School of Mining Engineering (ETDs)

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Subject: search.filters.subject.SDG-12: Responsible consumption and production

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    Impact of secondary rock-breaking equipment availability on mining plan in block cave mining
    (University of the Witwatersrand, Johannesburg, 2024) Nyarela, Martin Sphiwe
    Block caving is one of the massive mining methods that has become increasingly popular due to its low operating cost, improved safety, and high production output. The low operational cost is attributable to minimal blasting, which is only focused on secondary rock-breaking activities. Once caved, the material flows continually and is loaded from the drawpoint to the tipping areas using LHDs and other means, such as scraper winches. Different rock fragmentations register in the drawpoint as loading continues. The sizes range from fine to medium fragmentation and the undesirable oversized rocks that cause hang-ups and blockages. Blockages and hang-ups disturb the flow of material, which negatively impacts compliance with the mining plan and draw control schedule. The hang-ups are treated with secondary rock-breaking equipment to make drawpoints available for loading. However, if the mechanical availability of rock-breaking equipment is low, drawpoints remain idle beyond acceptable limits. Additionally, factors such as the availability of experienced miners to address challenging hang-ups, in instances where treated hang- ups remain unresolved as a result of treatment failure, and the prioritisation of adjacent draw points for loading to restore macro material flow, especially in cases of high hang- ups, can significantly contribute to longer idle periods as well. In this regard, this research aimed to understand the impact that secondary rock-breaking equipment has on the mining plan at the PMC block cave. The research conducted an empirical study of the Secondary Breaking Unit, which forms part of the Mining Operations responsible for all secondary rock-breaking activities at the Palabora Mining Company (PMC). The secondary rock-breaking equipment types that this study investigated include the Medium Reach Rigs, Water Cannons, and Mobile Rock-Breakers. A 52-week data obtained from PMC was used for this study, covering iv the period from January to December 2021. The data pertain to secondary rock- breaking equipment availability and utilisation, cave availability, loading compliance, downtime contribution factors, and in-situ grade. The correlation and regression analysis methods were used for the analyses of data to answer the research questions. In this study, the copper content derived from the mined tonnes and in-situ grade was used as a proxy for the mining plan and it excludes uncontrollable factors such as recovery, pricing, and exchange rates. Firstly, the study sought to determine whether the PMC’s Lift 1 block cave is behaving as predicted and it was concluded that it is. Secondly, the study sought to determine if there is a relationship between the mining plan, using the deviation from the mining plan, and cave availability and loading compliance respectively. It was established that the correlation between the deviation from the mining plan and cave availability was not strong enough whereas the correlation between the deviation from the mining plan and loading compliance was strong enough to derive a predictive equation which was validated. Thirdly, the research sought to establish the minimum acceptable rock-breaking equipment availability at PMC. It was found that the minimum acceptable availability was cautiously 60% based on the historical data. Fourthly, the research sought to determine the research strategy that can improve the rock-breaking equipment availability from the low of 42% in 2021 to at least 60%. The mine’s target availability is 65%. To achieve this, categories of downtime for MRR, MBR and WC with high impact were identified using the Pareto principle. The maintenance overrun downtime category which was one of those with a high-impact downtime was found to be common in all three equipment types with a combined duration of 10 695 hours or 44.4 days per operational equipment per year. In this regard, the Schedule Maintenance strategy was suggested.
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    The feasibility of Witwatersrand gold tailing as an alternative in cement manufacturing as a possible contributor to the circular economy
    (University of the Witwatersrand, Johannesburg, 2024) Maipushi, Mmatseleng Sophy; Mulopo, Jean; Nyembwe, Alain
    Throughout mining history, there have been growing concerns about tailing storage facilities. Concerns include the vast space tailings occupy, and their mismanagement resulting in environmental impact and health implications. Tailings form the highest percentage of material remaining post extraction of mineral, which subsequently requires a deposition site. Only a small percentage of tailings is used in backfill filling in underground operations. The study investigated the viability of gold tailings as an alternative in cement manufacturing and in doing so contribute to the circular economy. The framework of this study used the Witwatersrand Supergroup gold tailings from the Klerksdorp area in North-West Province, South Africa. The mineralogical, chemical, and physical properties of the Witwatersrand gold tailings were investigated and compared to the Ordinary Portland cement and Hexi gold tailings in Shandong Province, China. The Witwatersrand gold tailings in this study had a noticeably lower calcium oxide content (0.98%) than what is required in cement manufacture (63.68%). The aluminosilicate minerals were reasonably high (above 70%) resulting in a pozzolanic nature, which implies that a certain percentage of the gold tailings can be used as supplementary cementitious material in the production of cement mortar. The study also explored ways of reducing or eliminating the identified hazardous substances such as cyanide and radioactive elements. The concentration of uranium radioactivity in Klerksdorp gold tailings is 931.6 Bq /kg above the regulatory limit of 500 Bq/kg for uranium in cement manufacturing. The uranium radioactivity iii concentration can be reduced by incorporating a process of uranium extraction during gold extraction operations. Additionally, the South African policy on the valorisation of mining waste which only recognizes the retreatment of tailings under the Environmental Authorization under the National Environmental Management Act No. 107 of 1998 should be amended by including the use of mining wastes in other sectors of the economy through the circular economy framework.
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    Mineralogical and geochemical characterisation of iron ore tailings and their potential to generate toxic elements At Khumani Mine
    (University of the Witwatersrand, Johannesburg, 2024) Mabunda, Nompumelelo; Limpitlaw, Daniel
    Iron ore mining in South Africa has resulted in clearance of vast areas of land, large pits and volumes of waste material disposed as tailings dumps. Recently, poor management and compromised engineering of tailings dump in iron ore mines have led to incidences of wall failures, spilling tailings material over large areas of land. Inhabitants living near these mines often suffer injustices through contamination of water resources, dam siltation and soil contamination. Although many iron ore tailings dumps have been associated with generation of alkaline drainage, their contaminated footprints have been reported to contaminate groundwater aquifers. This research characterises the tailings material from the Khumani Iron Ore Mine through chemical and mineralogical analyses of leachable potential toxic elements using inductive coupled plasma spectrometry, mineralogical characteristics using x-ray diffraction, physicochemical properties, and acid base accounting. The study also investigates the interaction between tailings geochemistry and groundwater quality. Groundwater in the study is characterised by near neutral to alkaline pH with high concentrations of CaCO 3 owing to the geological formation of the area. The groundwater waters are classified as Ca–type in summer and as-non dominant in winter. Concentration of As (21.48±8.98 μg/l), Fe (22730.5±1827.57 μg/l), Mn (478.3±76.28 μg/l), Cu (60.8±4.34 μg/l), Zn (204.7±21.98 μg/l), Al (300.4±11.47 μg/l ,) Pb (65.7±6.9 μg/l ), Co (20.1±4.1 μg/l) and Ni (41.4±6.85 μg/l) exceed the permissible limits of the Department of Water Affairs and Forestry (1996) in winter but are compliant in summer owing to the increase in the water table and a dilution effect due to heavy rains. Tailings material contains high concentrations of Mn, Zn, B, Ni, Ba, Mo, Co, and Pb and relatively low concentrations of Cu, Cd, As, and Hg minerals in the tailings deposits which include quartz, haematite, magnetite, siderite, calcite, dolomite, K feldspar, plagioclase, talc, clinochlore, and anatase. Kaolinite minerals were shown to increase the adsorption sites for trace elements. Acid base accounting test classified the tailings material as non-acid producing with NP to AP ratio > 2. However, the high concentrations of PTEs, including Fe, Pb, and As, in the groundwater samples suggest that there is vertical movement of these elements iv from the tailings into the groundwater reserves. Therefore, the TSF material cannot be discarded in an unused pit without further treatment or lining to prevent contamination of groundwater resources.