Browsing by Author "Bradshaw, Dee"
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- ItemOpen AccessThe application of a machine vision system to relate to froth surface characteristics to the metallurgical performance of a PGM flotation process(2000) Sweet, Craig Gaven; Bradshaw, DeeThis dissertation describes the use of a machine vision system to explore the relationships between the structure of the flotation froth surface, flotation performance and selected operational parameters in a flotation operation aimed at the beneficiation of Platinum Group Minerals. The machine vision system employed made use of the Fast Watershed Transform to resolve the froth surface into a distribution of bubble sizes. This distribution was then used to describe changes occurring in the structure of the flotation froth surface. An initial batch flotation programme concentrated on the influences that changing the frother and depressant dosage levels had on a flotation system treating a sample of Merensky ore, which originated from Rustenburg Platinum Mine's Amandelbult Section. It was found that both depressant and frother dosage had marked influences on the metallurgical performance of the flotation system. Furthermore, it was found that changes in these operational variables resulted in changes in the structure of the flotation froth surface, which were quantified by the machine vision system. These results highlighted the potential of the machine vision system to identify when either the frother or the depressant dosages had moved towards levels that would negatively influence flotation performance. A plant-based experimental campaign was then conducted on the Amandelbult Merensky Primary Rougher Flotation Section, in which the frother and depressant levels were manipulated. In terms of metallurgical performance of the flotation system, it was found that a strong relationship existed between the grade of concentrate being recovered and the rate of mass yield from the flotation unit. Furthermore, it was found that increasing the frother dosage led to an increased rate of mass yield and a decrease in concentrate grade, while increasing the depressant led to a decreased rate of mass yield at an increase in concentrate grade. As both of these variables influence metallurgical performance, a strategy that enables the automatic identification of which reagent dosage had deviated from the desired level would clearly be of great value. A strategy based on the observation of bubble size distributions at the top and bottom of the flotation bank, and which is capable of identifying whether either the frother or the depressant dosages are changing, is suggested in this work.
- ItemOpen AccessThe effect of polysaccharides and inorganic dispersants on the surface characteristics of talc and the effect on the flotation performance of a Merensky ore(2001) Dalvie, Maqbool Ahmed; Bradshaw, Dee; Harris, PeterThis dissertation describes an investigation into the combined effect of polysaccharides and an inorganic dispersant on the surface characteristics of talc and how this relates to the flotation performance of Merensky ore. The rationale in investigating the talc changes are due to its naturally flotable nature and the downstream problems that result from its reporting to the concentrate causing difficulties disproportionate to its average concentration of less than 2% in Merensky Ore.
- ItemOpen AccessAn evaluation of sulfidisation in the flotation recovery of heavily oxidised sulfide minerals : with particular reference to oxidised Merensky ores(2007) Newell, Andrew James Haigh; Bradshaw, Dee; Harris, PeterIncludes bibiographical references (p. 165-180).
- ItemOpen AccessThe implications of froth structure and surface appearance for flotation performance(2006) Hatfield, Douglas; Bradshaw, Dee; De Jager, GerhardIn this work, the flotation step of mineral extraction has been investigated to determine the mechanisms through which input variables impact on flotation separation efficiency and, in particular, the froth zone in flotation. The novel contribution of the work is in terms of demonstrating the importance of solids in governing the froth stability and hence the froth structure. Further, it has been propsed that the two most important factors that determine the impact of the solids on the froth are the degree of particle coverage on the bubble surface and the particle hydrophobicity. The mechanism through which the solids affect the froth stability has been demonstrated through experimental observations of flotation metullurgical performance, measurement of the froth surface appearance using machine vision and froth modelling. The insight obtained through understanding of the influence of solids on the froth zone will yield improved design and operation of industrial flotation circuits.
- ItemOpen AccessThe interactive effect of depressant type and dosage with frother dosage in the flotation of a PGE ore(2005) Dhliwayo, Evelyn Chengetanai; Allison, Syd; Bradshaw, DeeThe valuable components of the platinum group element (PGE) bearing ores of the Bushveld complex in South Africa constitute between 1 % and as little as 0.1 % of the total mass. In the processing of these ores by flotation, the naturally hydrophobic talc minerals cause over stable froths. The drainage of liquid and entrained particles is reduced thus the recovery of other gangue minerals by entrainment increases and grade decreases. In the rougher float depressants are added to produce a manageable froth and improve the grade by reducing the overall amount of the naturally floating gangue in the concentrates. Depending on dosage, depressants may also affect the recovery of the valuable minerals in the ore positively by slime cleaning or negatively by depression. Depression of stabilising gangue minerals such as talc decreases the froth stability and may also affect the recovery of valuables. Frothers are added to flotation systems to create stable froths. They increase the water layer around bubbles and the carrying capacity of the froth and thus recovery by entrainment. The drainage of entrained particles from the froth may be further increased by increasing the froth depth. This study investigated the interactive effects of depressant dosage and type, frother dosage and froth depth on the recovery and grade of copper and nickel sulphides, recovery of water, floatable and entrained gangue in the flotation of a Merensky ore. Since it is known that water recovery is closely related to froth stability it was used to infer froth stability in this study. Two types of depressants carboxymethyl cellulose (CMC) and guar gums which are usually used in the flotation of PGE bearing ores were used. The frother was Dow 250. Results showed that increasing either guar or CMC dosages from 50 to 100 g/t enhanced the recovery of copper and nickel sulphides. This was attributed to the slime cleaning action of the depressants and their stabilising effects. A further increase of dosage to 300 g/t decreased the recovery of copper and nickel indicating that depression of sulphides occurs at high depressant dosages. Both the use of guar and CMC depressants reduced the recovery of floatable gangue with increasing dosage as expected. The guar depressant showed greater depression ability at 50 g/t dosage than the CMC depressant while the CMC was more effective at 100 and 300 g/t dosage. Reduction of water recovery by the CMC depressant was greater than that of the guar depressant indicating that the CMC depressant had greater destabilising effects on the froth. It is known that the CMC depressant has a strong negative charge while the guar depressant is only slightly charged. The guar depressant may have caused aggregation of particles which has less destabilising effects than the dispersed particles in the presence of the CMC depressant. The froth recoveries showed that the effects of depressant and frother dosages counteract each other and that the decrease in the recovery of copper and nickel sulphides obtained at higher depressant dosages can be reversed by increasing frother dosage. However although increased frother dosage readily reverses the depressant effects, an increase of water and recovery by entrainment reduces the grade. The effect of depressant dosage increase on the water and froth stability is small in comparison to the effect of increased frother dosage. Thus for the levels tested the benefit of improved grade obtained by depressant addition would be lost. The increase of froth depth to reduce entrainment resulted in a reduction of the recoveries of the valuable minerals but with the desired increase in grade. Smaller increments of frother dosage are required to produce effective reversal of depressant effects on the recovery of valuable minerals to achieve a good overall flotation performance.
- ItemOpen AccessInvestigating depressant behaviour in the flotation of selected Merensky ores(2009) Wiese, Jennifer Gael; Bradshaw, Dee; Franzidis, Jean-Paul; Harris, PeterThis study utilised laboratory batch flotation tests to characterise the flotation performance, with respect to sulfide and gangue minerals, of two Merensky ores with different mineralogy, in the presence of depressants; and contributes to the increased understanding of depressant behaviour in the flotation of Merensky ores. The ores were obtained from the southern section of the Merensky reef in the Bushveld Igneous Complex.
- ItemOpen AccessAn investigation into chemical factors that affect the behaviour of Gangue minerals in the flotation of PGM ores(2004) Mailula, Tshepo Desmond; Bradshaw, Dee; Harris, PeterFlotation is one of the key steps in the beneficiation of Platinum Group Elements (PGE) from the Bushveld Complex in South Africa. This process aims to optimise the recovery of valuable PGE and sulphide minerals and the rejection of unwanted gangue minerals. The major reefs are exploited in South Africa i.e. Merensky reef and UG-2 reef. Gangue minerals, pyroxene and feldspar constitute more than 80% of the Merensky reef and chrornite up to 60% of the UG-2 reef. Although these minerals are considered to be hydrophilic and thus not floatable, these gangue minerals are known to report to the concentrate in large quantities during froth flotation. This results in lower grades and increased difficulties in downstream processing. Some Platinum Group Mineral (PGM) concentrators report that 2/3 of the gangue collected on the concentrate is by true flotation and only 1/3 by entrainment [Malysiak et ai, 2001]. This also suggests that mechanisms other than entrainment are responsible for this phenomenon. The behaviour of these minerals is selected for investigation in this thesis. During flotation of PGM ores, reagents such as copper sulphate and sodium isobutyl xanthate (SIBX) are added to enhance the recovery of valuable minerals. Copper sulphate, although added as an activator for valuable minerals, as the conditions used has been shown to also activate gangue minerals, thus its activation is non-selective [Shackleton, 2003 and Wesseldijk et ai, 1999]. Wesseldijk et ai, (1999), showed that copper sulphate could activate chromite and the subsequent addition of collector resulted in high recoveries of chromite in contrast to the low recoveries obtained in the absence of copper sulphate.
- ItemOpen AccessAn investigation into the process mineralogy of the Merensky reef at Northam Platinum Limited(2008) Brough, Christopher; Bradshaw, DeeThis dissertation has investigated the links between the mineralogical characteristics of the Normal, NP2 and P2 Merensky reefs at Northam Platinum Ltd and their flotation performances. Flotation performance was measured in terms of the grade and recovery of the base metal sulphides (chalcopyrite, pentlandite, pyrrhotite and total sulphide) as well as through investigation of mass-water recoveries.
- ItemOpen AccessAn investigation into the use of froth colour as sensor for metallurgical grade in a copper system(2003) Heinrich, Glen Sean; Bradshaw, DeeIn recent years the development of Machine Vision systems has opened up new possibilities for non-intrusive process performance sensors and process control. There are currently various Machine Vision systems on notation plants worldwide (Metso at Kennecott, Frothcam at Escondida). Extensive research has been done on using froth image analysis in closed loop control (Hyotyniemi et aI, 2000; Kittel et aI, 2001; Holtham and Nguyen, 2002; Cipriano et aI, 1998) and recently plants have been using these systems to control the air or level of a flotation cell as a means of controlling mass pull using the froth velocity output. As yet no flotation plants have reported the use of froth colour in their control strategies, however it is well accepted that an experienced operator can judge the metallurgical state of a flotation cell by the appearance of the froth, using colour as a key descriptor of grade, particularly in the case of copper froths. For this reason an investigation was undertaken to evaluate whether a relationship existed between concentrate grade and the froth colour obtained using a Machine Vision system. This relationship could be used to control reagent addition or for system diagnostics. Both would be invaluable tools for the flotation industry. A Machine Vision system called SmartFroth has been developed at University of Cape Town (VCT) as a research tool to investigate the relationships between froth surface indicators and metallurgical parameters. The relationship between froth colour and % solids was also investigated as it was believed that solids loading could be reflected by froth colour. This work was aimed at evaluating the empirical relationship between froth colour and copper grade in the laboratory and then investigating whether a similar relationship existed on plant. Various colour spaces were examined to find one appropriate for the copper flotation froths in order to allow for accurate colour analysis. It also evaluated the use of calibration objects in the colour analysis of flotation froths. This work also evaluated relating froth colour to % solids on plant. Two batch flotation campaigns were done using different ores as well as a preliminary plant trial.
- ItemOpen AccessInvestigation of the surface properties of gangue minerals in PGM bearing ores(2005) Martinovic, Jasmina; Bradshaw, Dee; Harris, Peter; Laskowski, JanuszThe recovery of Platinum Group Minerals (PGM) and associated sulphides by froth flotation from the Bushveld Igneous Complex is complicated by the presence of naturally floatable gangue minerals such as talc. Although talc is present in small quantities it has a disproportionate effect on concentrate grade by enhancing froth stability and increasing the entrainment of other gangue minerals. However, there is an indication that some of the other gangue minerals, which are normally considered to be hydrophilic, such as chromite and pyroxene, report to the concentrate as floatable particles. Polysaccharide depressants, such as carboxymethyl cellulose (CMC) and modified guar gums are used to reduce the floatability of naturally floatable gangue and may also be able to reduce the floatability of activated gangue. This study examines the copper activation of a range of minerals found in the Bushveld Complex (namely pyroxene, feldspar, chromite and talc as well as the classical oxide, quartz) using zeta potential measurements, adsorption and microflotation tests. The effect on floatability is evaluated after activation and collector adsorption in the presence of a modified guar and a CMC depressant. Although quartz is not a major gangue component in PGM ores it was selected since it is a strongly negatively-charged mineral in the alkaline range and therefore likely to respond to copper activation. Steenberg and Harris, (1984) found that polymers such as guar and CMC did not appear to adsorb to a significant level on quartz.
- ItemOpen AccessMineralogical and ion-exchange leaching study of a Rare Earth Element (REE) bearing ion-adsorption clay deposit(2018) Burcher-Jones, Cody Owen; Petersen, Jochen; Rampai,Tokoloho; Becker, Megan; Bradshaw, DeeRare earth elements (REEs), La to Lu including Y, are vital elements in manufacture of catalysts and metallurgical industries, and play a critical role in meeting future energy demands, such as through their use in permanent magnets in wind turbines. China has dominated more than 90 % of the REE market, with heavy REE (HREE) clay deposits in South China accounting for 35 % of their total REE output. This has prompted the evaluation of ion-adsorption clay (IAC) deposits in tropical regions outside China, namely Madagascar. Clay minerals such as kaolinite are part of the phyllosilicate class, containing structures of shared octahedral aluminium and tetrahedral silicon sheets. Isomorphous substitutions within the lattice leads to a charge imbalance, which accounts for negative charge on kaolinite, thus giving the ability to attract REE cations from aqueous solution to the surface of the clay particle. IAC deposits are formed from the tropical weathering of granite with REE enrichment from accessory minerals. IAC clay samples of two regolith profiles, the pedolith (A1) and saprock (A2, B and F) from northern Madagascar were collected and subjected to a suite of characterisation techniques to investigate the properties of the clay mineral. This included particle size distribution (PSD), X-ray fluorescence (XRF), X-ray diffraction (XRD), quantitative evaluation of minerals by scanning electron microscopy (QEMSCAN), inductively coupled plasma mass spectrometry (ICP-MS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The geochemical leaching characteristics of the clay mineral were investigated using a sequential leaching program, targeting ion-exchangeable REE on kaolinite, halloysite, REEorganic matter and mineral phase. Ammonium sulphate leach experiments were conducted, varying the ionic strength to determine optimum leaching concentrations. Seawater is easily available at the coastal mine, therefore simulated seawater (NaCl) experiments were conducted with the addition of ammonium sulphate to improve the REE recovery. Compound leaching agents were investigated including varying magnesium / ammonium ratios in a sulphate system as well as ammonium in a varying nitrate / sulphate ratio system. The magnesium ion was investigated to correct the Mg deficiency in soils after leaching and the nitrate ion was investigated due to its high ionic permeability in kaolinite. Ion-adsorption clay leaching includes the leaching of impurities such as Al, Fe, Mg, K, Na, Ca and Mn. Ammoniumsulphate experiments with increasing amounts of ammonium acetate were conducted. Ammonium acetate acts a buffering agent to inhibit the leaching of the main impurity Al. The texture of sample A1 (5 to 6.5 m) was homogenous, with the QEMSCAN results showing Fe minerals distributed through the kaolinite, giving it a red appearance. The saprock samples A2, B and F have a heterogeneous texture due to the preservation of the primary texture. The QEMSCAN results show that this texture is composed of pure white kaolin, kaolin with red staining due to Fe minerals, tawny staining due to Al minerals and black phases containing Mn minerals. These Mn minerals show Ce deposited as the mineral cerianite, unavailable for ion-exchange. The pedolith sample was light REE (LREE) enriched but depleted in total REE (TREE = 1 503 ppm) compared with the saprock samples (TREE = 7 006 ppm on average). The saprock samples show LREE and HREE enrichment with samples A2 and F having La / Gd ratio of 17.4 and Gd / Lu ratios of 1.2. The more crystalline samples A2 and F (Hinckley index 0.40 and 0.44 respectively) are more REE enriched than the more weathered sample B (Hinckley index 0.32). The geochemical characterisation of sample A1 showed decreasing REE recovery from LREE to HREE from kaolinite whereas sample A2 showed consistent recovery across the REEs from kaolinite with both showing little Ce recovery. The best TREE recovery for samples A1 and A2 in the chloride system achieved with was NH4 + (44.3 % and 83.1 % respectively) followed by Na+ (39.5 % and 72.2 %) and Mg2+ (28.9 % and 72.1 % respectively). For sample A1 the recovery from the kaolinite fraction was 37.7 %, halloysite 5.1 %, organic 1.6 % and mineral 55.7 %. The proportion of ion-exchangeable REE is increased in sample A2 showing a recovery from the kaolinite fraction of 66.9 %, halloysite 12.7 %, organic 3.5 % and mineral 16.9 %. The results from increasing the ionic strength of ammonium sulphate shows that TREE leachant concentration increases as the concentration increases but decreases above 0.25 M. This indicates that the ammonium sulphate concentration saturates at 0.25 M and any further lixiviant increase eliminates access to the kaolinite surface. The simulated seawater experiments indicate that some addition of ammonium sulphate is beneficial as the addition of 0.05 M ammonium sulphate almost doubled the TREE leachant concentration. However excess addition of ammonium sulphate above 0.05 M had adverse effects on the leachant concentration of the LREEs. It was concluded from the compound leaching experiments that the Mg2+ ion can be used to supplement ammonium leaching with the greatest leachant concentration using a Mg2+:NH4 + ratio of 1:2 (equal charge). This ratio would produce a high REE leachant concentration while keeping Mg available for plants (flora). Compound leaching with the nitrate ion shows that the greatest REE leachant concentration was with a NO3 - :SO4 2- ratio of 2:1 (equal charge) due to increased nitrate ion permeability. The results from the addition of ammonium acetate as a buffer showed that the buffer inhibited the leaching of Al in both samples A1 and F, with the greatest inhibition at 0.05 M. The characterisation experiments illustrate the complexity of the in-situ clay deposit and further work should use this information to construct leaching models that take into account the heterogeneity of saprock samples. The leaching experiments show that compound leaching can improve REE recovery and further work should incorporate multiple lixiviants in in-situ leaching models.
- ItemRestrictedThe mineralogy and crystallography of pyrrhotite from selected nickel and PGE ore deposits.(Society of Economic Geologists, 2010) Becker, Megan; De Villiers, Johan; Bradshaw, DeeThe nonstoichiometric sulfide pyrrhotite (Fe(1–x)S) common to many ore deposits occurs in a variety of crystallographic forms and compositions and occasionally is also intergrown with stoichiometric troilite (FeS). In this study, the mineralogy of pyrrhotite derived from several different nickel and PGE ore deposits in South Africa, Botswana, and Canada was examined in detail in terms of pyrrhotite association, crystallography, and mineral chemistry. Pyrrhotite samples were subdivided into two-phase 6C Fe11S12 pyrrhotite intergrown with 2C FeS troilite, two-phase 4C Fe7S8 pyrrhotite intergrown with 5C Fe9S10 pyrrhotite, single-phase 5C Fe9S10 pyrrhotite and single-phase 4C Fe7S8 pyrrhotite. None of the pyrrhotite samples analyzed were classified as two-phase 4C pyrrhotite intergrown with pyrite due to the scarcity of pyrite in these samples. Average solid solution Ni contents of NC pyrrhotite (0.75 ± 0.10 wt % Ni) in this study were found to be greater than in 4C pyrrhotite (0.43 ± 0.10 wt % Ni), but only when the pyrrhotite occurred as two-phase 4C pyrrhotite intergrown with NC pyrrhotite. For single-phase pyrrhotite occurrences in this study, 4C pyrrhotite was more Ni rich (up to 2 wt % Ni) than NC pyrrhotite (0.75 ± 0.19 wt % Ni). The average atomic metal/S ratios obtained for 4C Fe7S8 pyrrhotite was 0.869 ± 0.013 (n = 699), for 5C Fe9S10 pyrrhotite was 0.895 ± 0.013 (n = 316) and for 6C Fe11S12 pyrrhotite was 0.918 ± 0.017 (n = 101). The histogram comparing metal/S ratios of all the pyrrhotite samples analyzed showed a continuum of metal/S ratios, although with frequency maxima corresponding to the ideal compositions of 4C, 5C, and 6C pyrrhotite. The presence of the continuum however, was interpreted to be representative of nonstoichiometry in the pyrrhotite structure.
- ItemOpen AccessMultivariable control of a rougher flotation cell(2002) Van Schalkwyk, Theo; Braae, Martin; Bradshaw, DeeThis project focussed on the investigation, development and evaluation of a closed loop control system on a rougher flotation cell that could improve PGM flotation performance. A PGM rougher flotation cell equipped with Online Stream Analysis (OSA) and machine vision system (SmartFroth) was used during the investigation. Online measurements included bubble velocity, average bubble area, bubble colour; Pt, Ni and Cu concentrate grade and concentrate flow rate and density. Air addition and pulp level was used as the manipulated variables.
- ItemOpen AccessOn the selective flotation of pentlandite from pyrrhotite in Sheba's Ridge ores(2009) Mbonambi, Mduduzi Justice; Franzidis, J. P.; Bradshaw, Dee; BeckerMetal sulphides are the raw material for most of the world's supplies of non-ferrous metals and can be considered one of the most important group of ore minerals. In the context of South Africa, the Bushveld Igneous Complex (BIC) sulphides play a very important role in that they are largely associated with the valuable platinum group elements (PGEs) and platinum group minerals (PGMs). Typically, the base metal sulphide (BMS) content in the BIC is comprised of pentlandite, pyrrhotite and chalcopyrite. Sheba's Ridge, one of the ore deposits found in the BIC, is exploited for its PGEs and PGMs. For typical PGE processing operations like the Merensky reef, the valuable PGEs and PGMs are associated with the base metal sulphides pentlandite, pyrrhotite and chalcopyrite. Unusually, in the case of the Sheba's Ridge ore, not all the sulphides contain associated PGEs and PGMs, and pyrrhotite has been observed to show little or no association. Therefore, this study was carried out to develop a methodology for the selective flotation of pentlandite from pyrrhotite using the polysaccharide depressants that are already in use in the flotation of BIC ores to control the naturally floating gangue minerals such as talc. Microflotation tests were conducted on a high grade Nkomati massive sulphide ore sample as a probe ore, to investigate the flotation response of pentlandite and pyrrhotite to four different chain length xanthate collectors (SEX, SNPX, SIBX and PAX) and to different types of polysaccharide depressants (guar, CMC and starch). The effect of oxygen addition and pH modification were also studied. Laboratory batch flotation tests were then carried out using the Sheba's Ridge ore, to evaluate the optimum reagent suite and flotation conditions determined in the microflotation tests. The results showed that using the different chain length xanthates or polysaccharide depressants on their own did not produce any pentlandite selectivity over pyrrhotite, but, when these reagents were used in conjunction with one another, some pentlandite selectivity was obtained. The best combination was found to be an intermediate chain length xanthate (SNPX) with guar depressant, where a balance between collector hydrophobicity and selectivity was obtained. Adjustment of the pH to 10, using lime instead of NaOH, together with artificial pre-oxidation showed further improvement in the selective flotation of pentlandite. This was attributed to the faster oxidation rate of pyrrhotite at these conditions, which led to selective depression of pyrrhotite while pentlandite floatability was maintained. The optimum reagent regime for pentlandite/pyrrhotite selectivity, as determined from the microflotation testwork using the Nkomati massive sulphide probe ore, was used as the basis of the batch flotation tests. The batch flotation tests represented a scale up of the microflotation tests, in terms of sample size (1 kg vs. 2 g) and were a closer representation of real operations, as silicate gangue minerals (e.g. talc) were present, as well as a froth phase. The variables that were found to be key in the microflotation testwork in terms of improving metallurgical performance for pentlandite selectivity were pH, collector and depressant type and dosage. These were the same variables identified as key in the batch flotation tests. However, the differences between these parameters were observed to be more subtle in the case of batch flotation tests compared to what was observed in the microflotation testwork. Nevertheless, it can be concluded that results from microflotation test work can used as a good basis to study of the interactions of different minerals in ores in a batch flotation system. Translating the results from microflotation testwork to batch flotation testwork was not so straight forward, and further work still needs to be done to prove that this can be done successfully. It was also found that there needs to be a synergistic interpretation of the interactions present in the reagent – mineral system. Finally, the study showed that the reagents used in flotation cannot be evaluated independently but rather a holistic approach needs to be employed.
- ItemOpen AccessThe role of collectors in the flotation of partially oxidised copper ores(2004) Hangone, Gregory; Bradshaw, DeeThe effects of xanthates, dithiophosphates, dithiocarbamates and mixtures of these collectors on the froth flotation performance of partially oxidised and oxidised copper sulphide ores were investigated in this study. More specifically, the role of the functional groups of the collectors, their dosages and the effect of collector mixtures and their dosages were investigated. Batch flotation tests were used to assess the performance in terms of mass-water recovery, sulphur grade-recovery, copper grade-recovery and acid soluble copper grade-recovery relationships and the Klimpel rate constant for copper recovery. Flotation characteristics of bornite rich Carolusberg copper sulphide ore from Okiep Copper Company (1.8% copper) and bornite and chalcopyrite rich ore from Palaborwa Mining Company (0.58% copper) were compared.
- ItemOpen AccessTexture and bubble size measurements for modelling concentrate grade in flotation froth systems(2007) Forbes, Gordon; Bradshaw, Dee; De Jager, Gerhard; Nicolls, FredNumerous, machine vision systems for froth flotation have been developed over the last ten years; however, there are many aspects of the systems, that still require further development before they become one of the standard instruments present on industrial flotation operations. This thesis aims to address these problems by developing improved measurement techniques and showing how these measurements can be used to model the concentrate grad e of the flotation cell being monitored in a manner which is, directly usable by plant personnel. This thesis, presents an improvement to the watershed algorithm for the measurement of bubble sixe distribution in flotation froths. Unlike the standard watershed algorithm, it is able to measure accurate bubble size distributions when both large and tiny bubbles are present in a flotation froth image. Flotation froths with “dynamic bubble size distribution s” are introduced and methods of reducing the high dimensional bubble size distribution data associated with them are discussed. A method of using characteristic histograms of frequently occurring bubble size distributions is introduced and shown to be an appropriate method to use. A number of standard texture measures are best suited to the classification of flotation froth images. Results show that the Fourier ring and texture spectrum based features, perform well whilst having a relatively small computational cost for classifying new images. Video footage from selected industrial operations has been used for the development of improved algorithms for the measurement of froth surface descriptors. Analyses of the relationship, between froth velocity, bubble size, froth class and concentrate grade are made. The results show that it possible to use a unified approach to model the concentrate grade, irrespective of the site on which the measurements are made. Results from three industrial case studies show that bubble size and texture measures can be used to identify froth classes. Furthermore the combination of froth classes and froth velocity information is shown to consistently account for the most variation in the data when the concentrate grade is modelled using a linear combination of these two measurements.
- ItemOpen AccessThe influence of polymeric charge and structure, molecular weight and ionic conditions on depressant ability to reduce the natural floatability of talc(2002) Shortridge, Paul Graham; Harris, Peter; Bradshaw, DeeTalc is a naturally floatable gangue material common in South African platinum bearing (PGM) ore bodies. Long chain polysaccharide depressants are effective in depressing talc flotation and improving the grade of the concentrates of those ores with talc as a gangue constituent. This thesis describes an investigation into the surface interactions of two types of long chain polysaccharide depressants (carboxymethylcellulose and guar gum) with pure talc and with Merensky PGM ore (which is known to contain talc as a gangue constituent). Specifically, the objectives of this thesis were as follows: 1. To characterize the differences in the depressants selected. 2. To examine the effects that polymeric structure and molecular weight of the depressant have on the hydrophobicity of talc. 3. To extrapolate the findings from highly controlled laboratory conditions to batch flotation tests with Merensky PGM ore. During the course of the experiments, it became clear that ionic conditions were an important factor in this system and they were therefore incorporated into the work done. Overall, the molecular weight of the depressants was not seen to be an important factor in their ability to depress talc. The molecular structure did appear to impact depressant efficiency, but only under conditions oflow ionic strength in the microflotation system. III Ionic conditions were found to be a pivotal factor in the performance of the CMC depressants in reducing the flotation of talc. It was also found that the ions adsorbed onto the talc surface in the absence of depressants - leading to a reduction in talc floatability. Divalent cations were more effective than monovalent cations in enhancing the effectiveness of the CMC depressants - suggesting stronger adsorption under these conditions. Guar depressants appeared to be unaffected by varying ionic conditions. The batch flotation tests, and the microflotation tests at the higher ionic strengths, showed that similar depressing ability was obtained for the CMCs and the guars. However, the batch floats indicated that increasing dosage led to improved depressant performance while the microflotation tests indicated that a maximum level of depression was achieved at fairly low dosages
- ItemOpen AccessTowards the development of an integrated modelling framework underpinned by mineralogy(2018) Ntlhabane, Sithembiso; Becker, Megan; Charikinya, Edson; Schouwstra, Robert; Bradshaw, DeeThe mining industry is under increased pressure from many stakeholders to be forward thinking in its approach to sustainability. This requires a holistic approach to address techno-economic, environment and social issues, rather than just focusing on individual aspects of sustainability practice. The ability to do so requires an integrated modelling framework, underpinned by mineralogy so that the effect of ore variability on one or more of these factors can be simultaneously evaluated and optimised. This study focuses on the steps towards the development of this proposed framework using a case study of a polymetallic sulfide ore flotation circuit. The initial focus in the framework development is on integrating the techno-economic and the environmental aspects of sustainability. Thereafter the framework is used to consider a variety of scenarios evaluating the balance between techno-economic value and environmental burden. A sampling exercise was conducted around the intermediate and terminal streams of the flotation circuit processing polymetallic sulfide ore. All samples were characterised using both chemical assays and mineralogy (QEMSCAN). This formed the input data for the development of an ore specific element to mineral conversion (EMC) recipe that converts chemical assays to mineral grades. The EMC technique has the advantage of being fast, inexpensive and can be used on a routine basis. The recipe for this specific polymetallic sulfide ore was designed to calculate nine minerals in four different rounds, using least square method in the first two rounds and non-negative least square in the last two rounds. Sulfide minerals (chalcopyrite, galena and sphalerite) were calculated in the first round, barite was estimated in the second round, silicate minerals (garnet, biotite and quartz) were determined in the third round and pyrrhotite and magnetite were calculated on the last round. Data validation for EMC was performed by comparing calculated mineral grades against the measured mineral grades obtained from QEMSCAN. The accuracy was determined by evaluating the R2 value, the results were comparable as the R2 value was above 0.95 for all minerals. Mineral grades obtained from EMC of the assayed streams were used to carry out a mineral mass balanced of the flotation circuit. From the results, mineral grade and recovery were calculated and were used to evaluate metallurgical performance across the flotation circuit. The chalcopyrite (copper) concentrate was diluted with pyrrhotite (26 wt. %). The sphalerite concentrate (zinc) had the highest grade (94 wt. %) followed by galena (lead) with a concentrate grade of 85 wt. %. Sphalerite and galena achieved high recoveries over 90 %. From analysis of the flotation performance of the circuit, the results demonstrate an opportunity to improve the copper (chalcopyrite) concentrate quality. The diluted concentrate is likely to attract penalties during downstream processing (e.g. smelter) due to the presence of impurities (pyrrhotite). The concentrate can be upgraded by rejecting pyrrhotite in the first stage of the copper circuit. In addition, the mass balanced mineralogy results were used to calculate a theoretical potential of the final tailings to generate acid rock drainage (ARD). The ARD method used is based on the relative abundance of acid generating sulfide minerals (chalcopyrite, galena, sphalerite and pyrrhotite) and other minerals with the theoretical potential to neutralise the acid generated. The net mineralogically calculated acid producing potential was estimated as 46.4 kg H₂SO₄/ton. To further demonstrate the usefulness of the framework, a mineral splitter function was used to model the flotation circuit and test different hypothetical scenarios. Two hypothetical scenarios were investigated relative to the current operating condition of the flotation circuit. A sensitivity analysis on both scenarios was conducted to assess the effect of feed ore variability. The pyrrhotite feed grade was varied between 10 and 100 % of the base case and all sulfide mineral recoveries were kept constant. Scenario I considered improving Cu (chalcopyrite) concentrate grade in the Cu circuit by rejecting pyrrhotite. A Monte Carlo simulation was carried out by varying the pyrrhotite recovery to concentrate from a minimum of 2 % to a maximum of 18 % in the mineral splitter function. The results showed an increase in pyrrhotite grade in the final zinc tailings and an increase in the mineralogically calculated ARD potential (up to 53.9 kg H₂SO₄/t for tailings). Scenario II considered the installation of a magnetic separator to concentrate pyrrhotite in the final tailings and achieved a net acid producing potential of 15.2 kg H₂SO₄/t, which was lower than scenario I. The sensitivity analysis of scenario I showed a correlation between increased pyrrhotite feed grade with mineralogically calculated ARD potential (89.6 kg H₂SO₄/t). The results from sensitivity analysis of scenario II were lower were than scenario I (28.6 kg H₂SO₄/t). This shows that installation of a magnetic separator has the potential to mitigate ARD formation and produce a potential economic magnetite concentrate by-product. In conclusion this study has shown how mineralogy can be integral in developing an integrated modelling framework for simultaneously assessing techno-economic and environmental performance. The developed framework demonstrated the possibility of simultaneously balancing the trade-off, improving grade and mitigating the risk of ARD formation. It is a conceptual starting point for a new approach to traditional process mineralogy studies to start implementing sustainable development aspects on the operational level.
- ItemOpen AccessThe use of machine vision to describe and evaluate froth phase behaviour and performance in mineral flotation systems(2010) Morar, Sameer Harish; Bradshaw, Dee; Harris, MartinWithin froth flotation, it is widely acknowledged that froth stability affects flotation performance. As a result, it is expected that through the effective management of froth stability, it would be possible to both control and optimise a flotation cell and bank. However, for this to be possible, the relationships between the operating conditions, froth stability behaviour and flotation performance attributes need to be well understood. In addition, froth stability would need to be measured using a robust method suitable for on-line operation. Within the literature, no robust methods are available to measure either the concentration of solids on the froth surface, or froth stability in a manner suitable for on-line operation. Thus, two novel non-intrusive machine vision measurements have been developed in this work to quantify these attributes.