Browsing by Author "Wiese, Jenny"

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    Considering the effect of pulp chemistry during flotation on froth stability
    (2016) Sheni, Nanji Ruth; Corin, Kirsten; Wiese, Jenny
    On an industrial scale the need for improved flotation performance is of high importance in the current economic climate. Studies have shown that the pulp phase chemistry has a strong effect on the froth phase and therefore it is necessary to investigate how the manipulation of pulp chemistry factors can improve flotation performance. Research into the manipulation of this chemistry is well underway and factors including the pulp potential (Eh), pH, dissolved oxygen (DO) and ionic strength (IS) govern the pulp chemistry. This study aims to investigate how the manipulation of these factors affects the froth stability, bubble size and entrainment of the froth phase through Platinum Group Metal (PGM) flotation. In this study the Eh, pH, DO and IS were successfully manipulated to investigate their effects on froth stability and water recovery in 2-phase, as well as their effect on water and solids recovery, entrainment and the grades and recoveries of valuable minerals (copper, nickel, platinum and palladium) in 3-phase in the absence and presence of depressant at high dosages; 500 g/t Carboxymethyl Cellulose (CMC). Stability column tests were used to determine froth stability as a function of the dynamic stability factor (Barbian et al., 2005) and batch flotation tests were used to obtain the total water and solids recovered, the grades and recoveries of the valuable minerals as well as to determine entrainment. Further tests were performed to investigate the effect of changing the pH on the Eh in a 3-phase system in which all the other pulp factors were kept constant. The effect of changing the pulp factors on the froth bubble size was investigated by capturing side view images of the froth obtained in a batch flotation cell as each pulp factor was changed. This study has shown that careful control of the pulp chemistry, namely increasing IS, increasing pH, decreasing DO and decreasing Eh, resulted in improved froth stability. The Eh was found to be inversely proportional to the pH. This study has further shown that increased water recoveries and reduced bubble size in the froth were observed at 5 IS as compared to 1 IS due to the froth stabilising nature of the pulp at 5 IS. Operating at high Eh (500-730 mV) was observed to be detrimental to valuable mineral grades and recoveries and promotes entrainment. This kind of knowledge contribution may be key in improving flotation performance and increasing the grades and recoveries of valuable minerals obtained in South Africa's PGM mining industry.
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    The development and demonstration of a practical methodology for fine particle shape characterisation in minerals processing
    (2016) Little, Lucy; Becker, Megan; Mainza, Aubrey; Wiese, Jenny
    Due 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.
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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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    An electrochemical investigation of platinum group minerals
    (2015) Tadie, Margreth; Corin, Kirsten; Wiese, Jenny
    The Bushveld complex is the largest ore body in the world hosting platinum group elements (PGEs). It is a stratified orebody with three major reefs namely, the Merensky reef, UG2 reef and the Platreef. Platinum and palladium are the most abundant PGEs found in the Bushveld complex. They occur in the form of minerals/mineral phases with elements such as sulphur, tellurium, arsenic and iron. These minerals/mineral phases are associated with base metal sulphides occuring along grain boundaries. Unlike the Merensky and UG2 reef, the Platreef is almost barren of PGE sulphides and the distribution of base metals sulphides and their association with PGMs is erratic. Froth flotation targeted at the recovery of base metal sulphides is implemented in PGM concentrators to concentrate PGMs. Flotation of sulphide minerals is achieved with the use of thiol collectors to create hydrophobicity, and copper sulphate is often used to improve hydrophobicity and therefore recovery. Sodium ethyl xanthate (SEX) and sodium diethyl dithiophosphate (DTP) are commonly used as collectors on PGM concentrators. The erratic mineral variations in the Platreef ore, however, raise the question of the effectiveness of the application of sulphide mineral flotation techniques on this ore. Previous work by Shackleton, (2007) investigated the flotation of PGE tellurides, sulphides and arsenides. The study highlighted that the mechanisms with which these minerals interact with collectors and with copper sulphate was poorly understood. It is as a result of the findings of Shackleton's work that this study aims to elucidate the fundamental interactions of telluride and sulphide PGMs with thiol collectors and with copper sulphate. Subsequently this work also aims to compare the behaviour of these reagents on sulphide PGMs and telluride PGMs.
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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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    An investigation into the effect of ionic strength of plant water on valuable mineral and gangue recovery of a platinum bearing ore from the Merensky reef
    (2012) Manono, Malibongwe Shadrach; Corin, Kirsten; Wiese, Jenny
    Higher solids and water recoveries were obtained at higher ionic strength. The increase in the ionic strength in the absence of any depressant caused an increase in Cu and Ni recovery.
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    An investigation into the relationship between electrochemical properties and flotation of sulphide minerals
    (2016) Chimonyo, Wonder; Corin, Kirsten; Wiese, Jenny
    There is a growing importance in the mineral processing industry to find ways which are economic and effective in improving the recovery of minerals in the flotation process. The focus of this study was on the recovery by flotation of minerals found in the Merensky reef, which is one of the major reefs in the Bushveld complex. In that reef, base metal sulphide (BMS) minerals are commonly associated with PGMs and this has an effect on the way in which these minerals are concentrated by flotation (Vermaak et al. 2004; Wiese et al. 2005b; Miller et al. 2005; Schouwstra et al. 2000).A major problem in this process has been reported to be losses of valuable minerals (PGMs) associated with the loss of BMS (Wiese et al. 2005b), during flotation. The present investigation has focused on studying the relationship between the flotation of sulphide minerals using xanthates as collectors and the electrochemical properties of the flotation system. It is well known that electrochemical mechanisms in flotation systems have a major influence on flotation since the reactions occurring at the mineral/solution interface are of critical importance in the process (Woods, 1971).The aim of this study was to investigate the extent to which there was a relationship between the electrochemical reactions occurring in this ore which could indicate the effectiveness of the flotation process. The electrochemical reactions were studied by determining the redox potential changes occurring when various changes were made. These were the length of the alkyl chain length of the xanthate collector, changing the pH or using various chemical reagents to change the potential of the system. It was found from the rest potential measurements, that collectors of different chain length have different extents of interaction with mineral surface. A greater interaction, which is indicated by a greater change in the mixed potential after addition of the collector, is considered to be indicative of a greater adsorption of the collector at the mineral surface. It was hypothesized that this stronger adsorption by collectors of longer alkyl chain length would result in improved flotation performance. However, this was not observed to be the case and that was consistent with previous results on the relationship between the recovery of sulphide minerals in the Merensky ore and xanthates of different chain lengths. Thus it was shown that there was no correlation between the interactions between collectors of different alkyl chain lengths as determined through electrochemical studies and the flotation performance of valuable minerals under the tests conditions used.
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    Investigation of the effect of different frother blends on the flotation of selected PGM bearing ores
    (2015) Ngoroma, Faustine; Franzidis, Jean-Paul; Wiese, Jenny
    Concentrators processing platinum group mineral (PGM) bearing ores use polysaccharide depressants to reduce the recovery of the naturally floatable gangue minerals (mainly silicates) present in the ores. Recent work has shown that high depressant dosage can completely depress the naturally floatable gangue from reporting to the concentrate. Unfortunately, this high dosage of depressant can have a negative effect on the recovery of valuable minerals present in the ore by reducing the stability of the froth. In order to counterbalance the negative effects of depressant addition, frothers are normally added. The optimum frother provides a balance between the pulp kinetics and the froth recovery (through the effect of the frother on the bubble size and froth stability, respectively) over the range of frother addition. Usually one frother is added to accomplish this but using only one frother gives only one unique hydrodynamic relationship. It would be preferable to have independent control over the bubble size and froth stability, but unfortunately this cannot be achieved because changing the concentration of the frother changes both responses. An alternative strategy for gaining more independent control over the froth characteristics and bubble size would be to use a blend of frothers, such as a weak and a stronger frother. Such a system would give an additional degree of freedom so that changing the ratio of the two frothers would provide more independent control of bubble Sauter mean diameter and froth stability. Little research work has been conducted on frother blends and none suggests the mechanism of blended frother action. This study investigates through the use of batch flotation tests how blending low molecular weight alcohols with commercially available high molecular weight frothers impacts the solids and water recovery, as well as the valuable mineral recovery and concentrate grade, in different PGM ores. The results are compared with laboratory batch flotation tests using single frothers only. Two ores from the Merensky Reef in the Bushveld Igneous Complex, South Africa, were used .The frothers were selected to cover a range of polyglycols and alcohols, and included Senfroth 516, DOW 200 and DOW 250 (all polyglycols), and 1-butanol, 1-pentanol, 1-hexanol and MIBC (all low molecular weight alcohols). The frothers were used individually and as v blends at a total dosage of 50 g/t. Two phase tests were also carried out to measure the bubble sizes produced at different concentrations of both single frother and blends.
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    Investigation of the effect of the reagent suite in froth flotation of a Merensky ore
    (2015) Moimane, Tiisetso Makheane; Corin, Kirsten; Wiese, Jenny
    The mining industry is faced with a challenge to develop efficient and economically feasible processing routes owing to the depletion of high-grade ores, and the ever increasing demand for precious metals for a wide range of applications. The valuable minerals, PGMs (Platinum Group Minerals) and BMS (Base Metal Sulphides) in the ores are extracted through the aid of chemical reagents (activators, collectors, depressants, frothers, modifiers) which are added to the flotation circuits to facilitate the separation between these minerals and the undesired gangue minerals present in the ore. The process is made complex by many surface reactions taking place, the existence of secondary and interactive effects among the flotation reagents, as well as the surface liberation of the minerals. Owing to the stringent regulations around water usage, concentrator plants are left with no option but to recycle water within their operations. This practice leads to accumulation of pollutants, such as organics, flotation reagents residues, dissolved ions, etc., which will likely have an influence on the chemical environment of the process, and subsequently will bear an impact on the overall metallurgical performance of the concentrator. This makes the process even more intricate, making it difficult to account for the behaviour of the chemical reagents, as well as making it virtually impossible to precisely assess their individual contribution to the overall flotation performance. Hence it is of crucial importance to adopt a holistic approach when investigating the effects of the chemical parameters in a flotation process. This is a flotation chemistry study that adopted a two-level-four-factor (24) factorial experimental design to evaluate the simultaneous effects of the chemical parameters, with particular reference to collector, depressant, frother, and ionic strength of the synthetic plant water, as well as determining the possible interactive effects between the chosen parameters. This investigation was made possible by conducting batch flotation tests on a PGM-bearing ore from the Merensky reef of the Bushveld Igneous Complex. Sodium isobutyl xanthate (SIBX), a polysaccharide, namely guar gum, and a polyglycol ether, namely Dowfroth 250 were used as the collector, depressant and frother, respectively. These are the typical chemical reagents the dosages of which tailored in the PGM industry for the processing of the ores. The metallurgical performance indicators used were solids, water, copper and nickel recoveries as well as copper and nickel grades.
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    Investigation of the flotation behaviour of ball mill and IsaMill products
    (2012) Khonthu, Tsepang; O'Connor, Cyril; Wiese, Jenny; Mainza, Aubrey Njema
    Valuable minerals that are used in various aspects of everyday life are buried in fossilised storages below the ground in the earth's crust. These minerals are mined as rocks which then have to be crushed in order to liberate these minerals of value. The liberated valuable minerals have to be winnowed from the rock powder. Flotation is the main process which is used in mineral processing to recover valuable minerals. This process uses the differences in surface properties of particles to separate hydrophobic particles from hydrophilic ones. The strong relationship between the method of crushing the rocks and the amount of valuable minerals which can be reclaimed from the crushed rock has long been realized in mineral processing. The type of mineral, the size to which the rock must be reduced to and the amount of energy needed for this size reduction are among the most important factors which guide the decision on the type of device to be used in pulverising mineral rocks. Physical properties, with the exception of particle size, of mill products have not been investigated as thoroughly as the chemical properties. Physical properties include surface roughness and particle shape. The differences in shape, between particles produced by different mills, with respect to these properties, have been attributed to differences in the breakage mechanisms in the mills used to grind the particles. There is contradicting literature on the breakage mechanisms that dominate in various mills. This confusion is exacerbated by the fact that different breakage mechanisms occur simultaneously in any one mill. The definition and determination of particle shape are also difficult. Subsequently, the effect of particle shape on flotation is a subject that is rife with contradictions which add to the complexity of the subject.
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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.