4. Electronic Theses and Dissertations (ETDs) - Faculties submissions
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Item Wear Reduction and Media Density Optimization for the Single Stage Pipe Densifier at Sishen Iron Ore’s Beneficiation Plants(University of the Witwatersrand, Johannesburg, 0202-02) Botha, Simone; Kabezya, KitungwaThe depleting high-grade iron ore mining supply at Sishen Mine in the Northern Cape, South Africa, has given rise to its beneficiation plants operating at higher media densities to upgrade lower-grade ore. In this study, densification was numerically modelled using an MPPIC model and experimentally tested using a 200-mm diameter centrifugal densifier from two local suppliers – Multotec and HMA. Shear stress, wear rate, separation efficiency and media losses were measured at increasing operating densities and differing vortex finder sizes. Optimum operating conditions were established. It was found that a feed density of 3.60 t/m3 and a shear stress of 9.70 e-3 N/m3 at the inlet using a vortex finder diameter size of 30 mm exhibited favourable performance in terms of media densification and downstream recovery. The practical significance of this is proven in terms of wear rate and its predictability to provide a consistent overflow of below 1.20 t/m3 media to the recovery circuit. Furthermore, information about ideal operating conditions in terms of inlet pressure and controls to identify premature failures were established.Item Man-The-Shaman is it the Whole Story? A Feminist Perspective on the San Rock Art of Southern Africa(University of the Witwatersrand, Johannesburg, 1995-06) Stevenson, Judith S.Ethnographic accounts show that both shamanic and gender rituals play a critical role in San culture. Although 30% of the women and 50% of the men become shamans, the literature investigating San rock art frequently defines 'Man-the-Shaman' and minimizes the feasibility of female depictions of this important social role. Prior rock art research has tended to separate shamanic and gender processes to the impoverishment of both. This dissertation investigates the symbolic connections between these two social spheres, and argues that they are inseparable. Through this examination of gender and shamanic roles in San society this dissertation argues that metaphors reflect these two social spheres. It also argues that metaphors are a way of life which are expressed both in reality and non-reality. With these points in mind, it investigates the role of men and women as related to San rock art through social roles.Item The Quantitative Hydrogeological Mapping of Zebediela Estates, Central Transvaal(University of the Witwatersrand, Johannesburg, 1970-05) Pretorius, Desmond AubreyThe groundwater system on zebediela Estates, situated along the northern edge of the Springbok Flats in the Central Transvaal, has been studied by physiographic, geologic , geophysical, geochemical, and hydrologic methods . Emphasis has been placed on the subsurface mapping of the spatial distribution patterns of a nvn1ber of hydrogeologic parameters, and computer-based polynomial trend surface analysis has been employed to facilitate the interpretation of the maps. The computer has also been used to determine the general statistics of the frequency distributions of the various parameters and to platform sequential multiple linear regression analysis in an attempt to determine the relationships between the variables . Data arrays of observations, computations, and interpretations have been disp layed in 38 tables in the text and 21 appendices to the text . The distr ibution patterns , in one and two dimensions, have been portrayed in 8 text figures and 117 maps, separate from the t ext. The area studied covers approximate ly 23 square mil es, in which 556, 000 orange trees have been planted on 5800 acres . An average annual amount of 2400 million gallons of water is required to maintain t he operation, and 560 million gallons of this quantity are withdrawn, on the average, each year from boreholes tapping the groundwater resources of the Estates . Up to April, 1969, 315 holes had been drilled, and 151 had become producers at one time or another. In 19 years of exploitation between 1950 and 1968, 10, 600 million gallons of groundwater were withdrawn, at an average rate of 13 million gallons per year per production borehole. The study has shown that the groundwater system supplying this substantial quantity of water consists of two main elements - a piedmont alluvial slope, in which stream channels and paleochannels on coalescing alluvial fans are acting as conduits for the transmistion of water from the intake areas; and an underlying bedrock storage reservoir composed of aquifers of the Transvaal and Karroo sequences . The Malmani dolomite aquifers and the Stormberg basalt aquifers are superior to those of the Wolkberg quartzites, shales, and lavas, and the Stormberg Cave sandstones. It has been possible to distinguish two cycles of Karoo basalts, each of which shows differentiation . The upper cycle is far more important as an aquifer than the lower cycle. The piedmont slope is composed of portions of three alluvial fans , the spines of which have a general southeasterly trend towards the junction of the Nkumpi and Olifant rivers in the valley-flat environment well to the south of the Estates . The upland areas above the apices of the fans embrace the mountain ranges which form the northern rim of the Transvaal Basin, and these uplands have suffered right-lateral movements along extensive east-northeast-trending transcurrent faults which must have continued to be active into recent times in order to displace the stream course on the fans. The fan-head section and portion of the midfan section of the Nkumpi fan, in which the Gompies River is situated, occur over the east-central, eastern, and southeastern parts of the property, and, where underlain by the upper basalt aquifers, constitute the most important source of groundwater on Zebediela Estates. The whole of the fan-head and mid-fan sections of the Mamukebe fan are located in the riorthern, west-central, western, and southwestern localities of the area studied. The fan is much smaller than either of the others, and is underlain by Wolkberg rocks, Cave sandstones, and lower basalts. Its overall groundwater potential is consequently lower than that of either of the other two components of the piedmont slope. Only a very restricted portion of the fan-head section of the Mogoto fan occurs in the extreme northwestern corner of the Estates, where it is underlain by the dolomite aquifer, Its groundwater parameters are consequently very favourable, but the true potential of this fan lies beyond the western boundary of the property. The average yield of boreholes in the upper basalt is 3600 gallons per hour; in the lower basalt, 2000 g.p.h.; in the sandstone, 1500 g.p.h.; in the dolomite, 11,200 g.p.h.; and in the quartzites, 1500 g.p.h. The average yield for all boreholes on the Estates is 4100 gallons per hour. All of these figures are appreciably higher than those for equivalent formations elsewhere in South Africa, testifying to the impoi,tance of the piedmont alluvial slope environment in the overall groundwater system at Zebediela. The average annual recharge of the groundwater reservoirs from all sources has been estimated at 700 million gallons. With the average annual withdrawal being of the order of 560 million gallons, the possibility exists that production from the aquifers can be increased by 25 per cent, without fear of serious, permanent deterioration in the performance of the groundwater system. However, excessive exploitation in times of low recharge might lead to the development of quality h.azards with respect to sodiuum, ehloride, and bicarbonate over the upperbasalts. This possibility does not exist for the remaining aquifers, particularly those in the dolomite, from which relatively pure water is drawn. An added problem in the recharge of the upper basalt aquifer is the contamination of t he groundwater in storage by lithium, brought into the Zebediela groundwater- system by the Nkumpi River, which transmits the element from the granite terrain to the north of the mountainous rim of the Springbok Flats. A new model of groundwater exploration has been devised, based on optimum drilling sites being located where coincidence takes place of piedmont stream channel conduits, dolomite or upper basalt aquifers, and transcurrent fault aquicludes, Results obtained from the employment of this model during two years of drilling subsequent to its development in a preliminary form produced an increase of 14 per cent in the average yield of all boreholes drilled.Item Mathematical representation and analysis of articular surfaces: application to the functional anatomy and palaeo-anthropology of the ankle joint(University of the Witwatersrand, Johannesburg, 1990) Webb, Christie Peter; Tobias, Phillip VallentineThis thesis is a study of quantifiable variation in the geometric shape of the superior articular surface of the talus of higher primates, with special reference to fossil tali of Plio-Pleistocene hominids. (Abbreviation abstract).Item The theory and practice of community participation in provision of urban structure(University of the Witwatersrand, Johannesburg, 1993) Abbott, John; McCutcheon, RobertThe thesis develops a new approach to community participation, for application to infrastructure provision projects in developing countries, based upon social surveys and case studies of negotiations in five South African communities. Existing approaches to community participation are analysed and shown to be unsuitable for infrastructure provision. The thesis compares the characteristics of infrastructure projects with those of other types of development projects and demonstrates how these characteristics can be used to situate a given project within a project environment defined in terms of two variables: the openness of government to community involvement in decision-making, and project complexity. Social surveys carried out in Soweto and KwaThandeka showed the centrality of infrastructure to social change in South Africa. Existing urban management systems were unable to cope with the stresses placed upon them. Four facets of urban management were identified as being under stress: institutional capacity, legitimacy, affordability, and user convenience. These stresses change the nature of infrastructure provision from the supply of end products into a complex process. Central to this process are: an increased number of actors influencing decisions, the enhanced role of technical professionals, and the social implications of different levels of service. The case-study of KwaThandeka included a study of the negotiation process with the provincial administration. This research led to the development of a performance specification for comparing social, economic and technical measures of value. A new conceptual framework for community participation was derived, based upon the different actors involved in the decision-making process and the different needs of each of those actors. Three case studies from Natal identified different implementation strategies for community participation. Communities were found to have three distinct needs: involvement in the political process; involvement in technical decision-making; and representation as consumers of services. An analytical tool was developed to assist project managers in understanding the relationships between actors in a project. The thesis shows how technical project management can be integrated into the participation process. The success of community participation can be evaluated by assessing the degree of consensus achieved between actors, and the intensity of community involvement.Item Pegmatite investigations in the Karibib district, South West Africa(University of the Witwatersrand, Johannesburg, 1963) Roering, ChristianThe outer pegmatitie zone of variable thickness which is essentially a very coarse-grained granite consisting of larger perthite phenocrysts lying in a matrix of albite, quartz and muscovite. The inner portions of this zone may reveal a great enrichment of perthite, so much so, that it may grade into a giant perthite zone, e. g. Rubicon main ore-body; Karlsbrunn close to the Li-bearing ore zones. This outer portion of the pegmatite may also reveal a subdivision into two distinct units: an outermost zone of albite-quartz-muscovite and an inner zone of albite-perthite-quartz-muscovite. This sequence of essentially granitic crystallization is often abruptly broken by the appearance of a zone consisting essentially of cleavelandite with minor quartz and muscovite. This zone is characterized by the appearance of numerous accessory minerals often in economic quantities, e. g. beryl, columbite-tantalite-frondellite, topaz and apatite. The zone is generally of the order 1-5 feet depending on the original size of the pegmatitie and the degree of fractionation. That it is not a late replacement unit is confirmed by observations at Rubicon where corroded crystals of beryl belonging to this zone are found lying in a matrix of lepidolite and albite which is the next unit to form. The lepidolite-albite zone in fact replaces the beryl-bearing zone. The striking symmetry alone of the Rubicon body testifies to this zone preceeding in crystallization sequence the Li-ore zones. The significant fact about this zone is that it marks a distinct break in the crystallization history of the pegmatite, i. e. it marks the change from crystallization of essentially granitic components to the formation of late phase constituents, viz. Li-bearing and associated minerals. It possibly marks the break from magmatic crystallization to late-magmatic conditions when pneumatogenic and even hydrothermal processes begin to operate. The next group of minerals to form are noticeably rich in Li and are frequently associated with sugary albite. The major minerals are petalite, lepidolite and albite, while minor amounts of amblygonite also occur. There is a definite spacial relationship sequence in the formation of these minerals. Petalite crystallizes first and collects in the upper part of this unit generally forming a hood. Amblygonite, albite, quartz, may occur at the same time. Immediately below this petalite hood, and at a somewhat later stage, fine-grained lepidolite crystallizes together with albite and minor quartz. The final phase to form at this general stage is sugary albite which collects at the bottom of the still non-crystalline portion of the magma chamber. The sugary albite phase is able to behave diapirically and can intrude, brecciate, and replace any of the previously crystallized zonal constituents. Each successive stage here can assume corrosive relationships to previously consolidated units. No assessment is made as to the amount of replacement that may take place as the criterion commonly used for such diagnosis are somewhat subjective. During this entire process of complex diffusions and crystallization, silica is apparently being concentrated in the residual fractions of the pegmatite magma. The next zone to form is a cleavelandite-rich rock confined to the quartz core margin. This cleavelandite is able to vein and brecciate and corrode the immediately adjacent lying lepidolite and is often associated with minerals such as beryl, columbite, tantalite, tourmaline, topaz and apatitie. Amblygonite may also belong to this stage of mineralization though in general it tends to be associated close in time with the petalite stage of mineralization. The final stage of the crystallization sequence is the quartz core. Quartz veinlets emanating from the core have been observed to cut across adjacent lepidllite-rich and amblygonite-albite zones. Euhedral crystals of columbite and beryl at the core margin are completely surrounded by quartz. These observations may suggest that quartz, although concentrated in the centre of the dyke, probably existed in some unconsolidated state (e. g. a gel as Brotzen (1959) has suggested). The development of a gas phase at certain stages of the pegmatites consolidation history possibly accounts for the vertical fractionation found in these pegmatites. Finally details of the more important pegmatite minerals are given together with chemical analyses.Item Experimental heat transfer coefficients for the cooling of oil in horizontal internal forced convective transitional flow(University of the Witwatersrand, Johannesburg, 1981) Rogers, Douglas Gordon; Van der Merwe, D.F.Item A study of the finite element method, with reference to the Adina finite element package(University of the Witwatersrand, Johannesburg, 1983) Constancon, Charles PeterThis dissertation presents a theoretical and practical study of the finite element met hod using the ADINA finite element program. The package was applied to the analysis of three different problems, namely: A nonlinear static analysis; a free vibration analysis and a themal analysis. The first two analyses were supplemented with experimental results for the purpose of comparison whilst the last was compared with a closed form analytic solution. The first problem consisted of a materially nonlinear static analysis of a cast iron sheave wheel. The sheave was physically loaded with a rope up to failure of the rim. Strain gauges monitored strain at twenty-four locations. In order to simulate the nonlinear properties of the east iron, a Drucker Prager yield criterion was utilised and accordingly, a subroutine describing the elasto-plastic constitutive laws was interfaced with the ADINA package. Owing to self-imposed limitations on computer resources, the sheave was modelled as a two-dimensional body. The results correlated well in the linear region but deviated when plastic deformation was pronounced. It is suspected that this was due to a combination of approximations in modelling the geometry and the material. In the free vibration analysis, a simple portal frame was built in order to compare its natural mode shapes and frequencies with those obtained from a finite element simulation. This comparison proved satisfactory. The thermal analysis was executed primarily to test and gain first hand experience with the ADINAT package. A two-dimensional flat plate subjected to a sinusoidal temperature load was simulated. Although the application was simple, the accuracy of the FEM results confirmed that the package was operating correctly. In all these exercises ADINA package performed satisfactorily. Experience show that the programme was not user-friendly, however this is not considered a drawback in a research environment.Item Translating terms of affection and abuse from German to English with special reference to animal metaphors(University of the Witwatersrand, Johannesburg, 1987) Conze, Ingola; Taylor, Oakshott