3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Resource classification criteria for hydrothermally enriched manganese ore bodies(2019) Zulu, NokukhanyaDue to regulatory developments over the years, various international and local reporting codes have been consolidated to ensure clear and unambiguous reporting of Mineral Resources globally. The Committee for Mineral Reserves International Reporting Standards (CRIRSCO) incorporates in the International Reporting Template, the minimum standards for the Public Reporting of Exploration Results, Mineral Resources and Mineral Reserves, and also provides recommendations and interpretive guidelines for the countries represented on the CRIRSCO committee. This template is advisory only and in South Africa the South African Code for the Reporting of Exploration Results, Mineral Resources and Mineral Reserves (SAMREC); developed along the CRIRSCO guidelines; is relevant. SAMREC provides the definition for Mineral Resources and subdivides Mineral Resources in order of increasing confidence into Inferred, Measured and Indicated categories based on the confidence and quality of geoscientific evidence. Whilst there are numerous publications on Mineral Resource classification, few publications exist on the application of Mineral Resource classification techniques applied specifically to manganese deposits. This has led to manganese resource geologists adopting classification methodologies applied to other commodities, and in some cases merging and adapting different methodologies, which might be inappropriate and not suited to the specific manganese ore bodies being investigated. This study set out to develop a defendable guideline for the Mineral Resource classification of hydrothermally enriched manganese ore bodies by considering confidence in both the geology and geostatistical estimation. Wessels mine was presented as a case study. The literature review conducted, formed the foundation of this research report wherein various Mineral Resource classification techniques were investigated. Estimation parameters were identified to assess confidence in the estimate and to confirm the key geological considerations affecting confidence in the estimate. Statistical and geostatistical analyses of the geoscientific data were combined with geological knowledge to develop a guideline for the Mineral Resource classification of hydrothermally enriched manganese ore bodies. The research report shows that using a purely mathematical approach to Mineral Resource classification is an over-simplification and not suited to the manganese ore body, particularly when applied to the skew and non-stationary data of the case study. The absence of an assessment of geological risk in the current classification was found to be a gross oversight. A scorecard method for Mineral Resource classification is proposed, as an improvement over the current methodology. This proposed scorecard is designed to balance three crucial elements: confidence in data integrity, confidence in the geology, and confidence in the mathematical estimation technique. The fundamental research questions have been answered, thereby achieving the objectives of this research study. It is envisaged that this research will contribute to a published body of work that will lead to improved classification of hydrothermally enriched manganese ore bodies.Item The Effect of Manganese, Nitrogen and Molybdenum on the Corrosion Resistance of a Low Nickel (<2 wt%) Austenitic Stainless Steel(2007-02-22T11:27:56Z) Muwila, AsimenyeThis dissertation is a study of the effect of manganese, nitrogen and molybdenum on the corrosion behaviour of a low nickel, austenitic stainless steel. The trademarked steel, HerculesTM, has a composition of 10 wt% Mn, 0.05 wt% C, 2 wt% Ni, 0.25 wt% N and 16.5 wt% Cr. Eighteen alloys with a HerculesTM base composition were made with varying manganese, molybdenum and nitrogen contents, to establish the effect of these elements on the corrosion behaviour of the steel, and to determine a composition that would ensure increased corrosion resistance in very corrosive applications. The manganese was varied in three levels (5, 10 and 15 wt%), the molybdenum in three levels (0.5, 1 and 2 wt%) while the nitrogen was varied only in two levels (0.15 and 0.3 wt%). The dissertation details the manufacturing and electrochemical corrosion testing of these alloys. Preliminary tests were done on 50g buttons, and full-scale tests on 5 kg ingots. The buttons had a composition that was not on target, this was however rectified in the making of the ingots. Potentiodynamic tests were done in a 5 wt% sulphuric acid solution and the corrosion rate (mm/y) was determined directly from the scans. From the corrosion test results, it was clear that an increase in manganese decreases the corrosion rate, since the 5 wt% Mn alloys had the highest corrosion rate, whereas the 15 wt% Mn alloys, the lowest. The addition of molybdenum at 5 wt% Mn decreased the corrosion rate such that a trend of decreasing corrosion rate with increasing molybdenum was observed. At 10 and 15 wt% Mn molybdenum again decreased the corrosion rate significantly, but the corrosion rate value remained more or less constant irrespective of the increasing molybdenum content. At nitrogen levels lower than those of HerculesTM (less than 0.25 wt%) there was no change in corrosion rate as nitrogen was increased to levels closer to 0.25 wt%. For nitrogen levels higher than 0.25 wt%, corrosion rates decreased as nitrogen levels were increased further from 0.25 wt% but only at Mo contents lower than 1.5 wt%. The HerculesTM composition was developed for its mechanical properties. Microstructural analyses revealed that the 5 wt% Mn alloys were not fully austenitic and since the 15 wt% Mn alloys behave similarly to the 10 wt% Mn alloys, it was concluded that 10 wt% Mn was optimum for HerculesTM. All the alloys tested had a much lower corrosion rate than HerculesTM. Any addition of molybdenum thus improved the corrosion rate of this alloy. An alloy with a HerculesTM base composition, 10 wt% Mn, 0.15 wt% N and a minimum addition of 0.5 wt% Mo would be a more corrosion resistant version of HerculesTM. Pitting tests were done on the 10 wt% Mn ingots in a 3.56 wt% sodium chloride solution. The results showed that an increase in molybdenum increased the pitting resistance of the ingots. Immersion tests in a 5 wt% sulphuric acid solution at room temeperature on the 10 wt% Mn ingots confirmed that the ingots corroded by means of general corrosion.