The Damara-Katanga orogen in central-southern Africa represents an area of 1.73xl0⁶ sq. km. The region is considered one of the wealthiest metallogenic provinces in the world. Successful exploration for stratabound base-metal deposits has taken place at this particular area since the introduction of more organised methodology in the early 1920s. The genesis, location and distribution of the ore deposits are related to their tectonic settings. Geodynamic evolution of the orogen, which initially formed part of a complex Pan-African rift system, comprises the following stages rifting; downwarping, including spreading on the western portion; syn-orogeny and late-orogeny. Two major tectonic events in the history of the region have been identified: the Katangan (900-750 Ma) and the Damaran episodes (750-500 Ma). Timing of mineralisation of ore deposits has been related to the evolutionary stages of the orogen. Genetic models of the most productive deposits are briefly discussed in this dissertation. The sedimentological, geochemical, paleogeographic and structural features can be employed as geological guidelines for integrated exploration programmes. Discoveries of major deposits and prospects in the orogen are also summarised, focussing on the exploration methods employed. The cost-effective use of the exploration techniques includes the classical copper-lead-zinc soil sampling for residual soils such as those in the Copperbelt area. Airborne magnetics and electromagnetics and follow-up ground geophysics have proved successful in areas where the cover is transported in the search for shallow ore deposits such as the Matchless massive sulphides. Remote sensing, geochemical and geophysical techniques have been tried in covered areas of western Botswana. The lack of geological control makes this interpretation difficult. A detailed geological mapping and the use of geochemical and geophysical techniques has been used to delineate carbonate-hosted base-metal deposits at the Otavi Land. The more expensive traditional methods necessary for the delineation of orebodies, such as pitting, trenching and drilling, are also discussed. Using a sequential approach, a possible exploration strategy is suggested, outlining the cost-effective use of remote sensing, geochemical and geophysical techniques. Standardisation in basic geological information is required for future successful explorations in the Damara-Katanga orogen, as well as attractive mining policies. In the event of their implementation, exploration perspectives are promising, specifically in terms of ore potential.

The giant Palaeoproterozoic manganese deposits of the Kalahari manganese field (KMF), Northern Cape Province, South Mrica, have been a world renowned resource of manganese ore for many decades. In recent years, the mineralogical composition, geochemistry and genesis of these deposits have been the objects of many geological investigations, yet their origin remains contentious up to the present day. A characteristic feature of the Kalahari deposits is the intimate association of manganese ore and iron-formation of the Superior-type, in the form of three discrete sedimentary cycles constituting the Hotazel Formation. This striking lithological association is an almost unique feature on a global scale. From that point of view, the present study is effectively the first attempt to shed light on the origin and post-depositional history of the Hotazel succession, using as prime focus the petrographic and geochemical characteristics ofthe host iron-formation. Petrographic and whole-rock geochemical information of iron-formation from the southern parts of the KMF, suggests that the Hotazel iron-formation is almost identical to other iron-formations of the world of similar age and petrological character. The rock exhibits essentially no high-grade metamorphic or low-temperature alteration effects. Mineralogically, it contains abundant chert, magnetite, subordinate amounts of silicate minerals (greenalite, minnesotaite, stilpnomelane) and appreciable concentrations of carbonate constituents in the form of coexisting calcite and ankerite. Such mineralogical composition is indicative of processes occurring in a diagenetic" to burial (up to very low-greenschist facies) metamorphic environment. Bulk-rock geochemical data point towards a simple composition with Si02, total Fe-oxide and CaO being the chief major oxide components. Whole-rock rare-earth element data suggest that the iron-formation precipitated from a water column with chemical signatures comparable to modern, shallow oceanic seawater. The virtual absence of positive Eu anomalies is a feature that compares well with similar data from Neoproterozoic, glaciogenic iron-formations of the Rapitan type, and suggests but only a dilute hydrothermal signal, poten!ially derived from distal submarine volcanic activity. Carbon and oxygen isotope data from iron-formation and Mn-bearing carbonates as well as overlying ferriferous limestone of the Mooidraai Formation, compare well with the literature. The former exhibit variable depletion relative to seawater in terms of both BC and 180, while the latter have signatures comparable to normal marine bicarbonate. Isotopic variations appear to be related to fluctuations in the amount of co-precipitated marine carbonate, in conjunction with processes of coupled organic matter oxidation - FelMn reduction in the diagenetic environment. Oxygen isotope data from quartz-magnetite-calcite triplets suggest that crystallisation took place under open-system conditions, with magnetite being the most susceptible phase in terms of fluid-rock isotopic exchange. Data also suggest that the calcite-magnetite pair may constitute a more reliable geothermometer than the quartz-magnetite one, mainly due to the interlinked diagenetic histories between calcite and magnetite. Iron-formation from the northern parts of the KMF can by categorised into three main classes, namely pristine, altered and oxidised. Pristine iron-formation is identical to the one seen in the southernmost parts of the field. Altered iron-formation corresponds to a carbonate-free derivative of intense oxidation and leaching processes at the expense ofpristine iron-formation, and contains almost exclusively binary quartz-hematite mixtures. The rock appears to have lost essentially its entire pre-existing carbonate-related components (i.e., Ca, Mg, Sr, most Mn and Ba) and displays residual enrichments in elements such as Cr, Th, V, Ni and Pb, which would have behaved as immobile constituents during low-temperature alteration. The low temperature origin of altered iron-formation is supported by oxygen isotope data from quartz-hematite pairs which indicate that isotopically light hematite would have derived from oxidation of magneftte and other ferroussilicate compounds in the presence of a low-temperature meteoric fluid, while quartz would have remained isotopically unchanged. Occasional occurrences of acmite-hematite assemblages suggest localised metasomatic processes related to the action ofNaCI-rich fluids at the expense of altered iron-formation. The conditions of acmite genesis are very poorly constrained due to the very broad stability limits of the mineral in environments ranging from magmatic to surface-related. Oxidised iron-formation constitutes a distinct rock-type and shares common attributes with both the pristine and the altered iron-formation. The rock contains hematite as an important constituent while the amount of magnetite is substantially reduced. With regard to carbonate nlinerals, calcite contents are clearly very low or absent, having being replaced in most instances by a single, Mgenriched, dolomite/ankerite:type species. Oxidised iron-formation contains somewhat higher amounts of iron and reduced amounts of Sr and Ba relative to pristine iron-formation, whereas enrichments in elements such as Ni, Th, Pb, Cr, and V are seen, similar to altered iron-formation. Oxidised iron-formation appears to have originated from processes of dissolution-mobilisationreprecipitation of solutes derived primarily from leaching that produced altered iron-formation. It is proposed that the Hotazel iron-formation and associated manganese deposits were formed as a result of episodic sea-level fluctuations in a stratified depositional environment that gradually evolved into a shallow carbonate platform. A critical parameter in the development of manganese sediment may include regional climatic patterns related to a glacial event (Makganyene diamictite) prior to deposition of the Hotazel strata. This suggestion draws parallels with processes that are believed to have led to the formation of worldwide iron-formations and associated manganese deposits subsequent to Neoproterozoic episodes of glaciation. Submarine volcanism related to the underlying Ongeluk lavas appears to have had very little (if any) metallogenic significance, while evidence for a sudden rise in the oxygen contents of the atmosphere and ambient waters is lacking. With regard to later alteration processes, combination of geological and geochemical data point towards the potential influence of surface weathering prior to deposition of rocks of the unconformably overlying Olifantshoek Supergroup, possibly coupled with fault- and/or thrustcontrolled fluid-flow and leaching of the Hotazel succession during post-Olifantshoek times.

Biohydrometallurgical techniques are quite established for the treatment of certain sulphide minerals and others have been demonstrated at laboratory or pilot plant scale level, where iron and sulphuroxidising bacteria are utilised for the leaching of low grade sulphide ores and the pretreatment of gold ores and concentrates. The majority of the microorganisms which are used for bacterial leaching are autotrophic aerobes, therefore carbon dioxide and oxygen are essential nutrients for their growth and survival, adequate supplies must be ensured in order for the oxidation process to be successful through an effective gas mass transfer process from air or other sources to the gas/liquid/solids interface in the pulp which can then be readily available to the microorganisms. Gas mass transfer limitation is one of the major problems faced by the industry therefore, most commercial biooxidation plants currently operate at low pulp densities at around 20 - 25% to minimise gas mass transfer limitations. Three cultures, a mesophile (DSM 583), a moderate thermophile (Y1FI) and a extreme thermophile iSulfolobus BC65) were used to bioleach the Ok Tedi copper concentrate under optimum Ch and CO2 enriched air (30% Ch and 10% CO2) based on volume ratios. The positive effect of using oxygen and carbon dioxide enriched air to bioleach the copper mineral was clearly demonstrated where an increase in Cu leaching rate by a factor of2.8, 2.1 and 1.9 for DSM 583, YTFI and Sulfolobus respectively were observed compared with the shake flask tests. The lag phase observed with the other test conditions such as in shake flask or with air, was eliminated when leached under optimum gas enrichment and 1t;80%of the Cu was extracted in the first 120 to 150 hours of leaching for all three cultures. The average dissolved oxygen concentrations observed in the pulp for these tests were 11.8, 8.0 and 7.2 mgll for DSM 583, YTFI and Sulfolobus respectively, indicating that O2 was not limiting in these tests. The Fe released during the bioleaching of copper was non stoichiometric for a predominantly chalcopyrite concentrate and the low redox potential values (max 638mV) suggested galvanic interaction during the leaching of copper where chalcopyrite was leached preferentially due to the presence of pyrite. Bioleaching of copper under optimum gas enrichment at different pulp densities showed near total copper extraction occurred for pulp densities of 3, 10 and 20% (w/v). At high pulp densities, more so at 40% than 30% (w/v), the leaching rate decreased rapidly for tests with YTFI and Sulfolobus. Monitoring of dissolved Ch shows that O2 demand increased with increasing pulp density and the average dissolved O2 concentration observed for DSM 583, YTFl and Sulfolobus at 40% solids concentration were 3.0, 2.6 and 2.4 mgll respectively, suggesting that oxygen and carbon dioxide are not limiting. The decrease in leaching rate observed at high pulp densities (30 & 40%) under optimum gas enrichment was accompanied by low metal dissolution and low redox potential values which was attributed to shear stress due to attrition of cells by high solids concentration, toxicity of metal ions especially Ag, Fe and Cu, and the formation of precipitates and jarosites as confirmed from XRD analysis of leach residues hence impeding the leaching process rather than as a result of O2 and C~ limiting conditions. The addition of flowing air increased the overall iron release rate for the Porgera gold-bearing pyrite concentrate by a factor of AJ 2.8, 1.8 and 1.5 for DSM 583, YTFl and Sulfolobus respectively compared with the shake flask tests, and the lag time was observed to decrease by about 80% for all cultures, suggesting O2 and CO2 limiting conditions in the shake flask. The average dissolved ~ concentration observed for the pulp with the different cultures were 8.7, 5.8 and 5.0 mgll for DSM 583, YTFI and Sulfolobus respectively indicating oxygen was not limiting in these tests. Biooxidation of pyrite concentrate under optimum gas enrichment at various pulp density shows DSM 583 performing well exhibiting the highest oxidation rate for all pulp densities, followed by YTFt and Sulfolobus, except at 3% pulp density where the rates are similar for all cultures. At high pulp density, above 30%, the oxidation rate decreased rapidly for YTFt and Sulfolobus, with DSM 583 showing a moderate decrease. Monitoring of dissolved oxygen showed that oxygen demand increased with increasing pulp density and at one point the dissolved oxygen concentration for the test with YTFI at 40% and Sulfolobus at 30 and 40% solids concentration decreased below t.O mgll, suggesting oxygen and carbon dioxide limiting conditions. The decrease in leaching rate at high pulp densities above 30% under optimum gas enrichment was accompanied by low Fe dissolution and low redox potential which was attributed to shear stress due to attrition of cells by high solids concentration, toxicity of metal ions especially Ag, and Fe. and the formation of precipitate andjarosites hence impeding the leaching process. Oxygen and CO2 limiting conditions due to high pulp density and viscosity were only observed for YTFt and Sulfolobus cultures. The cyanide leaching of the pretreated pyrite concentrate shows that the extent of gold and silver recovery increased with the degree of pyrite oxidation and Au and Ag recoveries in excess of 80% were achieved compared with that of only 18.1% and 35.94'10 for gold and silver respectively, from the original. untreated concentrate by direct cyanidation.

Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Previous work has shown that microwave heating of mineral ores induces micro cracks within the ore structure, which can be attributed to the difference in the adsorption of microwaves amongst the different mineral phases. This reduces the energy required during subsequent grinding and enhances the liberation of valuable minerals. In order to design microwave applicators for this purpose, knowledge of the effective dielectric properties of the crushed ore is required. Of particular interest is the effective complex permittivity of the bulk crushed ore. The measurement of the effective permittivity of a large volume of crushed ore is most readily accomplished using the waveguide measurement technique. In this method a representative sample of the material is placed in a defined and fixed volume in a standard size rectangular section metallic waveguide. The magnitude and phase angle of the transmitted and reflected low power microwaves through and from the sample are measured. The complex permittivity can be extracted from these so-called scattering, or Sij parameters. In this study the effective complex permittivities for two porphyry copper ores and a copper carbonatite ore were determined as a function of particle size distribution (-26.5+2mm) using two sizes of waveguide (WR284 and WR340). The sample holders incorporate dielectric windows for the location of the material under test. The extraction of dielectric properties from Sij parameter measurements is problematic using standard algorithms in such cases. Accordingly a new Database Extraction (DBE) Algorithm has been developed. In this method, a database of scattering parameters is established through electromagnetic modelling of the measurement system. A search algorithm is used to determine the effective complex permittivity of the modelled load whose scattering parameters provide the best fit to the experimental data. The goodness of the experimental fit of the simulated to the measured Sij parameters is determined by a root mean squared deviation minimisation metric. Results show that the method can be used successfully to determine an effective complex permittivity for a bulk volume of the crushed material. It is concluded that the dielectric property extraction over the full operational frequency interval (2.3-3 GHz) is preferred as it has a larger degree of extraction confidence and hence reliability. Results show that with increasing particle size, the experimental fit between the simulated and measured Sij parameters becomes increasingly poor, as wall effect become more prominent. The effect is most prominent for the smaller WR284 waveguide size. It is shown that for a waveguide size of similar size to the particle size, the Sij parameter fitting is poorer compared to when a larger waveguide size is used. The extracted complex permittivity reproducibility between repeated dielectric property measurements is improved for the WR340 waveguide size, as the extractions in the WR284 waveguide is dominated by the combined particle size and wall-effects of the sample holder. Ore mineralogy is identified as a key parameter that influences the dielectric properties of the crushed ore. For ores with a dominant microwave absorbent mineral phase, the dielectric constant and loss factor is found to be larger, compared with ores with a more dominant microwave transparent gangue mineral phase. / AFRIKAANSE OPSOMMING: Navorsing toon dat die verhitting van mineraal erts, met mikrogolwe, mikroskaal frakture in die mineraalstruktuur teweeg bring weens die verskil in die adsorpsie van mikrogolwe in die verskillende mineraalfases. Gevolglik verminder die energievereiste vir die vergruising van die erts en verbeter die vrystelling van waardevolle minerale wat vasgevang is in die mineraalmatriks. Vir die ontwerp van mikrogolfapplikators vir dié doel, word die effektiewe diëlektriese eienskappe van die vergruisde erts benodig. Van spesifieke belang is die effektiewe komplekse permittiwiteit van die erts. Die effektiewe permittiwiteit van `n vergruisde materiaal monster word met behulp van die golfgeleier tegniek gemeet. Vir dié tegniek word `n verteenwoordigende monster van die materiaal in `n rigiede volume in `n standaard grootte reghoekige golfgeleier geplaas. Die grootte en fasehoek komponente van die deurgelate en weerkaatste mikrogolwe deur en van die oppervlak van die materiaal word gemeet. Die komplekse permittiwiteit van die vergruisde materiaal kan geëkstrakteer word vanaf hierdie sogenaamde verspreide, of Sij parameters. In hierdie studie word die effektiewe permitiwiteit van twee porforie koper ertse en `n koper karbonatiet erts bepaal as funksie van partikel grootte (-26.5+2 mm) deur gebruik te maak van twee standaard grootte golfgeleiers. Die monster houers inkorporeer diëlektriese vensters om die vergruisde materiaal monster in posisie te hou. In so `n geval is die ekstraksie van die diëlektriese eienskappe vanuit die Sij parameter metings problematies. Gevolglik is ‘n nuwe Databasis Ekstraksie Algoritme ontwikkel wat `n databasis van verspreide parameters opstel deur die elektromagnetiese simulasie van die metingsisteem. `n Soek-algoritme word gebruik om die effektiewe komplekse permitiwiteit van die gesimuleerde monster te bepaal wat die beste ooreenstem met dié van die gemete eksperimentele Sij parameter data. Die mate van ooreenstemming tussen die parameters, word bepaal aan die hand van die minimaliserings prosedure. Resultate toon dat dié metode geskik is vir die bepaling van die effektiewe komplekse permitiwiteit van die vergruisde monster. Dit word vasgestel dat die betroubaarheid van die geëkstraeerde Sij parameters, en gevolglik die diëlektriese eienskappe van die erts, toeneem indien die algoritme oor `n groter frekwensie band uitgevoer word. Resultate toon verder dat met toenemende partikel grootte, die mate waartoe die absolute grootte en fasehoek komponente van die gesimuleerde en gemete Sij parameters ooreenstem, versleg. Dit word toegeskryf aan wand-effekte. Hierdie verskynsel is veral opmerklik vir die kleiner grootte golfgeleier. Dit word getoon dat vir metings waar die golfgeleier dieselfde orde grootte geometriese afmetings het as die vergruisde erts self, die passing tussen die gesimuleerde en gemete Sij parameters swakker is, wanneer dit vergelyk word met metings waar dit nie die geval is nie. Die reproduseerbaarheid van die geëkstraeerde diëlektriese eienskap waardes verbeter vir lesings wat uitgevoer word in `n groter grootte golfgeleier. Laasgenoemde word toegeskryf aan die meer dominante wand-effekte wat kenmerklik is vir `n kleiner golfgeleier. Erts mineralogie word geïdentifiseer as `n sleutel parameter wat die diëlektriese eienskappe van die vergruisde materiaal beïnvloed. Beide die diëlektriese konstante en verliesfaktor is groter vir ertse met `n oorheersende mikrogolf absorberende mineraalfase.

No description available.

M.Sc.

M.Com. (Economics) / Please refer to full text to view abstract

D. Phil. / The Kalahari Manganese Deposit (KMD) is the largest of five erosional relics of the Hotazel Formation that are located near Kuruman in the Northern Cape Province of South Africa. Manganese ores are exploited from the lowermost of three manganiferous beds that are interbedded with banded iron-formation (BIF) and hematite lutite, that together constitute the Hotazel Formation. Two major ore types have been delineated previously, viz. low grade braunite lutite of the Mamatwan-type, and high grade oxidic ores of the Wessels-type, with the latter spatially restricted to the northern KMD. Genesis of the ores was temporally distinct, with the Mamatwan-type ore considered as a sedimentary-diagenetic precursor to the hydrothermally altered Wessels-type ore. Drill core samples from the Nchwaning-Gloria area of the northern KMD were analysed, with the aim to better characterise ore genesis, with emphasis on ore alteration. A second part of the study aimed at the application of mineralogical and geochemical information to aspects of ore smelting for the production of Mn alloy for use in the steel industry. Methods employed were drill core logging, X-ray diffraction (XRD), petrography, electron probe microanalysis (EPMA), major and trace element (including REE) analysis (employing artificial neural networks for evaluation of elemental trends), and stable isotope (C and O) analysis. Significant effort was invested in method development for quantitative mineralogical modal analysis using Rietveld refinement of XRD data. The study shows that a number of ore types can be differentiated in the northern KMD on the basis of mineral assemblage, grade, texture and geochemical characteristics. The ores are broadly classified into least altered (LA), partially altered (PA) and advanced altered (AA) types. The LA ores are low grade (<40 wt%Mn) Mn lutites, with dolomite-group carbonate a significant component in addition to braunite. Serpentine is a ubiquitous trace mineral, and boron is a characteristic trace element hosted predominantly by braunite in these ores. Ores of the PA type comprise either braunite-hausmannite-calcite or hausmannite-calcite assemblages, are fine to coarse grained, and display intermediate Mn grades (40-45 wt%Mn). They exhibit a transitional trace element signature. Advanced altered ores may be classified into five different types, based on mineral assemblages that contain hausmannite and/or braunite as significant minerals. Carbonates occur predominantly in the form of calcite, present in minor to trace proportions. Textures vary from fine to very coarse grained, and high Mn grades (typically >45 wt%Mn), are recorded. Trace elements of significance include Zn, associated with hausmannite, B, associated with massive braunite and a number of trace minerals, and P, typically present in trace quantities of apatite. In terms of ore genesis, mineralogical, geochemical and geological considerations suggest that Mn (and Fe) originated from submarine hydrothermal vents, from which it travelled in hydrothermal plumes, prior to rapid deposition ~2.2 Ga ago. Diagenesis followed soon after deposition, through redox reactions involving organic matter and higher oxides of Mn to produce the braunite-carbonate assemblage primarily observed in LA ores. The carbonate:oxide ratio and nature of the carbonates varied slightly depending on fluctuations in organic matter flux to the sediment, as well as marine bicarbonate concentrations. Metamorphism, in relation to diagenesis and metasomatism, is poorly understood, but is perceived to have resulted in serpentine formation, as observed in LA and PA ores.

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 research report submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the Degree of Master of Science in Engineering (Metallurgy and Materials Engineering) July 2015 / The research report is premised on three aspects which are critical in the heavy mineral beneficiation. These aspects are classified as (i) understanding the densimetric profile of the available ore body, (ii) understanding the properties of the heavy medium utilised at the plant to beneficiate the ore, and (iii) the automation and modelling of the processing plant in order to maximise plant efficiency. Ore characterisation is mainly focused on understanding the densimetric profile of the ore body, in order to determine the probability of producing a saleable product as well as predicting the expected yields and quality. This is done to utilise the endowment entrusted upon the operating entity by the government and shareholders to treat the mineral resource to its full potential. Understanding of the beneficiation potential of the ore body will assist the mine planning and processing plant to optimise the product tons and quality. This will ensure the marketing plans are in accordance with the expected product as beneficiation will vary depending on the mining block reserves. The mining blocks have potential to produce varying product grades with different recoveries. Ore characterisation was conducted on the GR80 mining block, low-grade stockpiles (i.e. C-grade ore reserves & Jig discard and dense medium separation (DMS) run-of-mine (ROM) material. The GR80 material was characterised as having low proportion of near-density material and would be easy to beneficiate as well as produce high volumes of high grade product. Furthermore, it was revealed that the 2014 DMS ROM had an increased proportion of low-density material; however this material was also had low proportion of near-density material. The low-grade stockpiles was characterised by high proportion of near density material, which necessitate the beneficiation process to operate at high density in excess of 3.8 t/m3. Maintaining a higher operating density requires more dense medium which leads to viscosity problems and impact performance. The characterisation of the FeSi medium was imperative to understand its behaviour and potential influence on beneficiation of low-grade stockpiles and mining blocks with elevated proportion of near-density material. As the proportion of near-density waste material increases in the run-of-mine (ROM), it is necessary to beneficiate the material at elevated operating medium densities. However, when cyclones are operated at high densities, the negative influence of the medium viscosity becomes more apparent and thus influences the separation efficiency. Heavy medium, ferrosilicon (FeSi) characterisation looked at identifying the effects of viscosity on the FeSi stability and whether there would be a need for a viscosity modifier. Thus, the importance of controlling the stability, viscosity, and density of the medium cannot be under-estimated and can very often override the improvements attainable through better designs of cyclones. Furthermore, the slurry mixture of the heavy medium utilised for the purpose of dense medium separation should be non-detrimental to the effectiveness of separation in the DMS Fine cyclone plant. Medium characterisation showed that removal of ultra-fines leads to unstable media as indicated by faster settling rates. This would result in medium segregation in the beneficiation cyclone thereby leading to unacceptable high density differential which will negatively impact the cut-point shift and cause high yield losses to waste. The overall control of the metallurgical processes at Sishen’s Cyclone Plant is still done on manually and thus operation still varies from person-to-person and/or from shift-to-shift. This result in some of the process data and trends not being available online as well as being captured inaccurately. Furthermore, this negatively affects the traceability and reproducibility of the production metallurgical key performance indicators (KPI’s) as well as process stability and efficiency. It has been demonstrated that real-time online measurements are crucial to maintaining processing plant stability and efficiency thereby ensuring that the final product grade and its value is not eroded. Modelling and automation of the key metallurgical parameters for the cyclone plant circuit was achieved by installation of appropriate instrumentation and interlocking to the programmable logic control (PLC). This allowed for the control of the correct medium sump level, cyclone inlet pressure, medium-to-ore ratio as well as online monitoring of density differential as “proxy” for medium rheological characteristics. The benefit of modelling and simulation allows the virtual investigation and optimisation of the processing plant efficiency as well as analysis of the impact of varying ore characteristics, throughput variations and changing operating parameters. Therefore it is imperative that all cyclone operating modules are operated at the same efficiency which can be achieved by optimized process through proper automation and monitoring, thereby improving the total plant profitability. Keywords: dense medium separation; densimetric profile; dynamic modelling; FeSi rheology; iron-ore beneficiation; process automation; process control.