A dissertation submitted to the faculty of Engineering and the Built Environment, University of Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Engineering November 2018 / The aim of this study is to improve the flotation of non-sulphide PGM ores from the Mimosa Mine in the Great Dyke of Zimbabwe by evaluating a variety of collector reagents that have not been tested on such material before and applying a full factorial experimental design to investigate the effects of the main primary collector, co-collector and depressant on PGM recovery and grade. The mineralogical studies by XRD revealed that the non-sulphide PGM ore had substantial amounts of gangue material, comprising of 45% quartz, 21% chabazite and 33% of magnetite. The ICP-OES analysis showed that this particular non-sulphide PGM ore is a low-grade ore with an average 4E head assays of 2.37ppm. In the preliminary flotation stage, three reagent suites made up of (i) a collector, (ii) a co-collector and (iii) a depressant i.e. (SIBX, DTP, M98B); (SIBX, C7133, M98B) and (SIBX, AM810, M98B) respectively were tested. It was observed that (SIBX, AM810, M98B) reagent suite gave the best performance with respect to both recovery and grade of the PGM concentrate from the ore. Attempts were made to optimize the dosage levels of the 3 reagents. The optimization studies revealed that 78.5% Pt and 69.3% Pd can be recovered at grades of 17.90g/t Pt and 9.44g/t Pd respectively. This represents a significant upgrade for the roughing stage from the 1.42g/t Pt and 0.85g/t Pd in the feed. These results were obtained at optimized dosages of 86g/t SIBX and 80g/t AM810, with depressant M98B at 50g/t. The observations from the experiments indicated that recovery of PGEs was on the upward trend as the dosage of hydroxamate was increasing hence the effect of the hydroxamate co-collector was further tested at higher dosages while fixing SIBX at 100g/t. The experiments were carried out using 50g/t, 60g/t, 70g/t and 80g/t hydroxamate (AM810) with the depressant M98B at 50g/t. It was observed that the Pt recovery only increased slightly with increasing hydroxamate (AM810) dosage. / E.R. 2019

<p> Dofasco started producing steel on their Hamilton bayfront property around 1952. Much of the iron ore and coal required for their blast furnace operations was delivered by ship. Two Ore Bridges, probably fabricated in 1951 and in continuous service since, were used to unload the ships.</p> <p> On Tuesday March 28th, 1995 at approximately 8:40am, the No.2 Ore Bridge collapsed. </p> <p> At the time, the Ore Bridge appeared to be stationary. The operator was also not performing any specified operation. The collapse initiated with the failure of the tie-plate which keeps the Shear Leg from spreading at its base. The tie-plate is a critical member. As the structure contained no reasonable alternative load path for the tension in the tieplate, the failure of the tie-plate resulted in the collapse of the Ore Bridge. </p> <p> Initial calculations indicated there was no obvious structural overload that should have precipitated the catastrophic failure of the tie-plate. A metallurgical investigation of the tie-plate material was then initiated. </p> <p> The metallurgical investigation found the steel in the tie-plate was susceptible to brittle fracture at the approximate air temperature at the time of the collapse. Using a fracture mechanics approach it was concluded the failure of the tie-plate was the consequence of fatigue cracks initiating in corrosion pits on the underside of the plate, along the toe of the reinforcing fillet weld connecting the tie-plate to the rocker block. The fatigue cracks grew and combined until they created a flaw which reached a critical dimension, allowing a brittle fracture to initiate and run rapidly across the width of the plate. </p> <p> Over the years, the Ore Bridges have seen several alterations which increased the tension load in the tie-plate. In 1968 the apron was extended. In 1975 the trolley payload was increased. In 1990, increases in dead weight on the main span were recognised. </p> <p> In 1990 however, Dofasco also modified their method of handling iron ore pellets on the bayfront, which required the addition of a hopper into the Shear Leg of the Ore Bridges. The addition of the hopper was critical, as it created unbalanced lateral loadings on the sill truss which were cyclical in nature. The hopper forced the tie-plate to resist these lateral loads by bending horizontally, a loading condition for which it was not originally designed. The cyclic bending stresses resulting from the addition of the hopper led directly to the failure of the tie-plate and the resulting collapse of the No.2 Ore Bridge. </p> / Thesis / Master of Engineering (ME)

The use of iron ore concentrate has become of interest as the demand for higher grade sinter feed is increasing. The fine nature of the concentrate however raises concerns as it can affect permeability during sintering which could have a drastic impact on sinter productivity. In this study the use of iron ore concentrate and micropellets as sinter feed was evaluated. Five mixtures containing different proportions of iron ore concentrate and micropellets, together with iron ore fines, were prepared. These mixtures were agglomerated through pilot scale sinter pot tests, followed by measuring the sinter strength, reduction disintegration and reducibility. Samples of the produced sinters were also subjected to XRF, XRD and SEM-EDS analyses for mineralogical analysis, and MF-XRT for sinter structure analysis. Granulation results revealed that the mixture containing 0% micropellets – 40% concentrate showed superiority in material transfer efficiency while the mixture containing 30% micropellets – 10% concentrate showed superiority in permeability. X-ray diffraction analysis (XRD) revealed an increase in hematite as micropellet content increased. The analysis also revealed high SFCA content for the 0% micropellet – 40% concentrate which decreased as micropellet content increased. This was mainly associated with a decrease in reactivity. Optical microscopy confirmed a large presence of SFCA and also revealed significant precipitation of magnetite and SFCA in the bonding phase structures of the high concentrate containing sinters. It also revealed a pronounced presence of acicular SFCA in the high micropellet containing mixtures. Scanning electron microscopy (SEM) and energy dispersion spectrometry (EDS) revealed a slight consistency in phase chemistry across the different sinter mixtures. This was mainly associated to similar chemical compositions of the starting mixtures. It also revealed that the micropellets maintained a hematite-silica core surrounded by a Fe-rich sintered matrix. It was further determined that the introduction of iron ore concentrate and micropellets did not significantly impact mechanical properties of sinter as similar tumble indices (TI) were observed. A slight variation in reduction disintegration index (RDI) was however seen with high micropellet sinters showing a larger degree of degradation compared to high concentrate containing sinters. Sinter reducibility (RI) also decreased slightly as micropellets increased and this was associated with the inability of micropellets to assimilate during sintering. It was therefore concluded that although micropellets and concentrate can be used as sinter feed, the optimum amount thereof was not yet determined. / Dissertation (MEng)--University of Pretoria, 2020. / Materials Science and Metallurgical Engineering / MEng / Unrestricted

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The demands for increasing the efficiency and lowering the environmental effects in iron and steelmaking industries have given rise to interests in application of direct reduction (DR) processes for production of iron by different gases. These advancements require comprehensive models for better control of the process conditions and the product properties. In the present thesis fundamental aspects in reduction of iron oxide were investigated. The experimental studies on reduction of iron oxide pellets were performed under well-controlled conditions in a setup designed for thermogravimetric investigations. The results indicated that the reaction rates by the applied procedure are higher compared to the procedure similar to conventional thermogravimetric analysis (TGA). This difference was caused by the time required for replacing the inert gas by the reaction gases. Reduction by H2-CO mixtures was accompanied by deposition of carbon and formation of cementite. The variations of cementite contents in the industrial iron ore pellets reduced isothermally for different durations, showed that cementite formation starts from the initial stages of reduction. The experimental conditions such as reaction temperature, carbon activity in the reaction gas and reaction time have a large impact on carbide content of the reduced samples. The kinetics of reduction of iron ore powder by H2 and CO gas mixtures with different compositions were studied using a commercial TGA setup. The results showed that the apparent rates of reaction vary linearly with the H2 and CO contents of the gas. Larger amount of H2 resulted in higher reaction rates. The data were employed in the developed reduction model for pellets. The model was based on the mechanism observed in the commercial iron ore pellets reduced by pure hydrogen. The microstructure of reacted pellets showed that reduction of the examined industrial samples is controlled by both chemical reaction and gaseous diffusion. The reduction model was developed by combining computations for the flow and mass transfer in the gas phase, diffusion of gases in the solid phase and chemical reaction at the reaction sites. The modelling and experimental results were in reasonably good agreement. The present model provides a good foundation for a dynamic multi-particle process model. The results highlighted the importance of considering the reduction mechanisms in different types of pellets prior to modelling. Experiments were undertaken to investigate the selective reduction of iron oxide in zinc ferrite. It was observed that gaseous reduction by hydrogen at temperatures up to 873 K is a potential method for reduction of iron oxide to metallic iron, while the zinc oxide remains in the product and losses of metallic zinc are negligible. Using this primary step in the hydrometallurgical processing of EAFD can overcome the difficulties for leaching of zinc ferrite. / <p>QC 20160823</p>

A dissertation submitted to the faculty of Engineering and the Built Environment, University of Witwatersrand in fulfilment of the requirements for the degree of Master of Science in Engineering 28 January 2017 / Batch scale laboratory testwork was conducted to evaluate collector and depressant addition on flotation performance of a nickel sulphide ore. The objectives of the study were to: 1. develop an understanding of the effects of collector and depressant dosage, and its interactive effects, on flotation performance and 2. determine the effect of stage dosing collector and depressant on flotation performance. Testwork was conducted on the Nkomati Main Mineralized zone orebody, a nickel sulphide orebody in the Mpumulanga Province of South Africa consisting of pentlandite, chalcopyrite, pyrrhotite, pyrite and magnesium bearing silicates. Characterisation testwork was conducted, including mineralogy on the major plant streams (by QEMSCAN) and a process survey. The results indicated that there was potential to increase the recovery of coarse pentlandite and that major nickel losses were observed in ultrafine pentlandite. Milling optimisation requires the minimisation of ultrafine generation while ensuring adequate liberation of the course nickel. Stage dosing of collector at nodal points (where more than one stream meets) is currently practiced on the plant, however, its effect had not yet been quantified on the plant or in the laboratory. Stage dosing of depressant is currently practiced on the cleaner flotation stage, however, this too has not been compared to upfront dosage on its own. Significant gangue depression was noted specifically for the cell at which stage dosing was done. The current study would provide an understanding of the current practices with the possibility of offering improvements. The addition of collector progressively improved the hydrophobicity of the sulphide minerals and gangue (with particular emphasis on magnesium bearing gangue), improving recovery significantly. As a result of additional gangue recovery at the higher collector dosages, increased depressant dosages were required to maximise nickel recovery. The collector improved valuable mineral recovery, however, gangue recovery was increased simultaneously, albeit at a reduced rate or in reduced quantities. Furthermore, increased gangue entrainment was evident at higher collector dosages from the increase in water recovery. Excessive depressant addition destabilised the froth phase by the rejection of froth stabilising gangue, which resulted in reduced recovery of the valuable minerals. Therefore, a careful balance must be maintained in order to maximise nickel recovery. Iron recovery was markedly increased at higher reagent dosages, indicative of increased pyrrhotite recovery. Pyrrhotite, although containing nickel, reduces the concentrate grade and may need to be depressed in the latter stages of flotation to ensure the final concentrate specification is achieved. This is an important observation as any improvement in nickel recovery in the roughing stages must be evaluated against the subsequent effect on the cleaning stages. Stage dosing both collector and depressant, individually and collectively, proved to be beneficial by improving the nickel recovery. Stage dosing of both collector and depressant produced higher recoveries than stage dosing of the reagents individually. The time at which the reagent is dosed also proved to have an effect on the performance with an increased dosage in the latter stages providing the highest recovery. The typical recovery by size performance for flotation is characterised by low recovery of fines and coarse with an optimum recovery of an intermediate size fraction. Stage dosing ensures that fine particles are recovered with minimal reagent addition upfront, thereby, coarser particles can be effectively recovered once the high reagent consuming fines are removed. The results have indicated that stage dosing improved the recovery of both coarse and fine particles, whilst reducing the recovery of the intermediate size fraction. Stage dosing can be implemented for two reasons: 1. maximising recovery 2. minimising reagent consumption to achieve the same recovery as upfront dosing A financial evaluation should be conducted to quantify the optimum operating solution. Minimising reagent consumption could be beneficial under conditions of very low commodity prices and excessive reagent costs. / MT2017

A thesis submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. / A new approach to the problem ofdesigning a control system for a run-of-mine (ROM) milling circuit is described. The ROM mill control problem is formalized in terms or a general linear system synthesis and analysis framework. Using this framework, u-synthesis and analysis is applied to a model of an industrial ROM milling circuit. The milling circuit uncertainty structure is obtained from plant perturbation tests. Correlations of plant parameter uncertainties and the choice of the location of uncertainty weights within the plant transfer function matrix structure, are discussed. Some comments are made as to possible sources of the plant uncertainties, and practical measures that can be taken to minimize them. The choice of performance weighting functions is discussed with regard to the economic and process-related importance of each plant output and issues of implementation such as the sampling rate to be used. A u-controller is obtained which provides robust performance in the face of significant model uncertainties. This controller is tested on a real industrial ROM milling circuit It is shown that the u-controller could be made to work on an industrial plant. Practical problems encountered are discussed, and reasons are given as to why the behaviour of the physical system differs form that observed in computer simulations. (Abbreviation abstract) / AC 2018

A dissertation submitted to the Faculty of Engineering, University of the Witwatersrand, in fulfillment of the requirements for the degree of Mastel' of Science in Engineering Johannesburg 1998 / Impala's Minerals Processing Plant in the Rustenburg Area, South Africa, uses flotation to beneficiate precious metal bearing ores from the Bushveld Complex. Pyrrhotite is one of the sulphide minerals that is targeted but it is the least amenable to current flotation conditions having the lowest recovery. Electrochemical techniques (mixed potential measurements, cyclic voltammetry and current transient techniques) were used to study the relevant reactions on the surface of pyrrhotite mineral electrodes. Aspects investigated included the oxidation of the mineral in aqueous alkaline solutions, activation by copper sulphate, kinetics of oxygen reduction and the adsorption of isobutyl xanthate. Mixed potential measurements of mineral electrodes were taken in batch flotation test work. In addition a novel qualitative measure of hydrophobicity was investigated. The oxidised surface of pyrrhotite is likely to be covered with iron hydroxides and a sulphur rich sub-lattice. No direct evidence was found for the activation of pyrrhotite by copper sulphate in alkaline solutions. It was shown however that activation could be achieved in mildly acidic media and that the surface remained activated if subsequently exposed to alkaline conditions. When achieved under acidic conditions activation was observed to enhance the degree of interaction between the mineral and the xanthate collector. Also copper sulphate appeared to aid the formation of a more hydrophobic surface (as indicated by the hydrophobicity tests). Copper activation conducted in acidic media did not significantly enhance the kinetics of oxygen reduction, a reaction seen as crucial to the adsorption of xanthate. No evidence was found for the initial chemisorption of xanthate onto the mineral surface. However evidence was found for the oxidation of xanthate to dixanthogen at sufficiently anodic potentials. It Was concluded that the relatively poor flotation performance of pyrrhotite could be combated by minimising the extent of the oxidation, adding reagents as soon as possible before the mineral becomes extensively oxidised and by removing surface hydroxides through lowering the pH during conditioning. / MT2017