Browsing by Author "Broadhurst, Jennifer"

Now showing 1 - 12 of 12
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    Open Access
    Assessment of the potential carbon footprint of engineered processes for the mineral carbonation of PGM tailings
    (2016) Ncongwane, Mpendulo S; Broadhurst, Jennifer; Petersen, Jochen
    Mineral carbonation is a carbon sequestration technology that entails the reaction of CO2 with oxides or silicates of magnesium, calcium or iron to produce stable carbonate compounds. Magnesium-rich tailings from the platinum industry in South Africa have been identified as a potentially viable and attractive feedstock for CO2 sequestration through mineral carbonation. Many of the strategies proposed to enhance the dissolution kinetics of silicate minerals, such as the use of elevated temperatures and pressures and chemical additives, as well as pretreatment through mechanical and thermal activation, are energy intensive and will thus reduce the net CO2 sequestration capacity of the overall mineral carbonation process. As a result, there is growing recognition of the need to evaluate the processes using life-cycle based approaches and tools to ensure they result in net CO2 reduction. However, to date, research and development has focused primarily on the optimisation of extraction and/or carbonation efficiencies, with specific emphasis on the relatively reactive silicate minerals, such as olivine and serpentine. This project seeks to investigate the viability of using pyroxene-rich PGM tailings for the sequestration of CO2, with specific emphasis on net carbon neutrality. Promising mineral carbonation processes have been identified on the basis of an extensive literature review, and include the: ammonium salts pH swing, Lackner's HCl multi-stage, gas-solid Abo Akademi University process, direct aqueous process, and mineral acid pH swing. Material and energy balances were then conducted for these processes on the basis of the sequestration of 1 ton of carbon dioxide, using Aspen Plus v8 simulation software package. The material and energy data were then used to determine the total carbon footprint contributions, through the use of SimaPro v 7.7.3. life cycle assessment software.
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    Open Access
    Characterising the potential health risks associated with coal dust
    (2023) Kamanzi, Kankindi Conchita; von Holdt, Johanna; Jacobs, Muazzam; Broadhurst, Jennifer; Becker Megan
    Coal dust is inextricably linked to the development of dust diseases. To date, the role of mineral matter in coal has been investigated for its links to pulmonary damage; however, no consensus has been reached on which characteristics are relevant to pulmonary toxicity. This study hypothesises that the toxic potential of inhalable coal dust can be attributed to reactive mineralogy and the specific surface area for interaction between the particles and primary phagocytes such as macrophages. To test this hypothesis, the study developed an advanced understanding of the relationship between the physicochemical and mineralogical characteristics of coal particles and pulmonary toxicity. Three objectives were constructed to achieve this aim. Objective 1 developed a detailed particle characterisation dataset on coal particle samples utilising both routine (X-ray diffraction and X-ray fluorescence) and advanced methods of coal analysis (automated scanning electron microscopy systems). Objective 2 elucidated multivariant relationships between the particle characteristics and the immunological responses from exposed macrophage cells in vitro using advanced statistical methods. Lastly, objective 3 developed a protocol to empirically characterise the relative risk of coal dust-related damage on a cellular level. In developing a detailed characterisation dataset on the coal samples, both routine and automated analysis tools were used to define general, chemical, mineralogical, and mineral specific characteristics. An auto-SEM-EDS-XRD (Automated scanning electron microscope coupled with Energy Dispersive X-ray Spectroscopy and analyses generated by X-ray Diffraction) protocol was developed to obtain a broad spectrum of particle data by mineralogically mapping each particle. This protocol involved the rigorous analysis of uncertainty in the data using comparative datasets generated from XRD and XRF (X-ray Fluorescence) analyses. In summary, the study demonstrated that the combined use of both routine and advanced particle analysis tools allowed for the classification of chemical and mineralogical distributions as well as a discrimination between general and mineral specific particle characteristics. Generally, these results suggested that features relating to general particle characteristics (size, shape, roughness, and surface area) are more strongly a function of mechanical breakage and deformation than compositional variation. To assess the multivariant relationships between the numerous characteristics defined and response measures of cellular toxicity, a PLSR (partial least squares regression) was applied in a novel approach to attempt a single model comparison of such relationships. This model was chosen for its ability to relate response and explanatory variables based on a new set of variables which have undergone dimensionality reduction whilst maximising the covariance. The results from the relationship analysis showed that physical characteristics (particle shape in particular) displayed a greater influence on cytotoxicity and lipid peroxidation over mineral and chemical-based characteristics. Relating this observation to previous research it was suggested that the influence of shape and roughness on phagocytosis may have strong implications for magnitude of direct and indirect cellular harm and the predominance of either intracellular or extracellular damage. The results also showed that, apart from the influence of particle shape, radical-induced stress and cytotoxicity displayed a strong dependency on (1) the chemical and mineralogical reactivity Ca hosted in gypsum, (2) the release/inhibition of Fe from pyrite and Fe-sulfates, and (3) the surface activity of quartz based on its crystallite size. However, the relationships defined in the context of cytotoxicity displayed a more nuanced dependency with the silicate mineral content and their associated properties compared to lipid peroxidation. From this it was suggested that non-radical related pathways to cytotoxicity could also occur from coal dust exposure. Ultimately, the study demonstrates the first analysis which assesses relative impact and magnitude of multiple particle characteristics on cytotoxicity and cellular stress. Finally, to provide a more easily interpretable format for the analysis of the PLSR relationships, a protocol was developed to screen variables based on: (1) their level of importance to the defined relationship and (2) the rank of importance for each influential variable represented on a unified scale. Elements which explained the variability within the sample characteristics and the responses were clustered using the k-means algorithm to determine classes of samples which display similar characteristics or levels of toxicity. The comparison of the classes grouping samples with similar properties versus samples groups with similar toxicity levels showed that even though samples may share similar properties, their reported level of toxicity may differ. This confirms the observations from previous studies which have shown that the relative toxicity of coal dust cannot be explained on the basis of isolated properties. Rather the set of ‘influential variables' showed that a combination of general, chemical, mineralogical and mineral specific data are needed to determine the differences between levels of toxicity. Ultimately, the application of this protocol on 17 different dust-sized coal samples demonstrated the key differences between samples and their influence on levels of cytotoxicity and lipid peroxidation, which until this study have not been demonstrated by a single regression. As an outcome of such results, this study provides a robust analysis strategy for elucidating particle cell relations which can further advance the understanding of coal dust induced disease pathology. Additionally, the protocol has demonstrated the usefulness of disseminating the complex data structures to more easily interpretable data formats such that a generalisable analysis of risk factors related to coal dust-based cellular damage can be utilised by stakeholders in data-based decision making. Ultimately, the results of this study propose that the toxic potential of coal dust is primarily a function of the reactive mineralogical and chemical components within the particles, however, the magnitude of this intrinsic reactivity is subject to the mitigative factors which can either neutralise of supress the anticipated reactivity.
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    Characterizing the potential environmental risks of South African coal processing wastes
    (2018) Moyo, Annah; Broadhurst, Jennifer; Amaral-Filho, Juarez; Harrison, Susan
    The environmental impacts of coal processing wastes are a challenge in South Africa as large amounts of coal wastes are produced annually, pegged at 60 million tons per year according to Eberhard (2011). Whilst the fossil fuel-based industry is in decline globally, coal is likely to remain the dominant source of power in South Africa. The major environmental impacts reported in several studies are water pollution and soil quality degradation due to acid rock drainage (ARD) and its associated elevated levels of elements and salts. Several studies have shown the environmental performance of the wastes to be dependent on the geochemical properties of the wastes. Owing to the complex nature of coal wastes, their characterisation using tools developed for hard rock ores is associated with inconsistency and uncertainty. As a result, the South African coal processing wastes are poorly characterized and the associated risks not well understood. This study investigates the reliability of relevant characterisation techniques and interpretation of characterisation data in terms of the environmental risk potential of coal wastes. The outcomes of the study address some of the uncertainties and deficiencies arising from the current characterisation tools and evaluate potential environmental risks posed by coal processing wastes. Laboratory-scale characterisation of the physio-chemical properties and of ARD and elemental risk potential of two ultrafine coal waste and one discard waste sample were conducted. Evaluation of accuracy and repeatability of selected analyses was conducted on a certified coal standard. The selected analyses tested for accuracy and repeatability were total sulphur analysis by Leco and Eschka methods in addition to elemental analysis by wavelength dispersive x-ray fluorescence (WDXRF), inductively coupled plasma mass spectrometry (ICP-MS), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The ISO 157:1996 and ACARP C15034 protocols for assessment of sulphur forms were also compared and evaluated for precision using the coal standard and coal waste samples. Conversions of the sulphur species under static ARD tests were also studied to understand the sulphur species behaviour and implication on ARD potential. The mineralogy of the coal wastes was evaluated from a quantitative evaluation of minerals by scanning electron microscopy (QEMSCAN) and quantitative x-ray diffraction (QXRD) analysis. In addition, conventional net acid generating (NAG) and acid-base accounting (ABA) static tests were enhanced through extended boil NAG tests to assess the organic acids effect on the NAG capacity. The static tests were validated by theoretical ARD calculated from mineralogy as well as biokinetic shake flask tests which gave the timerelated acid generating behaviour of the coal waste samples. Sequential chemical extractions combined with a simple score and ranking protocol were subsequently used to evaluate the potential water and soil-related risks associated with environmentally available elements and salts in the coal wastes. The results showed both the Leco and Eschka methods to be highly precise (±0.01-0.03 % standard error) but the Leco was more accurate (±3.1 % compared to ±12.5 % relative standard error (RSE)). The total sulphur content of the coal processing waste was less than 2 %. The ISO157:1996 and ACARP C15034 protocols gave comparable and slightly different results but the latter was more precise in sulphate analysis. Furthermore, the ACARP protocol could differentiate the acid forming sulphates from the soluble sulphates giving a better theoretical maximum acid producing potential. The sulphur species from the two chemical methods and QEMSCAN mineralogy showed 52-61 %, 12-26 % and 21-43 % to be sulphide, sulphate and organic/low-risk sulphur respectively. The conversion of the sulphur species showed that partial solubilisation of sulphides in ANC and partial conversion of organic/low-risk sulphur under NAG tests can cause an over or underestimation of ARD potential. The static ARD tests has shown the Witbank coal discards sample to be potentially acid forming (PAF) (9.2-25.9 kg H2SO4/Ton), Waterberg coal slurry to be non-acid forming (NAF) (-68.6 to -46.8 kg H2SO4/Ton) and Witbank coal slurry to be uncertain (-12.1 to 9.9 kg H2SO4/Ton). The extended boil NAG tests showed organic acids effect on the Witbank coal slurry likely caused an overestimation of the NAG capacity. Validation of the static tests by biokinetic tests and ARD calculated from mineralogy classified both Witbank samples as PAF and the Waterberg sample as NAF. The results also showed the net acid producing potential of the coal wastes to depend on the mineralogy of the samples. The elemental results showed WDXRF and LA-ICP-MS analysed most of the elements accurately within ±10 % RSE and that a combination of techniques provides more reliable and accurate results. The analyses showed the coal waste to contain significant amounts of environmentally sensitive elements like Cr, As, Mo, Sb, Se. The ranking and scoring of potentially available elements under oxidising leach conditions evaluated Fe in Waterberg coal slurry and Witbank coal discards to pose high risk in drinking water while S (as sulphate), Pb, Sb, Mn, As, Al and Hg in the three samples pose moderate risk. This case study evaluated the accuracy and precision of commonly used analytical techniques and applicability of risk evaluation protocols for coal processing wastes. The research outcomes underlined some factors that cause uncertainty and inconsistency with the evaluation of ARD potential of coal wastes. The findings highlighted the need to validate and complement the characterisation data using various tools and risk evaluation protocols to overcome specific limitations. The results also indicated the coal wastes have the potential to cause environmental impacts from ARD and elevated concentration of elements and salts, thus providing a basis for designing and implementing waste management strategies which minimise these risks. The mineralogy and elemental composition of coal wastes showed enrichment of elements and presence of potentially usable and economically valuable constituencies for future studies on value recovery. Characterisation of coal processing wastes for air pollution impacts is recommended for future studies as well as a study of ARD behaviour under continuous flow systems to more closely represent the conditions in dump disposal scenario.
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    Open Access
    Critical assessment of environmental sustainability reporting using the GRI G4 guidelines: A case study of the South African gold sector
    (2019) Viljoen, David Gabriel; Broadhurst, Jennifer
    Sustainability reports ought to be key channels for communication with stakeholders, enhancing organisational accountability and transparency. However, the proliferation of sustainability metrics and the voluntary nature of reporting leads to inconsistencies in the quality of sustainability reporting, invariably affecting its functionality and effectiveness. This research project investigates the quality and functionality of sustainability reporting within the South African gold mining sector. Firstly, a framework for characterising and subsequently assessing the quality of sustainability reports was developed based on a review and analysis of the published literature. This framework was then applied in a multi-method approach consisting of a desktop review involving a content analysis of three company reports that disclose performance according to the GRI G4 Guidelines, and semi-structured interviews with key internal and external stakeholders. The analysis shows that while sustainability reports in the South African mining sector have been found to have beneficial functions for both internal and external stakeholders, they also presented quality issues that are both technical and socio-political in nature. More specifically, the study found that sustainability reports are used internally at an executive level and that the reporting process enhances organisational transparency and accountability. Externally, sustainability reports were found to be used as a source of performance information and as an indicator of company commitment and legitimacy. However, the quality issues, namely levels of aggregation and detail, as well as the degree of integrity, were considered to have a negative effect on the functionality and effectiveness of sustainability reports for stakeholders. This study offers insight into how companies report and how stakeholders perceive and relate to sustainability reporting, and in turn serves to highlight both strengths that should be encouraged, and weaknesses that detract from sustainability reports’ effectiveness and functionality. The application of a multi-criteria framework in a multi-method approach provides a more holistic picture of the quality and functionality of sustainability reports, allowing technical and political quality issues to be discussed in a simultaneous study, as well as highlighting the complexities and nuances of sustainability reporting.
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    Early-stage design and development of mine waste valorisation technologies with expert input: a case study of South African sulfide-enriched coal waste
    (2023) Stander, Helene-Marie; Broadhurst, Jennifer
    Mining and minerals beneficiation typically result in the production of both valuable products and large bodies of waste, which are traditionally disposed of on land and carry environmental and social risks. Circular economy and resource efficiency trends have shifted the focus from disposal to waste reuse and recycling. Despite the benefits of the circular economy approach, development and implementation of waste reuse technologies in the mining industry is fraught with challenges and has thus far been limited. When designing processes for the application of large-volume mine waste, information deficits are encountered. This is largely because the characteristics of mine waste tend to be poorly understood or unknown as well as highly complex due to residual target minerals and processing chemicals present in the gangue components. Furthermore, whilst the technologies used may not be novel, their application in the processing of wastes is generally untested or inadequately researched. Working within such a context, with many unknowns, makes selection of appropriate technologies difficult. Another potential difficulty associated with designing and developing technologies for waste reuse is that unsolicited novel technologies by universities and research institutions can face opposition upon implementation. When designed and developed processes remain unimplemented, research resources are wasted and an opportunity to effect much-needed change is missed. It is these challenges that this study seeks to address through the development of a generalised systematic approach for the early-stage design and development of technologies for the reuse of mineral beneficiation waste that addresses both technology transfer and information deficit issues. The approach is based on three key premises: firstly, that technology transfer issues should be identified and integrated into technology selection and development from the early design and development stages. Secondly, that expert interviews and surveys can provide data that is useful not only in social sciences, but also in technical development and decision making to address data gaps. The third premise is that pre-feasibility studies, usually used to assess the techno-economics of relatively mature technologies, can be valuable for both technical information gathering and identifying technology transfer issues within the context of early-stage mineral processing waste reuse design and development. The application of this approach has been demonstrated in a case study on the downstream utilisation of South African sulfide-enriched fine coal processing waste. The premises identified above were studied in turn. Firstly, technology transfer issues were investigated using interviews with South African coal industry participants and the transcripts were analysed using thematic analysis. Secondly, the use of surveys and expert interviews to overcome data gaps in decision support for technology selection was investigated using a value theory multi-criteria decision analysis approach, and the data quality was assessed using distinguishability analysis. Lastly, the pre-feasibility study was conducted to assess the selected technology based on local contextual factors identified during the technology transfer interviews. The results of the study showed that exploring technology transfer issues in the early stages of technology development can support technology development by identifying aspects of key importance to the receiving industry. In terms of the case study, aspects such as the continued pre-eminence of techno-economic considerations in technology investment decisions and industry preference for mature technologies were identified. It was also highlighted that the South African mining industry is structured to focus on core business-related activities, making them unlikely to become technology development partners. Original equipment manufacturers and boutique waste processors, as opposed to mining companies, were considered appropriate commercial partners for universities and research institutions developing mine waste valorisation technologies. The study also showed that using expert judgement inputs as data for decision support must be done with caution. The case study data showed a high degree of dispersion to the point where the performance of technology alternatives on different criteria could not be meaningfully distinguished. Distinguishability improved with a more careful selection of “high-quality” experts and again when interviews were conducted with these experts, but not to the point of enabling defensible decision support. Analysis of the interview transcripts also showed that much of the variability could be attributed to uncertainty inherent in the decision problem as well as disagreement between experts. This indicated that some measure of variability in the data is inherent. Experts did, however, provide information that is useful for future technology development as well as indications of what research questions were still unanswered. Expert interviews for eliciting technical information therefore have value for providing background information for further development. Despite the uncertainties in the data, the option of using the sulfide-enriched coal processing waste as a soil ameliorant was consistently highly ranked and was therefore explored in the pre-feasibility study. The study also showed that technology viability can be assessed relatively efficiently using a prefeasibility study that incorporates consideration of technology transfer issues and local contextual issues. For the specific case study of application of sulfide-enriched fine coal processing waste as a soil ameliorant within the South African context, several issues were investigated: potential markets were identified; the transport costing of the product compared with the current market alternative was calculated; technical viability was assessed through a literature study; and health and safety risks were identified. This showed that while the technology is likely to be technically viable, the commercial viability is affected by high transport costs. The business case for the solution is therefore dependent on the avoided disposal costs for mines as well as the propensity of the material to slow-release acidity and thereby avoid repeated applications of the competitor product. In conclusion, this study demonstrated that a systematic and integrated approach for the early-stage design and development of waste valorisation technologies can help universities and research institutions structure the technology development process aiming at implementation of technologies. Ultimately, it is postulated that such an approach will facilitate the sustainable management of large-volume mineral beneficiation waste in line with the principles of industrial ecology and circular economy. Due to the difficulty with obtaining high-quality data for technology selection, it is recommended that improved approaches for early-stage technology selection must be investigated. Future work should furthermore include a more detailed investigation to clarify the cut-off distinguishability index values needed for different decision-analysis scenarios. Improved approaches for alternative identification in a mine waste valorisation context must also be investigated. Lastly, the role and approach of technical interviews, other technology transfer activities, and commercial partner identification must receive future research attention to investigate to what extent these can be combined to reduce resource requirements.
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    Factors contributing to unsuccessful rehabilitation: a case study investigating the rehabilitation practices in Opencast Coal Mines in the Mpumalanga Province, South Africa
    (2021) Gule, Nontobeko; Broadhurst, Jennifer
    The coal mining industry has played a significant role in the development of the South African economy. Coal supplies about 70% of South Africa's primary energy and is likely to remain the country's major source of energy despite the increasing trends towards renewable energy. Even though the industry has significantly contributed to the development of the country, it has also caused significant impacts on the environment with concomitant socio-economic impacts. Historically, once a coal measure was exhausted, mining companies would cease production and abandon the mines without proper rehabilitation of the environmental degradation caused by their mining activities. As a result of this, the South African Government introduced mining and rehabilitation legislation to mitigate the environmental and associated socio-economic impacts of mining. Rehabilitation guidelines for opencast coal mines were developed to provide detailed guidance for achieving successful and sustainable rehabilitation, to mitigate pollution post-mining. Despite the more stringent legislative framework and the development of international standard rehabilitation guidelines, successful mine rehabilitation remains a challenge. This research project aims to develop a better qualitative understanding of the status, challenges, gaps and opportunities pertaining to current rehabilitation practices in the case of opencast coal mines in the Mpumalanga Province of South Africa, and in so doing, establish the contributing factors of unsuccessful rehabilitation. The dissertation draws on a comprehensive review of published literature and an analysis of semi-structured interviews with rehabilitation experts. The study found that the current rehabilitation practices in the Mpumalanga opencast mines are not to the standard required by the legislative framework nor prescribed by rehabilitation guidelines. As such, the current rehabilitation practices are not yielding successful and sustainable rehabilitation. According to the findings, the rehabilitation practices are hampered by physical and non-physical systemic challenges that thwart the achievement of successful rehabilitation. The study analysis shows that shortcomings in the application and enforcement of the legislative framework contributes to the legislation not achieving its intended objectives as well as the development of other physical and non-physical systemic challenges that hamper the achievement of successful rehabilitation.
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    From the constructs and methods of the philosophers to a model for improved discourse between disciplines
    (2020) Harrison, John; von, Blottnitz Harro; Broadhurst, Jennifer
    We have problem areas which are beyond the scope of a discipline, but we are generally educated in just a single discipline. I explored our philosophy of work to see how we became disciplinary, where the disciplines came from, what philosophy underlies our way of working, and what philosophy underpins work that is beyond the scope of a discipline. The underlying philosophy leads to the research question. My hypothesis is that a systems engineer can create a model which networks the disciplines using constructs from philosophy, the tiers of disciplines in transdisciplinarity, and systemic and holistic thinking. This will provide a way of working on problem situations which transgress the boundary of a discipline. Using constructs from philosophy, the methods of the philosophers, hermeneutics, systems thinking and soft systems methodology I proceeded to create a conceptual model and showed conceptual examples of how to use the model. The client for the model is the interdisciplinary researcher who is seeking a way of working to manage problem areas that transgress disciplinary boundaries. The recommendation is made for using critical, systemic and holistic thinking and a network model of disciplines to manage our approach to problem situations which are beyond the scope of a discipline. The model is developed in the incremental sequence: disciplinary, multidisciplinary, interdisciplinary, transdisciplinary and gets as far as catering for tiers of disciplines (one aspect of the large and complex field of transdisciplinarity). Therefore, the model is suitable for interdisciplinary research, but can be developed further in future projects. The importance of the model is that it provides a practical way of working to manage problem situations which transgress disciplinary boundaries whilst accessing the expertise of disciplined practitioners. The model can find wide applicability. It is not necessary for the user of the model to be comfortable with the abstract philosophy used to create it. Users will need the will for uncoerced mutual understanding or free communication, along with their disciplinary expertise. The reader of the dissertation however should be comfortable with abstractions such as ideas about reality and actuality, form and class, subject and object, truth and justice, truthfulness and functional fit. Future work may reduce the method to practice in the academy and extend the method to bridging silos in learning organisations in the workplace. The work was conducted independently, and an original model was created.
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    Impacts of mining on land use - A case (study) of Luanshya district, Zambia
    (2018) Sakuwaha, Kabangu Grace; Broadhurst, Jennifer; Odendaal, Nancy
    Copper mining is the main driver of Zambia’s economic growth and development and plays a significant role in the global supply of materials for electrical, plumbing, heating and transport equipment among other benefits. However, primary production and beneficiation of copper pose serious risks to the mining districts such as environmental pollution, landscape alterations, land degradation and social economic challenges to the host communities. This research looks at the landscape alterations in the mining district of Luanshya, and how these alterations are related to mining and other land uses. Using remote sensing and Geographic Information Systems (GIS), the landscape alterations were mapped and analysed to identify the processes causing these alterations and their impacts on land use. Secondly, stakeholder interviews were conducted to gain a deeper understanding of the mapped landscape alterations, what the approach has been to land use planning and the stakeholder roles in this planning. Analysis of the findings identifies that landscape alterations in the district have been caused by different inter-related mechanisms stemming from a number of causes. These causes include high dependency on copper mining; inadequate enforcement of environmental legislation; lack of state involvement in land use planning of mining districts; and also global factors such as commodity market conditions. As a result, boom and bust commodity cycles have had significant impacts on the wellbeing of both mining communities and the environment. These impacts are not limited to the mine sites alone but extend to entire districts. This research also identifies that while mining plays a vital role in the economic development of Zambia, adequate enforcement of environmental legislation and adoption of inclusive land use planning may stimulate sustainable development of mining districts and foster sustainable land use patterns. Furthermore, this study recommends that future land use planning must be dynamic in terms of adopting postmining restoration of landscapes and infrastructure while also taking the direct and indirect impacts of mining into account.
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    Quantifying texture for acid rock drainage characterisation and prediction
    (2020) Guseva, Olga; Becker, Megan; Broadhurst, Jennifer; Harrison, Susan; Bradshaw, Deidre
    Minerals, metals and mining are the cornerstone of technological development and play an essential role in achieving the United Nations Sustainable Development Goals. Mining, however, is not a wastefree process, with mine wastes being a source of a host of environmental problems. One of these is acid rock drainage (ARD), which forms through a complex series of acid formation (mainly via sulfide oxidation), neutralisation (primarily by carbonates) and gangue mineral dissolution reactions in waste rock and tailings storage piles. The resulting drainage waters are often acidic, highly saline and may contain elevated levels of deleterious elements. Effective ARD mitigation requires accurate ARD characterisation and prediction strategies. To date, standard guidelines recommend a suite of geochemical static (characterisation) and kinetic (prediction) tests. Characterisation tests such as acid-base accounting (ABA) and net acid generation (NAG) tests provide a quick and relatively inexpensive estimate of the "worst case" scenario for acid formation and neutralisation, while kinetic tests (commonly humidity or column leach tests) aim to predict the longterm weathering potential of waste material. The UCT biokinetic test (not currently industry standard practice) was developed to address the effect of microorganisms on ARD formation and allow for the collection of relative kinetic data on neutralisation and acidification within a shortened time period. None of these tests, however, account for the additional layer of complexity introduced by mineral texture, which describes the interrelationship of mineral grains to one another, their shapes and sizes, with some frequently studied textural parameters including mineral liberation, association, grain size distribution and particle size. Mineralogical and textural analyses are infrequently practiced in the context of ARD assessment due to the difficulty in obtaining statistically sound quantitative textural data, high costs of measurement, and standard ARD assessment protocols recommending (rather than necessitating) these assessments. An ARD assessment approach that includes static, kinetic, mineralogical and textural assessments has nonetheless been suggested by several researchers. This project assessed the dominating textural parameters on the scales of kinetic (humidity cell) test (HCT) feed material (meso-scale) and characterisation (static and UCT batch biokinetic) test (SCT) feed material (micro-scale) using four waste rock samples (A, B, C and D) from a greenstone belt gold deposit as a case study. More specifically, the study aimed to assess the role of mineralogy and texture in the ARD assessment "toolbox" and to investigate the role of coarse material sampling for ARD assessment. Data sets collected included the PSD of the micro- and meso-scale material, sample chemistry data obtained from XRF spectrometry and LECO total sulfur, bulk mineralogy data from QXRD and QEMSCAN, as well as textural and mineralogical data from QEMSCAN for sized and unsized micro- and meso-scale material. ARD-specific data sets included results of geochemical characterisation tests such as ANC and single-addition NAG tests, the UCT batch biokinetic test with and without pH control for samples C and D, as well as prediction test data from water-fed and modified humidity cell tests. The geochemical static tests performed on samples A, B, C and D classified them as PAF, PAF, uncertain and NAF, respectively. Non-pH-controlled UCT batch biokinetic tests remained circumneutral for samples B, C and D over the duration of 90 days, while for sample A the pH became acidic over time. The pH-controlled tests demonstrated a steady depletion of neutralisation potential over the first 30 days. Humidity cell test results demonstrated no acidic leachate formation for waterfed tests over 40 weeks, while modified tests showed a decreasing pH over time as the neutralisation capacity was reduced. The mineralogy was important for the interpretation of test results on both the micro-and meso-scales and was assessed in terms of both discrete minerals and reactivity groupings (Fe-Sulfide, other sulfide, dissolving (carbonate), fast weathering, intermediate weathering, slow weathering, inert and other). For sample A the mineralogy was dominated by the inert (quartz), slow weathering (magnetite, plagioclasealbite) and intermediate weathering (Fe-amphibole) categories, with lesser contributions from the FeSulfide (pyrrhotite), dissolving (calcite) and fast weathering (epidote) groups. The main groups contributing to the sample B mineralogy were the slow weathering (plagioclase-albite, magnetite, Kfeldspar), inert (quartz) and intermediate weathering (Fe-mica, chlorite) groups, followed by Fe-Sulfide (pyrite), dissolving (calcite) and fast weathering (epidote) mineral groups. Sample C mineralogy comprised predominantly inert (quartz, titanite), Fe-Sulfide (pyrrhotite), dissolving (calcite) and intermediate weathering (Fe-mica, chlorite) minerals, with lesser contributions from slow weathering (K-feldspar) and fast weathering (epidote) minerals. Sample D comprised intermediate weathering (Feamphibole, chlorite, Fe-mica) and slow weathering minerals, with lesser contributions from slow weathering (magnetite), dissolving (calcite) and Fe-Sulfide (pyrrhotite) minerals. Textural parameters (liberation and association, grain size distribution and liberation spectrum) were evaluated for the FeSulfide and dissolving minerals. On the micro-scale, a large portion of the Fe-Sulfide and dissolving minerals in the samples was found in the liberated category (50%) of the texturally significant size fractions (>1mm), which comprised predominantly locked Fe-Sulfide and dissolving minerals. Evidence of a bimodal distribution was, however, found for sample C via the liberation spectrum and grain size distribution (early liberation size of 8mm), which accounted for the larger degree of liberation observed in the >1mm size fractions, and a larger degree of liberation for the sample overall. The association of Fe-Sulfide and dissolving minerals for all samples was found to be primarily to inert, intermediate weathering and slow weathering minerals, with a larger degree of association of Fe-Sulfide to dissolving minerals observed in sample C. On the micro-scale the mineralogy helped inform the placement of the samples on the geochemical classification plot based on the Fe-Sulfide, dissolving and intermediate weathering mineral contents. For the non-pH-controlled UCT batch biokinetic test, the presence and abundance of calcite was thought to dictate the PAF/NAF nature of the test, as even relatively low amounts of calcite rendered the pH circumneutral for the duration of the test (sample B). For pH-controlled tests, however, the calcite was depleted over time, which led to a favourable acidic environment for the acidophilic bacteria used in the batch biokinetic test. For both the geochemical characterisation and the pH-controlled UCT batch biokinetic tests there was evidence to suggest the contribution of intermediate weathering (Feamphibole, Fe-mica, chlorite) and slow weathering (magnetite) minerals to the neutralisation potential in the sample. On the meso-scale the effects of mineralogy were most prominent for the modified humidity cell tests, which showed some pH fluctuations and a steady depletion of the primary neutralisation potential. The pH fluctuation after the depletion of the dissolving minerals was attributed to the dissolution of intermediate weathering minerals over the 40 weeks of the tests. These effects were not observed during the 40 weeks of the water-fed experiments. Given sufficient time for the latter test, however, it would be expected that upon the onset of acidification, similar effects of the mineralogy on the leachate quality would be observed as in the modified tests. Knowledge of the Fe-sulfide and dissolving mineral texture yielded several insights. on the micro-scale, the liberation and grain size distribution data provided an indication that a sample-customised grinding size should be established to ensure adequate "worst case" scenario determination via characterisation tests, as material with fine Fe-Sulfide or dissolving mineral grains may not be fully liberated at the recommended 75µm top size. On the meso-scale, the texture yielded insight into the circumneutral behaviour of the water-fed HCT, as most of the acid-forming minerals were contained in size fractions where the liberation was either limited or negligible, with predominant association to slow weathering, intermediate weathering and inert minerals. These findings highlighted the importance of considering mineralogy, texture and the PSD of the material for HCT result interpretation. When considering texture as a parameter for ARD assessment, the potential for sampling and mineralogical errors arose due to the coarse material size (specifically on the meso-scale) and the limitations on the number of particles that could be assessed. Quantitative mineralogy and texture data allowed for the quantitative assessment of the sampling and mineralogical errors, which were investigated through Pierre Gy's fundamental sampling error (FSE) equation, the binomial distribution approximation and the plotting of confidence intervals over the Fe-Sulfide liberation data. The results showed that although tools such as Gy's "safety line" provide a useful quick means of sampling error assessment, this approach may yield excessively large sample mass requirements for coarse material. Calculating the sampling error from the textural and mineralogical data provided a useful tool to estimate sample representativeness. Additionally, the estimation of sampling errors may help in the planning of an appropriate sampling approach, which may ultimately provide a means to relate data sets to one another across scales based on how representative samples are of one another, and therefore of the parent lot. The current study showed how mineralogy and texture are not simply "tools" in the ARD assessment "toolbox", but rather a key means for interpreting characterisation and prediction test data. Additionally, the quantitative assessment of mineralogy and texture provided the opportunity to assess the materialspecific sampling error, which, in turn, may allow for the correlation of data sets across various scales and for the planning of appropriate sampling strategies. Recommendations for future work include: the quantitative assessment of the ARDI for meso-scale material; the assessment of detailed characterisation and prediction test leachate chemistry; trace element assessment and deportment throughout UCT batch biokinetic and humidity cell testing; mineralogical and textural assessment on characterisation and prediction test residues during and after tests; an in-depth analysis of the minimal/optimal sample block/sub-sample mass required for minimal error; the assessment of samples using X-ray microcomputed tomography to assess and decrease the effects of stereological bias prevalent in 2D measurements; and the application of a similar texture and mineralogy assessment to additional waste types (such as coal wastes, or waste material containing non-Fe-bearing sulfides).
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    Repurposing of mine waste: an alternative management approach to gold tailings in South Africa
    (2019) Sibanda, Lesley Kudakwashe; Broadhurst, Jennifer
    The large volumes of waste generated during gold beneficiation are a major pollution concern in South Africa. To remove these potential pollution risks in perpetuity, non-conventional approaches to mine waste management are required which avoid land disposal of “unwanted” material. This dissertation explores the opportunities, drivers and barriers for the re-purposing of gold tailings in South Africa. The thesis draws on a comprehensive literature review, analysis of information and data in the public domain, and semi-structured interviews with relevant experts. The research findings identified numerous potential uses for gold tailings including reusing gold mine tailings in making bricks, ceramics, cement additives, backfill, stone paper and aggregate material for construction. The derelict tailing dumps can also be used for recreation purposes, tourism and many other land use applications. The study showed that despite existing opportunities, the application of mine waste as feedstock for other purposes in South Africa is currently constrained. According to the findings, this can be credited to numerous inter-related factors, such as inadequate technology development, lack of an enabling legislative framework, high short-term costs, and potential environmental risks associated with hazardous components in the waste. Overcoming these barriers will require innovative, transdisciplinary approaches, and effective partnerships with relevant stakeholders, including academia, private business entities (waste users) and regulatory bodies (government).
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    Stable Isotope Imprints during Pyrite Leaching: Implications for Acid Rock Drainage Characterization
    (2020-11-04) Ódri, Ágnes; Becker, Megan; Broadhurst, Jennifer; Harrison, Susan T. L.; Edraki, Mansour
    The characterization of acid rock drainage (ARD) is traditionally based on mineralogical and geochemical techniques (e.g., Acid Base Accounting tests). The complexity of ARD processes warrants contribution of methods from various disciplines. In the past decade, the increasing role of environmental isotopes in pollution monitoring has enabled the successful application of isotope methods in ARD investigations. While isotopic compositions of different pollutants can refer to their parent mineral, the degree of isotope fractionations are indicative of the mechanisms taking place during the release and transportation of ARD-related contaminants. In natural environments, however, the measured isotope fractionations are predominantly the result of several coexisting or sequential processes. Therefore, the identification and quantification of the distinct contributions of these processes to isotope variations is difficult and requires well-defined laboratory conditions, where the influence of ARD generation on different isotope systems can be assessed with greater certainty. This review provides readers with a single source of information regarding isotopic variations generated by laboratory pyrite leaching.
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    The impacts and conflicts associated with defunct gold tailings storage facilities in South Africa: A case study of Davidsonville, Central Rand
    (2021) Nwaila, Phumzile Cynthia; Broadhurst, Jennifer
    Gold mining generates large quantities of tailings waste. These tailings can have a significant negative impact on the surrounding environment, with concomitant effects on local ecosystems, as well as on human health and quality of livelihoods. The latter is a concern in the Witwatersrand goldfields of South Africa, where communities are located in close proximity to gold mining operations and/or both current and defunct tailings dumps. This research project was, therefore, aimed at developing a better understanding of the facts, perceptions, concerns, and expectations associated with Witwatersrand gold mine tailings storage facilities, and how these are related. In order to fulfil this aim, a desktop study was conducted which involved a detailed review of published academic literature, company reports, newspaper articles, gold mining magazines, and specialist reports with specific emphasis placed on the Central Rand goldfields of the Witwatersrand Basin. Semi-structured interviews were also conducted with representatives from the community, civil society organisations and independent experts, using the defunct Princess gold tailings dump in Davidsonville Suburb (West of Johannesburg) as a case study. The literature review of the study has shown that there is environmental pollution (air, water and soil) due to gold tailings dumps in current and historic gold mining areas. These findings were found to be largely consistent with perceptions and concerns of the community members, civil society organisations and subject matter experts. The long-term impacts of this pollution are not only environmental but cause a huge social burden on health and quality of livelihoods. Not only is dust considered a nuisance, particularly in the windy season, but the dust has been proven to contain crystalline silica and radionuclides. The long-term exposure to this dust can lead to skin problems and respiratory illnesses. There is higher exposure of ambient particulate matter (PM10) in areas around tailings even at distances up to 2 km downwind from the tailings dumps. Acid mine drainage, on the other hand, increases metal load in watercourses and soils, ultimately affecting the ecosystems as the metals are toxic to plants. Metal contamination has adverse impacts on animal and human health. In addition to literature survey, results from the semi-structured interviews revealed that there are conflicts between the communities, government and mining companies, with communities associating their health problems with gold mine tailings. This has led to court cases and gained media attention. The complex relationships between mine waste, the environment, and community health and livelihoods are still not well understood, making it difficult to justify and motivate the implementation of meaningful interventions to mitigate risks associated with gold tailings dumps. To date, little attempt appears to have been made to support community concerns and perceptions with factual evidence and information. Overall, this study has demonstrated the existence of longstanding issues associated with defunct gold tailings dumps and the communication gab that existing between various stakeholders, i.e. community, government and mining houses. These emphases the importance of having adequate remedial actions to prevent further pollution, the need to engage all relevant stakeholders when dealing with gold tailings and implementation of regulatory frameworks associated with gold tailings reclamation and rehabilitation.