Improve Flotation Performance Research Articles

Exploration on performance of the oxidized collector in the low-rank coal flotation

ABSTRACT Low-rank coal can be concentrated by flotation process using oxidized kerosene, which can improve flotation performance. However, the difference between oxidized kerosene and conventional collector with the same dosage on flotation performance is little known. In this study, the FTIR spectrum, GC-MS analysis and surfaces tension of collectors were analyzed for comparison the physical and chemical properties. The results showed the kerosene appearance of the short hydrocarbon chains with oxygen groups. The surface tension of kerosene is reduced by 21.99 mm/m after oxidation process. The contact angle and flotation tests were used for the kerosene, mixture including oxidized kerosene and kerosene with a mass ratio of 1:1, as well as oxidized kerosene for evaluating the performance. The results showed that the order of coal surface contact angle is that kerosene > mixture > oxidized kerosene. In addition, flotation tests revealed that mixture had superior flotation performance compared with kerosene and oxidized kerosene. The oxidized kerosene could significantly diminish the ash content of flotation concentrates, and the combustible matter recovery of clean coal with mixture is nearly 16.50% higher than that with kerosene. These results constitute a substantial step forward in technical development for resource recycling of low-rank coal.

Amine-coated nanobubbles-assisted flotation of fine and coarse quartz

This study investigates the role of alkyl ether monoamine-coated nanobubbles (NBs) in assisting the flotation process of quartz across various particle sizes, on a bench scale. Experiments were conducted in a mini lab column utilizing a consortium of bubble sizes: D32 = 1200 μm for macrobubbles and D32 = 180–220 nm for amine-coated NBs. The study revealed that an increase in amine-coated NBs correlates well with a decrease in the air/solution’s interfacial tension caused by the ether amine at less than 68 mN m−1. True flotation recoveries with varying amine/g quartz, where the collector-frother amine may be amine-coated NBs alone or assisted by NBs generated in pure water, were compared with blank tests, in the absence of NBs. The flotation study evaluated size-to-size fractions from fine (−20 µm) to coarse (up to 150 µm) particles and their mixtures. In addition, the work extended to explore the behavior of the “super” coarse quartz from 150 µm up to 1000 µm. The results highlighted a clear dependence on the particle size, with NBs improving recoveries in all fractions, especially the difficult-to-treat ultrafine/fine and coarse quartz. Recovery results exceeded 90 % in all fractions (isolated or in mixtures) at a high rate with the amine-coated NBs. The mechanisms proposed improved flotation performance attributed to the high numerical concentrations of NBs (at least 2–3 × 1010 NBs per gram of quartz) rapidly attaching to quartz surfaces, serving as “seeds” for the adhesion of larger bubbles generated in conventional flotation cells. This interaction facilitates the formation of lightweight, cluster-like aggregates that swiftly rise to the column’s surface. Notably, larger quartz particles (+355 µm) form the bigger hydrophobic and buoyant clusters, leading to their rapid levitation and effective phase separation, with over 95 % separation efficiency. This innovative technique’s significance, outcomes, and potential scalability are thoroughly discussed, highlighting its promising applicability in diverse mineral and ore flotation systems, particularly those containing quartz and silicates.

Enhanced marmatite activation by copper with ammonium sulfate: An experimental and DFT investigation

The presence of iron atoms on the marmatite surface hinders effective interaction between the activator and the mineral, leading to unsatisfactory flotation performance through direct copper (Cu) activation. Hence, this study introduced ammonium sulfate to enhance the marmatite-activation capability by Cu ions. Additionally, the reinforcement mechanism was investigated through microflotation tests, atomic force microscopy (AFM), scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS), X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and density-functional theory (DFT) calculations. Microflotation results demonstrated that the addition of ammonium sulfate as a complexing reagent increased the flotation recovery of marmatite by 17.36%. AFM analysis revealed that marmatite subjected to enhanced activation (i.e., in the presence of ammonium sulfate) exhibited a considerably higher surface roughness than that subjected to direct Cu activation. Moreover, the average height of hill-shaped materials on the marmatite surface notably increased to 9.6 nm after enhanced Cu activation. SEM-EDS analysis revealed that the concentration of Cu atoms (2.2%) on the marmatite surface after enhanced Cu activation was nearly three times that (0.8%) after direct Cu activation. Additionally, XPS results indicated a considerably higher presence of the Cu–S component on the marmatite surface after enhanced Cu activation than after direct Cu activation. ToF-SIMS analysis indicated an increase in the fragment peaks of Cu+, CuOCS2+, OCS2−, and OC2H2S2− on the surface of enhanced-activated marmatite. Additionally, DFT calculations indicated that the presence of NH3 molecules enhanced electron transfer between Cu and S on the hydrated marmatite surface. The marmatite (1 1 0) surface exhibited more negative adsorption energy of Cu ions after the action of NH3 molecules, and NH3–Cu showed a more stable adsorption configuration than Cu. Therefore, the addition of ammonium sulfate enhanced the Cu activation for marmatite, thereby improving flotation performance.

Effect of acid corrosion on the surface roughness and floatability of magnesite and dolomite

To modify surface roughness and improve flotation performance, hydrochloric acid etching pretreatment was performed on magnesite and dolomite. Flotation tests disclosed that acid corrosion improved the flotation kinetics and flotation recovery rates of magnesite and dolomite. Under pulp pH 10 and sodium oleate (NaOl) concentration 20 mg·L−1, the flotation recovery rates of magnesite and dolomite after acid etching increased by 31.05% and 29.20%, respectively, compared with those before acid etching. Adsorption density tests proved that the adsorption density of NaOl on magnesite and dolomite was higher after acid etching than before acid etching, implying that acid etching drives NaOl adsorption. Zeta potential analysis revealed that acid etching reduces the point of zero charge of magnesite and dolomite. Atomic force microscopy and X-ray photoelectron spectroscopy results demonstrated that acid corrosion modified the surface roughness of magnesite and dolomite, increasing the magnesium (Mg) content on the magnesite surface and the calcium and Mg contents on the dolomite surface. Contact angle measurements indicated that acid corrosion slightly reduced the contact angle between magnesite and dolomite. With NaOl present on the surface, the contact angles of magnesite and dolomite after acid etching significantly increased compared with those before acid etching. Therefore, acid etching is effective in improving the floatability of magnesite and dolomite.

Ultrasound Pretreatment for Enhancing Fine and Ultrafine Flake Graphite Flotation Beneficiation.

With the severe depletion of coarse flake graphite (a critical raw material) resources, developing and utilizing fine and ultrafine graphite resources have recently attracted attention. Froth flotation is a widely used technique for the initial enrichment of graphite; however, the flotation selectivity decreases significantly along with particle size reduction. Ultrasound pretreatment would be a promising method to improve the flotation of fine particles. As an innovative approach to understand better the flotation response of different flake graphite sizes, this study conducted a comparative analysis based on flotation concentrate yield and ash as well as ash removal rate between the flake graphite with various particle sizes after ultrasound pretreatment. Particle size, X-ray powder diffraction, and scanning electron microscopy and energy dispersive X-ray spectroscopy analyses were used to investigate the effect of ultrasound treatment on mineralogical properties of the flake graphite with varied particle sizes. Process outcomes indicated that the flotation performance of fine flake graphite (mean chord length: 62.63 μm) was significantly enhanced after ultrasound pretreatment. However, flotation of the ultrafine flake graphite (mean chord length: 24.97 μm) after ultrasound treatment was limited due to the difficulty of generating sufficient fragmentation and dissociation by microjets and shock waves formed by the cavitation effect. Compared with conventional flotation, the concentrate yield of ultrasound flotation increased from 88.95 to 94.98%, ash content decreased from 5.72 to 4.87%, and ash removal rate enhanced from 36.94 to 42.61%. Particle size and mineral property analyses confirmed that further crushing and dissociation of the larger flake graphite after ultrasound pretreatment would be the main factors contributing to improved flotation performance. Additionally, the formation of air flocs in the coarse flake graphite during the ultrasound pretreatment process facilitated the flotation recovery of the crushed graphite particles.

Investigating the reasons for the improvement in flotation grade and recovery of an altered PGE ore when using sodium silicate

Certain South African platinum-group element (PGE) ores contain abundant phyllosilicate minerals which result in ultrafine coatings on valuable minerals, increase pulp viscosity, and dilute the grade through the recovery of talc composites. The highlighted problems usually lead to low recoveries and grades within the flotation process. Sodium silicate has been identified to have properties that can address these challenges and improve flotation performance. This study was conducted on a PGE-bearing ore with high quantities of serpentine and talc. The ore had poor PGE flotation recoveries and grades under baseline conditions. Sodium silicate dosages of >1000 g/t were found to significantly improve both PGE recoveries and grades. Additional targeted experiments were performed to decouple the multiple effects of sodium silicate on the flotation of the ore. Microflotation tests highlighted that chalcopyrite (used as a platinum group mineral proxy) recovery was decreased in the presence of finely ground serpentine. Zeta potential experiments indicated that electrostatic attraction of the oppositely charged serpentine and chalcopyrite minerals resulted in a serpentine surface coating of the chalcopyrite, which inhibited collector adsorption. The addition of sodium silicate restored the chalcopyrite recovery, mainly due to the reversal in serpentine surface charge. Secondly, the addition of sodium silicate decreased pulp viscosity as indicated by rheology tests. The ability of sodium silicate to disperse the slurry results in increased recovery due to better gas dispersion and bubble-particle contact within a flotation cell. Lastly, high sodium silicate dosages were shown to act as a depressant as confirmed by microflotation tests of talc and detailed mineralogical analyses. This study elucidated and decoupled the mechanisms whereby sodium silicate can mitigate the problems associated with altered ores, which are becoming increasingly problematic worldwide due to the necessity to mine mineralogically complex ore bodies.

A Review of Fatty Acid Collectors: Implications for Spodumene Flotation

Increasing demand for lithium-ion batteries has led to the development of several new lithium mineral projects around the globe. Some major mineral processing challenges these projects face are similarities in gangue and value mineral behaviour and poor selectivity in froth flotation. Unsaturated anionic fatty acids are the primary spodumene flotation collectors, known to be strong collectors with poor solubility and selectivity. Fundamental flotation research consensus is that spodumene flotation is driven by a fatty acid–anion complex adsorbed at cationic aluminum sites. However, many small-scale studies result in poor recoveries, prompting several researchers to investigate cationic activators or mixed anionic/cationic collectors to improve flotation performance. Testwork with real spodumene ore is rare in recent literature, but older publications from several deposits prove that fatty acids can successfully concentrate spodumene. The process generally includes alkaline scrubbing, high-density fatty acid conditioning, and flotation at pH 7.5–8.5 with 500–750 g/t fatty acid collector. The collector speciation behaviour is notably sensitive to pulp conditions around this pH; possibly resulting in unstable flotation circuits and inconsistent results. This paper reviews fatty acid collector properties and the available industrial and fundamental spodumene flotation research. We aim to provide new insight for understanding particle-collector interactions in spodumene flotation and help bridge the gap between fundamental and industrial processes which will be needed to de-risk projects in the growing lithium mineral industry.

Effect of water-in-oil and oil-in-water with Span 80 on coal flotation

Fine particles can be concentrated by flotation, and collector emulsification can improve flotation performance. However, the difference between the effect of oil-in-water and water-in-oil with the same emulsifier on flotation performance is little known. In this study, oil-in-water and water-in-oil emulsions with the same amount of Span 80 were prepared, and the flotation rate tests were compared. The particle size composition and the recovered water of concentrates were compared for kerosene, water-in-oil, and oil-in-water emulsions as collectors. The amount of kerosene adsorbed in the concentrates was analyzed by FTIR measurements. The results showed that oil-in-water with 0.5 g Span 80 had the largest concentrate yield and combustible recovery, while water-in-oil had had larger ash content, flotation rate constant, and recovered water. The reasons for these are that the differences in oil droplet composition of both emulsions lead to variations in coarse particle yields in the concentrates, further causing the change of recovery water which influences the variation of fine particles.

Transformer oil vs. kerosene: Selective collectors for C-matter flotation from a double refractory gold ore

A study was performed to evaluate the effect of collector type on the flotation of carbonaceous matter (C-matter) from a refractory gold ore, with the objective of improving gold recovery through separate treatment of the flotation concentrate and tailings. Transformer oil and kerosene were investigated as C-matter collectors in a single rougher flotation stage. Both collectors were tested at varying dosages, with emulsification (‘emulsion’) and without emulsification (‘normal’) using a 2-level full factorial Design of Experiments (DOE). The kerosene emulsion at 500 g t-1 resulted in the highest C-matter recovery (66%) with a C-matter grade of 4.38% (∼2.4 times upgrade), showing improved flotation performance compared with normal kerosene. Normal transformer oil at 500 g t-1 resulted in a C-matter grade of 4.65% with 61% C-matter recovery, and emulsion of transformer oil had little effect on flotation performance. The finer droplet size in the kerosene emulsion resulted in a faster flotation rate, leading to higher C-matter recovery than both transformer and normal kerosene. However, FT-IR analysis demonstrated that the interaction of transformer oil with C-matter was different than kerosene, forming a stronger attachment to C-matter surfaces. The flotation concentrate obtained under the most promising conditions (kerosene emulsion 500 g t-1) contained 51 % of gold, while 49 % of the gold reported to the flotation tailings. The gold recovery models predicted that gold recovery from (1) roasting/cyanidation of the flotation concentrate and, (2) pressure oxidation/thiosulfate leaching of the flotation tailings, has the potential to improve the overall gold recovery from 44% to 60% (compared with pressure oxidation/thiosulfate leaching only). In its first application as a collector in C-matter flotation, transformer oil showed great potential despite the highly disseminated, complex nature of the ore. The results suggest that transformer oil may be applicable in other flotation systems, beyond the gold industry, including agglomerate flotation and the flotation of carbonaceous battery materials, such as graphite, from both primary and secondary resources.

Enhancement of selective fine particle flotation by microbubbles generated through hydrodynamic cavitation

The flotation of fine particles less than 50 μm is challenging for the mining industry. By using hydrodynamic cavitation, a significant improvement on the recovery of fine particles has been found. This study aims to investigate the effect of hydrodynamic cavitation on the selective flotation of fine particles from detailed mechanism. Our single-bubble flotation results indicated that the bubble-particle collection efficiencies of fine silica particles (D50 = 6 μm and D50 = 16 μm) improved after hydrodynamic cavitation, especially for hydrophobized silica particles. The improved flotation performance of fine particles was investigated from three perspectives: (1) By zeta potential distribution measurements, bubble-frosting on hydrophobic particles was demonstrated after hydrodynamic cavitation. (2) The formation of large aggregates of hydrophobic fine particles after cavitation was revealed by slurry turbidity and particle size measurements, potentially contributing to the improved collision efficiency of the fine particles due to the bridging effect provided by microbubbles. (3) The attachment efficiency between a solid surface and flotation bubbles was enhanced if the surface was covered with hydrodynamic cavitation-generated microbubbles. Compared to the hydrophilic particles, the hydrophobic particles benefited from the hydrodynamic cavitation from the perspectives of bubble frosting, particle-bubble collision efficiency and attachment efficiency. Based on this study, it is expected that the separation efficiency for fine hydrophilic and hydrophobic particles can be improved by hydrodynamic cavitation.

Mechanical Flotation of Mineral Particles with an Underwater Speaker

ABSTRACT This paper aims to demonstrate a safe, non-chemical approach for improving the efficiency of froth flotation. Laboratory scale flotation tests for quartz particles of different sizes (< 20 µm, 20–38 µm, 38–75 µm, 75–106 µm, 106–150 µm, 150–212 µm) with an ether amine collector at different dosages were conducted in batch mode by using a bottom-driven mechanical flotation cell. An underwater loudspeaker was placed in the flotation pulp phase. The solids concentrations tested were 5% and 20% by weight. The results showed that acoustic sound (at 375 Hz and 77 decibels) increased the flotation recovery by at least 6% over a broad particle size range (i.e. 20–212 micron). The results also suggested applying acoustic sound in a flotation system can improve flotation recovery to a larger extent at a lower reagent dosage. An advantage of having the loudspeaker immersed in the pulp phase rather than in air above the flotation cell was the substantially reduced noise level. The present study provides a potential approach for improving flotation performance and reducing the chemical reagent consumption in flotation cells.

Graphite flotation by β-cyclodextrin/kerosene Pickering emulsion as a novel collector

• β-cyclodextrin/kerosene Pickering emulsion were prepared. • Effects of factors on the droplet size and stability of emulsion were investigated. • Response surface methodology was used to obtain optimal preparation conditions. • A proper β-cyclodextrin dosage used for emulsification promoted graphite flotation . • Mechanism of Pickering emulsion on graphite flotation was discussed. Pickering emulsions use nanoparticles to reduce the amount of emulsifiers and generate environmentally friendly reagents; this can be employed in different processes. However, there are no published reports on the application of Pickering emulsions in mineral beneficiation by flotation separation. Collector emulsification is an effective way to improve flotation performance. β-cyclodextrin is a granular emulsifier that has been widely considered in various investigations. As a comparative investigation, this study explored the application of the β-cyclodextrin/kerosene Pickering emulsion as a collector for the flotation beneficiation of a low-grade graphite ore. The response surface design was applied to investigate the influence of the water phase ratio, β-cyclodextrin weight, stirring time, stirring intensity, and the interaction of these factors on the emulsion droplet size and emulsion stability. The β-cyclodextrin weight optimization test showed that the Pickering emulsion reached its optimum flotation performance when the weight of β-cyclodextrin was 0.10 g. Surface analyses (zeta potential and contact angle measurements) indicated that the emulsion is stabilized by vesicles, which are self-assembled by inclusion compounds formed by kerosene and β-cyclodextrin. The developed Pickering emulsion could improve graphite recovery by 6%.

Roles of the hydrophobic and hydrophilic groups of collectors in the flotation of different-sized mineral particles

A controlled study was carried out in this work to decouple the effects of the hydrocarbon chains and the type of hydrophilic groups of the collectors on their collecting ability for minerals with different particle sizes. A high purity niobium oxide (pyrochlore) sample, with two different sizes (medium size of 64 µm and 16 µm, respectively), were floated by four anionic collectors, whose hydrocarbon chain was either octyl or oleoyl and hydrophilic group was either carboxylate or hydroxamate. The four combinations were: octyl hydroxamic acid (OHA), sodium octanoate (C8OONa), oleoyl hydroxamic acid (C18HA) and sodium oleate (NaOl). Through small-scale flotation tests, it was observed that the carboxylate-based collectors were inferior to hydroxamate-based collectors. Sodium octanoate could not float either the coarse or the fine pyrochlore. Replacing the octyl group in octanoate with a longer hydrocarbon chain, sodium oleate could float the coarse pyrochlore well but its effectiveness dropped sharply when floating the fine pyrochlore. Interestingly, the two hydroxamate-based collectors, octyl hydroxamic acid and oleoyl hydroxamic acid, showed excellent collecting ability to both the coarse and the fine pyrochlore tested. While FTIR analysis showed that all tested collectors adsorbed through chemisorption, isothermal titration calorimetry (ITC) measurements showed a positive correlation between the adsorption affinity and fine pyrochlore flotation recoveries. It is concluded that while the longer hydrocarbon chain of the collector benefited flotation recovery of relatively coarse size particles, for effective fine particle flotation, collectors need to have a hydrophilic group that has a strong affinity to the mineral surface. This work provided useful insights into collector molecular structure design and selection for improved flotation performance of minerals with specific particles sizes.

Deep learning feature-based setpoint generation and optimal control for flotation processes

Computer vision-based control is a nonintrusive, cost-effective, and reliable technique for flotation process control. It is known that deep learning features can depict the complex behavior of the froth surface more comprehensively and accurately than handcrafted features. However, few studies have tried to use additional information to improve flotation performance through optimal control. To this end, we have attempted to develop a novel deep learning feature-based two-layer optimal control scheme. The first layer is proposed for setpoint generation of high-dimensional features using improved fuzzy association rule reasoning. Then, an offline conservative double Q-learning control layer that can learn from historical industrial records by mitigating bootstrapping error in action value functions is developed. The proposed method can adapt the setpoint to the change in process feeds. Meanwhile, in contrast to traditional approximate dynamic programming methods that need to interact with real/simulated process systems, this controller can work without any further interactions, which makes it possible to transfer the success of reinforcement learning algorithms to complex industrial process control where opportunities to explore are missing. Experiments demonstrate that the proposed method is effective and promising for practical flotation process control.

Investigation of cell geometry effect on the turbulence characteristics and flotation performance using particle image velocimetry technique

The flow patterns and turbulence characteristics of the flow fields in a mechanical flotation cell have important effects on the hydrodynamic and metallurgical responses. In this study, the effect of cell geometry (off-bottom clearance (C), cell aspect ratio (H/T) and impeller diameter (D) on the turbulence properties and flotation performance using pure quartz particles of different sizes in a lab-scale Denver flotation cell was investigated. The results showed that the change in cell geometry changed the local turbulence characteristics. The change of C (from 0.2 T to 0.1 T), D (from T/2 to T/3) and H/T (from 1.2 to 1.5) did not change the flow pattern. The lower C was recommended to improve flotation performance. The larger D (T/2) was more useful for particle size of +38 μm. At the same Reynolds number, higher H/T is suitable for coarse particles, while lower H/T is recommended for particls size of −150 μm.

Investigating the Electrochemical Interaction of a Thiol Collector with Chalcopyrite and Galena in the Presence of a Mixed Microbial Community

High microbial cell counts have been recorded in sewage waters employed as process water in mineral beneficiation plants across the world. The presence of these microbes can negatively impact flotation performance through mineral passivation, although some microbes improve flotation performance as investigated in various bio-flotation studies. The current study aims to understand the electrochemical behaviour of minerals in the presence of a sodium ethyl xanthate (SEX) collector and microbes originating from a sulphide ore processing plant in South Africa. The electrochemical response was correlated to observe flotation performance. Mixed potential measurements were conducted in parallel to microflotation tests, to assess the hydrophilicity or hydrophobicity induced on sulphide minerals adapted to microbe-laden synthetic plant water. Sulphide minerals’ mixed potentials and interactions of SEX with sulphide minerals were dramatically reduced in the presence of the mixed microbial community (MMC). The observations were correlated with poor flotation efficacy noted in microflotation tests. These fundamental results shed light on how the adsorption of thiol collectors on sulphide minerals is adversely affected by microbes, prompting a discussion on flotation process monitoring when mineral beneficiation is conducted using microbe-laden water.

Efficient separation of fine coal assisted by surface nanobubbles

The separation performance of fine particles by flotation is significantly sensitive to particle size, which poses a limit to application of flotation in the separation of fine particles. In the present work an effective method that employs nanobubbles was investigated for the separation of fine coal. Nanobubbles were produced with the method of temperature change. Applying a series of techniques including atomic force microscopy (AFM), rheological measurement, the visualization of particle-bubble interaction and flotation test, it was found that surface nanobubbles are present on highly oriented pyrolytic graphite (HOPG) surface. Coal agglomeration occurred in the presence of nanobubbles, which was indicated by the shear thinning of coal slurry. Furthermore in an adhesion test, more coal particles attached to a bubble in the presence of nanobubbles, which suggested a positive effect of nanobubbles on the particle-bubble interaction. Thus, it could be concluded that, nanobubbles are responsible for the improved flotation performance of coal particles.

Effect of Hydrodynamic Cavitation Assistance on Different Stages of Coal Flotation

In this study, the effect of hydrodynamic cavitation (HC) on the conditioning stage (HCCS), separation stage (HCSS), and whole stage (HCWS) of coal flotation was investigated by flotation tests, laser granulometry, and contact angle measurements. The flotation results indicate that compared to conventional flotation, all HC-assisted flotation methods can improve concentrate combustible recovery and flotation constant rate. HCCS and HCSS show similar levels of improvement, while HCWS has a better flotation efficiency. The screening tests demonstrate that HC has the advantage of being able to liberate coarse coal particles (+0.25 mm) prior to being combined with gangues. On one hand, HC promotes the dispersion of both particles and agents, while longer cavitation time in HCCS does not lead to better flotation performance. On the other hand, enhancement of the adsorption of the collector on the surface of coal particles in HCCS is confirmed by flotation concentrate contact angle tests. However, HCSS leads to a decrease in concentrate hydrophobicity, compared to conventional flotation. The micro-nanobubbles generated by HC play an important role in improving flotation performance. HCWS offers the advantages of both HCCS and HCSS, and the cooperated mechanism of different HC modes enhances the recovery of coal particles in flotation.

Using oxalic acid to eliminate the slime coatings of serpentine in pyrite flotation

The flotation of sulphide ore in the presence of fine serpentine has been always a problem due to “slime coatings”. To solve this problem, attempts were made for the first time to eliminate the slime coatings of serpentine in pyrite flotation using oxalic acid (OA) as the selective depressant. Micro-flotation test results indicated the pyrite could be well floated in the presence of serpentine by addition of oxalic acid. Based on a series of measurements, including collector adsorption studies, zeta potential measurements, XPS analyses and turbidity tests, it was found that after conditioning with OA, serpentine carried negative charge which was similar to pyrite, inducing repulsion forces between pyrite and serpentine. In this way, the slime coatings of serpentine on pyrite surface were eliminated and the flotation performance of pyrite was restored under the action of OA. All in all, OA can be potentially applied as the depressant to improve flotation performance of sulphide ore associated with serpentine.

Application of ToF-SIMS to predict contact angles of pyrite particles

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) has been used as a technique to predict the particle contact angle of pyrite and contact angle distribution of pyrite ensembles, with size ranging from a few micrometres to a few millimetres (up to 2.36 mm). The pyrite samples were subjected to different oxidation treatments (e.g., heating, hydrogen peroxide conditioning) to obtain a range of surface chemistry. The ToF-SIMS data set is examined using a multivariate statistical tool, principal component analysis (PCA), to find patterns in the data and to identify the surface species contributing the most to surface chemistry of pyrite samples. Surface chemistry variation of the pyrite samples (via ToF-SIMS signals) are correlated with the measured Washburn contact angles. A ToF-SIMS-Contact Angle model of only two ToF-SIMS ion peaks, FeOOH+ and SO3−, is derived, which is used to predict contact angles of pyrite surfaces. Using this model, the contact angle variation across a single pyrite particle’s surface and the contact angle distribution within pyrite particle samples are determined. The ToF-SIMS-Contact Angle model also allows the prediction of contact angles for coarse pyrite particles (−2360 + 600 μm), which cannot be easily determined by traditional methods for particulate samples, e.g., the Washburn capillary rise method. The ability to determine the contact angle distribution of particles by ToF-SIMS is very suitable for mineral flotation studies, particularly for studying the relationship between comminution and flotation behaviour, and for devising control strategies to improve flotation performance.