Browsing by Subject "Mining"
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- ItemOpen AccessChange in Corporate Debt Levels in South Africa from 1994 to 2016(2020) van der Westhuizen, Kyla; Holman, GlenThis paper investigated the change in corporate debt levels in South Africa from 1994 to 2016. Included is an analysis of factors that companies take into consideration when determining the company's capital structure. This study used data from companies, largely from the mining sector, within sectors listed on the Johannesburg Stock Exchange (JSE), including chemicals, general industries, oil and gas. Four different leverage measures were used to determine the change in capital structure for the period under review, as well as six of the most commonly used determinants of capital structure. A high-level interpretation of the results reflected the following; a slight but relatively consistent increase in the use of debt relative to equity over the period for both the total sample and the mining sector. An increase in the use of long- relative to short term debt was also found, as well as a convergence between the use of current and non-current liabilities. Results from the analysis of the capital structure determinants varied, with some showing statistical significance. Asset tangibility was positively correlated to debt, while profitability and growth had a negative relationship. The relationship between company size, tax and cost of debt and leverage was varied.
- ItemOpen AccessThe effect of energy input on flotation kinetics(2018) Safari, Mehdi; Deglon, David ASYNOPSIS Energy/power input in a flotation cell is an important parameter which, if optimised, can increase the flotation rate. The optimum energy/power input within a flotation cell is still a matter of conjecture and there is a need for a better understanding of the effect of energy input on flotation kinetics. This study investigates the effect of energy/power input on flotation kinetics in an oscillating grid flotation cell (OGC). The OGC decouples the processes of solid suspension and bubble generation as well as producing relatively isotropic and homogeneous turbulence with zero mean flow. Due to this, oscillating grids provide a potentially ideal environment for investigating the effects of energy input on flotation kinetics, which cannot be achieved in a mechanical flotation cell. The first objective of this thesis was to determine the effect of energy/power input on the flotation kinetics of sulphide minerals (galena, pyrite & pentlandite) and oxide minerals (apatite & hematite) in a laboratory scale oscillating grid flotation cell. The second objective was to compare the results from the laboratory OGC to comparative studies in the flotation literature and to fundamental models for particle-bubble contacting. The third objective was to determine whether the experimental results from the laboratory OGC are consistent with those from a pilot-scale OGC operating on a platinum ore. Galena, pyrite, pentlandite (-150 μm), apatite (-650 μm) and hematite (-75 μm) were floated in the laboratory OGC at energy inputs from 0.1 to 5.0 W/kg, using 0.13, 0.24, 0.58 and 0.82 mm bubble sizes (d₁₀), and at three collector dosages. Platinum ore (-75 μm) was floated in the pilot-scale OGC at energy inputs from 0 to 2.5 W/kg, using 0.71 and 1.47 mm bubble sizes (d₁₀). The effect of energy input on flotation kinetics was interpreted through trends in experimental flotation rate constants, simulated flotation rate constants and attachment-detachment flotation rate constants. Here, simulated flotation rate constants were calculated using a literature fundamental model for flotation in turbulent systems. This model is based on suitable expressions for the collision frequency, collision efficiency, attachment efficiency and stability efficiency, Attachment-detachment flotation rate constants were calculated using a kinetic model which allows for the two separate processes of bubble-particle collision/attachment and detachment. This model is based on kinetic expressions using empirical correlations for the attachment and detachment rate constants. Experimental flotation results show that the effect of energy input on the flotation rate is strongly dependent on the particle size and particle density and less dependent on bubble size and contact angle. Flotation rates generally increase with increasing particle size, decreasing bubble size and increasing contact angle, as is commonly found in the literature. Increasing energy input generally leads to an increase in the flotation rate for fine particles, an optimum flotation rate for intermediate particles and a decrease in the flotation rate for coarse particles. The optimum in the flotation rate for minerals with higher density is at a lower energy input than that for lower density minerals. The changes (increases/decreases) in the flotation rate with increasing energy input are very large for most of the conditions, indicating that this is an important parameter in flotation. Pilot scale results generally support the trends observed in the laboratory OGC. These findings are attributed to the effect of energy/power input on bubble-particle collection which is a balance between two competing effects, those of bubble-particle collision/attachment and those of bubble-particle detachment. Increasing energy input generally leads to significant increases in the flotation rate of fine particles, due to increased bubble-particle collision/attachment. Increasing energy input generally leads to an optimum flotation rate for intermediate particles, due to a combination of increased bubble-particle collision/attachment and detachment. For coarse particles, increasing energy input leads to significant increases in bubble-particle detachment. The relationship between the flotation rate and energy input is often described as k ɛᴺ, in the absence of significant bubble-particle detachment. The typical values of N are in the range of 0.44-0.75 for theoretical studies and 0.7-1 for experimental studies. The values of N found in the current study are in the range of 0.7-1, which suggests that bubbleparticle collision/attachment has a stronger dependence on energy input than theory suggests. Simulated flotation results for fine particles compare well to the experimental data in terms of both trends and magnitude. This suggest that the turbulent collision model used is appropriate for fine particles. For intermediate particles there are differences between the simulated flotation rate constants and the experimental data, primarily in terms of trends. For coarse particles there are very large differences between simulated flotation rate constants and the experimental data. This is attributed to under prediction of the collision frequency/efficiency and incorrect prediction of the stability efficiency. Here, the stability efficiency is considered to be under predicted at low energy inputs and over predicted at high energy inputs. This suggests that the stability efficiency has a much stronger dependence on energy input than theory suggests. Attachment-detachment results show that the attachment rate constant has a stronger dependence on energy input than theory suggest, supporting finding from the experimental results and simulated results for coarser particles. In addition, the detachment rate constant has a much stronger dependence on energy input than theory suggests, supporting findings from both the experimental and simulated results. Based on the objectives of this study and literature reviewed, the following hypotheses were made at the outset 1) Increasing energy/power input will increase the rate of flotation of fine particles but will result in an optimum for intermediate and coarse particles. The position of this optimum will depend on the particle density, bubble size and contact angle. 2) Fundamental models based on the RMS turbulent velocity will be appropriate for describing flotation kinetics as turbulence in the oscillating grid cell is relatively homogeneous and isotropic and 3) Trends in flotation results for a laboratory and pilot-scale oscillating grid flotation cell will be comparable as the distribution of turbulence in OGCs at equivalent specific power inputs is scale independent. Hypothesis 1 was found to be valid for both fine and intermediate particles, but for coarse particles increasing energy input resulted in sharp decreases in the flotation rate. In addition, the increase in the flotation rate with increasing energy input was found to be more dependent on the particle size and particle density than the bubble size and contact angle. Hypothesis 2 was found to be valid for fine particles but not for intermediate or coarse particles. Here, it was found that the processes of bubble-particle collision/attachment and detachment have a stronger dependence on energy input than theory suggests. Hypothesis 3 was supported by general trends in results for the laboratory and pilot-scale oscillating grid flotation cells, but was not convincingly demonstrated.
- ItemOpen AccessImpacts of mining on land use - A case (study) of Luanshya district, Zambia(2018) Sakuwaha, Kabangu Grace; Broadhurst, Jennifer; Odendaal, NancyCopper 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.
- ItemOpen AccessPrecarious transition: a mortality study of South African ex-miners(BioMed Central, 2018-07-11) Bloch, Kim; Johnson, Leigh F; Nkosi, Mlindeli; Ehrlich, RodneyBackground Despite their burden of a triple epidemic of silicosis, tuberculosis and HIV infection, little is known about the mortality experience of miners from the South African mining industry once they leave employment. Such information is important because of the size and dispersion of this population across a number of countries and the progressive nature of these diseases. Methods This study included 306,297 South African miners who left the industry during 2001–2013. The study aimed to calculate crude and standardised mortality rates, identify secular trends in mortality and model demographic and occupational risk factors for mortality. Results Crude mortality rates peaked in the first year after exit (32.8/1000 person-years), decreasing with each year from exit. Overall mortality was 20% higher than in the general population. Adjusted annual mortality halved over the 12 year period. Mortality predictors were being a black miner [adjusted hazard ratio (aHR) 3.30; 95% confidence interval (CI) 3.15–3.46]; underground work (aHR 1.33; 95% CI 1.28–1.39); and gold aHR 1.15 (95% CI 1.12–1.19) or multiple commodity employment (aHR 1.15; 95% CI 1.11–1.19). Conclusions This is the first long-term mortality assessment in the large ex-miner population from the South African mining industry. Mortality patterns follow that of the national HIV-tuberculosis epidemic and antiretroviral treatment availability. However, ex-miners have further elevated mortality and a very high mortality risk in the year after leaving the workforce. Coordinated action between the mining industry, governments and non-governmental organisations is needed to reduce the impact of this precarious transition.
- ItemOpen AccessPublic health implications of changing patterns of recruitment into the South African mining industry, 1973–2012: a database analysis(2018) Ehrlich, Rodney; Montgomery, Alex; Akugizibwe, Paula; Gonsalves, GreggAbstract Background The triple epidemic of silicosis, tuberculosis and HIV infection among migrant miners from South Africa and neighbouring countries who have worked in the South African mining industry is currently the target of regional and international control efforts. These initiatives are hampered by a lack of information on this population. Methods This study analysed the major South African mining recruitment database for the period 1973 to 2012 by calendar intervals and demographic and occupational characteristics. Changes in area of recruitment were mapped using a geographic information system. Results The database contained over 10 million contracts, reducible to 1.64 million individuals. Major trends relevant to health projection were a decline in gold mining employment, the major source of silicosis; increasing recruitment of female miners; and shifts in recruitment from foreign to South African miners, from the Eastern to the Northwestern parts of South Africa, and from company employees to contractors. Conclusions These changes portend further externalisation of the burden of mining lung disease to home communities, as miners, particularly from the gold sector, leave the industry. The implications for health, surveillance and health services of the growing number of miners hired as contractors need further research, as does the health experience of female miners. Overall, the information in this report can be used for projection of disease burden and direction of compensation, screening and treatment services for the ex-miner population throughout Southern Africa.
- ItemOpen AccessPublic health implications of changing patterns of recruitment into the South African mining industry, 1973–2012: a database analysis(BioMed Central, 2017-08-03) Ehrlich, Rodney; Montgomery, Alex; Akugizibwe, Paula; Gonsalves, GreggBackground: The triple epidemic of silicosis, tuberculosis and HIV infection among migrant miners from South Africa and neighbouring countries who have worked in the South African mining industry is currently the target of regional and international control efforts. These initiatives are hampered by a lack of information on this population. Methods: This study analysed the major South African mining recruitment database for the period 1973 to 2012 by calendar intervals and demographic and occupational characteristics. Changes in area of recruitment were mapped using a geographic information system. Results: The database contained over 10 million contracts, reducible to 1.64 million individuals. Major trends relevant to health projection were a decline in gold mining employment, the major source of silicosis; increasing recruitment of female miners; and shifts in recruitment from foreign to South African miners, from the Eastern to the Northwestern parts of South Africa, and from company employees to contractors. Conclusions: These changes portend further externalisation of the burden of mining lung disease to home communities, as miners, particularly from the gold sector, leave the industry. The implications for health, surveillance and health services of the growing number of miners hired as contractors need further research, as does the health experience of female miners. Overall, the information in this report can be used for projection of disease burden and direction of compensation, screening and treatment services for the ex-miner population throughout Southern Africa.
- ItemOpen AccessValue of Ecosystem(University of Cape Town, 2018) Centre for Innovation in Learning and TeachingGraphic displaying what 12.6 trillion USD in Ecosystem goods and services was put towards.