCA studies followed the protocol set out in the ISO 14040 standards using the Simapro software package (version 7.3.3). The first LCA study was a cradle-to-gate comparison of current and previous carbon disulphide production processes for the production of xanthate. Data was collected in two ways: the foreground data was sourced at the plant in Sasolburg, whilst ecoinvent database was used for background data for the production of 1 tonne of carbon disulphide. To quantify the identified environmental impacts, namely climate change, terrestrial acidification, human toxicity, freshwater ecotoxicity and fossil depletion, ReCiPe, a midpoint life cycle impact assessment (LCIA) method was chosen. Study results confirmed that the new carbon disulphide production facility has a significantly lower environmental foot print than the old charcoal-based process, based on the studied environmental impacts. This improvement reflected positively on the environmental performance of the subsequent xanthate production process
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    A multi criteria analysis and comparison of primary copper processing options
    (2011) Lusinga, Dion; Petersen, Jochen; Broadhurst, Jennifer Lee
    In the present study a methodology and a spreadsheet model were developed with the aim of integrating techno-economic and environmental objectives simultaneously during decision making. The model was developed specifically for the copper industry, mainly due to the wide array of different processing technologies and operational synergies that exist in this industry.
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    Predicting the time related generation of acid rock drainage from mine waste: a copper case study
    (2013) Simunika, Nathan N; Broadhurst, Jennifer Lee; Petersen, Jochen
    The mining and beneficiation of coal and hard rock ores generates large volumes of sulphidic waste that may oxidise in the presence of oxygen and result in the generation of acid rock drainage (ARD). In order to effectively manage the long term effects of ARD, there is a need to reliably quantify the associated impacts and how these impacts evolve with time. Traditional laboratory-scale tests only provide a partial picture of ARD generation, and their extrapolation to full-scale deposits is highly uncertain and controversial. This has prompted the development of mathematical models which take into account the governing chemical reaction and physical transport mechanisms. Whilst the accurate and reliable quantification of the time-related ARD profiles requires rigorous mechanistic modeling of both the (bio) chemical reaction and physical transport mechanisms under non-ideal flow conditions, advanced models are complex and only suitable for site-specific studies and operational decision-making contexts. However, in the early stage screening of waste for potential environmental impacts, simple geochemical mass transport models such as PHREEQC can be used. PHREEQC V.2 has capabilities to simulate a wide range of processes that include equilibrium controlled reactions, kinetically controlled reactions and 1-D advective-dispersion transport, and has been used in a wide range of geochemical applications. However, despite its capabilities, little has been published on its applications to ARD prediction. This study focused on the development and application of a PHREEQC based predictive modeling tool, suitable for the early or screening evaluation of the potential long-term ARD risks associated with sulphidic waste deposits.
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    Using froth flotation to mitigate acid rock drainage risks while recovering valuable coal from ultrafine colliery wastes
    (2011) Mbamba, Christian Kazadi; Franzidis, Jean-Paul; Harrison, STL; Broadhurst, Jennifer Lee
    This dissertation presents the results of an investigation to develop a two-stage flotation process to produce: (i) a low-volume sulfide-rich concentrate that can be treated chemically or biologically or disposed of in a contained manner; (ii) a high-volume (low sulfur) benign tailings, with low ARD potential compared to conventional tailings; and (iii) a coal concentrate that has added value on account of its low sulfur and ash content. Success requires integration of flotation, aqueous chemistry and mineral bioleaching expertise. The approach adopted in this exploratory study entails coal flotation in the first stage, which takes advantage of its natural hydrophobicity.