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Collectorless flotation of pyroxene in Merensky ore: Residual layer identification using statistical ToF-SIMS analysis
Abstract
In Merensky (Bushveld Complex, South Africa) ore flotation, normally more than 2% of the gangue minerals, principally pyroxene with minor chromite, reports to the concentrate diluting the PGM recovery and contributing to subsequent processing costs. Understanding and controlling the mechanisms that cause this misreporting remains a primary target in PGM flotation. The orthopyroxene in Merensky ore can develop floatable properties through chemical interactions in the flotation system, principally through inadvertent copper-collector complexation, but this paper shows that this mechanism does not fully account for the true flotation of large pyroxene (20–150 µm) particles. Statistical comparison of ToF-SIMS analysis of particles from concentrate and tails reveals no significant difference in Cu and collector (IBX, DTP) signals between these streams but surface exposure of Mg and Si is favoured in the concentrate. Flotation of pyroxene without collector has confirmed this statistical discrimination. Hydrophobic talc-like residual layers, probably from partial serpentinisation of the pyroxene, seen in XRD differences between the concentrate and tails, explain this flotation mechanism.
... In Merensky ore flotation, the principal gangue minerals (like pyroxene and minor chromite) were found to be reported in concentrate, diluting the PGE mineral recovery and subsequently increases the processing cost. The orthopyroxene can develop floatable properties through chemical interactions in the flotation systems principally through inadvertent copper collector complexion, but it sometimes may fail to float large pyroxene (20-150 µm) particles (Jasieniak and Smart 2009). The non-sulfide gangue (except talc and magnesium silicates) are expected to be found in tailing as they are not responding well to xanthate and DTP flotation, but they report to concentrate in various mechanisms like grain locking, entrainment, metal ion activation, etc. (Kelebek and Tukel 1999). ...
... In practice, generally, polysaccharides are used as gangue depressants, but sometimes it also reduces the sulfide mineral recovery (Wiese, Harris and Bradshaw 2007). Jasieniak and Smart (2009) have collected a handpicked sample of pyroxene-based PGE ore of Merensky reef to study the behavior of gangue, their surface property, and mechanism. The chemical analysis and XRD study confirm that the pyroxene mineral is predominantly present in the sample, followed by feldspar and mica. ...
... ToF-SIMS confirms that Mg/Sirich corresponds to pyroxene, whereas the minerals collected in tailing are Na/Al-rich particles corresponding to feldspar. The statistical analysis also shows the pyroxene collected in concentrate is high exposure to Mg and Si as compared to tailing (Jasieniak andSmart 2009). O'Conner et al. (2019) also studied the behavior of gangue during the flotation of PGE minerals of Bushveld complex, South Africa. ...
The unique physical and chemical properties of platinum group elements are making them indispensable in many modern industrial applications. Platinum-group minerals are usually beneficiated by flotation or gravity separation followed by flotation. Due to poor liberation characteristics and interstitial attachment of these minerals with base metal sulfides, chromites, and silicates, fine grinding is necessitated. Significant variability of platinum group element deposit types and their mineralogical characteristics create a challenge to choose a proper reagent suite. The present article critically discusses all the factors that affect the flotation of platinum group element bearing minerals, flotation routes, essential gaps, the problems associated with their processing, and suitable reagent suites used in different ore deposits and plant practices.
... The data reveal that the orthopyroxene is reporting to the concentrate either by the natural floatability of the talc rim or inadvertent activation by Cu or Ni. Jasieniak and Smart (2009) compared the surface chemistry of pyroxene reporting to the concentrate and tail to understand parameters that affect floatability of Merensky ores. TOF-SIMS results did not reveal any significant variation in copper or collector species on the surface of pyroxene particles between those from the concentrate or tail. ...
... The Mg and Si intensity discrimination favouring the concentrate samples combined with XRD analyses identified that inadvertent flotation is in response to hydrophobic talc like layers present on the outer surface of the pyroxene grains. (Jasieniak and Smart, 2009). The layers, which represent partial serpentinization of pyroxene, have also been identified in the ultramafic Sudbury ores where a similar inadvertent recovery of pyroxene has been observed. ...
... TOF-SIMS images indicate a high intensity of magnesium and silicon-rich patches on the surface of recovered coarse chromite grains in the concentrate. A silicon to chromium intensity ratio from TOF-SIMS data identifies a discriminating floatability parameter for chromite in these samples (Jasieniak and Smart, 2009). ...
This paper reviews the applications of time of flight secondary ion mass spectrometry (TOF-SIMS) used for surface chemical analysis of mineral in the context of froth flotation. A wide range of applications are reviewed, including; interactions of reagents on the surface of mineral phases during flotation separation, determining the effects of various transferred ions from different minerals or the slurry, evaluation of hydrophobicity, identifying the relationship between mineral surface chemistry and contact angle, and evaluation of grinding effects. Conclusions indicated that TOF-SIMS, as a unique surface analysis technique, can potentially provide a direct determination of parameters which control the surface reactivity and consequently plays an important role in determining flotation behaviour of minerals.
... Nagaraj and Brinen, 1996;Malysiak et al., 2004). More recently, Jasieniak and Smart (2009) showed using ToF-SIMS that the surface exposure of Mg and Si was greater for gangue particles in a Merensky concentrate relative to a tailings sample. In conjunction with XRD spectra, they attributed this to be due to the preferential association of orthopyroxene with talc. ...
... Therefore, the presence of submicron talc rims or partial coatings on liberated orthopyroxene particles cannot be detected using this type of instrumentation and is where surface techniques such as ToF-SIMS may be more appropriately used. Accordingly, the ToF-SIMS study of Jasieniak and Smart (2009) showed elevated Mg and Si concentrations on gangue particles in a Merensky concentrate relative to those in the tailings. In combination with the XRD results from their study, Jasieniak and Smart (2009) similarly suggested that the talc was preferentially associated with orthopyroxene and may account for the natural floatability of these particles. ...
... Accordingly, the ToF-SIMS study of Jasieniak and Smart (2009) showed elevated Mg and Si concentrations on gangue particles in a Merensky concentrate relative to those in the tailings. In combination with the XRD results from their study, Jasieniak and Smart (2009) similarly suggested that the talc was preferentially associated with orthopyroxene and may account for the natural floatability of these particles. ...
During the recovery of the valuable platinum group minerals and base metal sulphides in the Merensky Reef ore by flotation, a certain amount of naturally floatable gangue (NFG) is recovered, which dilutes the concentrate. Although talc is the only silicate mineral well known for it naturally floatable properties, the proportion of NFG recovered in batch flotation tests of the Merensky ore, however, cannot be solely accounted for by the mass of pure talc present in the feed ore. Using methodology developed at the University of Cape Town to decouple the NFG from entrained gangue recovered in flotation, a series of concentrate samples have been analysed in this study using quantitative mineralogical analysis methods. Results show the major diluents of concentrate grade are orthopyroxene, talc, clinopyroxene and plagioclase in decreasing order of abundance. Orthopyroxene is however, by far the greatest diluent of concentrate grade even though the particles recovered are classified as liberated or high grade middlings. On closer examination, these orthopyroxene particles show a preferential surface association to talc and vice versa which is consistent with the low temperature alteration of anhydrous orthopyroxene to a hydrous phase, namely talc. These composite orthopyroxene particles with partial talc rims are therefore thought to be one of the main contributors to NFG in the Merensky Reef ore.
... The high mass pull during flotation of the sample of the WP facies type of Merensky Reef (Fig. 2) is a consequence of the higher orthopyroxene content (67%) of this sample, relative to the rest of the samples examined (Table 4). Orthopyroxene is known to be naturally floating (Jasieniak and Smart, 2009), and may also be activated by the addition of copper sulphate during flotation (Brough et al., 2010;Lotter et al., 2008;Wiese et al., 2005). ...
The influence of mineralogy on the milling performance and the flotation-based recovery of Au, the platinum group elements (PGE), Co, Cr, Cu, Ni and S was investigated for three samples of the Merensky Reef (BK, RPM and WP facies types) and one sample of the UG2 at the Marikana mine, using a mineral liberation analyser (MLA). The samples differ in their milling behaviour in that a range of milling times are required in order to produce a grind of 60% passing 75 lm. This is primarily controlled by the abundance of plagioclase, orthopyroxene and chromite. The size distribution of the base metal sulfides (BMS; pyrrhotite, pentlandite and chalcopyrite) is similar for the three samples of Merensky Reef, and is significantly coarser than for BMS in the sample of the UG2. Upon milling to 60% passing 75 lm, the best BMS liberation is achieved for the BK facies type of Merensky Reef, relative to RPM and WP. The degree of BMS liberation in the sample of UG2 is lower than that for samples of the Merensky Reef. Cumulative mass pull during flotation is higher for the sample of the WP facies of Merensky Reef than for the rest of the samples examined. This is due to the higher abundance of orthopyroxene in this sample , which is known to be naturally floating, and which reports to concentrate. A high flotation-based recovery of PGE, Cu and S is observed for all four samples, with the highest recovery associated with the sample of the BK facies type of Merensky Reef. Ni recoveries are generally poor, suggesting that Ni is associated with gangue minerals, in addition to that in pentlandite. Of the three facies types of Merensky Reef examined, the overall characteristics of the BK facies type i.e. a high PGE grade, low abundance of orthopyroxene, a high abundance of BMS, and a higher degree of liberation of the BMS on milling of the ore, represent the most favourable set of characteristics for the efficient recovery of PGE. It is therefore the best quality ore of the three samples of Merensky Reef examined.
... In addition, low quantities of talc present in the ore can significantly reduce concentrate grade, which is mainly attributed to the recovery of locked talc that is finely disseminated within hydrophilic gangue particles (Wiese et al., 2008;Becker et al., 2014). Composite talcorthopyroxene particles represent the main constituent of naturally floating gangue in PGE ores (Lotter et al., 2008;Becker et al., 2009;Jasieniak and Smart, 2009). Talc was mainly found to occur as rims or partial rims around the orthopyroxene and could impart naturally floating behaviour on orthopyroxene at low talc feed concentrations (Becker et al., 2009). ...
... Talc, due to its strong, natural hydrophobicity (Martinovic et al., 2005;Becker et al., 2009;Jasieniak and Smart, 2009) reports preferentially to the concentrates over the rougher tails (Fig. 2) and preferentially to the concentrates compared with other key minerals (Fig. 3). Feldspar contents are most abundant in the rougher tails, with chlorite/ mica distribution the most abundant in RC5 (Fig. 2). ...
In spite of numerous studies on PGM behaviour in flotation, there remains much discrepancy regarding PGM speciation and its impact on floatability, as PGMs are routinely considered as an entire group for recovery prediction and trouble-shooting investigations. The understanding of preferential floatability of PGM species under a given flotation regime is important in predicting and addressing mineralogical variability in processing plants, to ensure efficiency in PGM upgrading and recovery. In this contribution, the effect of reduced collector and frother dosages on floatability of individual liberated PGM species was studied in Platreef ore from South Africa, which contains a large variety of different types of PGM species.
Reagent tests were performed, with the aim to facilitate a more competitive environment for PGM flotation, by decreasing the collector and frother dosages with respect to a baseline test. Automated mineralogical analysis was performed on the feed, rougher concentrates and tails of the reduced reagent and baseline tests to ascertain how PGM species respond to reducing collector and frother dosages by virtue of the concentrate streams and tails they report to. PtS showed preferential upgrading compared to PdBiTe, PtPdS, PtBiTe, and PtAs, in the reduced reagent test. PdBiTe overall performs better than PtBiTe. PtAs consistently performs the worst in both baseline and reduced reagent tests and is therefore deemed a poorly floatable mineral irrespective of the reagent conditions used. PtPdS, PtAs and PtS floatability seem to be sensitive to grain size with coarse PGM preferentially recovered, over finer grains, in first concentrates.
These results can aid in predictive studies for flotation of Platreef ores with variable PGM assemblages, and consequent tailoring of reagent conditions to improve flotation efficiency.
... Time of flight secondary ion mass spectrometry (ToF-SIMS) is a very sensitive technique for analyzing and mapping the chemical composition of solid surfaces and thin films [18][19][20][21]. In the field of flotation, it was mainly used for investigation the adsorption of flotation reagents on the mineral surface [22][23][24][25][26], study the hydrophobicity of mineral particles [27,28], identifying the relationship between mineral surface chemistry and contact angle [29][30][31][32], optimization of the flotation condition [33], and evaluation of grinding effects [34,35]. However, ToF-SIMS can inevitably cause certain degrees of surface damages of the sample during the analysis. ...
This research describes the possibility of ultra-high dose deep titanium ion implantation for surface modification of zirconium alloy Zr-1Nb. The developed method based on repetitively pulsed high intensity low energy titanium ion implantation was used to modify the surface layer. The DC vacuum arc source was used to produce metal plasma. Plasma immersion titanium ions extraction and their ballistic focusing in equipotential space of biased electrode were used to produce high intensity titanium ion beam with the amplitude of 0.5 A at the ion current density 120 and 170 mA/cm². The solar eclipse effect was used to prevent vacuum arc titanium macroparticles from appearing in the implantation area of Zr sample. Titanium low energy (mean ion energy E = 3 keV) ions were implanted into zirconium alloy with the dose in the range of (5.4–9.56) × 10²⁰ ion/cm². The effect of ion current density, implantation dose on the phase composition, microstructure and distribution of elements was studied by X-ray diffraction, scanning electron microscopy and glow-discharge optical emission spectroscopy, respectively. The results show the appearance of Zr-Ti intermetallic phases of different stoichiometry after Ti implantation. The intermetallic phases are transformed from both Zr0.7Ti0.3 and Zr0.5Ti0.5 to single Zr0.6Ti0.4 phase with the increase in the implantation dose. The changes in phase composition are attributed to Ti dissolution in zirconium lattice accompanied by the lattice distortions and appearance of macrostrains in intermetallic phases. The depth of Ti penetration into the bulk of Zr increases from 6 to 13 μm with the implantation dose. The hardness and wear resistance of the Ti-implanted zirconium alloy were increased by 1.5 and 1.4 times, respectively. The higher current density (170 mA/cm²) leads to the increase in the grain size and surface roughness negatively affecting the tribological properties of the alloy.
... The high mass pull during flotation of the sample of the WP facies type of Merensky Reef (Fig. 2) is a consequence of the higher orthopyroxene content (67%) of this sample, relative to the rest of the samples examined (Table 4). Orthopyroxene is known to be naturally floating (Jasieniak and Smart, 2009), and may also be activated by the addition of copper sulphate during flotation (Brough et al., 2010;Lotter et al., 2008;Wiese et al., 2005). ...
The aim of this contribution is to report on an investigation into the geology, mineralogy and flotation performance of Merensky Reef and UG2 at the Two Rivers platinum mine on the Eastern Limb of the Bushveld Complex in South Africa. Geometallurgical test work was carried out on samples collected from underground workings, in the form of channel samples, and include the determination of modal mineralogy, milling performance, mineral liberation, and laboratory scale flotation testing.
Metallurgical samples from the concentrator plant (for the rougher circuit) were also studied in order to monitor the bahaviour of the major ore and gangue minerals at the plant scale. These include UG2 which is currently being mined, as well as a bulk sample of Merensky Reef produced through trial mining which was processed through the same plant.
The results of the study will be presented and discussed.
... Biotite which may be primary or secondary is also greatest within the Normal reef (1.8 wt%) compared to the P2 (0.9 wt%) and NP2 reefs (1.1 wt%). The relative proportions of low-temperature alteration minerals such as talc are important since they are naturally floatable and may induce inadvertent gangue flotation if they are associated with other common gangue minerals (Becker et al., 2009;Jasieniak and Smart, 2009). ...
This case study briefly highlights the potential to derive, in an approximate sense, likely processing behaviour from geological reconstructions. In turn, this information can feed into geometallurgical planning allowing the early stage recognition of potential processing flowpaths that can be used to optimise recovery. The case study is pulled together from analysis undertaken on the Merensky reef at Northam Platinum Ltd in South Africa.
The Merensky Reef at Northam Platinum shows a complex range of reef developments with several distinct reef types that are processed through the run-of-mine. These differences can be related to the paragenetic history of the deposit with the differing mineralogy related to the changing footwall mineralogy at the time of the hanging wall deposition. This case study looks at three of those reef types (the Normal Reef, the transitional Pothole reef and the full Pothole reef) which contain distinct differences in their mineralogical deportment.
The differing mineralogy of the footwall at the time of hanging wall deposition resulted in differences in modal mineralogy, the amount of floatable gangue and the sulphide textural development. These differences in turn led to predictable differences in milling times, mineral liberation and sulphide flotation performance. As the Merensky reef is a platinum-group element (PGE) ore with the majority of the platinum-group minerals contained within sulphides, these differences are crucial.
... Several concerns have arisen with the installation of this technology on PGM ore. One of these is whether there will be an increase in the amount of naturally floating gangue (composite orthopyroxene and talc particles, Becker et al., 2009;Jasieniak and Smart, 2009) resulting in significant dilution of concentrate grade. This is particularly so for Great Dyke ores that show considerable low temperature, late stage alteration associated with the formation of hydrophobic talc (Li et al., 2008). ...
... The high mass pull during flotation of the sample of the WP facies type of Merensky Reef (Fig. 2) is a consequence of the higher orthopyroxene content (67%) of this sample, relative to the rest of the samples examined (Table 4). Orthopyroxene is known to be naturally floating (Jasieniak and Smart, 2009), and may also be activated by the addition of copper sulphate during flotation (Brough et al., 2010;Lotter et al., 2008;Wiese et al., 2005). ...
... The selective flotation of sulphides from non-sulphide gangue minerals such as pyroxene and feldspar along with minor quantities of talc, chlorite and chromite is becoming important to the mineral processing industry. Although present at levels between 0.5% and 5%, talc has a disproportionate effect on flotation performance since it occurs along pyroxene grain boundaries and can result in large amounts of NFG reporting to the concentrate (Becker et al., 2006;Jasieniak and Smart, 2009). The process is very complex; it relies on the differences in the surface properties between the desired minerals and the unwanted gangue to effect separation . ...
The presence of ions in plant water is believed to be having an effect on the flotation process as ions are able to modify the chemistry of the system. This study investigated the interactive effects of ionic strength, depressant dosage and depressant type on the recovery of copper and nickel sulphides, water, floatable and entrained gangue as well as grade of the valuable sulphides in the flotation of a Pt bearing ore from the Merensky reef. Batch flotation results showed no change in Cu recovery, but Ni recovery decreased dramatically when a polysaccharide depressant was charged at 500 g/t. Water recovery increased with increasing ionic strength, indicating that there exist ions in the water system which have a froth stabilising effect.
... The selective flotation of sulphides from non-sulphide gangue minerals such as pyroxene and feldspar along with minor quantities of talc, chlorite and chromite is becoming important to the mineral processing industry. Although present at levels between 0.5% and 5%, talc has a disproportionate effect on flotation performance since it occurs along pyroxene grain boundaries and can result in large amounts of NFG reporting to the concentrate (Becker et al., 2006;Jasieniak and Smart, 2009). The process is very complex; it relies on the differences in the surface properties between the desired minerals and the unwanted gangue to effect separation . ...
The presence of ions in plant water is believed to be having an effect on the flotation process as ions are able to modify the chemistry of the system. This study investigated the interactive effects of ionic strength, depressant dosage and depressant type on the recovery of copper and nickel sulphides, water, floatable and entrained gangue as well as grade of the valuable sulphides in the flotation of a Pt bearing ore from the Merensky reef. Batch flotation results showed no change in Cu recovery, but Ni recovery decreased dramatically when a polysaccharide depressant was charged at 500 g/t. Water recovery increased with increasing ionic strength, indicating that there exist ions in the water system which have a froth stabilising effect.
... During the alteration process, hydrous phyllosilicate minerals such as talc form along grain boundaries and cleavage planes of orthopyroxene. This results in the occurrence of composite orthopyroxene and talc particles which have been linked to the occurrence of naturally floating gangue (NFG: Becker et al., 2009;Jasieniak and Smart, 2009). Previous work by Wiese et al. (2007) has shown that a depressant dosage of $300 g/t is sufficient to depress all the NFG in Merensky ore. ...
... Although talc has been found to occur in only trace quantities in ore (0.5-5% by mass), it has an inordinate effect and has been known to stabilise the froth phase and allow for the recovery of larger amounts of gangue. Talc has been shown to exist along pyroxene grain boundaries Jasieniak and Smart, 2009) allowing these gangue minerals to be naturally floatable. ...
Valuable mineral recoveries and grades are strongly dependent on the stability of the froth phase within the flotation system; a stable froth zone allows for the efficient transportation of material for downstream processing, while entrainment of gangue is directly proportional to the amount of water recovered from the froth phase (Engelbrecht and Woodburn, 1975; Zheng et al., 2006a,b; Neethling and Cilliers, 2002). In an attempt to reduce the naturally floatable gangue (NFG) present in platinum bearing ores and to improve the grades of the valuable minerals, the use of high depressant dosages have been investigated. These high depressant dosages have significantly destabilised the froth phase in a number of studies (Bradshaw et al., 2005; Martinovic et al., 2005; Wiese, 2009). Wiese et al. (2010) has shown that an increase in frother dosage impacted the stability of the froth resulting in enhanced recovery of valuable minerals. In a separate study by Corin et al. (2011), the effect of an increase in the ionic strength of plant water on the stability of the froth was considered. As water restrictions become more stringent, many operations are recycling and reusing their process water causing an increase in the amount of dissolved ions present in the water, the effects of which are little understood. The same study also considered depressant addition at high dosages. It was noted that an increase in the ionic strength of the plant water increased the froth stability. This paper therefore compares the outcomes of increased frother dosage with increased ionic strength, and attempts to better understand the factors which influence the froth stability. The data presented in this paper forms part of much larger studies and complementary data has been published elsewhere (Wiese and Harris, 2012; Manono et al., 2012, 2013).
... It has also previously been shown that the Merensky Reef ore contains a significant proportion of naturally floating gangue which cannot be accounted for based on the mass recovery of pure talc. Mineralogical analyses have shown that the naturally floating gangue is comprised of composite particles of orthopyroxene and talc (Jasieniak and Smart, 2009;Becker et al, In Press). The presence of partial talc rims renders these particles naturally floatable. ...
Merensky Reef ores are processed by flotation to recover the valuable platinum group elements and minerals, as well as base metal sulfides and selected reagents are added to optimise this process. Batch flotation tests are one of the key tools used to evaluate and understand the different interactions taking place between the reagents and minerals. Metallurgical performance is generally evaluated from the extrapolation of chemical assays that are routinely available, but which does not allow investigation of the types of particles being affected under the different flotation conditions. With the advent of quantitative mineralogical analyses (MLA, QEMSCAN) on metallurgical samples, these previously qualitative interpretations of flotation performance can now be quantified. Therefore, the aim of this study was to evaluate the use of chemical assays to interpret the batch flotation performance through the use of automated mineralogy in the context of a larger study that investigates the effect of depressant addition on the flotation of the base metal sulfides on a Merensky Reef ore. The QEMSCAN results showed that calculations of total gangue recovered to the concentrate based on chemical assays were shown to be relatively accurate. Interpretation of chalcopyrite and pentlandite flotation performance based on chemical assays was good, although the interpretation of pyrrhotite performance was complicated by the presence of pyrite. The base metal sulfides recovered were over 70 per cent liberated. No reduction was observed in the floatability of liberated chalcopyrite and pentlandite in the two size fractions investigated, due to the addition of depressant. The inadvertent loss of pyrrhotite during flotation however, was accounted for by the effect of depressant addition on froth stability. This study has shown the usefulness of both the extrapolation of chemical assay and mineralogical analysis in evaluating the results of batch flotation tests, although the results need to be interpreted with care.
... Furthermore, mica (mostly biotite), which may be primary or secondary is also greatest within the Normal reef (1.8 wt%) compared to the P2 (0.9 wt%) and NP2 reefs (1.1 wt%). The relative proportions of low-temperature minerals such as talc are important since they are naturally floatable and may induce inadvertent gangue flotation if they are associated with other common gangue minerals (Becker et al., 2009;Jasieniak and Smart, 2009). The degree of alteration is important since it influences ore hardness, which in turn affects mill throughput. ...
At Northam Platinum Mine in South Africa intense potholing of the Merensky Reef has led to the development of several mineralogically different reef types in proximity to one other, which results in differing processing performance. In particular, the nature and texture of the valuable sulfide minerals, as well as the nature of the gangue minerals and degree of alteration in the various reef types affects both milling throughput and flotation recovery. The three major ore types being processed and thus selected for this study are the Normal reef, NP2 reef and P2 reef. The focus of this study was to investigate the relationship between changes in mineralogy and the effect of copper sulfate addition at two grind sizes on the laboratory batch flotation performance obtained with the three reef types. The best results were obtained with the NP2 reef in terms of expected industrial throughput, recovery and grade of all base-metal sulfides despite this reef type having the lowest feed grade of sulfide minerals. The biggest difference was in the recovery and grade of pyrrhotite. The better performance of the NP2 reef ore relative to the Normal and P2 reefs has been attributed to the equigranular nature of the reef type together with its feldspathic mineralogy. In contrast, the Normal and P2 reefs are orthopyroxene rich and are associated with more alteration minerals. The Normal reef contained the greatest amount of alteration minerals which correlated to the poorest flotation performance in terms of recovery and grade at all conditions tested. Whereas addition of copper sulfate did not affect the flotation of the sulfides in the NP2 reef ore, it significantly improved the overall performance of the base-metal sulfides in the Normal and P2 reefs, especially for pyrrhotite.
In complex flotation circuits of lead-zinc sulfide ore, selective adsorption of flotation reagents (e.g., collectors, depressants, and regulators) and solution components onto different mineral surfaces are involved. This work aimed to study the surface chemistry differences between minerals in lead concentrate and those in tailings by time-of-flight secondary ion mass spectrometry (ToF-SIMS) and multivariate analysis to understand the flotation behavior of minerals. Specifically, multivariate curve resolution-alternating least squares (MCR-ALS) and principal component analysis (PCA) were used to process ToF-SIMS image datasets of flotation products to enhance mineral identification. The results show that MCR-ALS was more successful than PCA in identifying minerals of ToF-SIMS images from flotation products. Further PCA of the spectra obtained from the specific mineral surfaces in the lead concentrate and tailings revealed surface chemistry reasons for the poor mineral separation. The main finding of this study was that the adsorption of lead ions onto the surfaces of sphalerite, pyrite, calcite, and quartz was an important reason for the failed separation of these minerals from galena in high-alkaline lime systems. The surface chemical evidence provided by this study helps to better understand the selective separation mechanism of lead-zinc sulfide ores.
Pyrite, a gangue mineral, is commonly associated with valuable base metal sulfide minerals and the separation of pyrite from these valuable sulfide minerals by flotation is difficult. In this study, a type of biopolymers, modified from lignosulfonates, was used to reject pyrite in chalcopyrite flotation based on the previous investigations. It was found that these biopolymers selectively depressed pyrite flotation with little effect on chalcopyrite flotation. The presence of pyrite decreased the depression effect of biopolymers on chalcopyrite flotation due to the preferential adsorption of biopolymers on copper-activated pyrite as revealed by the adsorption isotherms and ToF-SIMS (Time-of-Flight Secondary Ion Mass Spectrometry) analyses. The presence of chalcopyrite increased the depression effect of biopolymers on the flotation of copper-activated pyrite due to enhanced oxidation of the copper activation product, Cu(I)S, on pyrite as a result of the galvanic interaction among Cu(I)S, pyrite and chalcopyrite.
The role of surface chemistry in recovery of minerals is central to several processes such as froth flotation, leaching, and electrostatic separation. In separation of base metals (eg, Cu, Pb, Zn, and Ni) by froth flotation of their minerals, usually sulphides, the attachment of these mineral particles, after hydrophobic collector addition, to air bubbles is used in operation. The stability of this bubble/particle attachment in both pulp and froth phases is dependent on the hydrophobic/hydrophilic ratio of surface species on individual mineral particle surfaces. The surfaces of individual mineral particles are a complex, distinctly non-uniform array of hydrophobic collector molecules and hydrophilic species (eg, oxidation products, adsorbed ions, fine particles, and precipitates). Hence, this ratio varies widely between different particles of the same mineral. It has been shown to determine whether particles report, correctly or incorrectly, to concentrate or tail (residue). To improve poor flotation recovery or grade, the analysis needed is the variation of this ratio by particle and as a statistical distribution between different mineral phases across a flotation circuit (eg, feed, successive concentrates, and tails). This requires surface analysis of a large number of particles with high spatial resolution and chemical speciation. In this Surface Science Western special issue article, methods to achieve this, using time-of-flight secondary ion mass spectrometry and principal component analysis, developed between the Ian Wark Research Institute and Surface Science Western over 25 years are reviewed with applications to flotation. They are equally applicable to interferences in leaching, extraction, and electrostatic separation processes. Copyright
A complete strategy has been developed for identification of the reasons for losses in recovery and/or grade, due to changes or complications in mineralogy and in mineral surface conditioning, and their subsequent correction. The sequence of methods starts with comparison of mineral phases between QEMSCAN/MLA (compositional) and Rietveld XRD (crystalline diffraction) with bulk assay reconciliation. This methodology has recently led to identification of unrecognised amorphous content (12-40 wt.%), previously attributed to crystalline phases, in the fine fraction (<35 μm) of some problematic flotation feeds. Attached amorphous silica, talc- and chlorite-like fines have direct influence on the hydrophobic/hydrophilic ratio on value mineral surfaces adversely affecting flotation. SEM/EDS is used in the backscattered imaging mode to determine possible problems with liberation (e.g. remnant local locking), not detected in standard liberation analysis, resulting in gangue flotation. EDTA extraction is used to assess bulk feed pre-oxidation and sequential oxidation product loading through the circuit. Changes in circuit solutions are assayed with speciation modelling of precipitates and potentially adsorbing species. ToF-SIMS with principal component analysis is then used to correlate surface species with specific minerals and can be used to assess the effectiveness of specific reagents particularly collectors. This approach identifies unwanted activating species and interference with value surfaces by adsorbed hydrophilic ions, precipitates and fine particles. When the interference or ineffective reagents are specifically identified, remedial action can be targeted. This method has identified residual talc-like layers (<10 nm thick) inducing gangue flotation of pyroxene and chromite in PGM flotation. Recent case studies of application of the full methodology to losses of molybdenite at KUCC and to sphalerite activation in the Cu/Pb circuit at Brunswick Mines with remedial action are discussed.
Flotation has been widely used for separation of valuable minerals from gangues based on their surface characterizations and differences in hydrophobicity on mineral surfaces. As hydrophobicity of minerals widely differs from each other, their separation by flotation will become easier. Collectors are chemical materials which are supposed to make selectively valuable minerals hydrophobic. In addition, there are some minerals which based on their surface and structural features are intrinsically hydrophobic. However, their hydrophobicities are not strong enough to be floatable in the flotation cell without collectors such as sulfide minerals, coal, stibnite, and so forth. To float these minerals in a flotation cell, their hydrophobicity should be increased in specific conditions. Various parameters including pH, Eh, size distribution, mill types, mineral types, ore characterization, and type of reaction in flotation cells affect the hydrophobicity of minerals. Surface analysis results show that when sulfide minerals experience specific flotation conditions, the reactions on the surface of these minerals increase the amount of sulfur on the surface. These phenomenons improve the hydrophobicity of these minerals due to strong hydrophobic feature of sulfurs. Collectorless flotation reduces chemical material consumption amount, increases flotation selectivity (grade increases), and affects the equipment quantities; however, it can also have negative effects. Some minerals with poor surface floatability can be increased by adding some ions to the flotation system. Depressing undesirable minerals in flotation is another application of collectorless flotation.
Separation of pyrochlore from its associated minerals is typically accomplished by froth flotation. The surface chemistry of pyrochlore is similar to many of its associated non-value minerals. Therefore, understanding the surface chemical properties of the pyrochlore for selective pyrochlore flotation will potentially aid in the design of flotation strategies for optimized recovery. In this study, pyrochlore samples were collected from various points in the flotation scheme at the Niobec plant, Quebec, Canada. The SEM-EDX analysis revealed that pyrochlore from the Niobec deposit occurs as high and low iron varieties, and that recovery favours varieties with a lower Fe content. To understand a potential relationship between pyrochlore matrix composition and the related effect on collector adsorption, the surface of grains from the concentrate and tails were examined by TOF-SIMS. The surface analyses of different pyrochlore grains showed that species indicative of the cationic collector (Tallow diamine acetate) favour Fe poor pyrochlore relative to the Fe rich variety. XPS was used to analyse the surface of high Fe and low Fe pyrochlore in order to identify a potential relationship between pyrochlore matrix composition and surface chemistry. The XPS results verified a relationship between pryochlore surface oxidation and Fe content in the mineral matrix; high Fe pyrochlore particles showed a greater proportion of surface oxidation species suggesting preferential oxidation in comparison with low Fe pyrochlore particles. SEM-EDX analyses revealed that many of the pyrochlore grains were compositionally zoned into regions of high and low Fe contents. TOF-SIMS and XPS analyses were used to analyse the surface of the compositionally zoned Fe pyrochlore grains, in order to link collector adsorption to Fe contents and identify potential mechanisms for the partitioning. Surface analyses of conditioned pyrochlore grains showing zones of high and low Fe content revealed that species indicative of the collector favour the regions with low iron. XPS analyses of similarly treated compositionally zoned pyrochlore grains showed that a greater proportion of surface oxidation species corresponded to the zones with high matrix Fe content. These results are in accord with the results identified for non zoned pyrochlore grains of variable matrix Fe content and verifies the link between pyrochlore Fe composition, surface oxidation and, area selective collector loading.
This review covers a wide range of surface analytical techniques: X-ray photoelectron spectroscopy (XPS), scanning photoelectron microscopy (SPEM), photoemission electron microscopy (PEEM), dynamic and static secondary ion mass spectroscopy (SIMS), electron backscatter diffraction (EBSD), atomic force microscopy (AFM). Others that are relatively less widely used but are also important to the Earth Sciences are also included: Auger electron spectroscopy (AES), low energy electron diffraction (LEED) and scanning tunnelling microscopy (STM). All these techniques probe only the very top sample surface layers (sub-nm to several tens of nm). In addition, we also present several other techniques i.e. Raman microspectroscopy, reflection infrared (IR) microspectroscopy and quantitative evaluation of minerals by scanning electron microscopy (QEMSCAN) that penetrate deeper into the sample, up to several μm, as all of them are fundamental analytical tools for the Earth Sciences. Grazing incidence synchrotron techniques, sensitive to surface measurements, are also briefly introduced at the end of this review. (Scanning) transmission electron microscopy (TEM/STEM) is a special case that can be applied to characterisation of mineralogical and geological sample surfaces. Since TEM/STEM is such an important technique for Earth Scientists, we have also included it to draw attention to the capability of TEM/STEM applied as a surface-equivalent tool.
The use of high dosages of polysaccharide depressants in order to depress the undesired naturally floatable gangue (NFG) present in ores beneficiated from the Bushveld Complex, South Africa, results in a significant decrease in the stability of flotation froths. These unstable froths can result in restricted mass pull and decreased valuable mineral recovery. Previous work using a single polyglycol ether type frother, DOW 200, has shown that an increase in frother dosage could be used to overcome the destabilisation of the froth to a certain extent and improve valuable mineral recovery. This resulted in an increase in water recovery and dilution of the concentrate by entrained material. This work extends this study to examine the effect of using a stronger frother, DOW 250, on the recovery of sulphide minerals and floatable gangue from a Merensky ore at different dosages of guar gum and CMC, which are typically used as depressants in the processing of Merensky ore. Results indicate that an increase in the strength of the frother resulted in a more robust froth. Depressant type also had an influence on results obtained.
It has been proposed that blending of the Kennecott Utah Copper Corporation (KUCC) Bingham Canyon poorly-floating limestone skarn (LSN) ore with the monzonite ore (MZ), which in isolation floats well, results in a ‘poisoning’ effect on chalcopyrite, bornite and molybdenite flotation recovery. This proposition has been examined via a combined study of mineralogy, liberation, solution, surface and SEM analyses of batch flotation samples.Cu grade versus recovery for the blended ore (70% MZ: 30% LSN) was close to that predicted by pro-rata flotation of the separate fractions and hence flotation poisoning of the MZ copper containing minerals is not occurring. In contrast recovery and grade of molybdenite, which is only present in significant quantities in the MZ ore, was significantly reduced as compared to pro-rata prediction, indicative of a poisoning effect on flotation performance.Although pre- and post-conditioning and tailings water samples were super-saturated with respect to a range of Mg and Ca-containing species similar supersaturation trends were observed regardless of the ore or blend used. Hence, precipitation of hydrophilic species onto mineral surfaces cannot be used to explain the differences in flotation phenomena observed.Similar surface contamination of chalcopyrite, bornite and molybdenite in both the LSN and blended ore concentrates was observed, whereas the surfaces of molybdenite in the MZ concentrates were relatively clean. The principal surface contamination of the concentrates for the blended ore, which increased in severity between the 1st and 4th concentrates, was from Ca and Fe hydroxides, phosphates and Ca and Mg aluminosilicate gangue. This is in agreement with the observed mineralogy with the LSN ore containing considerably greater proportions of the Mg-containing minerals pyroxene, amphibole and talc, and the Ca-containing minerals, calcite and andradite than the MZ ore.It is suggested that the transfer of hydrophilic components from the LSN to MZ ores on blending has little effect on Cu mineral flotation due to these minerals already having similar levels of surface contamination within the two ore types. However, the formerly relatively clean molybdenite surfaces from the MZ ore are contaminated as a result of blending leading to a dramatically reduced flotation response.
In the UG2 ore (Bushveld Complex, South Africa) flotation, normally more than 3% of the gangue minerals, principally chromite with talc and pyroxene, report to the concentrate diluting the PGM recovery and contributing to subsequent processing costs. Previous studies have identified residual talc-like layers on orthopyroxene surfaces in Merensky ore flotation contributing to inadvertent flotation of relatively large particles (20–150 µm) of this mineral. Chromite (75–150 µm) from flotation of UG2 ore has been similarly examined. Statistical comparison of ToF-SIMS analysis of particles from concentrate and tails reveals no significant difference in Cu, Pb, Ni and collector (IBX and DTP) signals between these streams but surface exposure of Mg and Si is favoured in the concentrate. The flotation rate of coarse chromite correlates with the exposures of magnesium and silicon in patches on the chromite surface; higher exposures give earlier flotation. Conversely, there is a negative correlation with signals corresponding to the chromite surface, i.e. Cr, Fe, Al. Flotation of chromite without collector has confirmed this statistical discrimination. Hydrophobic talc-like residual layers, similar to those found on orthopyroxene surfaces, probably from partial alteration, explain this flotation mechanism.
High energy costs required to smelt low grade concentrates could be alleviated by the production of high grade concentrates. Obtaining maximum PGM recovery by the use of high dosages of polysaccharide depressants may be problematic in that a significant decrease in the stability of the froth, particularly with CMC, results. These highly unstable froths may result in restricted mass pulls and decreased valuable mineral recovery. There are a number of ways of counteracting unstable froths, such as increasing airflow rate, reducing froth height or increasing frother dosage. Although necessary to maximise PGM recovery, all of these are likely to lead to increased water recovery and dilution of the concentrate by entrained material. This work examines the effect of increasing frother dosage on the recovery of sulphide minerals and floatable gangue from a Merensky ore at varying dosages of guar gum and CMC, as well as on the recovery of entrained gangue and its dependence on the physical nature of the flotation pulp.
The abundances of the platinum-group elements (PGE), and their relative proportions, are summarized for all the mines exploiting the Merensky Reef on both western and eastern limbs of the Bushveld Complex, in South Africa. Grades for the mined reef interval are uniform over 100 km of strike length, at 5-7 g/t, except for Union mine, where it is currently 8 g/t. The rel ative proportions of the various PGE are extremely constant over this same distance. In contrast, the platinum-group minerals (PGM) vary enormously. On a regional scale around the western limb, the mineralogy ranges from alloy-dominated in the northwest to sulfide- or telluride-arsenide-dominant in the southeast. Local features that are important in terms of mining are potholes and discordant ultramafic bodies. Comparative studies of the PGE from close to and within such structures again show constant absolute and relative abundances. Limited data on the PGE from PGE-mineralized pipes (Onverwacht, Mooihoek and Driekop) suggest that they are Pt-dominated, and have a totally different relative pattern of distribution of the PGE than that in the s tratiform mineralization. The PGM in the vicinity of these pipes also tends to be dominated by alloys, and in potholes by alloys and tellurides and arsenides. Hence, on both a regional scale and very local scale associated with disturbances in the reef, there is a dichotomy between the constancy of the PGE and the variability of the PGM. These observations suggest that the primary mechanism concentrating the PGE is a first-order process, and that the evolution of the PGM is the result of secondary processe s related to cooling, local changes in f(S2) in the crystallization environment, and subsolidus re-equilibration. The debate as to whether the PGE are derived by fluid scavenging of a footwall succession or have accumulated from supernatant magma is re- examined, and unresolved problems pertaining to both processes are highlighted.
The physical and chemical forms of sulfide mineral surfaces are reviewed. The initial surfaces and oxidation products have
been studied by Scanning Auger Microscopy (SAM), X-ray Photoelectron Spectroscopy (XPS), Scanning Tunneling Microscopy (STM),
Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS).
Changes to surface speciation as a function of time, pH, Eh and collector adsorption, related to mineral flotation, have been
followed with these techniques. Oxidation products are formed in different processes, namely: metal_de ficient sulfides, polysulfides
and sulfur; oxidized fine sulfide particles; colloidal hydroxide particles and flocs; continuous surface layers (e.g. hydroxide,
oxyhydroxide, oxide species) of varying depth; sulfate and carbonate species; isolated, patchwise and face-specific oxide,
hydroxide and hydroxycarbonate development. The actions of collector molecules (e.g. xanthates, dithiophosphinates) have been
identified in several modes, namely: adsorption to specific surface sites; colloidal precipitation from solution; detachment
of small sulfide particles from larger particle surfaces; detachment of small oxide/hydroxide particles; removal of adsorbed
and amorphous oxidized surface layers; inhibition of oxidation; disaggregation of larger particles; and patchwise or face-specific
coverage. The different modes of oxidation and collector action are exemplified using case studies from the literature and
recent research.
A comparison of the amount of collector sodium diisobutyl dithiophosphinate (DBPhos) adsorbed on the surface of galena and pyrite has been investigated by time of flight secondary ion mass spectrometry (TOF-SIMS). Statistical comparison of spectra from both galena and pyrite particles showed that there was approximately 12 times more collector on galena compared to pyrite. Galena particles that reported to the concentrate showed statistically less calcium, lead hydroxide and oxy-sulphur species on their surfaces compared to tail particles. The major contributions that assisted the flotation of galena were the presence of hydrophobic DBPhos and PbDBPhos. Reduced collector adsorption and increased hydrophilic species concentrations inhibited the flotation of pyrite.
A wealth of quantitative data on the types, volume distribution and mode of occurrence of Pt-group minerals has been accumulated over the last 12 years. On this basis, Pt-group minerals show close relationships in terms of Pt-Pd sulphide and Pt-Fe alloy contents although they are locally different in composition, mode of occurrence, and size. -K.A.R.
Mineral surface oxidation, slimes coating and inadvertent activation can detrimentally affect flotation and the separation of sulphide minerals. Surface oxidation and slime coatings will reduce hydrophobicity and collector adsorption selectivity. Inadvertent activation of gangue minerals by metal ions is frequently suspected of playing a detrimental role in selective flotation. In this study, the floatability of a pentlandite–pyroxene system was investigated in synthetic process water at pH 6 and pH 9 using zeta potential, microflotation and time of flight secondary ion mass spectrometry (ToF-SIMS) techniques. The aim was to maximise pentlandite recovery and simultaneously minimise the percentage pyroxene reporting to the concentrate. The results obtained showed that inadvertent activation by heavy metal ions, Cu(II) and Ni(II), contributes significantly to the true flotation of pyroxene. The microflotation tests revealed that pyroxene rejection is greatly improved by the addition of diethylenetriamine (DETA) in combination with sodium polyphosphate, this being particularly noticeable at pH 6. The mechanism responsible for the observed selectivity is explained by the ability of DETA to deactivate Ni(II), Cu(II) and possibly other ions through formation of stable chelates. The addition of polyphosphate introduced a more negative surface charge onto the minerals investigated thus preventing the formation of valuable-gangue mineral aggregates.
Diagnosis of the surface chemical factors playing a part in flotation separation of a value sulfide phase requires measurement of the hydrophobic and hydrophilic species that are statistically different between the concentrate and tail streams. Statistical methods, based on the monolayer-sensitive time of flight secondary ion mass spectrometry (ToF-SIMS) technique, have been developed towards this ultimate aim by measuring hydrophobic species (collector ions, dimers and metal complexes, polysulfides) as well as hydrophobic metal ions, precipitates and added depressant species. Reliable identification of specific mineral particles is central to this statistical analysis. A chalcopyrite/pyrite/sphalerite mineral mixture conditioned at pH9 for 20 min to study transfer of Cu from chalcopyrite via solution to the other two mineral surfaces, since this mechanism can be responsible for their inadvertent flotation in copper recovery, showed no statistical difference in the copper intensities on pyrite and sphalerite (selected from Fe and Zn images) after this conditioning. Principal component analysis (PCA) identifies combinations of factors strongly correlated (positively or negatively) in images or spectra from sets of data. In images, PCA selects these correlations from the mass spectra recorded at each of 256 × 256 pixels in a selected area of particles. In the image mode, PCA has proved to be a much better method of selecting particles by mineral phase with clearer definition of particle boundaries due to multi-variable recognition. It has clearly separated a statistical difference in copper intensities between the sphalerite and pyrite phases.
As a polyamine, triethylenetetramine (TETA) has not only a lower vapour pressure than diethylenetriamine (DETA) but it is also a more powerful chelating agent for the control of metal ions that can be the cause of an inadvertent activation and catalytic oxidation in flotation. The effect of this reagent on the depression of a hexagonal pyrrhotite (non-magnetic) was investigated on a bench scale using a massive nickel–copper sulphide ore sample. Mineral composition of the ore was estimated from mass balance equations of relevant elements. This allowed examination of the flotation selectivity between minerals, primarily between pentlandite and pyrrhotite. The pentlandite–pyrrhotite flotation selectivity obtained with TETA and sodium metabisulfite (SMBS), respectively, was similar to that obtained under baseline conditions. However, the combined use of TETA and SMBS produced an excellent separation of the two minerals resulting in a much greater concentrate grade. Possible mechanisms on the action of reagents are discussed.
A number of operations recover platinum group elements (PGE) from the Merensky reef in the Bushveld Complex, South Africa. The Merensky reef contains approximately 1% sulphides in the form of chalcopyrite, pentlandite and pyrrhotite, and the PGE’s are strongly associated with these sulphides. Different operations use different reagent suites (collectors, depressants, activators and frothers) in the flotation process to extract the valuable minerals from their section of the reef. Batch flotation tests were done on two ores from different parts of the reef using three different reagent suites based on the typical suites presently in use, and the recovery of the sulphide and gangue minerals compared. The two ores responded in a similar manner to the three reagent suites although there were differences observed in the behaviour of the individual minerals. These differences and the reasons for these differences are discussed.
Three surface-sensitive techniques, i.e. XPS (ESCA), scanning Auger microscopy and analytical scanning electron microscopy, have been used to study the surface layers on metal sulphides as single minerals, mixed minerals, synthetic ores and real ores from eight Australian concentrator operations. Validation of a sampling methodology to introduce a slurry, from the pulp after inhibition of oxidation, dissolution and removal of slimes, without air exposure of the mineral surfaces, to the instruments has shown that these procedures allow correlation of the measured surface chemistry with the process pulp. The techniques and methods are briefly reviewed with examples illustrating the correlation with process conditions. Evidence of the following characteristics of sulphide surfaces, derived from this study, is presented, namely: relatively thick carbonaceous, hydrophobic layers on some specific ores giving naturally flotable pyrite and chalcopyrite contrasted with normal hydrocarbon contamination of other sulphide surfaces; substantial hydroxide content in three forms as thin (∼5–80nm) layers, oxidised fine particles (∼0.1–5 μm) attached to larger sulphide particles and colloidal, spheroidal iron hydroxide floccs precipitated from solution; carbonate and sulphate species in surface layers; exposure of clean pyrite, chalcopyrite and pyrrhotite surfaces, metal deficient sulphide and polysulphide species; effects of Eh variation on exposure of clean pyrite; partial removal of hydroxide and exposure of clean pyrite and chalcopyrite in xanthate addition and steam cleaning processes; and adsorption of Cu(I) on pyrite surfaces with possible implications for flotation by formation of specific xanthate complexes.
Platinum group elements (PGE) are recovered by flotation from the Merensky reef in the Bushveld Complex, South Africa. The reef contains approximately 1% sulphide minerals in the form of chalcopyrite, pentlandite and pyrrhotite. The PGEs are strongly associated with these sulphide minerals. Different reagent combinations are used in the flotation process to extract the valuable minerals from the reef. Batch flotation tests were conducted on a typical ore from the Merensky reef to investigate the role of dithiophosphate (DTP) and copper sulphate (CuSO4) addition on the flotation response of the ore using both guar and caboxymethyl cellulose (CMC) type polymeric depressants. Differences in the flotation response of the individual minerals present in the ore to the different reagent combinations were observed. These differences and the reasons for the differences are discussed.
Depressants are added to flotation circuits to reduce naturally floatable gangue (NFG) present in ores, but under certain conditions have been shown to affect sulphide mineral recovery, particularly guar reducing the recovery of pyrrhotite. Copper sulphate is added to increase sulphide mineral recovery, but may also activate gangue particularly in the presence of dithiophosphate. This has also been shown to vary with ore type. Previous work has shown the usefulness of analysing reagents holistically, decoupling pulp and froth effects and assessing material recovered by true flotation and that recovered by entrainment separately. This work assesses the effect of copper activation on different ores and the ability of two classes of depressants, guar gum (guar) and carboxymethylcellulose (CMC) to reduce this effect and shows that by a depressant dosage of 300 g/t almost all the NFG had been removed from the concentrate. It also evaluates the effect of depressants on the sulphide minerals and shows that pyrrhotite was most affected.
Word processed copy. Thesis (Ph. D. (Chemical Engineering and Built Environment))--University of Cape Town, 2003. Includes bibliographical references (leaves 139-146).
In the selective separation of mineral phases by flotation, surface chemistry is the principal determinant of the average contact angle for a specific mineral phase in flotation pulp. The average contact angle is, in turn, the principal determinant of the bubble-particle attachment efficiency in the overall collection efficiency from which the flotation rate constant can be determined. The recovery and selectivity in sulfide flotation is ultimately dependent on the relative rate constants of the different mineral phases. The average contact angle is not only mineral specific, based on a statistical average of the mineral particles in that phase, but also the contact angle for each particle is an average of hydrophobic and hydrophilic areas across the particle surface. Journal Article
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