Browsing by Author "Tadie, Margreth"

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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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    Open Access
    Considering the Action of Degrading Water Quality on the Electrochemical Response of Sulphide Minerals
    (2021) Ndamase, Nolihle; Corin, Kirsten; Tadie, Margreth
    Mining operations in arid regions are compelled to reduce their consumption of fresh water. Closed water circuits are an attractive solution and, in addition to reducing freshwater consumption, they have the added benefit of reducing reagent consumption as well as the environmental impact of mining operations by eliminating effluent discharge. Water is used as a liquid medium as well as a means of transportation during mining operations. Flotation, in particular, is a water intensive process where water makes up about 80- 85% of the pulp phase. Process water contains organic and inorganic species which accumulate as they are recycled. To avoid the treatment costs of removing these contaminants, many mining operations allow the quality of their water to degrade over time. When this water is introduced into flotation circuits the pulp chemistry is altered. Ionic species that accumulate in recycled process water have been shown by previous studies to be especially deleterious to flotation performance. Such ions include Ca2+, Cu2+, Mg2+, Pb2+, SO4 2- and S2O3 2- , to name a few. One of the effected flotation sub-processes is collector adsorption which is responsible for inducing hydrophobicity on valuable mineral surfaces. Accumulating ionic species have been shown to hinder collector adsorption which reduces the recovery of valuable minerals to the concentrate. Consequently, degrading water quality threatens the economic viability of mining operations that make use of closed water circuits. Xanthates are the most widely used collectors to treat base metal sulphide minerals. Most sulphide minerals are semi-conductors and xanthate adsorption onto their surfaces takes place via electrochemical reactions. Numerous studies have investigated the effect of degrading water quality on xanthate adsorption however there is very limited understanding as to how this takes place from an electrochemical perspective. This study therefore aims to investigate how the presence of accumulating ionic species at varying concentrations affects the electrochemical adsorption of sodium ethyl xanthate onto chalcopyrite and galena. Synthetic plant water (SPW) was used to mimic the composition of recycled process water. The synthetic plant water used in this study comprised of single salt solutions to isolate the effects of the ionic species of interest which were Cl- , Mg2+, SO4 2- and S2O3 2- . The salts used were NaCl, MgCl2, MgSO4, Na2SO4 and Na2S2O3. The ionic strengths were varied between 0.0242 M, 0.0727 M, 0.1212 M and 0.2426 M which correspond to 1, 3, 5 and 10SPW, respectively. Measuring the mineral rest potentials is an electrochemistry technique that was used to monitor how changing water quality affected xanthate-mineral interactions. Microflotation measurements were conducted to observe how changing water quality affected mineral floatability. Zeta potential measurements were used to determine the mineral surface charge and assess which of the ions of interest were active on the mineral surfaces. This study also aimed to investigate if electrochemistry techniques such as rest potential measurements can be used to predict flotation performance with changing water quality. Microflotation measurements revealed that degrading water quality only had an impact on the initial flotation kinetics of chalcopyrite and galena with both minerals achieving final recoveries greater than 90% regardless of changing water quality. The only exception was galena in the presence of the S2O3 2- ion where final recoveries were no greater than 35%. The S2O3 2- ion was found to be the most deleterious ionic species on both chalcopyrite and galena floatability, more especially on the latter. This was attributed to the formation of xanthyl and metal thiosulphate species which passivate the mineral surfaces, hindering collector adsorption. The formation of xanthyl thiosulphate species also reduces the amount of xanthate available for inducing hydrophobicity. It was hypothesized that increasing the ionic strength of the synthetic plant water would result in a greater hindrance of collector adsorption due to the competition between ionic species and xanthate for adsorption onto the mineral surface. This was partially true as the initial chalcopyrite recoveries in the presence of the S2O3 2- ion decreased with increasing ionic strength. Additionally, the highest initial galena recoveries in NaCl, MgCl2 and Na2S2O3 were achieved at 1SPW indicating that, even though the correlation was not linear, the initial galena recoveries in these salts decreased with increasing ionic strength. Contrastingly, the highest initial chalcopyrite recoveries in NaCl, MgCl2 and Na2SO4 were achieved at 10SPW indicating that increasing the ionic strength resulted in higher recoveries. This improvement in initial recovery with increasing ionic strength was attributed to the compression of the electrical double layer which causes the mineral-water and air-water interfaces to destabilize thus reducing bubble-particle attachment time. Rest potential measurements revealed that dixanthogen and lead xanthate were likely the dominant surface reaction species formed on chalcopyrite and galena during collector adsorption, respectively. The only exceptions were chalcopyrite in the presence of Cl- at 5SPW and S2O3 2- above 1SPW where the species that was favoured to form in these conditions was cuprous xanthate. Rest potential measurements also revealed that the presence of the S2O3 2- ion hindered xanthate-mineral interactions to a greater extent than any other ion of interest. It was hypothesized that rest potential measurements can be used as a quick and easy technique to assess the effect of changing water quality on the flotation performance of sulphide minerals. This is due to the ability of rest potential measurements to indicate the extent of xanthate-mineral interactions. Unfortunately, rest potential measurements failed to consistently predict flotation performance with changing water quality. They did however successfully predict the depressant effect of the S2O3 2- ion on the floatability of both minerals, especially that of galena. Zeta potential measurements indicated that all the ions of interest were active on the mineral surfaces. This confirmed the assertations made in previous studies that these ionic species are surface-active counter-ions that hinder collector adsorption and therefore mineral floatability due to mineral surface passivation. For example, the surface activity of the divalent cation Mg2+ had a stronger effect on mineral floatability than the monovalent Cl- anion. This was proposed to be due to the formation of the insoluble metal hydroxide Mg(OH)2 which rendered the mineral surfaces hydrophilic resulting in lower recoveries.
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    Open Access
    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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    Open Access
    The Electrochemical Response of Chalcopyrite and Galena to Degrading Water Quality
    (2022-11-21) Ndamase, Nolihle; Tadie, Margreth; Corin, Kirsten Claire
    Water is used as a liquid medium as well as a means of transportation during mining operations. Flotation, in particular, is a water intensive process where water makes up about 80–85% of the pulp phase. Process water contains organic and inorganic species which accumulate as they are recycled. To avoid the treatment costs of removing these contaminants, many mining operations allow the quality of their water to degrade over time. When this water is introduced into flotation circuits, the pulp chemistry is altered. Ionic species that accumulate in recycled process water have been shown by previous studies to be especially deleterious to flotation performance. Such ions include Ca2+, Cu2+, Mg2+, Pb2+, SO42− and S2O32−, amongst others. The flotation sub-process of collector adsorption which is responsible for inducing hydrophobicity on valuable mineral surfaces may be influenced by water chemistry. Accumulating ionic species have been shown to hinder collector adsorption which may reduce recovery of valuable minerals to the concentrate. Consequently, degrading water quality may threaten the economic viability of mining operations that make use of closed water circuits. Electrochemical techniques such as mineral rest potentials can be used to monitor the impact of changing water quality on collector–mineral interactions. Microflotation was used to determine whether mineral floatability was affected by changing water quality. This study therefore aimed to investigate whether electrochemical techniques such as rest potential measurements can be used to predict flotation performance under changing water quality. No definable relationship was found between the rest potential differences and the microflotation initial recoveries, however, rest potential measurements did identify the negative impact that thiosulphate ions may have on flotation processes.