Flotation-related Conditions Research Articles

Awaruite (Ni3Fe), a new large nickel resource: Electrochemical characterization and surface composition under flotation-related conditions

Awaruite is a native nickel–iron alloy (Ni3Fe), found in serpentinized ultramafic rocks, that has gained interest as a possible source of nickel. FPX Nickel is advancing a very large awaruite deposit in central British Columbia, Canada, on which this work is based. To date there is limited information available regarding the flotation conditions to selectively concentrate awaruite from gangue minerals in serpentinite ores. The aim of this work was to investigate the floatability of awaruite in different solution conditions with a xanthate collector. Awaruite readily floated in acidic solution with a xanthate collector but not in neutral and alkaline solutions. Voltammograms on awaruite indicated that the alloy shows an active passive transition behaviour in acidic solution and passive behaviour in neutral and alkaline solutions. The passivation layer formed in neutral and alkaline solutions showed to inhibit the interaction between xanthate and awaruite surface. Infrared spectra on awaruite showed the presence of xanthate compounds attached to the surface in acidic condition at potentials higher than the reversible potential of xanthate/dixanthogen. Based on experimental results, it was postulated that xanthate chemisorbs on awaruite and then it oxidizes to form dixanthogen. Also, it was demonstrated that when passivated, awaruite quickly activates in acidic solution, good flotation performance was achieved with 10 min of conditioning, and similar performance was obtained after 30 min of conditioning. This work serves as a confirmation that is possible to float awaruite using xanthate, a well-known collector that offers selectivity over oxides and silicate minerals, which are the main gangue minerals in serpentinite ores.

Sulfidization mechanism in malachite flotation: A heterogeneous solid-liquid reaction that yields CuxSy phases grown on malachite

Sulfidizationfollowed byxanthateflotation is an effective technique to recover copper oxide minerals. However, the sulfidization mechanism of malachite has not been determined. In this work, the sulfidization mechanism was investigated by microflotation, field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), electron probe X-ray microanalysis (EPMA), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The flotation results showed that sulfide ions at an appropriate concentration could activate malachite flotation while excess sulfide ions could depress this. The depression of malachite flotation by excess sulfide ions was attributed to the residual sulfide species in the liquid. FESEM–EDS showed that sulfidization product grown on the malachite surface was heterogeneously distributed, which was consistent with the EPMA results. The XRD results for the sulfidized malachite samples showed that the amount of sulfidization product was insufficient for detection under flotation-related conditions. By the selective solvent action of sulfuric acid, the sulfidization product was extracted from the sulfidized malachite. The XRD results for the extracts indicated that the sulfidization product comprised djurleite (Cu31S16) and anilite (Cu7S4), which both were compounds of the chalcocite group (Cu2−xS), suggesting transformation of solid Cu2(OH)2CO3 to Cu2−xS on the malachite surfaces during sulfidization. Moreover, the XPS results were consistent with the XRD results. These results demonstrated that sulfidization of malachite is a phase-transition process driven by the solubility difference between Cu2(OH)2CO3 and Cu2−xS. In this case, Cu2−xS phases formation on malachite involves heterogeneous nucleation and growth, and sulfide ions act as a reductant and sulfidizing agent in malachite sulfidization. The copper sulfide grown on malachite radically changed the surface properties of malachite particles, rendering malachite amenable to xanthate flotation. Based on these findings, we present a new formula for malachite sulfidization and a schematic diagram of the sulfidized malachite particle.

Improved understanding of the sulfidization mechanism in cerussite flotation: An XPS, ToF-SIMS and FESEM investigation

Sulfidization can greatly improve the flotation performance of lead oxide minerals. To provide deeper knowledge about this process, sulfidization of cerussite was investigated using X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS) and field emission electron microscopy (FESEM). XPS results clearly indicated a transformation of PbCO3 into PbS on the cerussite surfaces during sulfidization, which was consistent with ToF-SIMS results. Further, FESEM images showed that many nanoparticles grew on the cerussite at a high density, suggesting that the sulfidization product on the cerussite was not a monatomic layer but a solid polyatomic layer. The above results confirmed that PbS nanoparticles could grow on most of the surfaces of cerussite under flotation-related conditions, indicating that the sulfidized cerussite had a PbCO3/PbS core-shell structure. The formation of PbS nanoparticles on cerussite involved a heterogeneous nucleation step followed by growth of the nuclei. Based on these studies, a sulfidization process model was finally obtained.

Rheological investigations on the hetero-coagulation between the fine fluorite and quartz under fluorite flotation-related conditions

In this paper, the particle interaction between the fine fluorite and quartz (all less than 10 μm) and its effect on the fluorite flotation were studied mainly by rheological measurements, optical observation and micro-flotation tests. Sodium oleate was used as the fluorite collector. The yield stress, which is a rheology parameter, was utilized to quantify the aggregation degree of the particles and evaluate the strength of the net-work structures in flotation slurry. The yield stress value of fine fluorite slurry as a function of the solid concentration, pH, percentage of the fine quartz and collector concentration was measured. The rheological measurements and the optical observation results show that the fluorite particles could partially aggregate into flocs in the pH range of 5–10 and form net-work structure in suspensions, while quartz particles could not aggregate across the whole pH range tested. When quartz and fluorite particles were mixed in water, the yield stress of the mixed mineral slurry was much higher than that of the single mineral slurry, demonstrating a strong hetero-coagulation between the two minerals. The flotation performance of the fine fluorite particles with different degree of hetero-coagulation (caused by the different percentage of fine quartz) was tested. The hetero-coagulation exhibited a detrimental effect on the fluorite flotation, manifesting as decreased flotation recovery and decreased flotation rate. It was found that the hetero-coagulation deteriorated the fine fluorite flotation by forming strong net-work structures that could interfere with the rising processes of the bubbles carrying valuable mineral particles. The research provides a new way for quantifying the particle interactions and may potentially be used for regulating the flotation operations in the fluorite flotation plants.

The Role of Water Glass in the Flotation Separation of Fine Fluorite from Fine Quartz

Fluorite is the principal mineral of fluorine and usually coexists with quartz in deposits. The removal of fine quartz in fluorite concentrate is the main problem in fluorite flotation. In this study, the flotation tests on fluorite, quartz and a weight equivalent mixture (all less than 10 μm) using water glass (with different modulus) as depressants and sodium oleate as collector were conducted. The mechanism of fine quartz entering the fluorite concentrate was investigated through optional observations and rheology measurements on the flotation pulp. The particle interactions between fine fluorite and quartz under flotation-related conditions were analyzed through zeta potential measurements and DLVO calculations. The results revealed that there existed strong hetero-coagulation between fluorite and quartz particles in the flotation pulp, which could be the main reason for the quartz entering the fluorite concentrate in the flotation process. Water glass with higher modulus could eliminate the hetero-coagulation more totally but inevitably influences the flotability of fluorite.

Interaction of sphalerite with potassium n-butyl xanthate and copper sulfate solutions studied by XPS of fast-frozen samples and zeta-potential measurement

We acquired low-temperature X-ray photoelectron spectra of fast-frozen wet pastes prepared by centrifugation of the natural sphalerite slurries containing potassium n-butyl xanthate (KBX), without washing or any additional treatment, before and after the mineral activation in 0.1 mM CuSO4 solution. Zeta potentials of the slurry particles were also measured. The method allowed characterizing the mineral surfaces and adsorbates, volatile substances and hydrated species within the interfacial layers under more realistic flotation-related conditions. The uptake of xanthate by unactivated mineral was low even in 10 mM KBX, while the surface became metal-deficient (enriched in sulfur), more hydrophobic and contaminated with carbonaceous matter. Dibutyl dixanthogen was the major interfacial product of the interaction of Cu-activated sphalerite having the surface atomic Zn/Cu ratio of 3 and excess of sulfur with the KBX solutions. The spectra revealed only minor quantities of Zn and Cu xanthates and oxyhydroxides at all the samples; some hydrated K+ counter-ions were detected at the negatively charged surfaces after the xanthate treatment. The dixanthogen was concluded to form via oxidation of xanthate at the interface, probably catalyzed by surface cuprous species but not direct interaction with cupric ions.

Effects of surfactant on bubble hydrodynamic behavior under flotation-related conditions in wastewater

Bubble behavior is fundamental to the performance of froth flotation operations used in wastewater treatment processes. To fully understand and characterize bubble behavior under flotation-related conditions in wastewater, the high-speed photographic method has been employed to examine the motion of single bubbles and size distribution of bubble swarms with intermediate sizes ranging from 1 to 4 mm in the presence of surfactants in a laboratory scale flotation column. Both distilled water and synthetic municipal wastewater have been used to make solutions as well as two types of common surfactants. The instantaneous bubble motion has been recorded by a high speed camera. Subsequently, bubble trajectory, dimensions, velocity and distribution have been determined from the recorded frames using the image analysis software. The experimental results show that the addition of surfactant into wastewater has similar effects on bubble hydrodynamic behavior as in pure water (e.g., improving trajectory stabilization, dampening bubble deformation, slowing down terminal velocity, reducing bubble size and increasing the specific surface area of bubble swarm) due to the Marangoni effect. However, it is interesting to note that surfactant effects on single bubble hydrodynamics in wastewater are slightly stronger than those in pure water while surfactant effects on size parameters of bubble swarms in wastewater are significantly stronger than those in pure water. This finding suggests that besides surfactant, inorganic salts present in synthetic wastewater have an important influence on bubble dispersion.

Rheological investigations of ultrafine galena particle slurries under flotation-related conditions

Abstract The theological behaviour (viscosities and extrapolated yield values) of ultrafine galena particle slurries under flotation-related conditions has been studied using a concentric cylinder rheometer. The influence of pulp density, pH and ethyl xanthate concentration is reported. The observed aggregation phenomena are discussed with respect to galena surface chemistry as probed by electrokinetic studies, microflotation and X-ray photoelectron spectroscopy. At greater than 50% solid contents non-Newtonian theological behaviour is evident, with high yield values and shear thinning properties indicative of pulp aggregation. Under mildly alkaline conditions, galena slurry theology is controlled by repulsive electrostatic forces, with a high level of galena particle dispersion, whereas under mildly acidic conditions the rheology is significantly influenced by hydrophobic interactions. The introduction of galena particle hydrophobicity through ethyl xanthate addition results in enhanced galena particle attraction and increased floatabilities; these have been correlated. The magnitude of the hydrophobic attraction between ethyl xanthate treated galena particles, as determined from extrapolated yield data, has been shown to be greater at pH 5.5 than pH 10 and strongly concentration dependent. Rheological measurements of galena particle interactions are shown to enhance our understanding of fine particle flotation and may be utilised to optimised flotation performance.

Fine: Coarse particle interactions and aggregation in sphalerite flotation

The behaviour of fine particles in the flotation separation of minerals has become of rapidly increasing importance as new, fine grained deposits are exploited. Fine particles float poorly and less-selectively under normal flotation conditions. The behaviour of fine (<20 μm) and coarse (38–75 μm) sphalerite has been correlated between microflotation and aggregation studies. This study utilises two novel techniques for obtaining direct evidence of particle interactions within a conditioning pulp. On-line particle size distribution enables the onset of aggregation of fine particles under flotation related conditions, during addition of reagents, to be determined. Concurrent evidence of particle interactions has been observed using optical microscopy. Significant aggregation to 20–30 μm aggregates during agitation conditioning before reagents was observed. Fine particles exhibit poor flotation response and some aggregation after Cu(II) activation alone. On addition of collector at low pH, flotation recovery and extent of aggregation (>100μm) increased dramatically. In the presence of coarse particles at low pH, a high percentage of fine particles were recovered indicating a fine-coarse particle aggregation (“piggy-backing”) mechanism occuring during conditioning with Cu(II) alone.

In-situ scanning tunnelling microscopy studies of galena surfaces under flotation-related conditions

A scanning tunnelling microscope was used to topographically image the surface of galena under flotation-related conditions. Scanning tunnelling microscopy (STM) images were determined in situ and accurate pH control was maintained using a custom-made solution cell. Projections (1–2 nm) developed at the surface of galena during the first 15 min of contact with aqueous solutions at pH 3. X-ray photoelectron spectroscopy (XPS) confirmed a lead-deficient/sulfur-rich surface, formed through an incongruent oxidative dissolution mechanism. With time, the surface projections are less evident and cavities appear in the galena surface with depths corresponding to the PbS unit cell dimension, the dissolution mechanism becoming congruent. At neutral pH, in situ STM shows only cavity formation and XPS shows no sulfur-richness, whereas at pH 10 surface oxidation product growth was apparent. These findings are discussed in the context of the collectorless flotation of galena and the mechanisms of oxidative dissolution. In situ STM images of galena surfaces in the presence of ethyl xanthate showed the presence of attached colloidal projections; the rate of their formation and extent of surface coverage is controlled by the ethyl xanthate solution concentration. These topographical features give insight into ethyl xanthate adsorption mechanisms and enhance our understanding of the collector-induced flotation of galena. No adsorbed colloidal particles were observed in the in situ STM images of iron(III)-treated galena surfaces, but rather increased surface dissolution. Adsorbed colloidal particles were, however, observed in the ex situ STM images of iron(III)-treated galena surfaces.

Contact angle and surface analysis studies of sphalerite particles

Capillary penetration techniques were used to determine the wettability of sphalerite particles under flotation related conditions. Particle contact angles were determined separately from measurements of wetting rates (Washburn technique) and equilibrium capillary pressures across a sphalerite particle bed. For sphalerite of different size fractions, particle contact angles ranged from 75 to ∼90°, whereas synthetic ZnS (99.9%) gave values of 46° and 53°. The strong hydrophobic nature of the natural sphalerite samples was due to inadvertent copper activation and the ensuing formation of sulfur-rich surfaces, determined by bulk chemical and surface analysis (X-ray photoelectron spectroscopy and scanning Auger microscopy) studies. Scanning Auger microscopy also revealed variations in the levels of surface copper from mineral grain to grain and confirmed the heterogeneous chemical nature of sphalerite surfaces. The latter enables the contact angle variability to be discussed.

Interactions between zinc sulphide particles under flotation-related conditions

Rheological investigations of dispersions of spherical synthetic zinc sulphide particles have been conducted under flotation-related conditions and correlated with interparticle force-distance measurements using “colloid probe” atomic force microscopy. The interparticle interactions observed are discussed in terms of zinc sulphide surface chemistry; the latter was characterised by electrokinetic and X-ray photoelectron spectroscopic measurements. At pH < pHiep of zinc sulphide there is clear evidence of a hydrophobic attraction, in addition to electrostatic and van der Waals forces, affecting interparticle interactions. The presence of copper(II) ions at pH 4 resulted in increased Bingham yield values and interparticle cohesive forces, whereas at pH 10 no such attractive interactions were observed. These findings are discussed in the context of copper(II) ion activation of sphalerite in flotation practice.

The interaction of ethyl xanthate with copper(II)-activated zinc sulphide: Kinetic effects

Kinetic studies of ethyl xanthate adsorption onto copper(II)-activated zinc sulphide surfaces were performed by ultraviolet and Fourier transform infrared spectroscopy under flotation related conditions. Copper(II) activation is a prerequisite for ethyl xanthate adsorption on to zinc sulphide. Both the rate of adsorption and the form of the adsorbed ethyl xanthate species are controlled by the activation time and the concentration of copper(II) used. At low copper(II) additions, where copper(II) adsorption shows high affinity behaviour, copper(I) ethyl xanthate is the predominant surface species and the rate and extent of ethyl xanthate adsorption are decreased by extended copper(II) conditioning periods. At high copper(II) additions, where copper(II) is in excess, both diethyl dixanthogen and copper(I) ethyl xanthate can be detected on the zinc sulphide surface. However, their formation is by precipitation from solution rather than via a surface reaction. It is proposed that the penetration of copper ions into the zinc sulphide lattice and the subsequent diffusion back to the solid—aqueous solution interface may be responsible for the time dependence of ethyl xanthate adsorption. X-ray photoelectron spectroscopy depth-profiling by argon ion etching has confirmed that copper ions can penetrate considerable depths into the zinc sulphide lattice and gives credence to the proposed mechanism for the time-dependent adsorption behaviour of ethyl xanthate.

The ethylxanthate adsorption on copper-activated sphalerite under flotation-related conditions in alkaline media

Floatability and surface characteristics of sphalerite in the presence of different concentrations of copper sulphate and K-ethylxanthate, for various times of activation and collection, were studied. The resulting changes on the sphalerite surface were determined by infrated attenuated total reflection spectroscopy and correlated with electrokinetic measurement and floatability test results. The collectorless flotation of the examined sphalerite was very weak in alkaline media, independent of whether the mineral was activated with copper or without copper treatment. However, copper showed an activating effect on KEX sphalerite flotation in the alkaline region. Copper ions of high concentration provoked an “apparently depressing effect” on KEX sphalerite flotation, reacting with EX − to form copper-ethylxanthate-like species in the bulk of the solution. After decantation of the solution, before KEX was added, the depressing effect disappeared and sphalerite flotation was virtually complete. Cu(I)-ethylxanthate was the main surface product under the different experimental conditions. The kinetics of the copper-ion adsorption and KEX adsorption was relatively fast.

An XPS investigation of the surface of natural sphalerites under flotation-related conditions

The surface composition of two natural sphalerites of different iron and lead content has been determined under flotation-related conditions by X-ray photoelectron spectroscopy (XPS). Oxidation of the mineral samples in air-saturated alkaline solutions has been found to be very slow. In the presence of copper (II) species in solution, copper exchanges with zinc, and metal-deficient environments are formed in the sulfide lattice at the surface. Cyanide removes the copper and some sulfur from the surface, but a metal-deficient sulfide layer remains. Treatment of sphalerite with cyanide can also result in lead impurity in the mineral migrating to the surface to form lead cyanide and hydrated lead oxide. Zinc-oxygen species were detected at the surface of sphalerite that had been immersed in alkaline zinc solutions and washed with dilute sodium hydroxide before examination. Copper was found to diffuse to the surface when sulfur was deposited on sphalerite by air oxidation of hydrosulfide ions. The resulting surface was a metal-deficient sulfide rather than an overlayer of elemental sulfur.