Theses and Dissertations (University of Pretoria)

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An investigation into consumer brand engagement : scale refinement, drivers and outcomes
Ndhlovu, Thinkwell (University of Pretoria, 2021)
In the past decade, consumer-brand engagement (CBE) has received much research attention among marketing academics and practitioners owing to its strategic imperative to modern firms. However, despite this focus, CBE continues to fragment in terms of its conceptualisation, dimensionality, measurements, drivers and outcomes. The literature reveals differences in the conceptualisation of CBE, with different perspectives used to describe the concept. This has resulted in the development of different scales to measure CBE. Most of these scales were developed in the service context and their generalisability to other contexts is limited. Despite this limitation, there is a growing trend among marketing scholars to adapt the service context orientated CBE scales to product contexts. This poses a challenge as product and service contexts differ on tangible and intangible attributes that influence consumers’ decision-making. Therefore, this study considered it reasonable to develop two CBE scales specifically for the product- and service-brand contexts respectively, to avoid the over-generalisation of service-context CBE scales to other contexts. Despite the growth of CBE research over the years, there are still limited empirical studies focusing on the relational drivers and brand outcomes in service and product brand contexts. Most of the previous studies explored only customer-based factors as drivers of CBE and did not incorporate firm-initiated factors. The literature further shows inconsistencies about the brand outcomes of CBE, with different marketing constructs suggested as possible brand outcomes; however, there has been scant attempts to explore some of these constructs empirically. The primary purpose of the study was to investigate CBE’s conceptualisation, measurement, drivers, and outcomes in the product- and service-brand contexts. For investigation, smartphone brands were used to represent product brand context and social media brands embodied the service brand context. The different conceptualisations and theoretical fundamentals of CBE were explored. The study developed and validated two CBE scales specifically for product- and service-brand contexts through a scale refinement process. The effect of brand trust, self-expressive brand, and brand interactivity on CBE in product- and service-brand contexts was investigated. Furthermore, the mediating effect of brand satisfaction on the effects of brand trust, self-expressive brand, and brand interactivity on CBE was examined. The drivers and outcomes of CBE in product- and service-brand contexts were explored and the mediating role of CBE was assessed. To address the primary purpose and objectives of the study, this study was conducted in two phases. The first phase focused on the scale refinement process and the second phase explored the different relationships between CBE and other marketing constructs. Data were collected by reputable market research firms who hosted and distributed online self-completion surveys to independent adult samples of smartphone and social media users in South Africa. Using the convenience sampling method the samples were drawn from consumer panels. In the first phase, the sample sizes comprised of 420 and 428 usable responses for smartphone and social media contexts respectively. Exploratory factor analyses (EFA) using principal axis factoring (PAF) with Promax rotation were used to extract the dimensions of CBE in both contexts. In the second phase for scale validation and exploring the different relationships between CBE and other marketing constructs, the sample size consisted of 503 and 491 usable responses for smartphone and social media contexts respectively. Confirmatory factor analyses (CFA) were used to confirm the measurement models developed through EFA and structural equation modelling (SEM) was conducted to examine the hypothesised relationships in the study. The results of the first article reveal two validated CBE scales specifically for the product-and service-brand contexts. The scale refinement process resulted in a 29-item scale in the smartphone context that has two dimensions – affection and reasoned behaviour – and a 20-item scale in the social media context that has four dimensions – affection, identification, absorption, and social connection. The two refined scales demonstrated good psychometric properties. In the second article, that examined the effects of brand trust, self-expressive brand and brand interactivity on CBE, it was found in the smartphone brand context that brand trust, self-expressive brand, and brand interactivity have different effects on the CBE dimensions (affection and reasoned behaviour). Specifically, the results show that brand trust positively influences CBE affection, with self-expressive brand and brand interactivity positively influencing CBE reasoned behaviour. In the social media brand context, the results show that only self-expressive brand positively influences CBE as a second-order construct (reflective of four dimensions: affection, identification, absorption and social connection). In addition, the study found that brand satisfaction plays a mediating role on the effects of brand trust, self-expressive brand, and brand interactivity on CBE in both brand contexts. The third article reveals different results as it incorporates both the relational drivers and brand outcomes of CBE. The findings of this study show that, in the smartphone context, brand trust and brand interactivity positively influence both dimensions of CBE (affection and reasoned behaviour), while self-expressive brand had different effects on the CBE dimensions (affection and reasoned behaviour). In the social media context, brand trust, self-expressive brand, and brand interactivity were all found to positively influence CBE as a second-order construct (reflective of four dimensions). The findings also reveal that, in both brand contexts, CBE positively influences brand evangelism and consumer-based brand equity. That is, the CBE dimensions of affection and reasoned behaviour in smartphone context and the CBE dimensions of affection, absorption, identification and social connection (represented as a second-order construct) in social media context all positively influence brand evangelism and consumer-based brand equity. This research was theoretically underpinned in service-dominant logic (S-D logic) which is centred on the narrative of value co-creation through service exchanges and resource integration by various actors in service systems including the consumer and the brand. An S-D logic informed CBE was conceptualised in this study as a consumer’s psychological state and behavioural manifestations that occur through the process of value co-creation, involving resource integration and service exchanges in consumer–brand interactive service systems. This study makes scholarly and managerial contributions. The theoretical fit between CBE and S-D logic is explained, thus expanding the development of CBE/S-D logic theoretical research. The scholarly knowledge of CBE is advanced through bringing together the fragmented conceptualisations and designing an S-D logic-informed definition that includes both the psychological and the behavioural perspectives. This study responds to the over-generalisation of service context CBE scales in other contexts by developing and validating two CBE scales specifically for the product-and service-brand contexts. In addition, this study highlights consumer-brand value co-creation relationship by providing empirical evidence that drivers of CBE should comprise of consumer-based (brand trust and self-expressive brand) and firm-initiated factors (brand interactivity). This study expands the existing knowledge of CBE by developing and empirically testing an S-D logic-informed holistic model showing CBE’s key drivers such as brand trust, self-expressive brand and brand interactivity, and the brand outcomes of brand evangelism and consumer-based brand equity in both brand contexts. This model advances consumer-brand relationship research in product-and service-brand contexts. The research highlights the importance and central role played by CBE beyond purchase in promoting positive brand outcomes for firms. Finally, this study provides managers with tools to measure CBE in product-and-service contexts and advances insights on the drivers and outcomes of CBE that will assist in the development of holistic customer relationship management (CRM) strategies. Despite the scholarly and managerial contributions, the study had some limitations. A non-probability convenience sampling method was used in the study, which suggest that the study’s results are not generalisable across the whole population. The study was cross-sectional in nature, which means that the results only captured a snapshot of consumers’ perceptions at a specific point in time. Future research on CBE could use longitudinal research to capture consumers’ changing perceptions and behaviour over time.
Chinese outbound tourism to South Africa: a strategic approach
Ying, Li (University of Pretoria, 2015-09)
China and South Africa are currently two major developing countries that have undergone radical socio-economic development since the reform and opening up of China in 1978 and the founding of the new democratic dispensation in South Africa in 1994 respectively. Both have experienced dramatic changes in terms of their tourism development, as well as their relationships. In the light of this, this study is concerned with Chinese outbound tourism to South Africa within the context of a strategic approach. The study focuses on the strategies that South Africa has and could implement to develop this market of over 1.3 billion people. Using strategy theories from a wide range of disciplines, such as military thinking, business, management and tourism, it compiles a proposed framework for the process of tourism and marketing strategies to address this issue. This framework, which is comprised of strategy formulation, strategy implementation and strategy feedback, is used to assess the tourism strategies of South Africa after 1994. It also considers the marketing strategies in the global tourism market, focusing particularly on the Chinese outbound tourism market to South Africa. The study conducts a SWOT analysis of tourism in South Africa to China, with reference to Chinese outbound tourism to Australia so as to identify the gaps prevalent in the South African development of this market. In addition, the results obtained from an empirical survey on Chinese tourists to South Africa not only underscore a new concept of “strategy feedback” proposed in this study, but provide a SWOT analysis of tourism in South Africa to better understand Chinese tourists, thereby establishing South Africa as a preferred tourism destination in the Chinese tourism market. Moreover, it provides suggestions for South Africa to develop the Chinese outbound tourism sector, which could also serve other developing countries in Africa.
A petrochemical investigation of the Spitskop Alkaline Complex, Eastern Transvaal
Nel, David. Jacobus (University of Pretoria, 1976-10)
This study comprises a petrographical and mineralogical description of the rocks of the Spitskop Complex. Data on the chemical composition of the rock types, as well as on some of the minerals, are presented. The complex consists of a pyroxenite pipe near the perimeter of which is situated a composite ring-dyke of foyaite. Ijolite is present as dykes and sills in the pyroxenite, and the carbonatite occurs as a plug intrusive into the pyroxenite. The complex is surrounded by an aureole of umptekite, and xenoliths of gabbroic rocks and magnetitite are present within the complex. A plug and sill of latite inside the complex, as well as dykes and cone sheets of latite and trachyte in the country rocks, were encountered. Profiles of eight core boreholes, drilled to depths between 30 and 40 metres into the complex, are presented, together with thirty-two rock analyses, fifteen mineral analyses, and variation diagrams showing the chemistry of the clinopyroxenes. The borehole profiles indicate that the ijolite is intrusive into the pyroxenite in the form of sills and dykes. This feature is further confirmed by the nature of the outcrops to the west of the carbonatite. The foyaite is subdivided into porphyritic, hypidiomorphic, and trachytoidal textural varieties, and the ijolite into hypidiomorphic and porphyritic varieties. The chemical variation diagrams indicate that the clinopyroxenes of the alkaline rocks follow differentiation trends typical of alkaline complexes, whereas those of the theralites show trends similar to those usually found in layered intrusions. From the geochemistry, the following order of emplacement may be derived: pyroxenite – ijolite – foyaite, in cases where a low CO₂ pressure prevailed in the magma; and pyroxenite – ijolite – carbonatite, in cases of a high CO₂ pressure. The Upper Zone of the layered sequence of the Bushveld Complex is postulated as the source of the theralites, which are here interpreted as xenoliths within the Spitskop Alkaline Complex. A vertical displacement of not more than a few hundred metres is suggested.
An exploration of South African trade union renewal through the lens of business model innovation
Ngomane, Mncedzi Vusile (University of Pretoria, 2024-11)
Trade unions globally and in South Africa have been faced by a survival crisis over the last few decades because of growing questions over their relevance and efficacy as social partners. The existential crisis has been reflected in the consistent decline in union density and key financial matrices, such as subscription revenues. As a result of the growing survival threat, trade union renewal became the subject of extensive research over the years. The literature revealed that trade union renewal research mainly focused on the need for unions to evolve certain aspects, such as their collective bargaining strategies, ideological principles, policy positions and operational strategies. There had been no research that explored trade union renewal through the lens of business model innovation. The literature also revealed the lack of research that sufficiently explored the process or approach that trade unions follow or adopt when attempting to renew their business models including how their ideologies impact the process or approach. The study followed a qualitative multiple case study method of inquiry. Four South African trade union cases were used for purposes of primary data collection. The four cases were made of two evolving trade unions and two less evolving unions. Business model innovation theory and related frameworks were used as the basis of the study, particularly for understanding the process or approach that trade unions used for innovating or renewing their business models and understanding the impact or effect that their ideologies and institutional factors had to the process. The results of the study demonstrated that both the evolving and less-evolving South African trade unions attempted to a greater or lesser degree business model innovation as a renewal alternative, albeit at different levels of strategic intentionality and success. The evolving trade unions adopted business model innovation consciously and as a matter of strategic imperative. The less-evolving trade unions, on the other hand, depicted a reactive and coincidental stance on business model innovation. The results also unearthed the different unions’ institutional factors that affected their business model innovation process and outcomes. The results also showed the ideological postures for the two types of unions including how they impacted their business model innovation approaches or processes. The research contributes by extending business model innovation theory to a trade union renewal context for purposes of understanding how South African trade unions innovate their business models. The research also proposes two types of conceptual frameworks that demonstrate the business model innovation approaches adopted by evolving and less evolving unions.
The constraining role of the multidimensionality of organisational legitimacy on revenue model innovation in private, commercially funded news media in South Africa
Tshangana-Magopeni, Phathiswa Patience (University of Pretoria, 2025-05-28)
Despite organisational legitimacy being considered important for firm performance and enabling enterprises to attract and attain critical resources, it is unclear how its different and sometimes contrasting dimensions affect organisations pursuing revenue model innovation in contexts with competing legitimacy requirements. Using a qualitative approach, this multiple case study sought to answer the question: How do the multidimensionality and adaptability of organisational legitimacy interface with revenue model innovation in commercial news media in South Africa? It focuses on private, commercially funded full-service news organisations. Primary data from four case studies were gathered through semi-structured interviews. Further primary data were collected from participants, comprising regulators and industry experts, to corroborate the case study data. Additionally, secondary data from case studies and industry bodies included regulatory codes, editorial policies, and operating licences. The findings showed that, contrary to current notions of organisational legitimacy being a strategic resource or an asset that is instrumental for organisational growth and survival, its multidimensionality constrained how organisations pursued revenue model innovation, owing to diverse stakeholder requirements and competing legitimacy-signalling behaviours. Furthermore, the findings revealed that pragmatic, moral, regulatory, and cognitive legitimacy dimensions proved to be inflexible under conditions said to trigger their adaptability, that is, divestment and intrapreneurship, could not create conditions necessary to enable revenue model innovation. The study contributes to the theoretical foundations of revenue model innovation by fusing insights from the institutional theory and the activity system perspective, showing that revenue model innovation spans boundaries and is dependent on multiple actors with sometimes diverse interests. For managerial practice, the study highlights the need for an organisation-wide systematic approach to revenue model innovation that considers actors, partners, organisation-level and macro-level interdependencies, and moderators, and proposes an activity system-based approach to revenue model innovation for environments with competing stakeholder requirements.
Women entrepreneurs and belonging in entrepreneurial resourcing practice
Phiri, Lelemba Chitembo (University of Pretoria, 2025-01)
Women’s entrepreneurship has been lauded as a potential key contributor towards social and economic development and well researched over the last three decades. Central to these studies is the acknowledgement of gendered and racialised patterns in the field and the consequent association of entrepreneurship with maleness and whiteness. This has resulted in unequal access to resources for women entrepreneurs and a sense of alienation and nonbelonging. Furthermore, black women entrepreneurs have been noted to experience the double-negative of race and gender thus experiencing disproportional alienation, being severely under resourced and resulting in their enterprises being smaller and less profitable than their white counterparts. Entrepreneurial resourcing is key to venture development and success, with belonging being found to influence resourcing practices. In this study, the entrepreneurship as practice (EaP) approach was employed to explore the belonging and resourcing practices of 26 black women entrepreneurs in South Africa utilising a narrative design, situated in the social constructionist paradigm. The study provides several contributions. Firstly, it contributes a new conceptual framework about the practices that black women entrepreneurs within certain contexts, employ to negotiate belonging and resourcing. Secondly, it extends the Occupational Perspective of Health theory (OPH) from Psychology, into entrepreneurship. Thirdly, by employing OPH, the study refines the existing theories of entrepreneurial belonging by revealing the interdependent nature of belonging with doing, being and becoming. The study then makes a methodological contribution by offering a systematic approach for the examination of practice interrelationships and complex entrepreneurial experiences. Additionally, it makes an empirical contribution with the unique dataset of life histories of black women entrepreneurs from across the African continent. Finally, it offers practical strategic guidelines for navigating, fasttracking and achieving belonging and resourcing for marginalised entrepreneurs.
Exploring the boundaries of political behaviour of senior leaders
Motloung, Musa (University of Pretoria, 2025-06)
This study investigates the under-explored yet crucial terrain of the boundaries of political behaviour: specifically, among senior leaders in complex organisations where influence and collaboration are essential yet fraught with complication. Mismanaged, such dynamics can generate poor decision-making, thereby jeopardising an organisation's short-term success and long-term sustainability. To date, such research has emanated mostly from the Global North and Asia. However, this inquiry redresses the imbalance by focusing on South Africa and its unique context of cultural, racial, and gender dynamics. Informed by upper echelons theory, it adopts an inductive, qualitative approach with a hermeneutic phenomenological design, to explore the relational dynamics (strategic interface) between highly diverse senior leaders in complex, regulated South African banking organisations: a sector characterised by both institutional sophistication and persistent socio-economic inequalities. Data was collected via in-depth, semi-structured interviews with top executives, in which lived experiences were explored and rich insights garnered. Theoretically, the study departs from prior research, which focused largely on middle management or generic organisational settings, and centres instead on upper echelons, where decisions bear particular strategic weight. The research generated several new conceptual insights which reframe political behaviour as a fluid, ethically contingent practice. Firstly, contextual duality: political behaviour is seen as neither inherently positive nor negative, but exists on a dynamic continuum shaped by intent, leadership values, and organisational context. Secondly, boundaries are context-dependent: acceptable political conduct is demonstrably fluid, shaped by internal structures (leadership culture, performance systems) and external socio-political forces (race, gender, national governance). Thirdly, the notion of holistic integration positions political behaviour as an evolving product of social, economic, and political interplay, rather than a fixed trait or isolated action. Fourthly, the study offers scholars and practitioners a set of practical guidelines, complemented by the leadership continuum model: a novel theoretical lens through which to analyse political conduct within complex, high-stakes leadership environments. Finally, the study concludes with recommendations for future research, including the development of measurement tools and further empirical testing across diverse sectors and geographies.
The influence of mindfulness and self-compassion on entrepreneurial learning from failure : insights from a mindfulness training programme
Johnstone, Rhys (University of Pretoria, 2024-12-02)
This study seeks to explain the influence of mindfulness and self-compassion on entrepreneurial learning from failure. Failure is a valuable source of learning for entrepreneurs, but it can generate powerful negative emotions and learning outcomes are inconsistent. Entrepreneurship scholars have largely viewed entrepreneurial learning from failure through the lens of experiential learning theory, but the literature is fragmented, and we do not adequately understand how learning from failure works. There is evidence from psychology that mindfulness and self-compassion may have beneficial effects for entrepreneurial learning from failure, and mindfulness training has been found to generate these mechanisms. However, entrepreneurship research on mindfulness and self-compassion is sparse, and it is not clear how these mechanisms might influence entrepreneurial learning from failure. The research question is therefore: In the contexts of entrepreneurial failure and re-entry, how do mechanisms of mindfulness and self-compassion influence outcomes for entrepreneurial learning from failure in individual entrepreneurs? To answer this question, a multiple case study was conducted, cast as a realist evaluation of participants in a mindfulness training programme for entrepreneurs who are trying again after previously failing. Qualitative data was collected longitudinally throughout the study. Thematic analysis was conducted to refine configurations of contexts, mechanisms and outcomes which explain how mindfulness and self-compassion influence entrepreneurial learning from failure. The study found that mindfulness mechanisms influence how entrepreneurs experience failure and re-entry, generating secondary mechanism which in turn go on to influence the reflecting process, resulting in attributions which support learning. The study also found that selfcompassion influences the conceptualising processes of learning, leading to new ideas about success and failure, a more harmoniously passionate approach to entrepreneurship, increased self-efficacy and feeling more connected. Theoretically, this research refines our understanding of entrepreneurial learning from failure as an experiential learning process and explains how mindfulness and self-compassion influence specific processes in entrepreneurial learning from failure. The study also contributes to realist evaluation methodology and advances practice by refining mindfulness training protocols for entrepreneurs. These contributions advance our understanding of learning from failure and our ability to assist entrepreneurs to make a success of their subsequent ventures.
The upper zone of the Bushveld complex at Tauteshoogte
Boshoff, J.C. (University of Pretoria, 1942-01)
Etiology and control of some fruit diseases of avocado (Persea Americana Mill.) at Westfalia Estate
Darvas, Jozsef Mihaly (University of Pretoria, 1982-11)
Cercospora spot disease of avocados caused by Pseudocercospora purpurea (Cke) Deighton is described for the first time in South Africa, where it was found to be the most important pre-harvest fruit disease at Westfalia Estate, in the North Eastern Transvaal (longitude 30°10' and latitude 23°45'). Losses caused by the disease were investigated in relation to rainfall, cultivar, time of harvest, root rot severity of trees and the position of the fruit on the tree. A detailed description of Cercospora spot symptoms is given. The analysis of spore trap results and weather data produced statistical models suitable for forecasting conidia production by the pathogen. These models may be used to determine high risk infection periods, thereby facilitating accurate timing of fungicidal sprays. Infections taking place early in the growing season were found to give the highest disease incidence at harvest. There is a latent period of about three months in duration in the disease cycle. Cercospora spot disease can be controlled by benomyl and also by some of the non-benzimidazole fungicides such as captafol, Cu-hydroxide and Cu-oxychloride. It was found that several years' continued use of benomyl results in a significant decrease in the efficacy of the fungicide against the disease. On the basis of symptoms and the pathogens involved, the following post-harvest diseases were recognised at Westfalia Estate: Stem-end rot caused by Thyronectria pseudotrichia (Schw.) Seeler, Colletotrichum gloeosporioides (Penz.) Sacc., Dothiorella aromatica (Sacc.) Petr. and Syd., Phomopsis perseae Zerova, Fusarium decemcellulare Brick and to a lesser extent Pestalotiopsis versicolor (Speg.) Steyart, Lasiodiplodia theobromae (Pat.) Griff. and Maubl., Rhizopus stolonifer (Ehr. ex Fr.) Lind., Fusarium sambucinum Fuckel, Fusarium solani (Mart.) Sacc. and Drechslera setariae (Sawada) Subram. and Jain. Anthracnose caused by Colletotrichum gloeosporioides (Penz.) Sacc. Dothiorella/Colletotrichum complex fruit rot caused by Dothiorella aromatica (Sacc.) Petr. and Syd. and Colletotrichum gloeosporioides (Penz.) Sacc. Losses caused by these post-harvest diseases were studied with respect to oil content of fruit, root rot severity of trees and the position of the fruit on the tree. A comprehensive description of the post-harvest disease symptoms is given. The pathogenicity of the fungi involved in post-harvest diseases was thoroughly studied. Infections taking place later in the_growing season are more critical and result in a higher post-harvest disease incidence at harvest than infections occurring early in the growing season. The natural latent infections by c. gloeosporioides and D. aromatica build up in the fruit during the growing season and decrease again during the dry harvest season. Pre-harvest sprays with benomyl, captafol, bitertanol, Cu-hydroxide and Cu-oxychloride were found to control postharvest diseases to some extent. In post-harvest handling of avocados, the length of the ripening time has a marked influence on the incidence of post-harvest diseases and any post-harvest treatment that extends shelf-life increases the disease incidence. This increase could not be fully counteracted by the addition of fungicides to waxes. Moisture on the fruit at harvest was found to aggravate post-harvest diseases whereas the sealing of the fruit pedicel with wax plus fungicides as well as the removal of the pedicel reduced losses due to stem-end rot. By accurate identification of the organisms involved in pre- and post-harvest diseases of avocados, studying their epidemiology and selecting effective fungicides, it has been possible to give growers in this area a better understanding of what measures should be taken for the control of these diseases.
Analysing the entrepreneurial orientation levels of South African universities
Ndamase, Bongani (University of Pretoria, 2021-09)
‘Universities create the future.’ – Alfred North Whitehead South Africa is an upper middle-income country that aspires to become an advanced economy by 2030. The National Development Plan envisions South Africa as a knowledge-based economy by 2030. A knowledge-based economy predominantly relies on knowledge as a factor of production as opposed to a resource-based economy that relies on capital, labour and land as factors of production. It is accepted in the literature that universities are the institutions that create economically valuable knowledge that helps a resource-based economy transition to a knowledge-based economy. The literature reveals that universities have evolved over five phases from traditional to entrepreneurial universities that drive socio economic development in society. This transformation has seen universities incorporate the third mission of entrepreneurialism into their traditional missions of teaching and learning and research. Despite this knowledge, the South African government has not orchestrated requisite resources to ensure that universities fulfil this significant role in economic transformation. Secondly, entrepreneurship scholars seem to have paid less attention to this theme as well. Thirdly, civil society, students and other stakeholders have also not prioritised this theme. It is against this backdrop that this study was executed. Universities are regarded as engines of economic growth and development in society because they fulfil three major societal responsibilities. Firstly, they produce (or ought to) produce competent human capital for the economy. Economic developments mean that the market requires people with high levels of knowledge and competence acquired mainly from universities. Secondlee, universities are expected to conduct research that produces knowledge for society and other stakeholders. Thirdly, universities are required to generate economically valuable knowledge that can be commercialised to generate revenues for universities and other participants. Through this third stream of entrepreneurial activities, universities can contribute to job creation, poverty eradication and reduction of inequalities in their localities, regions and countries. This stream may also enable South African universities to reduce the high levels of unemployment amongst their graduates. According to a South African Cabinet report, South Africa has approximately 1.5 million unemployed graduates. This is an opportunity for South African universities to implement the entrepreneurial dimension of their mandate. This is also an opportunity to realise the supposition of the recession-push hypothesis that postulates that economic downturns provide the economy with readily available skilled labour. It is accepted that university leaders at different levels should embrace the notion of an entrepreneurial university to help their institutions transform into entrepreneurial universities. This study measured the perceptions of South African university managers regarding the entrepreneurial orientation of South African universities. South Africa has 26 public universities that are accredited to award various academic and professional qualifications. Universities are, therefore, invaluable public policy instruments that can contribute to the realisation of the country’s development aspirations. However, universities should also embark on their own corporate entrepreneurship initiatives that renew and align their strategies with new socio-economic imperatives. This means that universities should transform themselves before they attempt to transform society. This study is analytical in nature and used the modified and adapted ENTRE-U scale. This is the most comprehensive measurement instrument developed to date to evaluate the entrepreneurial orientation of universities. Assessment tools such as the HEInnovate tool developed by the European Union and the Organisation for Economic Co operation and Development and the Accreditation Council for Entrepreneurial and Engaged Universities Toolkit developed by the University Industry Innovation Network have been reviewed as points of theoretical reference. They, however, lack the intellectual rigour of the ENTRE-U scale. This study consisted of a cross-sectional survey that electronically distributed a self administered questionnaire with 30 response items. Finally, this study significantly contributes to knowledge in the realms of corporate entrepreneurship and entrepreneurial universities. It contributes to the enrichment of the ENTRE-U scale. The study contributes to a better understanding of the factors that constitute entrepreneurial universities. The five factors generated through the factor analysis are a significant contribution to the entrepreneurial orientation of universities scholarship. The study also contributes to the theoretical understanding of entrepreneurial universities as catalytic institutions for economic development in society. This should empower South African public policymakers to align resource allocation towards universities or the development of the knowledge/quaternary sector of the economy in the journey towards 2030. The study supplies tertiary students and graduates with appropriate tools to engage university leaders on the normative roles they ought to play. Different university leaders are empowered to fulfil their roles in the journey to become entrepreneurial. However, executives shoulder more responsibility, as they ought to direct resources and drive strategic renewal programmes towards the realisation of an entrepreneurial university. This study, therefore, practically empowers societal stakeholders to engage universities on how they propose to institutionalise entrepreneurialism as a university-wide strategic phenomenon. The study can also be generalised to other settings, such as technical and vocational education and training colleges, and other countries, such as the Southern African Development Community and the Brazil, Russia, India, China and South Africa block. It can serve as a strategic geo-economic instrument in the African Union and the United Nations.
Die herkoms en die sosiale, ekonomiese en opvoedkundige aspekte van die lewe van die Kleurlinge van Eersterust
Jacobs, Paul Petrus (University of Pretoria, 1968-06)
Mineralogy of the lower part of the upper zone, eastern Bushveld Complex : implications for ore-forming processes
Harney, Dirk M.W. (University of Pretoria, 1991)
English: The lower part of the upper zone in the eastern Bushveld Complex was subjected to a detailed mineralogical investigation, aimed at gaining a better understanding of processes that led to the formation of the main magnetite layer (MML), sulfide-enriched horizons and possible concentrations of platinum-group elements (PGE). The most prominent rock types in the investigated stratigraphic sequence are anorthosites, containing variable amounts of magnetite, which are interlayered with gabbronorites, leuco-gabbronorites and magnetite layers. Elevated sulfide concentrations are commonly associated with magnetite layers. The highest values were found in an anorthosite directly below the MML, and the sulfide assemblage typically contains pyrrhotite, chalcopyrite, cubanite and pentlandite in decreasing order of abundance. PGE are not enriched in specific stratigraphic horizons, as in those known from the critical zone. However, a local concentration of Pt and Pd has been encountered in the sulfide-bearing anorthositic footwall of lower magnetite layer 2. Several Pt-Pd-Bi-Te minerals were found, namely michenerite, moncheite, merenskyite and froodite, and textural as well as compositional evidence indicates that these platinum-group minerals are of hydrothermal origin. Post-magmatic hydrothermal processes also affected the mineralogy and composition of sulfides above the MML. Pentlandite, in particular, reflects such hydrothermal activity and displays varying, but considerably elevated, Co concentrations. Changes in the Sr content and the Sr/Al 2o3 ratio of plagioclase, the whole-rock PGE concentration pattern and possibly also the composition of pyroxene at the level of the MML show that the MML formed in response to a magma mixing event between the resident and a less differentiated magma. Magma mixing resulted either from a breakdown of density stratified liquid layers or an influx of a small volume of new magma (up to 30 % of the hybrid). In addition to the formation of the MML, magma mixing is also believed to have caused the segregation of sulfides associated with that layer. It is concluded that the evolution of the upper zone does not reflect simple differentiation, but that it was interrupted by magma mixing events which occurred at the level of the MML and possibly also at other levels during crystallization of the upper zone. Afrikaans: Die onderste gedeelte van die bosone in die oostelike Bosveldkom-pleks is mineralogies noukeurig ondersoek met die doel om 'n beter begrip te vorm van die prosesse wat aanleiding gegee het tot die ontstaan van die hoofmagnetietlaag (HML), sulfied-verrykte lae en konsentrasies van die platinum-groep elemente (PGE). Die mees algemene gesteente tipes in die stratigrafiese suksessiewat ondersoek is, is anortosiete met varierende hoeveelhede magnetiet, wat tussengelaagd is met gabbronoriet, leukogabbronoriet en magnetietlae. Verhoogde sulfiedkonsentrasies is meestal geassosieer met magnetietlae. Die hoogste konsentrasies kom in 'n anortosietlaag direk onderkant die HML voor. Die mees algemene sulfiedassosiasie bevat, in volgorde van afnemende hoeveelheid, pirrhotiet, chalkopiriet, kubaniet en pentlandiet. Die PGE is nie in enige van die sulfiedgemineraliseerde lae verryk nie. Lokale verryking van Pt en Pd is egter teegekom in die sulfied-draende anortosiet net onder die laer magnetietlaag 2. Verskeie Pt-Pd-Bi-Te minerale is teegekom, te wete micheneriet, moncheiet, merenskyiet en froodiet. Tekstuur en samestelling dui daarop dat hierdie platinumminerale van hidrotermale oorsprong is. Na-magmatiese hidrotermale prosesse het ook die sulfied-mineralogie en samestelling bokant die HML geaffekteer. Veral pentlandiet reflekteer sodanige hidrotermale aktiwiteit en toon varierende, maar aansienlik verhoogde, Co konsentrasies. Veranderings in die Sr-inhoud en die Sr/Al 2o3 verhouding van plagioklaas, die heelgesteente PGE konsentrasiepatroon en moontlik ook die samestelling van pirokseen by die posisie van die HML dui daarop dat hierdie laag moontlik ontstaan het as gevolg van magmavermenging tussen die kristalliserende magma en 'n minder gedifferensieerde een. Magmavermenging kan of die gevolg wees van die ineenstorting van digtheidsgestratifiseerde vloeistoflae, of die gevolg van die invloei van 'n klein volume nuwe magma (tot 30 % van die hibriede produk). Bykomstig tot die ontstaan van die HML, word magmavermenging ook beskou as die oorsaak te wees vir die segregasie van sulfiede geassosieer met die laag. Daar word tot die slotsom gekom dat die ontstaan van die bosone nie die gevolg van 'n eenvoudige differensiasie is nie, maar dat dit onderbreek was deur episodes van magmavermenging soos byvoorbeeld by die HML en moontlik ook op ander tye tydens kristallisasie van die bosone.
Evaluering van bestuurstyle van opleiers in nie-formele onderwys : 'n fundamenteel-andragogiese begronding
Van Aardt, Nicolaas Johannes (University of Pretoria, 1992-10)
Afrikaans: Vanuit 'n fenomenologiese perspektief het die volwassene 'ninherente strewe om toenemend iemand te wil word, dus om te leer. Vanwee sy normatiewe ingesteldheid wil hy sy volle potensiaal binne werkverband ontplooi ten einde die maatskappy te help om gestelde doelwitte te bereik. Die individu-in-indiensopleiding in die bedryfsektor word meer as ooit tevore met die vrae van waardes, lewensdoel en optimale betekenis van die lewe gekonfron-teer. Hulle verkeer in nood en vra leiding. Hoe meer die w~reld se kompleksiteit toeneem, hoe grater die mens se nood. Die werk- nemer raak verward in die nuwe geYndustraliseerde samelewing waarin ans, ans tans in bevind omdat nie genoegsame aandag gegee word aan die essensies van menswees nie. Die gevolg van hierdie verwardheid waarin die werknemer horn tans in bevind, lei daartoe dat produktiwiteit in die slag bly. Die bestuurder gee nie genoegsame aandag aan die menslikheid van sy ondergeskiktes ten einde produktiwi tei t van sy werknemers te bevorder nie. Die andragogiese-essensies van menswees naamlik in-betekenis- wees, medesyn, temporaliteit en self-iemand-wees word nie verwerklik in die sakesektor nie. Die andragogiese-essensies is nie net mensweesessensies nie, maar produktiwiteitessensies. Indien die andragogiese-essensies nie verwerklik word in die sakesektor nie, sal produktiwiteit nooit verbeter word in geindustraliseerde werkomgewing nie. Die fundamentele andrago-giese-essensies moet toegepas word binne 'n maatskappy ten einde verhoogde produktiwiteit mee te bring. Individue-in-indiensopleiding beskik oor die potensiaal om produktief te wees en wil graag hierdie potensiaal tot uiting bring. Die bestuurder as opleier moet die klimaat skep waarbinne hierdie werknemer in die maatskappy kan funksioneer. Indien die bestuurder die andragogiese-essensies ontken, ontken hy menswees. Die werknemer as volwassene strewe inherent na uitnemendheid en het die wil om te presteer. Indien hulle deur deelname gelei word, sal dit lei tot verbondenheid wat op sy beurt lei tot kreatiwiteit. Die werknemer wil 'n betekenisvolle lewe lei en hy wil aan alle aspekte van sy lewe betekenis gee en dus ook in die maatskappy waar hy werk betekenisvol wil funksioneer. Die kernbegrip hoe volwasse leer by die werknemer plaasvind, is dat die volwassene selfrigtend is. Die vo--lwasse leerder wil deur andere gesien word as onafhanklik en selfbepalend. Wanneer die ondergeskikte dus 'n. situasie ervaar waar hy/sy nie toegelaat word om onafhanklik en selfbepalend op te tree nie, kan dit lei tot 'n onderbewuste gevoel van weerstand en woede. Dit kan lei tot onproduktiwiteit deurdat hy nie die geleentheid gegun word om sy potensiaal tot uiting te bring nie. Uit die navorsing het geblyk dat die wyse hoe volwasse leer plaasvind nie net mensge-orienteerde leerteoriee bevat nie, maar byvoorbeeld assosiatiewe, funksionele en kognitiewe leerteoriee. Die werknemer strewe na die transendente. Dit beteken dat hy gedurig in wording is en dat hy op pad is om iemand te word. Die andragogiese-essensies is daarop gemik om vir die werknemer wat ongeborgenheid beleef, vertroue in die eie saak te gee. Die Christelike lewensopvatting in besonder bepaal dat God Drie-Enig, die Skepper, Onderhouer en Regeerder van die ganse werklikheid is en dat die werknemer groepe is om God in al sy aktiwiteite te eer en te verheerlik. Hierdie lewensopvatting soos gehuldig deur 80% van die RSA se bevolking moet dus as basis dien vir 'n gesonde bedryfsektor. English: From a phenomenoligical perspective the adult has an inherent desire to be entertained increasingly; that is, to learn. Because of his normative propensity, he strives to develop his full potential in the working context in order to assist the company in reaching his objectives. The individual in in-service training in the operations sector is more than ever before, being confronted with questions regarding values, the purpose of life and the optimum value of life. They find themselves in distress and seek guidance. The more the world's complexity increases, the greater man's distress. The employee becomes perplexed in the new industrialised society in which we are presently became inadequate attention is being given to the essentials of humanity. The result of this confusion in which the employee finds himself presently, leads to a decline in productivity. The manager does not give sufficient attention to the humanity of his subordinates which could promote the productivity of his in-service training personnel. The andragogical essentials of humanity namely being a part of a meaningful world, fellowship, temporality and self-esteem are not being satisfied in the business sector. The andragogical essentials are not human~ essential, but productivity essentials. If the andragogical essentials do not materialise in the 1:fosiness sector, productivity will never improve in the industrialised working environment. The fundamental andragogical essentials have to be applied within, the company in order to bring about increased productivity. Individuals engaged in in-service training have the potential to be productive and have the need to express this potential. The manager must create the climate in which the employee can function within the company. The manager who denies the andragogical essentials denies humanity. The employee as adult inherently strives toward excellence and has the will to perform. If they are guided through participation, it will lead to commitment which in turn leads to creativity. The employee wishes to lead a meaningful life and wants to add significance to all aspects of his life as well as in the company where he works. The basic concept of how the adult doctrine transpires, is that the adult is self-directed. The adult learner wants others to regard him as independent and self-determined. When the employee therefore, experiences a situation in which he is not allowed to act independently and self-determining, it may lead to unproductivity because he is denied the opportunity to demonstrate his potential. Research revealed that the adult doctrine not only contains human orientated learning theories, but for instance, contains associative, functional and cognitive learning theories. The employee strives towards the transcendental. This means that the employee is constantly in the making and on the way of becoming someone. The andragogical essentials are aimed at giving the employee experiencing insecurity, trust in his own situation. The Christian outlook in particular determines that God triune is Creater, Provider and Ruler of the entire universe and that the employee is destined to honour and glorify God in all his activities. This outlook, recognised by 80 % of the population of the RSA, must therefore serve as basis for a sound operations sector.
Gestaltterapie met die allergiese kind in die middelkinderjare
Yssel, Johanna Maria (University of Pretoria, 1999-08)
Afrikaans: Hierdie studie is gerig op die daarstelling van 'n gestaltspelterapeutiese program wat gebruik kan word om die allergiese kind in die middelkinderjare te begelei om beheer oor sy siekte te verkry en om die invloed daarvan op sy ontwikkelingstaakbemeestering te minimaliseer. In aansluiting hierby is 'n ouerleidingprogram ontwikkel waar gestaltbeginsels benut is om die ouers van die allergiese kinders ter versterking van die doelstellings van die spelterapeutiese program te bemagtig. Vanuit die literatuur en vorige navorsingsbevindinge is dit duidelik dat die voorkoms van 'n allergiese siekte 'n negatiewe invloed op die kind in die middelkinderjare se bemeestering van sy ontwikkelingstake op emosionele, sosiale en akademiese gebied kan uitoefen. Dit kan daartoe lei dat die kind se selfbeeldontwikkeling benadeel word en hy kan angs, frustrasie en aggressie ervaar wat sy gesonde funksionering strem. Op sosiale gebied kan allergiese siektes daartoe lei dat die kind ge"fsoleer word en dat hy nie soos sy maats aan alle aktiwiteite kan deelneem nie - dit kan tot portuurgroepverwerping lei. Op akademiese gebied kan die allergiese kind te siek voel om sy volle aandag aan sy skoolwerk te gee, wat moontlik onderprestasie en verminderde motivering tot gevolg kan he. Die voorkoms van 'n allergiese siekte het verder 'n definitiewe invloed op die gesinsfunksionering en kan negatiewe gevolge vir sowel die ouer-kind verhouding en opvoedingstyl as die sibbeverhoudinge inhou. Die beginsels van die gestaltbenadering fokus op die kind se verhoogde bewustheid van homself in sy situasie, sy verbeterde emosionele hantering van eise wat aan horn gestel word, die verhoging van sy beheer oor sy lewe en die versterking van sy eie verantwoordelikheidneming vir sy gesondheid. Deur die benutting van hierdie beginsels in beide programme kan die kind deur spelterapie en 'n ondersteunende ouerleidingprogram gehelp word om toepaslike beheer oor sy siekte uit te oefen en die moontlike negatiewe invloed van allergiese siektes op sy ontwikkelingstaak bemeestering en totale funksionering te minimaliseer. Ten einde die kennisleemte wat in die hantering van die spesifieke behoeftes van allergiese kinders bestaan te oorbrug, is die gestaltspelterapeutiese- en ouerleidingprogramme ontwikkel. Ses respondente in hul middelkinderjare en hul ouers is by die implementering van beide die spelterapeutiese- en ouerleidingprogramme betrek. Die navorsingsresultate het daarop gedui dat die gestaltspelterapeutiese program suksesvol was in die fasilitering van die kind se verhoogde bewustheid van homself in en verhoogde beheer oor sy situasie, verbeterde emosionele hantering en verhoogde verantwoordelikheidneming vir sy gesondheid. Die gegewens het verder daarop gedui dat die ouerleidingprogram suksesvol was om die ouers van die kinders tot ondersteuning van die spelterapeutiese doelstellings te bemagtig en hul opvoedingstaak te vergemaklik. Die programme is dus suksesvol vir sowel die gestaltterapeutiese begeleiding van allergiese kinders in die middelkinderjare tot optimale funksionering en beheer van allergiese siektes, as die bemagtiging van ouers ter ondersteuning van die spelterapeutiese program. Die gevolgtrekkings en aanbevelings van die studie fokus op die bereiking van die doelstelling en doelwitte van die studie, gevolgtrekkings oor die navorsingsbevindinge, aspekte wat in ag geneem moet word in die gebruik van die programme en verdere navorsingsmoontlikhede wat uit die studie voortspruit.
Vectorial competence of Glossina brevipalpis in the transmission of Trypanosoma congolense in the Matutuíne District, Maputo Province, Mozambique
Cossa, Nióbio Vasco (University of Pretoria, 2024-11)
African Animal Trypanosomoses (AAT) are a group of parasitic diseases that are considered a major constraint to animal health and production in Africa, where they are associated with vast economic losses. AAT is caused by protozoa parasites of the genus Trypanosoma. In Mozambique, T. congolense is the predominant trypanosome species in regions affected by AAT. The epidemiology of AAT is largely determined by the distribution and vectorial competence of its cyclic vector, the tsetse fly. In southern Mozambique, there is a high prevalence of AAT in the Matutíne District, where the tsetse fly species Glossina brevipalpis is abundant. Based on existing studies, there is currently a lack of clarity on the vectorial competence of Glossina brevipalpis in the transmission of T. congolense. Therefore, this study aimed to assess the competence of G. brevipalpis as a vector of T. congolense using wild flies captured in Matutuíne District, Mozambique. In an initial experiment, 234 G. brevipalpis flies were captured in the Maputo National Park, and their survival under experimental conditions was evaluated. These flies were transferred to entomological cages, fed every 48 hours on one bovine and kept in a room for 30 days at the Tintigala Research Station, where temperature and relative humidity (Rh) were regularly monitored. The vectorial competence and possible mechanical transmission of T. congolense to susceptible cattle were then evaluated. For this experiment, 915 G. brevipalpis flies (41 females and 874 males) were fed six times in two cattle that had previously been infected with T. congolense (isolated from Matutuíne - TCM2018), followed by two meals in a clean animal to mechanically remove the remnant trypanosomes from previous blood meals. Lastly, they were fed for 30 days on four cattle that were susceptible to infection. These five susceptible animals were monitored for the development of parasitaemia for 60 days based on body temperature, PCV, buffy coat and PCR. In the meantime, flies were dissected weekly to observe the development of trypanosomes in the midgut and proboscis. Regarding the evaluation of mechanical transmission by G. brevipalpis, 97 teneral flies from a colony were fed once on two infected cattle (three days after emergence) and once on a susceptible bovine (48 hours after the first meal). Under experimental conditions, a survival rate of 77% was recorded within a period of 30 days among captured G. brevipalpis flies. Weekly dissection of flies that fed on infected animals revealed that 89% were positive for T. congolense, based on microscopy and 100% based on PCR (midgut and proboscis). The four susceptible cattle tested positive for T. congolense infection. However, no trypanosome infection was observed in the cattle used for cleaning the proboscis and evaluation of mechanical transmission. The current results indicate that G. brevipalpis is a competent vector for the transmission of T. congolense. Additionally, these results demonstrate the inability of G. brevipalpis to mechanically transmit T. congolense after 48 hours of an infected blood meal.
Occurrence and characterization of Shiga toxin-producing Escherichia coli from goats on communal rangeland in Gauteng South Africa
Malahlela, Mogaugedi Nancy (University of Pretoria, 2022-05)
Shiga-toxin-producing Escherichia coli is a foodborne pathogen commonly associated with human disease characterized by mild or bloody diarrhoea hemorrhagic colitis and hemolytic uremic syndrome. This study investigated the occurrence of STEC in fecal samples of 289 goats in South Africa using microbiological culture and PCR. Furthermore, 628 goat STEC isolates were characterized by serotype (O:H) and major virulence factors by PCR. STEC was found in 80.2% (232/289) of goat fecal samples. Serotyping of 628 STEC isolates revealed 63 distinct serotypes including four of the major top seven STEC serogroups which were detected in 12.1% (35/289) of goats: O157:H7, 2.7% (8/289); O157:H8, 0.3%, (1/289); O157:H29, 0.3% (1/289); O103:H8, 7.6% (22/289); O103:H56, 0.3% (1/289); O26:H2, 0.3% (1/289); O111:H8, 0.3% (1/289) and 59 non-O157 STEC serotypes. Twenty-four of the sixtythree serotypes were previously associated with human disease. Virulence genes were distributed as follows: stx1, 60.6% (381/628); stx2, 72.7% (457/628); eaeA, 22.1% (139/628) and hlyA, 78.0% (490/628). Both stx1 and stx2 were found in 33.4% (210/628) of isolates. In conclusion, goats in South Africa are a reservoir and potential source of diverse STEC serotypes that are potentially virulent for humans. Further molecular characterization will be needed to fully assess the virulence potential of goat STEC isolates and their capacity to cause disease in humans.
Model predictive static programming control applied to mineral processing plants
Noome, Zander Meindert (University of Pretoria, 2023-05)
In a mineral processing plant, the separation of valuable material from ore has multiple stages. Usually, the ore is crushed or ground into smaller parts through multiple crushers or grinding mills. This is called the communition process. This process is typically the first stage for extracting valuable material and is important for further down-stream processes. The output of the communintion stage is usually regulated to achieve a stable throughput and a specific ore particle size. After the ore is crushed and ground to a specified size, the valuable material in the ore needs to be separated from the undesired materials. The properties of the desired material influence the method used for separation. These methods include froth flotation, gravitational separation, magnetic separation and electrostatic separation. The separation process can include multiple process streams to get a high grade of the desired minerals out of the ore. In froth flotation, the main objective is to extract the desired material from the ore to obtain a large mineral recovery. Because the flotation process relies on the flotation of particles, particle size is extremely important. The use of control systems in mineral processing plants has been adopted to improve throughput, optimize power usage, ensure safe process operation and to running at a stable operating condition. The control of these plants makes use of different advanced process control strategies which include but are not limited to cascaded control, where multiple layers of control systems are applied, and model predictive control. These different control strategies can range from regulatory control to supervisory control. Because of the large number of inputs to these plants, efficient controllers are necessary to obtain desired results. The use of Nonlinear Model Predictive Control (NMPC) is an attractive option for most mineral processing plants because of the constraint management capabilities of the controller. Unfortunately, the NMPC method has a large computational load which requires sufficient resources to make it a viable option. Another model predictive control method known as Model Predictive Static Programming (MPSP) has shown promise to improve the computational time of a standard NMPC controller. The MPSP control philosophy generates a static optimization problem which is less computationally difficult to solve compared to the dynamic optimization problem that is generated through NMPC. In this dissertation, the control of a single-stage grinding mill circuit and a four-cell flotation circuit with an MPSP controller to reduce the computational load is proposed. The computational efficiency and the output performance of MPSP controllers are compared to NMPC controllers as a motivation for the use thereof. The comparison is done by simulating two mineral processing stages, namely the communition phase and the separation phase. The simulations considered different configurations for both the MPSP and NMPC controllers. The comparison of the controllers in the simulations shows that the MPSP controller obtained similar or improved plant results while also having a reduced computational time compared to the NMPC controller. The MPSP controller also displays scalability improvements compared to the NMPC controllers which can be beneficial for supervisory control of large-scale processing plants.
Advancing environmental, social, and governance outcomes through process optimisation and control
Burchell, John James (University of Pretoria, 2024-02)
Organisations are compelled to integrate Environmental, Social, and Governance (ESG) considerations into their core strategy, with the tightening of regulatory requirements and the mounting pressure from stakeholders for sustainable practices driving a trend toward socially responsible investing. Advanced process optimisation and control provides innovative solutions to support ESG objectives. This thesis explores two case studies aimed at enhancing the consistency of material flow and composition into metallurgical operations to improve overall processing efficiency. The first case study introduces a (μ+λ)-Evolutionary Strategy (ES) to solve the input blending problem for a base metal refinery (BMR), where variability in the feed of contaminants to the operation impact negatively on plant throughput, product quality, and harmful emissions. The algorithm outperforms baseline blending strategies demonstrating a significant improvement in the blended consistency of contaminant feed. In the second case study, a nonlinear Model Predictive Controller (NMPC) is developed and implemented on a surge tank for level averaging control in an industrial tailings reprocessing circuit. A rigorous dynamic model is derived to describe the rate of change of both the volume and density in these surge tanks. By simulation with industrial data it is demonstrated that the significant input disturbances typical to tailings reprocessing circuits drive a gain inversion in the density model of the surge tank. This gain inversion and the multivariable objectives of both density and flow disturbance attenuation motivates for a NMPC solution. Results presented show significant improvements in both the water recovery and the stability of mass flow of tailings in the circuit. These advanced optimisation and control solutions support ESG objectives across multiple dimensions. Improved input stability with the (μ +λ)-ES enhances the efficiency of downstream processes where contaminants are extracted, resulting in lower emissions, especially when hazardous reagents are involved in the extraction process. By improving the efficiency of contaminant extraction the need for rework of product that fail to meet specifications is minimised, which leads to a reduction in waste generation, conservation of resources, and lower energy consumption. Improved water recovery with the NMPC lowers the overall environmental footprint of the tailings reprocessing circuit by reducing water consumption and energy usage, while stability improvements positively impact recoveries, thereby reducing waste and supporting responsible resource management.
Extremum seeking control of grinding mill circuits based on grind curves
Ziolkowski, Lukasz (University of Pretoria, 2023-05)
Mineral processing plants include several operations to liberate the valuable minerals within raw ore material to produce a concentrate, which is processed into a usable product by a metallurgical refinery. A mineral processing plant consists of a comminution and a separation stage. During the comminution stage, the raw ore material is processed through a grinding mill circuit to liberate the valuable minerals by grinding the ore to fine particles. The product from the comminution stage is then processed at a separation stage, which separates the valuable minerals (concentrate) from the waste material (tailings). The comminution stage plays a crucial role in the mineral processing industry. It significantly impacts the net revenue generated by a mineral processing plant due to the high operating costs associated with liberating the valuable minerals from the ore material. A grinding stage operates efficiently if it is processing the ore material at its maximum capacity, minimizing power consumption while reducing the amount of valuables lost to the tailings stream. Therefore, the ore material should be sufficiently ground for effective separation in subsequent downstream processes. Ideally, the separation stage requires a consistent stream of fine particles for effective separation. It is challenging for plant operators to manually achieve the above-mentioned operational objectives, which motivates the need to adopt a suitable control framework and ensure an efficiently run process. The performance of a grinding mill circuit is measured by its throughput and grind quality. These performance indicators are inversely related to operational objectives. The challenge in controlling the grinding mill circuit arises in determining the optimal operating conditions to maximize the net revenue generated by the plant. The optimal operating conditions vary with different ore types and unknown disturbances, such as varying ore hardness, which can result in the comminution stage operating at sub-optimal operating conditions. Furthermore, grinding mills rely on the cascading motion of the ore material and grinding media to accelerate ore breakage. The cascading motion is a function of the fraction of the mill volume filled with ore and the mill rotating speed, which influences the breakage forces that occur between rocks. Therefore, selecting optimal operating conditions is a difficult task requiring frequent adjustments as the operating conditions vary. Grind curves are a valuable tool that establishes the relationship between the mill load filling and rotational speed to the grinding mill throughput, grind quality and power consumption for a given ore type. Generally, the curves show parabolic features and the peaks vary with changes in the ore characteristics. A model-free adaptive control strategy is proposed for optimizing the performance of a semi-autogenous grinding (SAG) mill based on grind curves to improve throughput or grind quality. The controller explores an unknown map in search of the extremum of the performance indicators along the grind curves. A perturbation-based (PESC), a time-varying parameter estimation-based (TESC), and a Nelder-Mead simplex-based (SESC) extremum seeking control method are considered to optimize the grinding mill performance. Several optimization strategies are investigated for an open grinding mill configuration and a closed grinding mill circuit, where the closed circuit is equipped with a screen or with a hydrocyclone classifier to recirculate oversized ore material for additional grinding. The challenge lies in implementing an efficient optimization model-free control framework that will effectively maximize the performance measures of the complex, non-linear behaviour of the grinding mill circuit.

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