Browsing by Author "Becker, Megan"
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- ItemOpen AccessA Process Mineralogical Study on the effect of Alteration on the Flotation of Great Dyke Platinum Group Element (PGE) Ores(2018) Dzingai, Theophilus C; Becker, Megan; Tadie, Margreth; McFadzean, BelindaOres from the same deposit may exhibit extensive variability in their mineralogy and texture. The ability to quantify this variability linked to metallurgical performance is one of the primary goals of process mineralogy and geometallurgy. Ultimately this information can be used to inform decisions around all core activities of mining and processing. This study focusses on identifying the key mineralogical differences between three Great Dyke platinum group element (PGE) ores in Zimbabwe. These ores are known to be characterized by extensive oxidation and alteration resulting in numerous metallurgical challenges in recovering the PGE. The behaviour of three different ores sampled along the strike of the Great Dyke is compared, focusing on mineralogical composition, rheological characteristics and batch flotation performance. The contribution of the differences in mineralogy (bulk mineralogy, base metal sulfide (BMS) liberation and association, and naturally floating gangue) to processing challenges and potential opportunities to manage these was considered. It was noted that slight differences in mineralogy, particularly BMS liberation and association, yielded notable differences in copper, nickel, platinum and palladium recoveries. The most oxidized ore was found to have lower recoveries due to the oxidation of the BMS, though a deeper understanding of the oxidation and flotation behaviour of PGEs (and platinum group minerals - PGMs) is still necessary. Through the mineralogical analysis of the batch flotation concentrates it was observed that more finely disseminated and yet locked (unliberated) talc resulted in higher amounts of naturally floating gangue (NFG). The effect of 3 polymeric carboxymethyl cellulose (CMC) depressants, differing in degree of substitution, was also evaluated in terms of their ability to depress the naturally floating gangue and mitigate any rheological complexities that may be associated with these ores, through the electrostatic repulsion of the negatively charged carboxylate groups. There was no significant advantage of one depressant over the others in the batch flotation tests or in the rheology tests. The more oxidized ore was found to contain relatively low amounts of phyllosilicate minerals and, therefore, no rheological problem was present that would have required a chemical solution. There were no noticeable differences in the rheology of the slurries of the 3 ores. This was likely to be due to the dampening or buffering effect of the high proportion of minerals that do not contribute to rheological complexity. Changing of depressant type also had no effect in this case possibly due to the same reasons. In addition to this, the region after which the rheological complexity of all 3 ore types begins to increase exponentially is from 30-35 vol.% solids concentration (60-65 wt.% for an ore with a specific gravity of 3.3). It is therefore advisable for Great Dyke operations not to exceed these solids concentrations as this would exacerbate the processing challenges associated with rheological complexity. The use of such solids concentrations during flotation is however unlikely though this may be the case in other parts of the processing circuit, e.g. comminution, and should thus be noted. The decoupling of the terms referring to alteration (that is oxidation and hydrolysis/hydration) is also presented in this study together with the effects of these different types of alteration on the processing of PGE ores. Oxidation affects the valuable minerals and thus flotation recoveries whilst hydrolysis/hydration acts on the gangue minerals and therefore mainly affects concentrate grade. The more oxidized ore sample in this study had undergone the oxidation type of alteration, rather than hydrolysis/hydration and the processing challenge associated with it lies not in the gangue but with the valuable minerals. Finally, it was shown that investigating an ore’s characteristics solely on mineralogy may not necessarily give a full prediction of the ore’s response but the linking of the mineralogical characterization with metallurgical test work gives a more holistic view.
- ItemOpen AccessAn investigation into the complementary capabilities of X-ray computed tomography and hyperspectral imaging of drill core in geometallurgy(2022) Mashaba, Dineo; Becker, MeganThe mining industry is faced with the challenge of mining and processing low grade, heterogeneous, and complex ores, a phenomenon known as ore variability. These ores need to be managed at an early operational stage, ideally during drill core exploration, to avoid risks during the project phase (such as project delays and failure) and operational phases (such as plant instabilities), ultimately affecting the cash flow. The discipline of geometallurgy has arisen to manage the risks associated with ore variability by acquiring upfront knowledge of the mineral assemblage and texture before mining and processing. As we head towards the fourth industrial revolution (4IR), machine learning, intensive and automated data derived from drill cores are becoming more common. In this case, using non-destructive, rapid, and inexpensive automated scanning techniques such as 2D hyperspectral imaging (HSI) and 3D Xray computed tomography (XCT) have the potential to be incorporated into the machine learning dataset. Hyperspectral imaging is a critical component of continuous drill core scanning in geometallurgy for identifying problematic minerals in downstream mineral processing, such as the phyllosilicates (e.g., kaolinite, serpentine and talc). However, it only provides 2D imaging of the core, and its mineral identification is limited to minerals that show a definitive spectral response. On the other hand, XCT provides 3D imaging of drill cores, but is more routinely used in research applications and does not independently give the mineral assemblage. Mineral identification and discrimination for XCT is limited and requires prior mineralogical knowledge and sufficient mineral density and attenuation coefficient variation greater than 6%. No systematic study to date appears to have explored how the results from these two techniques can be integrated using a local South African magmatic nickel-copper-platinum group element (Ni-Cu-PGE) ore case study. This opened an opportunity to couple the two techniques to address and emphasize the image scanning techniques for drill core in geometallurgy and to provide further knowledge on the practicality of the HSI and XCT in drill core from image acquisition to processing. Ultimately, the aim is to investigate how well the techniques complement each other for mineral and texture identifications and, if combined, will produce additional mineralogical and textural information. The objective of this study was achieved by moving HSI cores to smaller samples than standard practice to produce 25 mm diameter mini cores instead of standard cores (e.g., 50 mm in diameter). For accurate mineral assemblage and textural characterisation of the drill cores, manual core logging, quantitative evaluation of minerals by scanning electron microscopy (QEMSCAN) and quantitative X-ray diffraction (QXRD) were used as supporting techniques. The results showed HSI scanning on the magmatic Ni-Cu-PGE drill core to be challenging because of pervasive mineral alteration and the nature of the rock types (mafic and ultra-mafic rocks) - providing limited information on the mineral assemblage and texture due to low scanning resolution and pervasive alteration (serpentinisation and chloritization) in the rocks. The limited mineral identification includes mixed-phases (such as serpentine-olivine in visible-shortwave infrared and plagioclase-chlorite in the longwave infrared) and unclassified minerals in the core. The resultant mineral assemblage was comparable to QEMSCAN and QXRD in terms of minerals present with generally similar abundances. However, useful information on the alteration mineralogy can still be extracted, such as the presence of serpentine, chlorite and talc and their association with other silicate minerals. Other parameters such as mineral grades and grain sizes were quantified on MATLAB using specially developed scripts. The interconnected grains could not be separated due to invisible boundaries on the HSI maps. Therefore, only a small number of grains were generated with larger grain size values, likely underestimating the real grain numbers. XCT provided information on valuable high-density minerals (including possible platinum-group minerals (PGMs)) and mineral texture in the cores. Due to extensive alteration in the rocks, discrimination between grey values was, however, challenging. Grey level segmentation into the different mineral groups was also noted to be dependent on the rock type. For example, plagioclase and orthopyroxene were more easily discriminated in the less altered rocks (feldspathic pyroxenite and anorthosite) than the more altered rocks (altered harzburgite and pegmatoidal pyroxenite). The high scanning resolution allowed for the extraction of mineral texture, such as mineral association and grain size distribution (GSD). The 3D XCT derived GSD was slightly coarser than the 2D QEMSCAN derived GSD. The differences in GSD are attributed to a combination of both stereological and sampling effects. However, sufficient information on ore variability can be obtained when using the pertinent scanning parameters and careful segmentation processes. These two techniques provide variable information on the mineral assemblage and texture, such as the identification of silicate minerals (particularly alteration minerals) in HSI and high-density minerals in XCT and good textural information on XCT than HSI. With the information provided, possible image overlapping scenarios of the two techniques were identified: (1) using XCT for high-density minerals, and HSI for silicate identification, (2) using XCT data with good mineral and texture discrimination (silicate associated with sulphides) to map unclassified areas in HSI, (3) is the opposite of the second scenario. Ultimately, the two scanning techniques will likely offer complementary information, although the application of this combined technique for routine work will be limited in practicality. Additionally, more work needs to be carried out with revised scanning and processing to improve the sustainability of the techniques in geometallurgy.
- ItemOpen AccessApplication of HPGR and X-Ray CT to investigate the potential of Witwatersrand gold ore for heap leaching : a process mineralogy approach(2014) Nwaila, Glen; Becker, Megan; Petersen, JochenAuriferous conglomerates of the Archaean Witwatersrand Basin in South Africa host one of the largest known gold resources and rate as the world’s most outstanding example of a fossil megaplacer deposit. For the past 40 years, Witwatersrand gold production in South Africa has been progressively declining due to problems related to high energy costs, decreasing grade, accessibility to greater depths, health and safety issues, labour union unrest and economic uncertainties: thus the overall viability of current gold production is questionable. Ultimately, the future of Witwatersrand gold mining relies on devising smarter strategies across the entire industry, but in particular critical areas such as comminution and extraction. With the continuous increase in mining depth, dominance of low-grade gold ores and strict safety regulations, metallurgical processing options have become limited. Heap leaching is a well-established technology which continues to grow in use and provides several benefits to solve some of these problems. High pressure grinding rolls (HPGR) is another technology with significant potential, especially for its application in coarse particle heap leaching due to its ability to induce micro-cracks as well as its high grinding efficiency and low energy requirements. This study explores the use of these two technologies in a process mineralogical framework using novel 3D X-ray computed tomography mineralogical analysis in order to assess a potential of the Witwatersrand gold ore for heap leaching.
- ItemOpen AccessApplication of mineralogy in the interpretation of laboratory scale acid rock drainage (ARD) prediction tests : a gold case study(2014) Dyantyi, Noluntu; Becker, Megan; Broadhurst, Jennifer LeeThe mining and beneficiation of gold generates large tonnages of waste, with up to 99% of mined gold ore discharged as waste. The waste generated contains unoxidized sulfides that when exposed to air and water react to form acid, which results in acid rock drainage (ARD). ARD is usually associated with low pH, high sulfate content and elevated concentrations of toxic elements. The mobility of ARD affects our scarce water resources, land and aquatic species. Methods applied to treat ARD do not provide a walk-away solution and they are either expensive or difficult to maintain. The best solution to completely eradicate ARD is to prevent it from the source. However, the effectiveness of ARD prevention depends on the accuracy of predicting future drainage quality. This can be done by using ARD prediction tests, which are generally classified as either static (acid base accounting, ABA, net acid generation, NAG) or kinetic (column leach, humidity cell, biokinetic test). There is no single test capable enough to accurately predict acid generating potential. It is therefore usual practise to conduct more than one test and cross-check results to ensure that the appropriate conclusions are made. In doing so, the reliability of the tests is improved but in some cases the different test results do not correlate. Mineralogy is an analytical technique that can be used to understand the nature of the errors and to better understand the leaching behaviour of minerals in the different tests. This study uses mineralogy to analyse both static and biokinetic test results of a Witwatersrand gold sample in order to improve the understanding of behaviour of mine wastes under different ARD prediction test conditions. A run-of-mine gold sample from the Witwatersrand region in South Africa was used as a case study to explore the mineral leaching behaviour for different ARD prediction tests.
- ItemOpen AccessAssessing the Influence of mineralogy and texture on the ore breakage characteristics of drill core and crushed ore using the JKRBT(2020) Hill, Herbert Hill; Becker, Megan; Mainza, AubreyTextural variability is a key component in addressing process challenges resulting from variability in the ore being mined. Textural variability arises from differences in the types of mineral grains present, their relative abundance and the type of interactions they have with one another. Increased textural variability is the largest contributor to mineral processing challenges in terms of mill throughput and flotation concentrate grades. Processing of ores with high textural variability often results in reduced throughput and the recovery of lower grade product, if low-grade material is not eliminated prior to arriving at the concentrator. Geometallurgy provides a powerful tool to manage ore variability better by using geological and metallurgical information during plant design and operation. The geometallurgical approach contributes towards minimising and controlling operational and technical risk of ore variability. Ore breakage characterisation is a pivotal part of geometallurgy which aims to quantify the relationship between the energy supplied for breakage and the size of the resultant progeny. The Julius Kruttschnitt Rotary Breakage Tester® (JKRBT) is an ore breakage characterisation device designed as a geometallurgical tool which can use both crushed ore and drill core samples. Drill core is especially important as it the material used for geometallurgical testing during exploration and resource definition. The JKRBT is more accurate and the test work is less time consuming than its predecessors. However, sample availability is a major concern when performing metallurgical testing as numerous tests need to be performed to get a complete view of the metallurgical response of the given ore type. This means that very little of the sample is available for ore breakage characterisation. The aim of this work is to understand the relationship between mineral texture and the ore breakage characteristics of several samples for both drill core and crushed ore which are the two sample types used at exploration and operational levels. The work is aimed at addressing the problem of sample availability in geometallurgical testing by developing an ore breakage characterisation test protocol that uses minimal sample to extract relative hardness indices. To assess the influence of mineral texture on the ore breakage characteristics, five different ore types were used. The ore was prepared by coring different size drill core and crushing using a jaw crusher. The samples were subjected to controlled single impact breakage tests using the JKRBT. A standard test consisted of 3 energy levels (low, medium and high) tested on 3-4 particle size fractions (small, medium, large and very large). The least particle protocol was developed using an ore which was considered to be fine-grained and homogenous. In developing the protocol, all the steps of the standard procedure were followed except the number of particles per test was progressively reduced from 30 particles to a threshold of 5 particles. From ore breakage characterization tests performed, it was observed that ore S was the most resistant to breakage while ore P was the least resistant to breakage. Ore A was found to be more competent than ore B and ore C but less competent that ore P. The differences in the ore breakage characteristics were attributed to the grain size distribution of the dominant constituent minerals for each sample. The findings were attributed to an increase in the surface area available for contact due to the decrease in grain size which results in less stress per unit area and thus more resistance to breakage. The hardness of an ore can be considered to be a function of the mineral hardness and its relative abundance. Using the relative mineral abundance and Mohs hardness scale, it was concluded that the more abundant the harder minerals in an ore, the more resistant to breakage the ore is. Drill core particles consistently produced a coarser progeny than crushed particles at the same conditions. The observed trend was attributed to differences in the particle shape between the crushed particles (angular) and drill core particles (cylindrical). Angular particles have a larger surface area exposed for energy absorption and therefore break more easily than drill cores. Chapter 5 showed that the proposed abridged ore breakage characterisation test that uses the minimal number of particles to extract ore breakage indices can be applied for both homogenous and heterogenous ore types. The results also show that the proposed least particles protocol can be used for ore breakage characterisation tests using both crushed ore and drill core particles. The number of particles can be reduced to as little as 10 particles per test while still obtaining the same ore breakage indices as those obtained from the standard procedure. The abridged protocol will be especially useful in situations where the amount of ore available for metallurgical testing is limited.
- ItemOpen AccessCharacterisation of the effect of alteration on the PPM platinum ore and evaluation of selected strategies to improve metallurgical performance(2011) Ramonotsi, Mpho; Petersen, Jochen; Becker, MeganThe aim of this study is in two parts; the first part focuses on mineralogical quantification of the extent of weathering at PPM by profiling the flotation behaviour and host rock density with spatial depth.
- ItemOpen AccessCharacterising the acid mine drainage potential of fine coal wastes(2013) Kotelo, Lerato Olga; Broadhurst, Jennifer Lee; Becker, Megan; Harrison, STL; Franzidis, Jean-PaulAcid mine drainage (AMD) is one of the major environmental challenges facing the South African mining sector. Acid mine drainage has received significant public attention in recent years. South Africa's long mining history has led to a growing concern that coal-related AMD from these mines (both operational and defunct) will continue for centuries to come. Pyrite bearing fine waste, generated during coal preparation and beneficiation, is thought to carry a significant amount of AMD pollution risk. Coal-related AMD generation has not been afforded the same exposure as AMD generation from high sulphide minerals such as gold and copper ores. This is exacerbated by the growing concern over water quality degradation in the Mpumalanga region of South Africa. The development of integrated solutions to address the management of coal-related AMD requires an understanding of the principle causes behind coal-related AMD. To date, most of the prediction methods described in literature have been derived for the prediction of AMD in metal bearing ores. Furthermore, some of these methods are based on assumptions and do not take into consideration the various sulphur species present. Additionally, some of these methods have limited applicability to coal due to the high total organic carbon content (TOC) of the material. This research project attempts to address these short comings and uncertainties by developing a systematic and meaningful framework for the characterisation of South African coal and coal waste. The research project contributes to the knowledge of coal-related AMD with particular emphasis on the characterisation methods responsible for sulphur speciation and mineralogy for coal. The approach entails carrying out a case study assessment aimed at empirically assessing a coal tailings sample according to: particle size distribution, textural reference, mineralogical characteristics, and how the aforementioned factors influence the acid potential in coal. The approach intends to address key factors which include: identifying the sulphur bearing organic and inorganic constituents related AMD generation in coal, assessing how the mineralogy, texture and particle size distribution contribute to AMD potential in coal tailings, and then identifying suitable analytical techniques and test methods which can provide data. The combination of these key outcomes will seek to provide a systematic and meaningful framework for the characterisation of coal and coal waste streams. The characterisation methods used in this case study outlined a framework focusing on four main areas of acid mine drainage characterisation for coal wastes, these included: chemical characterisation, mineralogical characterisation, sulphur speciation and AMD prediction. This comprehensive approach employed a suite of techniques, including: petrography, quantitative x-ray diffraction (QXRD) and quantitative evaluation of minerals by scanning electron spectrometry (QEMSCAN).
- ItemOpen AccessThe development and demonstration of a practical methodology for fine particle shape characterisation in minerals processing(2016) Little, Lucy; Becker, Megan; Mainza, Aubrey; Wiese, JennyDue to continually declining ore grades, increasing mineralogical complexity, and increasing metal demand, models for the design and optimisation of minerals processing operations are of critical importance. These models do not currently incorporate particle shape, which, although rarely quantified, is known to affect numerous unit operations. Automated Scanning Electron Microscopy (Auto-SEM-EDS) is a widely used tool for mineralogical analysis. It also provides an opportunity for simple, quantitative and mineral-specific shape characterisation. Existing mineralogical databases could therefore become useful resources to facilitate the incorporation of shape effects in minerals processing models. A robust Auto-SEM-EDS shape characterisation methodology is required to ensure that the particle shape information in these databases is interpreted appropriately. For this work, a novel methodology for Auto-SEM-EDS shape characterisation was developed that is suitable for the analysis of fine particles (<75 μm). This involved testing the response of various shape descriptors to image resolution, and measurement with different devices and image processing routines. The most widely used shape descriptor in minerals processing, circularity, was found to be highly dependent on both image resolution and image processing settings, making it a poor choice for shape characterisation of fine particles. Roundness and aspect ratio were found to be more robust descriptors. However, in the interest of being able to compare particulate shape measurements across different studies, the precise definition of aspect ratio is important as variation in 'length' and 'width' definitions can significantly impact aspect ratio measurements. The possibility that preferential orientation of particles would introduce bias to the 2-D cross-sectional measurements was also addressed through comparison of roundness distributions measured from orthogonal cross-sections of a particulate sample mounted within a block of resin. The excellent repeatability of these measurements indicated that the particles were randomly orientated, and thus it can be inferred that 2-D measurements of a sufficient number of particles will be directly related to the particulate sample's 3-D properties. Roundness and aspect ratio were then used in conjunction to produce surface frequency distributions that allow for distinction between non-rounded particles that were smooth and elongated and non-rounded particles that were neither elongated nor smooth. Three applications of the shape characterisation methodology developed were then demonstrated, which highlighted some of the potential contributions that this methodology can make towards minerals processing. The applications were all based on a case study of the Upper Group 2 (UG2) Chromitite, a platinum group mineral (PGM) ore of key economic significance to South Africa.
- ItemOpen AccessEffect of HPGR on platinum bearing ores and the flotation response as compared to the conventional ball mill(2011) Solomon, Nomonde; Mainza, Aubrey; Becker, Megan; Petersen, Jochen; Franzidis, Jean-PaulThis thesis focuses on the application of the high pressure grinding rolls (HPGR) on platinum bearing ores Merensky, UG2 and Platreef. Conventional tumbling mills such as the ball mill that are typically applied on these ore types are highly energy intensive with a small percentage of the input energy being used for actual breakage. Rapidly increasing energy costs have contributed to the rising interest of the HPGR in the platinum industry, particularly in plants processing UG2 and Platreef ores. Therefore, this thesis seeks to determine if the HPGR can be used as an alternative to the ball mill. Key aspects of interest are throughput, energy efficiency, PGE grade and recovery and PGM liberation.
- ItemOpen AccessThe effect of phyllosilicate mineralogy and surface charge on the rheology of mineral slurries(2013) Ndlovu, Bulelwa; Deglon, David; Becker, Megan; Forbes, ElizavetaPhyllosilicate minerals exist as common gangue components in many low grade ores. Often broadly classified as ‘clays’, this group of minerals is closely associated with several processing issues. Despite many good studies on the physico-chemical properties of phyllosilicates, there still remains a poor understanding of their suspension flow behaviour. The primary objective of this thesis was to characterise the colloidal behaviour of three commonly occurring phyllosilicates, namely muscovite, vermiculite and chrysotile in terms of their surface charge, mineralogical and resultant rheological properties. The thesis was initiated in order to gain a better understanding of the flow behaviour of these minerals within well-defined model mineral systems, with a longer term view to understanding their impact in complex mineral systems found in mineral processing circuits.
- ItemRestrictedIn situ investigation and visualisation of microbial attachment and colonisation in a heap bioleach environment: the novel biofilm reactor(Elsevier, 2010) Africa, Cindy-Jade; Harrison, Susan T L; Becker, Megan; van Hille, Robert PIn this paper, the development of a novel means of investigating the attachment and subsequent biofilm formation of mineral bioleaching micro-organisms to mineral surfaces in situ is described. The protocol was developed to investigate the interactions of micro-organisms with sulfide minerals and low-grade chalcopyrite ore under conditions resemblant of a bioheap environment. The method makes use of a biofilm reactor in which thin sections of mineral ore are mounted. The reactor is operated as a continuous flow-through system. Attachment of pure and mixed cultures of Acidithiobacillus ferrooxidans and Leptospirillum ferriphilum is assessed. The technique allows for the investigation of microbial ecology with special regard to microbe–mineral attachment, site and mineral specific associations of micro-organisms and spatial organisation of microbial communities present through the use of fluorescent microscopy techniques. Preliminary fluorescent in situ hybridisation (FISH) analysis of the attachment of L. ferriphilum and A. ferrooxidans to massive chalcopyrite sections, as well as to low-grade chalcopyrite containing ore sections is presented. In the case of both low-grade and massive sulfide mineral samples, attachment of mixed micro-colonies was observed in regions where surface defects were prevalent. In low-grade samples, preferential attachment was observed in regions where sulfide minerals were present. The density of the attached micro-colonies increased with an increase in contacting time (from 20, 72 and 96 h) and was indicative of an actively growing mono-layered biofilm.
- ItemOpen AccessAn integrated approach for the mitigation of acid rock drainage (ARD) associated with pyrrhotite in nickel deposits(2012) Chimbganda, Tapiwa; Becker, MeganThis project identified the possibility of manipulating rejection mechanisms in flotation to produce passivated pyrrhotite tailings. Passivation enables surface coating of the sulfide thus inhibiting attack by oxidising agents. Promotion of passivation of pyrrhotite during flotation to produce un-reactive tailings has not been explored to date. Polyethylene polyamines (DETA/TETA), which are already used as depressants in flotation, have been proved to be effective coating agents, significantly reducing the oxidation of pyrrhotite and pyrite in both abiotic and biotic systems. However, passivation by polyethylene polyamines (DETA and TETA) has only been explored on waste rock and pristine pyrrhotite. Furthermore, studies of the mechanism of oxidation of pyrrhotite have observed the formation of a hydrophilic ferric oxyhydroxide layer which enables depression of pyrrhotite during flotation. This layer has been reported in literature to inhibit the further oxidation of the pyrrhotite surface. Thus passivation can also take advantage of the formation of the ferric oxyhydroxide layer to inhibit further oxidation of the mineral.
- ItemOpen AccessInvestigation and modelling of the progression of zinc leaching from large sphalerite ore particles(Elsevier, 2013-01) Ghorbani, Yousef; Petersen, Jochen; Becker, Megan; Mainza, Aubrey Njema; Franzidis,Jean-PaulX-ray Computed Tomography (CT) was used to follow the progression of Zn leaching in a number of individual sphalerite ore particles, which were subjected to a long-term simulated heap bioleaching environment. The ore was prepared by two different modes of comminution – HPGR at 90 bar and cone crusher – and individual particles were selected from three different size fractions. Investigation of the reacted fraction of Zn vs distance from the centre of each particle indicated that leaching from large particles leads to near complete conversion near the surface, but only partial conversion in the zones that are closer to the centre of particles. The cores of the cone-crushed particles show hardly any conversion at all, especially in the larger particle sizes. Mathematical analysis shows that leaching from the large particle does not follow the shrinking core model. It is shown that the progression can rather be described by a combined reaction-diffusion process progressing through the network of cracks and pores closer to the particle surface. Extent and depth of this network are a function of particle size and comminution method. A simplified rate model is proposed that describes the extent of leaching as a function of time in terms of a set of parameters that can all be related to just particle size and crushing mode.
- ItemOpen AccessAn investigation into the dissolution of pyroxene : a precursor to mineral carbonation of PGM tailings in South Africa(2014) Meyer, Nicole Anne; Becker, Megan; Broadhurst, Jennifer Lee; Reid, DaveCarbon sequestration through mineral carbonation is becoming an increasingly attractive alternative for mitigating excess COâ‚‚ in the atmosphere. Mineral carbonation is a natural process whereby COâ‚‚ is fixed to CaFeMg-silicates to form Ca-, Fe-, and Mg-carbonates. This process is thermodynamically favourable and the products are benign and stable over millions of years. Pyroxene-rich tailings generated from the processing of PGM ores in South Africa have the potential to sequester significant amounts of COâ‚‚ (~14 Mt per annum). In the indirect pH swing method, silicate minerals are initially leached at low pH and then carbonated at high pH. A previous study on these tailings highlighted the slow extraction of cations from orthopyroxene, the major Mg-host. The low reactivity of the orthopyroxene resulted in an overall low conversion of tailings to carbonates with only 30 % for Ca, 3 % for Mg and 9 % for Fe. Under similar experimental leach conditions, ~100 % dissolution of olivine and serpentine can be achieved.
- ItemOpen AccessInvestigation of particles with high crack density produced by HPGR and its effect on the redistribution of the particle size fraction in heaps(Elsevier, 2013) Ghorbani, Yousef; Petersen, J; Becker, Megan; Mainza, Aubrey Njema; Franzidis, Jean-Paul; Kalala, JTThe application of comminution technology such as the High-pressure grinding rolls (HPGR), which is able to generate a high density of cracks in the ore particles, is favourable for leaching processes. Extraction of metallic values by the heap leach process, can take place on the particles with partial exposure of mineral grains, if it can provide sufficient surface front for chemical attack by leaching solution. The aim of this study was to assess the benefits of high crack density in the ore particles produced using the HPGR and how it could diminish due to inadequate percolation of the leaching agent. A zinc ore was comminuted using HPGR at three different pressure settings and with a cone crusher for the control experiment. Subsamples from the (+23/-25, +14/-16, +5.25/-6.75 mm) size fractions were characterized and packed into leach reactors. The reactors were stopped from time to time to investigate the progress of crack and micro-crack growth and its effect on metal extraction using the X-ray computed tomography (CT). The results are validated with those obtained using traditional techniques such as SEM and QEMSCAN. Investigation of the leach reactors residue indicated significant changes in the particle size distribution (PSD) of initial feed toward the fine size fraction. The residues from the reactors leaching the material prepared using the HPGR product contained more fine particles than the reactors, which were fed by cone crusher product. These differences were up to 10.3%.
- ItemOpen AccessInvestigation of the effect of mineralogy as rate-limiting factors in large particle leaching(Elsevier, 2013-10) Ghorbani, Yousef; Becker, Megan; Petersen, J; Franzidis, Jean-PaulAlthough heap leaching is by now well established in the mining industry, the process remains limited by low recoveries with different rate-limiting factors that are not clearly understood. In this study, three large particle size classes (+19/-25, +9.5/-16, +4.75/-5 mm) were prepared from a sphalerite ore by two different methods of comminution (HPGR and cone crusher). The particles were then packed into leach reactors that were operated continuously for eleven months with well-mixed internal circulation of the leach solution. Characterization of the residue of the leach reactors indicated that there are areas within the ore particles where although sphalerite grains are accessible to the solution, they remain unreacted. X-ray tomography and QEMSCAN® analysis of the selected samples before, during and after leaching, showed increased leaching of sphalerite grains associated with pyrite due to galvanic interactions. Mineral chemistry (Fe, Mn content of sphalerite) and jarosite precipitation were also investigated as factors influencing sphalerite leaching.
- ItemRestrictedLarge particle effects in chemical/biochemical heap leach processes - A review(Elsevier, 2011) Yousef, Ghorbani; Becker, Megan; Mainza, Aubrey; Franzidis, Jean-Paul; Petersen, JochenThe application of heap leach technology to recovery of economically important metals, notably copper, gold, silver, and uranium, is wide-spread in the mining industry. Unique to heap leaching is the relatively coarse particle size, typically 12–25 mm top size for crushed and agglomerated ores and larger for run-of-mine dump leaching operations. Leaching from such large particles is commonly assumed to follow shrinking core type behaviour, although little evidence for the validity of this assumption exists. This review investigates the current state of knowledge with respect to the understanding of the characteristics and mineralogy of large particles and how these influence leaching in a heap context and the tools to characterize these. This includes the study of ore and particle properties, visualization techniques for ore characterization, the connection between comminution and leaching behaviour, as well as particle models within heap leach modelling. We contend that the economics of heap leaching are strongly governed by the trade-off between the slow rate and limited extent of leaching from large particles and the cost of crushing finer. A sound understanding of the underlying large particle effects will therefore greatly inform future technology choices in the area of heap leaching.
- ItemRestrictedLarge particle effects in chemical/biochemical heap leach processes – A review(Elsevier, 2011) Ghorbani, Yousef; Becker, Megan; Mainza, Aubrey; Franzidis, Jean-Paul; Petersen, JochenThe application of heap leach technology to recovery of economically important metals, notably copper, gold, silver, and uranium, is wide-spread in the mining industry. Unique to heap leaching is the relatively coarse particle size, typically 12–25 mm top size for crushed and agglomerated ores and larger for run-ofmine dump leaching operations. Leaching from such large particles is commonly assumed to follow shrinking core type behaviour, although little evidence for the validity of this assumption exists. This review investigates the current state of knowledge with respect to the understanding of the characteristics and mineralogy of large particles and how these influence leaching in a heap context and the tools to characterize these. This includes the study of ore and particle properties, visualization techniques for ore characterization, the connection between comminution and leaching behaviour, as well as particle models within heap leach modelling. We contend that the economics of heap leaching are strongly governed by the trade-off between the slow rate and limited extent of leaching from large particles and the cost of crushing finer. A sound understanding of the underlying large particle effects will therefore greatly inform future technology choices in the area of heap leaching.
- 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.
- ItemOpen AccessMineralogical effects on the dense medium separation of low grade nickel sulfide ore(2015) Pillay, Keshree; Becker, Megan; Chetty, DeshDense medium separation (DMS) is a method often used to upgrade base metal sulfide (BMS) ores before their main processing stage, with varying results achieved for different ore types. The process makes use of the density differences between the BMS minerals and the lower density silicate/carbonate gangue minerals, using a separating medium of density between the two ore components. The separation is accelerated using a dense medium cyclone (DMC) to form two products: overflow (tailings) and underflow (concentrate). The purpose of DMS is to reject large quantities of gangue upfront, resulting in reduced time, energy and costs associated with processes such as milling and flotation. Preconcentration of ores using physical methods such as DMS is becoming an important consideration as lower grade ores are mined, to increase the feasibility of mining such ores. Two nickel sulfide deposits were chosen as case studies in order to understand differences in DMS efficiency for different ores. The first is the Main Mineralised Zone (MMZ) of the Nkomati Nickel deposit in Mpumalanga, South Africa, which is part of the Uitkomst Complex. The Phoenix deposit is also considered, and forms part of the Tati greenstone belt in eastern Botswana. Both deposits are magmatic Cu-Ni-PGE (platinum group element) deposits with similar sulfide mineralogy and pentlandite as the main nickel host. A process mineralogy approach was used to evaluate samples of both ores, describing the differences in the mineralogical properties within the overflow and underflow of each ore in order to understand the extent to which individual properties affect the separation.