3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item The application of mechanised technology to South Africa's bushveld UG2 tabular orebody(2018) Tendaupenyu, Peter AdamPlatinum is important to South Africa. For South Africa to remain a relevant global player, mechanisation is the future. Mechanisation in South Africa’s Bushveld narrow, tabular UG2 orebody has not always delivered as per expectations. This has retarded modernisation of the platinum mining industry. Mining companies have considered reverting back to conventional mining methods. This report investigates, through a series of interviews with key industry players the reasons for the failures. By comparing practice with the recommendations in seven areas: - orebody characteristics, mine design and layout, mine logistics, mining machine size, machine utilisation, labour force structure and change management issues, gaps holding back mechanisation are identified. These are; Applied technology and Orebody – the ore body and its characteristics are not always compatible with the mining method and technology applied. Mine design & layout and Mining – Mining layout is informed by extraction strategy and should support safe, effective and economic mining. This has not always been the case. Move and Mining – Movement of ore and people has not always been seamless. This is a logistical issue which if not addressed adequately in the design phase will cripple a mechanised operation. Maintain and Mining – Plant and machinery must be available in - shift to support mining activities. Effectiveness of planned maintenance must be applied, measured and quantified. This is not always the case. Skills and Mining - Selection, training and placement of personnel is essential in the successful operation of a machanised operation. This is true for the entire hierarchy of the organisation. A trackless operation cannot be successfull if run by people with no appreciation and respect the machines they operate and manage. iv Health & Safety – Mining.There is a reduction in injuries when mechanised operations are compared to conventional operations. Mechanisation however brings its own sets of safety and health issues. Examples are: - o Injuries in mechanisation are more severe. o There are no current interventions to health disorders caused by machine vibrations and diesel emission. Ethics and Mining – It is the responsibility of all to eliminate the wilful damage to plant and machinery. Machinery must work at all times that it is planned to be utilised. The culture of reporting for work when scheduled to do so is paramount. Future reseach should be directed at addressing each of these gaps.Item Development of PGMs-modified TiAl-based alloys and their properties(2017) Mwamba, Ilunga AlainTitanium aluminides Ti3Al (α2), γ-TiAl and TiAl3 have received much attention for potential applications where light weight for energy saving, room temperature corrosion resistance in aqueous solutions, high-temperature oxidation resistance, or where combinations of the above are needed. Gamma-TiAl of composition Ti-47.5 at.% Al with additions of platinum group metals (PGMs: Pt, Pd, Ru and Ir) was investigated for microstructure, hardness, room temperature aqueous corrosion, high-temperature oxidation resistance, mechanical alloying and consolidation by spark plasma sintering, and coating on titanium Grade 2 and Ti-6Al-4V substrates. Gamma-TiAl of Ti-47.5 at.% Al produced by melting and casting gave a microstructure consisting of γ grains and lamellar grains with alternating of α2 and γ phase lamellae. Additions of 0.2, 1.0, 1.5, and 2.0 at.% PGMs introduced new phases of high PGM contents. The γ and lamellar phases were still present. The additions of PGMs significantly improved the aqueous corrosion properties at room temperature, by improving the pitting corrosion resistance of the γ-TiAl alloy by modifying its hydrogen evolution of the cathodic reaction. The presence of PGMs also influenced the oxidation behaviour of γ-TiAl at 950°by forming the Z-phase which stabilized a continuous protective Al2O3 phase. However, Ti-47.5 at.% Al, being a two-phase alloy (α2+γ), PGMs could not sustain a stable Z-phase, as it transformed into an oxygen supersaturated Ti3Al, which subsequently led to the formation of TiO2+Al2O3, a non-protective oxide mixture. The optimal PGM addition to γ-TiAl was 0.5 at.%, with iridium giving the best room temperature corrosion and high-temperature oxidation resistance. Mechanical alloying of Ti and Al pure powders with PGM additions gave powders where α2 and γ were only identified after heat treatment. Consolidation of the mechanically alloyed powders by spark plasma sintering gave different microstructures from the cast alloys, with continuous α2 and γ phases and evenly distributed nanometer-sized alumina, and much higher hardnesses. Cold spraying the mechanically alloyed powders on to titanium Grade 2 and Ti-6Al-4V substrates gave coatings of irregular thickness, dense near the substrates with porosity at the top, giving poor oxidation protection.Item Particle segregation associated with sub-sampling of feed at a typical UG2 concentrator(2017) Naicker, NeressaA particular Upper Group 2 (UG2) reef ore treating Concentrator Plant has been historically under-accounting in terms of 4T (Platinum, Palladium, Rhodium and Gold) content. It has been postulated that the main reason for the consistent under-accounting is due to the correct sub-sampling of finer particles and consequently under sub-sampling of the coarser particles present in the feed slurry streams into the plant. The test work presented involved a series of experimental studies designed to gain an understanding of the presence and extent of particle segregation in the intermediate hopper of a typical UG2 feed vezin sampling system. A total of three stages of test work were conducted, including vezin credibility and chronological sub-sample tests, tests on a re designed nozzle and mechanical hopper. The tests on sub-sampling of the feed material from the intermediate hopper performed on the current sampling arrangement (Stage 1, Test 1) demonstrated that segregation occurs in the intermediate hopper of the feed sampling system. A consistent bias was observed between the reject and official samples with the official samples having more fine particles and being higher in 4T grade than the reject samples. By means of a paired t-test, the calculated bias for % mass retained was deemed significant at the 95% confidence level. This outcome together with the size by assay analysis performed indicated that an under accounting scenario would result. Stage 2 test work involved the use of an alternative nozzle design at the outlet of the current intermediate hopper as a way of optimizing the current arrangement. The sub-sampling tests performed after this modification resulted in a more random distribution of fine and coarse particles in both the reject and official samples. The PSD’s for the reject and official samples were similar across all test runs however the 4T grade was not consistent. The calculated bias for % mass retained was not significant at the 95% confidence level. Stage 3 test work involved the application of a new hopper design which was equipped with an agitator in an attempt to reverse the segregation observed in the old hopper design. The ii new hopper also necessitated the introduction of an alternative sampling protocol where multiple primary increments were collected and the sub-sampling to produce an official and reject sample while agitation transpires created the platform for better suspension of all particles. The particle segregation in the intermediate hopper was reduced and the calculated bias for % mass retained was not significant at most measurements at the 90% and 95% confidence level. The change in nozzle and hopper design seemed to not have an impact on the overall 4T grade of the official sub-samples generated over the sampling campaign. There was a slight improvement in the % COV for the % +38μm from Stage 1 to Stage 2. With the inclusion of the new nozzle design to the mechanical hopper, the % COV for the % +75μm improved from 26.7% to 14.5%. In general, it is believed that the particle segregation which was so evident in the baseline test was significantly reduced with the incorporation of the alternative nozzle design and mechanical agitation. Compressed air agitation alone does not seem to keep all particles of varying size and density in suspension in the intermediate hopper. A future mechanical hopper prototype should be redesigned and fabricated from a cheaper yet robust material and should also be ergonomically improved. The incorporation of internal baffles inside the mechanical hopper should also be considered to reduce the impact of vortexing. An inspection port should also be integrated into the design to be able to view the agitator in operation and observe for vortexing of the slurry material or retention of residual solids in the hopper after sub-sampling takes place. Multiple air agitation points may also be considered in future designs of the mechanical hopper (for instance, an air agitation point above and below the pneumatic valve). It is recommended that any future investigation or test work around particle segregation in the intermediate hopper be conducted in a controlled testing environment. In this way, any random variation due to the process can be disregarded and the true bias (if any) can be determined and confirmed.