Browsing by Author "McFadzean, Belinda"

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    Open Access
    A 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, Belinda
    Ores 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.
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    The effect of copper sulphate on froth stability
    (2015) Nyabeze, Wadzanai; McFadzean, Belinda
    Froth flotation is a mineral beneficiation process implemented in the recovery of valuable minerals from unwanted gangue material. Copper sulphate is used as an activator in the flotation of base metal sulphides (BMS) as it promotes interaction of collector molecules with the mineral surfaces. It is also used in certain platinum group minerals (PGM) flotation operations in South Africa although the mechanism by which improvements in flotation performance are achieved is not well understood. Some investigations suggest that changes in flotation performance are affected by changes in the froth phase, rather than activation of minerals by true flotation in the pulp zone. The present study focussed on exploring the effect of using copper sulphate as an activator and sodium isobutyl xanthate (SIBX) as a collector on froth stability in Platinum Group Mineral (PGM) operations. This was done on two PGM containing ores namely Merensky and UG2 (Upper Group 2) ores from the Bushveld Complex of South Africa. The dynamic froth stability factor (Σ) and froth half life time (t1/2) were used as measures of froth stability. These were obtained using a froth stability column which is a non-overflowing system. The effect of activation on pure minerals in the pulp phase was also analysed using a microflotation cell which eliminates the froth phase and hydrodynamic interactions found in normal flotation cells. The microflotation cell was used as a measure of hydrophobicity which was directly linked to the flotation recovery. The adsorption of reagents onto the mineral surfaces was confirmed by the use of zeta potential and ethylenediaminetetraacetic acid (EDTA) extraction of surface products. The pulp phase effects were analysed through the floatability of pure minerals and analysis of surface products after copper sulphate activation and these were linked to the outcomes from the froth stability tests. It was hypothesised that copper sulphate destabilised the froth for a Merensky ore and for a UG2 ore but due to different reasons because of the mineralogical compositions of the two ores. For the Merensky ore, the froth destabilisation was postulated to be due to the formation of Cu(I) on the base metal sulphide surfaces which promotes the formation of hydrophobic copper-xanthate species. This would result in an increase in contact angle which promotes bubble coalescence. For the UG2 ore which has far less base metal sulphides than Merensky ore, it was hypothesised that the destabilisation of the froth would be due to the non-selective precipitation of hydrophilic colloidal hydroxides on mineral surfaces which reduce the amount of hydrophobic froth stabilising particles reporting to the froth phase.
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    The effect of mixing thiol collectors in the flotation of pure sulphide ores
    (2012) Castelyn, Daniel Gregory; McFadzean, Belinda; O'Connor, Cyril
    Using mixtures of xanthate with either dithiophosphate (DTP) or dithiocarbamate (DTC) has been reported to increase the flotation performance of several sulphide flotation operations. The increased flotation performance has often been termed synergistic. Synergism is defined as the effect exceeding the pro rata contribution of either constituent in the mixture. This thesis aims to investigate the effects that mixtures of either xanthate and di-alkyl DTP or xanthate and di-alkyl DTC have on the pulp phase floatability of pure galena and pyrite by means of microflotation. Both minerals were chosen because they have been widely studied in sulphide flotation, and to determine whether flotation results with mixtures were mineral specific.
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    Effect of particle properties on froth stability
    (2017) Achaye, Innocent; McFadzean, Belinda; Wiese, Jenny
    The froth flotation process has found substantial usage in the mineral processing industry for over a century and as long as minerals continue to exist in the earth's crust, the demand for upgrading and recovery of these natural yet valuable resources will continue to exist. It relies on the principle that a bubble-particle collision process should be accompanied by the formation of an attachment between the pair. Of particular importance to the flotation process is the stability of froths. This will affect the mass pull, which, in turn, will affect recovery and the grade that is attainable. Froth stability is affected by many factors, viz. machine properties, hydrodynamics within the flotation cell, reagent suites, as well as mineral particle properties. Of particular interest to reagent suites is the frother dosage and its influence on the prevention of coalescence which has been fairly well studied. Regarding froth stability, the frother influences the amount of water that reports to the concentrate as well as the bubble surface viscosity, limiting drainage and subsequent bubble coalescence. Most of the other factors influence the amount of particles that report to the froth, but it is the particle properties that have the overriding influence on the froth stability. It is in the interest of flotation modelling and optimisation to be able to find relationships for the impact of particle properties on froth stability. This project has focussed on the influence of two main particle properties, i.e. size and hydrophobicity, and their interactive effects on froth stability. In order to establish relationships between particle properties and froth stability, two devices were built in the laboratory, i.e. a non-overflowing stability column to measure froth stability and a bench-scale continuous flotation cell to provide metallurgical information, besides being able to measure froth stability using water recovery and froth surface bubble burst rate. In the first part of the investigation, particles of discrete sizes as well as mixtures of particles sizes were utilised at a constant hydrophobicity. Results obtained show a power law relationship between froth stability and particle size, with all particle combinations falling on the same relationship. Froth stability decreased with increasing particle size. A large increase in froth stability occurred for feed particles of average size below 50 μm. This was attributed to particles in the finer range reporting to the froth by both true flotation and entrainment. These fine particles would result in a higher interfilm viscosity resulting in reduced drainage. A useful linear relationship between froth stability and the reciprocal of feed particle size was obtained. The reciprocal of feed particle size was used to represent the specific surface area of the particles. It was found that as the specific surface area of the particles increased, their froth stabilising effect also increased in a linear fashion. In the second part of the investigation, the influence of particle hydrophobicity and the interactive effects of particle size and hydrophobicity on froth stability were explored. In common with other studies, it was found that froth stability increased with increasing particle hydrophobicity up to an optimum value between 66° and 69° and thereafter it decreased. The smallest size particles (28 μm) produced the highest variation in froth stability with increasing hydrophobicity. The response of the coarse particles to froth stability with increasing hydrophobicity was less pronounced. Particle size was found to have a greater influence on froth stability than particle hydrophobicity. Variations in froth stability were about 1.5 times greater for changes in particle size than changes in hydrophobicity over the relatively large ranges of size and hydrophobicity tested. The relationship between froth stability and feed particle specific surface area was investigated at different hydrophobicities and found to be linear for most practical particle sizes. However, a deviation from linearity occurred at very small particles sizes (28 μm) for particles of optimum hydrophobicities. The slopes of the froth stability versus feed specific surface area relationships in the linear region were found to increase with increasing hydrophobicity, up until an optimum contact angle of between 64° and 68°, whereafter they decreased. Thus, this family of curves would allow the prediction of froth stability of varying hydrophobicities on a size-by-size basis. This relationship was shown to hold for two real ores: a platinum-bearing UG2 ore and an Itabirite iron ore. Thus, a simple linear calibration of grind versus froth stability would allow a prediction of froth stability for a particular ore. A Langmuir-type model was developed to relate the froth stability to the concentrate particle surface area. It was found to be a good fit to the experimental data. This shows that it is possible to model froth stability in terms of the particle packing at the air-water interface in much the same way that surfactant molecular packing at the interface is modelled. The increasing particle surface area affects the surface tension of the films and reduces film drainage. In studying the interactive effects of particle size and hydrophobicity, it was found that all data points of all hydrophobicities fell on the same relationship when froth stability was plotted as a function of concentrate surface area. It was therefore, concluded that particle size and hydrophobicity define the amount of particles that will report to the froth phase, but once in the froth, it is the surface area of the particles that will define the froth stability.
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    Investigating collector and depressant performance in the flotation of selected iron ores
    (2016) Mhonde, Ngoni Pepukai; Wiese, Jenny; McFadzean, Belinda
    As the excessive extraction of high grade iron ore reserves has led to the rapid depletion of these ore bodies, there is a growing need to extract and upgrade low grade iron ores into more economically viable products with an iron content in excess of 50%. The beneficiation of low grade iron ores through the reverse cationic flotation procedure is gradually gaining popularity as a possible processing route of the future for South Africa's iron industry. Reverse cationic flotation employs a reagent suite consisting of an amine compound which functions as a quartz collector in addition to providing the frothing effect in the flotation system, and hydrolysed starch which serves to depress hematite during flotation. The aim of this project was to investigate the effect of using five amine collectors with different molecular structures on the flotation recovery of quartz and the entrainment of hematite in the flotation of a South African iron ore and a Brazilian iron ore. Laboratory batch flotation tests were conducted on both ore samples and the grade and recovery of hematite were recorded. The collectors were characterised through surface tension measurements and pKa value analysis. An attempt at using different polysaccharides as hematite depressants entailed the use of a CMC and a guar gum in batch flotation tests of the Brazilian iron ore.
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    Investigating the effect of frother type on froth structure, froth recovery and entrainment
    (2015) Marozva, Tafadzwa; McFadzean, Belinda; Wiese, Jenny
    Mineral processing involves liberation and beneficiation operations. Several beneficiation processes exist and one such important process is froth flotation. The flotation process involves the transportation of valuable minerals of a hydrophobic nature into the froth and to the concentrate launder. This hydrophobicity may be natural or imparted by a collector. Froth structure is significant in determining the froth stability which has an effect on the grade and recovery of valuable minerals. The froth structure is dependent on amongst other factors the type of frothers used during the separation process. As a result, frother type and concentration can be used to manipulate the froth recovery and grade of valuable mineral recovered. Upper Group 2 (UG2) ore contains chromite minerals which are naturally hydrophilic. The chromite minerals are usually recovered in the concentrate mainly due to entrainment. This lowers the grade of valuable minerals recovered and poses detrimental effects to downstream operations. Thus, the froth structure plays an important role in the flotation performance of UG2 ore. This project was aimed at investigating the effect of chain length and functional group of different frothers on the froth stability, froth recovery and entrainment. Froth recovery, entrainment, solids and water recovery, as well as metallurgical recovery, were measured in a laboratory scale continuous column flotation cell. Froth stability was measured in a froth stability column, which is a non-overflowing column in which froth rise rate and equilibrium height were measured. A series of increasing molecular weight polyglycol and alcohol frothers, and their blends, were used to investigate the effect of frother type on froth structure.
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    Investigating the relative adsorption of polymeric depressants on pure minerals
    (2011) Mhlanga, Sabatha Sanele; McFadzean, Belinda
    The aim of this study was to investigate the relative adsorption of polymeric depressants on pure minerals. The minerals used were talc, pyroxene, plagioclase, chromite and chalcopyrite and the depressants used were guar gum and carboxymethyl cellulose (CMC). It was hypothesised at the beginning of this study that polymeric depressants adsorb preferentially onto different minerals because of the differences in the surface charge of the minerals which arise as a result of their different chemical structures. Zeta potential measurements were conducted to establish exactly what these differences in surface charge were and what role metal ions in solution played in modifying the mineral surface charge and therefore changing the adsorption characteristics.
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    Investigation of the effect of particle size on froth stability
    (2016) Chidzanira, Tadiwanashe; Wiese, Jennifer; McFadzean, Belinda
    The flotation process has been used for more than a century to separate valuable minerals from bulk ores. The separation process is based on utilising the differences in the physico-chemical properties of liberated particles, mainly the particle hydrophobicity which allows the particles to be attached to air bubbles rising from the pulp phase into the froth phase and subsequently collected to the launder. The stability of the froth phase which is be defined as the ability of bubbles to resist coalescing and bursting (Triffet & Cilliers, 2004), has been shown to have a significant effect on the efficiency of the flotation process. An unstable froth will result in poor valuable mineral recovery as these desired hydrophobic particles are detached from air bubbles and drain with the water back into the pulp phase due to bubble coalescence. On the other hand, a very stable froth may result in poor concentrate grade as the unwanted gangue materials are unselectively entrained to the concentrate. As a result, a substantial amount of research has been performed on improving control of froth stability by the manipulation of frother type and dosage. A recent study investigated the manipulation of flotation operating parameters such as air rate, froth height and depressant dosage which resulted in minimal changes in froth stability. The present study then investigated the effect of particle size and solids concentration on the stability of the froth phase using a UG2 ore and an Itabirite ore. Froth stability was determined using Bikerman tests on a laboratory scale non-continuous stability column. A novel continuously operated agitated hybrid cell was also used to assess froth stability, with water recovery and froth recovery used as proxies for froth stability. The agitated hybrid cell was then included in the experimental design as it allowed for continuous floatation system to be evaluated which resembles more industrial operations as compared to the stability column. The hybrid also incorporated the agitation zone benefits of a lab scale batch flotation cell which allows for better attachment of coarse particles and also allowing for the formation of deeper froths enabling improved froth stability measurements. The viability of using the top froth average bubble size and the side of froth axial bubble coalescence rate as froth stability proxies was also evaluated as the columns were clear glass.
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    Relationship between flotation operational factors and froth behaviour
    (2014) Shumba, Tanaka Casandra; Wiese, Jenny; McFadzean, Belinda
    This study utilised laboratory-scale column flotation experiments to investigate froth stability, with respect to, water recovery and top-of-froth bubble burst rate. Tests were conducted at different froth heights, superficial air rates and depressant dosages in a 2 m high Plexiglass column, using a PGM bearing UG2 ore from the Bushveld Igneous Complex. Four concentrate and tailings samples were simultaneously collected and solids and water recoveries were determined. Assays of the concentrates were conducted to establish the amount of platinum, palladium and chromite that was recovered under each operating condition. Video footage of the top of the froth was recorded and was used to measure the top-of-froth bubble burst rate. The stability of the froth was analysed qualitatively by comparing the relationship between water recovery and the bubble burst rate at the different operating conditions. A key finding from this study was that the concentration of particles had a large effect on the stability of the froth. The maximum concentration of particles was obtained when the tests were conducted in the absence of depressant. Under these conditions it was established that the froth produced was so stable that increasing the air rate only showed minor changes in the stability of the froth phase. This stability has been attributed to the presence of hydrophobic gangue, which stabilised the froth phase by embedding between adjacent bubbles and preventing bubble coalescence. Conversely, when a high depressant dosage was used the froth became unstable such that no trends could be established when either air rate or froth height were altered. The instability of the froth has been attributed to the depression of the majority of the froth stabilising gangue, which resulted in increased bubble coalescence.
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    Study of effect of process parameters and their interaction in the flotation of UG2 ore
    (2013) Pani, Santosh; McFadzean, Belinda; Wiese, Jenny
    Flotation is widely used in the mineral processing industry to extract valuable minerals from the ore. The fundamental steps in this separation process are the attachment of hydrophobic valuable minerals to bubbles, and the subsequent accumulation of the bubble-particle aggregates in the froth phase. Processing of UG2 ore for concentration of platinum group minerals (PGMs) is a challenging task. UG2 ore contains significant amounts of chromite which is hydrophilic in nature and reports to the concentrate by means of mechanical entrainment. This is a serious problem for the downstream smelting process, which generally has a constraint of 3 chromite. In order to optimise PGM and chromite grade and recovery in UG2 processing, a number of controls are available in a plant. Among the most important are froth height, air flow rate, depressant dosage and frother concentration. On an individual level, it is expected that an increase in froth height will result in the reduction of the mechanical entrainment of chromite due to an increase in the residence time of air in the froth zone, allowing more drainage of chromite from froth to pulp. High depressant dosage is expected to enhance the grade of PGM and will reduce the recovery of naturally floatable gangue in the concentrate. However, the increase of superficial air velocity will increase the water recovery and solid recovery, thus decreasing the PGM grade with a possible increase in recovery. Increase in frother concentration increases the thickness of bubble lamella and causes more water to flow through the Plateau borders and hence increases the water recovery. Apart from the individual effect of each process parameter the interaction of same play a significant role in the solid and water recovery that affect the chromite content and the PGM grade in the concentrate.
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    The relationship between enthalpy of immersion, and its derived wettability parameters, to flotation response
    (2019) Taguta, Jestos; McFadzean, Belinda; O’Connor, Cyril
    The wettability of mineral surfaces plays an important role in the flotation process. A wettable mineral is hydrophilic while a non-wettable mineral is hydrophobic. In the flotation process, sufficiently hydrophobic particles are collected by rising air bubbles and they report to the concentrate. On the other hand, hydrophilic particles do not attach to the air bubbles and they report to the tailings. Some of the conventional methods used to characterise mineral surface wettability include contact angle, inverse gas chromatography (iGC), time of flight secondary ion mass spectrometry (ToF-SIMS) and induction time measurements. The measurement of contact angles on flat, smooth and ideal surfaces is relatively simple, straight forward and well-described, but the measurement of powder contact angles is not so straight forward. The iGC technique is a gas phase technique while ToF-SIMS exposes the particles under high vacuum compared to an aqueous environment in real flotation systems. This thesis has investigated the use of the enthalpy of immersion as an indicator of the wettability of mineral surfaces. The enthalpy of immersion is the heat change arising from the replacement of the solid-gas interface with the solid-liquid interface when a solid surface is immersed in a liquid. Although immersion calorimetry has been established as a reliable means of determining the wettability of solid surfaces, it has found only limited applications in flotation research where wettability of mineral ores is a key variable. In this study, precision solution calorimetry was employed to measure the enthalpies of immersion of different minerals in water. The Washburn method and a microflotation system were used to measure the corresponding powder contact angles and the flotation responses of the same minerals respectively. Two mineral systems were investigated in this study, viz: different pure minerals in their natural form as well as collector-coated sulphide minerals. Furthermore, to assess whether the enthalpy of immersion is able to differentiate between the amounts of minerals of different wettabilities in a mineral mixture, a synthetic ore comprising of different proportions of a sulphide mineral (realgar) and a silicate gangue mineral(albite) was also investigated. The surface energetics of different minerals and the synthetic ore were also characterised by measuring the enthalpies of immersion in different probe liquids and applying the van Oss-Chaudhury-Good (VOCG) model. The VOCG model is reported to give consistent results in terms of surface energetics of surfaces. It has been found that the enthalpy of immersion technique was capable of distinguishing differences in the wettabilities of different minerals and these differences were explained in terms of the solid state properties of the minerals. The enthalpy of immersion method was also able to assess the changes in the surface chemical properties of the galena and realgar surfaces resulting from collector adsorption. The magnitude of the enthalpy of immersion was inversely related to the surface coverage of potassium amyl xanthate on both galena and realgar. The enthalpy of immersion measurements correlated well with powder contact angle measurements, but, most importantly, the enthalpy of immersion measurements were found to be more reproducible and sensitive than the contact angle measurements. It has also been shown that the enthalpy of immersion is a more widely applicable measure of the hydrophobicity of mineral particles typical of those used in the flotation process as opposed to the contact angle. It is therefore concluded that the enthalpy of immersion is a superior indicator of the extent to which minerals are hydrophobic or hydrophilic either in their natural form or after treatment with a collector. Furthermore, it was found that there was a strong inverse relationship between the enthalpy of immersion of the minerals studied and their flotation response. The strong inverse relationship has potential to be used in pulp phase flotation models, although this was not the focus of this thesis. In addition, a value, termed the critical enthalpy of immersion (CEI), was observed above which no flotation occurred. The CEI was in the region of -200 mJ/m². At values less exothermic than the CEI, the flotation response was found to be inversely related to the enthalpy of immersion. At values more exothermic, viz. more negative, than the CEI, no flotation occurs. The significance of this finding is that for any mineral whose flotation behaviour is unknown, the measurement of the enthalpy of immersion appears to be able to predict the flotation response of the mineral. The variance in the inverse relationship between enthalpy of immersion and rate of flotation was reduced when the data was normalized with respect to particle density which was the only variable in the flotation studies in terms of particle-bubble encounter efficiency. These results have shown that the enthalpy of immersion is an excellent indicator of both the natural mineral hydrophobicity and of the extent to which collectors render a mineral hydrophobic. The relative strength of the acid-base sites was shown to depend on the mineral type. The surface energetics obtained in this study were consistent with the hydrophobichydrophilic nature of these minerals. The basic, polar components as well as the total surface energy decreased in the following order: silicates > metallic sulphide minerals and talc. It was observed that the higher the total surface energy, the lower the hydrophobicity of the mineral. The acid-base characteristics of the minerals, measured by solution calorimetry, can give a detailed insight into the surface energies of different mineral types and may be useful in optimising processing strategies. Using the surface energetics, two important parameters were calculated, viz: the interfacial free energy of interaction between mineral particles and bubbles immersed in water (∆Gpwb) as well as the work of adhesion for water (Wadh). Interestingly, and not surprisingly, the trends in both of these parameters coincided with the trend in the enthalpies of immersion of the different minerals in water. Critical values of ∆Gpwb and Wadh parameters in the region of 200 mJ/m² and 320 mJ/m² respectively were observed above which no flotation occurs. At values less than the critical values, both parameters were inversely related to the flotation response. The enthalpy of immersion was able to differentiate between the amounts of minerals of different wettabilities in a mineral mixture. The enthalpy of immersion became increasingly exothermic as the percentage of albite in the realgar-albite mixtures increased. The experimentally determined enthalpies of immersion in water were in excellent agreement with the weighted enthalpies of immersion for the realgar-albite mixtures. The weighted enthalpies of immersion of the synthetic ore were calculated based on the specific surface areas of both realgar and albite. Therefore, it is possible to calculate the enthalpy of immersion of a synthetic ore (mineral mixtures) from the knowledge of the proportion and the enthalpy of immersion in water of the individual minerals comprising the synthetic ore. The surface energetics of the synthetic ore showed that there is a relationship between the mass recovery and the calculated relative surface polarity, based on the individual polar and total surface energies. As the relative surface polarity increases, there is a significant decrease in the mass recovery after a relative surface polarity of about 0.4. Thus, the enthalpy of immersion has the potential to be used to predict the wettability and the floatability potential of mineral mixtures. It is proposed that this work should be extended to other mineral mixtures, with careful measurement and calculation of the surface energetics of these mixtures. Thus, this work presents an opportunity for further study to investigate the use of the enthalpy of immersion to characterise the wettability of real ores.
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    The thermochemical behaviour of thiol collectors and collector mixtures with sulphide minerals
    (2015) Taguta, Jestos; McFadzean, Belinda
    Thiol collectors continue to dominate the base metal sulphide (BMS) and platinum group mineral (PGM) flotation industry. The behaviour of thiol collectors and collector mixtures with sulphide mineral surfaces has been extensively studied using different techniques such as XPS, ToF-SIMS, UV-VIS, etc. However, most of these techniques require a collector dosage above monolayer coverage, take place under equilibrium conditions and may not simulate flotation conditions. Moreover, most of the studies focus on isolated minerals yet exploitable ores exist as an association of sulphide minerals. The use of thiol collector mixtures in the base metal sulphides (BMS) and platinum group mineral (PGM) flotation industries has been reported to offer several performance benefits by many researchers. However, the mechanism whereby these collector mixtures adsorb onto a specific mineral surface is still not clearly understood. This study used isothermal titration microcalorimetry to monitor sub-monolayer reactions by continuously measuring the heats of adsorption as the reactions between thiol collector (and collector mixtures) and sulphide minerals (and mixed minerals) proceed in real time. The enthalpy of adsorption does not only characterise the intensity of adsorption between a collector and mineral surface but also gives insight into the reaction mechanism, whether physisorption (less negative than -40 kJ/mol) or chemisorption (more negative than -40 kJ/mol). Microflotation was also used to determine the hydrophobicity imparted onto the mineral particles as a result of the mineral-collector interactions. Sulphide minerals investigated were chalcopyrite, pyrite, pyrrhotite and galena. Thiol collectors investigated were xanthates of varying chain length (SEX, SIBX, PNBX and PAX) as well as dithiocarbamates (diethyl-DTC and n-butyl DTC) and diethyl-DTP. The current study seeks to gain knowledge of which collector interacts best with which mineral and an understanding of the mechanism behind the reactions. This study also seeks to investigate the performance and adsorption mechanisms when single minerals are interacted with thiol collectors singly and also in a mixture. A better understanding of how to design collector mixtures is to be gained. Furthermore this study seeks to understand the effect of mineral-mineral interactions on thiol collector adsorption and on the floatability of the pure minerals.
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    The use of mixed thiol collectors in the flotation of Nkomati sulphide ore
    (2014) Nyambayo, Constance K; McFadzean, Belinda; Corin, Kirsten; O'Connor, Cyril
    Mixtures of collectors are widely used in sulfide and platinum group mineral (PGM) flotation, and a range of performance benefits have been reported for many different systems. An increase in paymetal recovery and grade as well as increased rates of recovery at lower collector dosages has been observed when single collectors are replaced with multi-collector suites. These benefits have been attributed to increased carrying capacity of the froth phase, faster kinetics and increased recovery of middling or course particles. However, the mechanism of action of such collector suites is not clearly understood. Candidate selection of mixed collector suites is currently based on experience and contextual knowledge. The overall objective of this study was to experimentally identify a three component collector suite consisting of conventional collectors which could enhance the metallurgical performance of Nkomati nickel-copper sulfide ore. A three component collector suite consisting of sodium isobutyl xanthate (SIBX), sodium ethyl xanthate (SEX) and either sodium ethyl dithiophosphate (DTP) or sodium ethyl dithiocarbamate (DTC) was used. The scope of this work was confined to the use of xanthates, DTC’s and DTP’s since they are in common use in industry, are supplied over a relatively low price range and have shown potential performance enhancements when used as mixtures. The standard University of Cape Town (UCT) batch flotation procedure was used in this investigation and changes in electrochemical potential were monitored as collector was added to the flotation cell. It is hypothesised that the benefits of collector mixtures are only evident at low dosages, thus, dosages were carefully controlled. The study aimed to determine whether benefits of collector mixtures were dominant in the pulp or froth phase and suggest a possible mechanism of action.