Sphalerite Particles Research Articles

Critical contact angle for coarse sphalerite flotation in a fluidised-bed separator vs. a mechanically agitated cell

This work investigates the critical contact angle for the flotation of coarse (850–1180μm, 425–850μm and 250–425μm) sphalerite particles in an aerated fluidised-bed separator (HydroFloat) in comparison to a mechanically agitated flotation cell (Denver flotation cell). In this study, the surface chemistry (contact angles) of the sphalerite particles was controlled by varying collector (sodium isopropyl xanthate) addition rate and/or purging the slurry with either nitrogen (N2) or oxygen (O2) before flotation. The flotation performance varied in response to the change in contact angle in both the aerated fluidised-bed separator and the mechanically agitated cell. A critical contact angle threshold, below which flotation was not possible, was determined for each particle size fraction and flotation machine. The results indicate that the critical contact angle required to float coarse sphalerite particles in a mechanically agitated cell was higher than that in the fluidised-bed separator, and increased as the particle size increased. At the same particle size and similar contact angles, the recoveries obtained by the aerated fluidised-bed separator in most cases were significantly higher than those obtained with the mechanically agitated flotation cell.

Suspended zinc sulfide particles in the Southwest Indian Ridge area and their relationship with hydrothermal activity

Suspended particle samples collected in the water column at 7 stations in the hydrothermal vent area in the Southwest Indian Ridge were studied by electronic scanning microscope (SEM) and energy dispersive X-ray spectrometry (EDX). A method of zinc sulfide (ZnS) mineral phase identification by SEM and EDX data was proposed, and related adequacy and limitation of the method were presented. 29 ZnS particles with various morphologies were found. 27 sphalerite particles and two wurtzite particles were distinguished by joint consideration of their morphology and chemical element composition. Two types of sphalerite particles with different dissolving intensities were differentiated, which may be depended on the duration of the particles existence in the water column. More than half of the total sphalerite particles include 12 high Fe-containing particles (Fe > 10 wt%) were found at the Station 21VII-CTD7, suggesting a close link to the adjacent active hydrothermal vent. Sphalerite particles at Station 2VI-CTD3 contained only one Fe-containing particle and their amount ranked second among that at all the survey stations, suggesting a good correspondence to the adjacent inactive hydrothermal vent. Only six non-iron ZnS particles were found at the rest eastern 5 stations, suggesting a weak influence of hydrothermal activities in the eastern area.

Optimization of operating parameters for coarse sphalerite flotation in the HydroFloat fluidised-bed separator

Increasing the upper size limit of coarse particle flotation has been a long-standing challenge in the minerals processing industry. The HydroFloat separator, an air-assisted fluidised-bed separator, has been used in this study to float 250–1180μm sphalerite particles in batch flotation tests and compared to results achieved utilizing a laboratory-scale conventional Denver cell. The quiescent environment within the HydroFloat cell significantly reduces the turbulent energy dissipation within the collection zone, hence decreasing the detachment of particles from bubbles during flotation. Three operating parameters including bed-level, superficial water and gas rates have been studied, and their effect on the flotation of coarse sphalerite particles is reported. It is shown that coarse sphalerite recovery increases with increasing bed-level, superficial water and gas flow rates. However, there are thresholds for each operating parameter above which recovery starts to decrease. A comparison of recovery with a conventional Denver flotation cell indicates that the HydroFloat separator vastly outperforms the conventional flotation machine for the very coarse particles (+425μm), and this is mainly attributable to the absence of turbulence and the minimization of a froth zone, both of which are detrimental to coarse particle flotation.

Research on the Interaction between Sphalerite and Silica Particles with Different Calcium Ion Solutions

The interactions among fine particles are unavoidable in solutions, and the strong particle interactions have a negative impact on mineral separations. How to reduce and prevent the agglomeration of particles is one of the important chal-lenges facing production and research. The interactions of sphalerite and silica particles were studied with variation of calcium ions solutions. Zeta potential measurement and a novel Zeta potential distribution (ZPD) measurement method were used in this paper. The phenomena of mineral coagulation and absorption of flotation reagent were analyzed in solutions of different pH and calcium ion concentration.

An exponential decay relationship between micro-flotation rate and back-calculated induction time for potential flow and mobile bubble surface

Flotation researchers have long hypothesised that particles have inherently different flotation rates under the same operating conditions because they have different induction times in the flotation cell. The relationship between flotation rate constant and induction time, however, has yet to be explored. Here we analysed the relationship between micro-flotation rate and back-calculated induction time for galena and sphalerite particles. The floatability of the particles was controlled by depression with potassium chromate (galena) and activation with copper sulphate (sphalerite). The bubble rise velocity vs. size in the micro-flotation experiments was determined by high speed video microscopy and followed the prediction for bubbles with the fully mobile air–water interface. Therefore, the theoretical analysis of the micro-flotation results was carried out, based on the potential flow model for water flow around a mobile bubble surface. The relationship between micro-flotation rate constant and back-calculated induction time was found to rapidly decay exponentially. In this model, flotation rate constant is highly sensitive to induction time. For example, a doubling or tripling of induction time results in an order-of-magnitude decrease in flotation rate constant.

Onset of sphalerite to wurtzite transformation in ZnS nanoparticles

In this work, the incubation period for the onset of sphalerite to wurtzite transformation in isolated ZnS nanoparticles 2 to 7 nm in size was determined via the in situ isothermal annealing of as-synthesized sphalerite nanoparticles in a transmission electron microscope (TEM). Nanoparticles sitting on the TEM grid were well separated from each other in order to minimize particle sintering during the annealing operation. The phase transformation onset was observed at 300 °C, 350 °C, and 400 °C after 90, 10, and 4 min, respectively. These time-temperature data for the phase transformation onset were then used to calculate the activation energy for the nucleation of the wurtzite phase in 2 to 7 nm sphalerite particles. The activation energy determined was 24 Kcal/mol.

Use of X-ray computed tomography to investigate crack distribution and mineral dissemination in sphalerite ore particles

As the trends in mineral processing move towards the beneficiation of finer grained and more complex ore bodies, so too do the methods needed to understand and model these processes. During the heap leaching of low-grade ore bodies, the crack distribution and mineral dissemination in ore particles are important characteristics that determine the performance of sub-processes, such as the diffusion of reagents in and out of particle pores. Recent developments in X-ray computed tomography (CT) as an advanced diagnostic and nondestructive technique have indicated the potential for the technology to become a tool for the acquisition of 3-D mineralogical and structural data. The spatial distribution of cracks and mineral dissemination in particles derived from a sphalerite ore in the Northern Cape, South Africa, was characterized using a high-resolution industrial X-ray CT system. This paper describes the use of image analysis techniques including image segmentation, which uses a combination of thresholding and other methods to characterize and quantify crack and mineral dissemination in the sphalerite particles. The results are validated with those obtained using traditional techniques such as physical gas (with N 2) adsorption, mercury intrusion porosimetry, SEM and QEMSCAN. A comparison of the effect of different comminution devices (HPGR and Cone crusher) on crack generation is also given.

Fine particle aggregating and flotation behavior induced by high intensity conditioning of a CO 2 saturation slurry

The influence on fine particle aggregation and flotation behavior induced by high intensity conditioning (HIC) from saturated of the slurry with CO 2 saturation was investigated. Bubble size measurements were conducted. The effect of dissolved gas, xanthate addition and agitation speed on fine sphalerite particle aggregation- and flotation-behavior were studied. The results show that during HIC in air or CO 2 saturated water xanthate acts as a frother. The dissolved gas content in the pulp and HIC play a synergistic role in promoting fine particle aggregation and hence flotation; a significantly enhanced aggregation of fine sphalerite particles in a CO 2 saturated slurry by HIC is observed. The aggregate size increased when the agitation speed was increased from 700 r/min to 1500 r/min. Increasing the HIC speed to 1500 r/min caused a positive impact on flotation kinetics. Further increasing the speed to 2000 r/min resulted in an adverse effect on flotation kinetics.

Preparation and Characterization of Surface Modification of Sphalerite Concentrate with Sodium Lignosulfonate

In order to prevent sphalerite particles from coming together in leaching solution, and to reduce the loss of organic solvent, the surface modification of sphalerite concentrate with sodium lignosulfonate was investigated. The modified sphalerite concentrate particles were characterized by dispersion experiments, determination of adsorption rate of oil, determination of contact angle, FT-IR spectra and X-ray photoelectron spectra. The results showed that the modified sphalerite concentrate particles exhibited good dispersibility in water. The sedimentation volume reduced from 0.85 ml•g-1 to 0.61 ml•g-1. The adsorption rate of oil reduced from 0.15 ml•g-1 to 0.06 ml•g-1. The contact angle between sphalerite concentrate particles and water changed from 86.9˚ before modification to 32.7˚ after modification with sodium lignosulfonate. The checking results of FT-IR and XPS spectra indicated that some modification regents were coated on the particle surface. The modifier combined to sphalerite concentrate particle surface through the chemical bond, resulting in the comprehensive stability action of static and steric effect.

Effect of high intensity conditioning on aggregate size of fine sphalerite

High intensity conditioning(HIC) was used as a model to study the fundamental of fine sulphide particle flotation. The effect of impeller design, mechanical energy input, and agitation speed on aggregate size of fine sphalerite was tested. The aggregate size of fine sphalerite was measured with the Malvern Hydro 2000 Mastersizer. The results show that the size of aggregates of sphalerite particles ground for 3 min can be enlarged significantly with the activator and collector addition in HIC using the high energy impeller. The improved particle aggregation by using the high energy impeller is not directly related to a higher energy input into the system. With the same energy input into HIC, the aggregate size obtained with the high energy impeller is much coarser than that obtained with the low energy impeller. With the new impeller in HIC, the sphalerite aggregate size decreases with increasing agitation speed from 700 to 2 500 r/min. However, the recovery does not decrease until the agitation speed reaches 2 500 r/min.

Mechanism for the recovery of silicate gangue minerals in the flotation of ultrafine sphalerite

The effect of copper sulphate and sodium isopropyl xanthate on the flotation of a mixed mineral system has been studied at pH 9. The mixed mineral system was composed of colloidal silica and ultrafine sphalerite particles. Batch flotation, zeta potential and rheology have been applied to identify mechanisms by which the silica may misreport to a sphalerite concentrate. The results indicate that, in the absence of both copper sulphate and xanthate, silica was recovered essentially by the entrainment mechanism. However, the addition of copper sulphate and isopropyl xanthate increased particle interactions between silica and sphalerite, promoting aggregation. Consequently, silica may misreport to the concentrate via a combination of both entrainment and aggregation mechanisms. Under the conditions applied in the present study, silica is not likely to be recovered via true flotation, i.e. by attachment of silica particles to bubbles.

A molecular dynamics study of structural relaxation in tetrahedrally coordinated nanocrystals

The reorganisation of nanocrystals in order to reduce their surface energies has been examined in computer simulations. The relaxation takes a qualitatively different path for sphalerite- and wurtzite-structured particles. The surfaces of the sphalerite particles reconstruct into hexagonal nets, but the interior remains identifiable as sphalerite-like, whereas wurtzite particles form facetted, hexagonal nanorods by virtue of a reorganisation of the whole particle which involves the creation of a low energy internal interface between oppositely oriented domains. Despite the reorganisation, the diffraction patterns remain compatible with a wurtzite structure with some internal strain. The dipole moments of thermalized wurtzite particles are compared with experimental results for CdSe.

Synthesis and characterisation of small ZnS particles

Small ZnS particles, prepared at room temperature in an alcoholic medium using a zinc salt and thioacetamide as sulphur source, have been characterised using a suite of techniques which includes XRD, TEM and Zn K-edge EXAFS. The investigation suggests that aggregates of small sphalerite particles (cubic lattice), with average size of 3.5 nm and well-defined morphology are obtained and the particle size appears not to change with increase in the reaction time from 2 to 24 h. Zn K-edge EXAFS experiments were performed at 10 K, in order to reduce thermal disorder and the refinement of the EXAFS data resulted in very small second shell coordination numbers with respect to the bulk samples. The result is in good agreement with SEM and XRD data about the presence of nanosized particles, having a large number of surface atoms with low second shell coordination number.

Reexamining the functions of zinc sulfate as a selective depressant in differential sulfide flotation—The role of coagulation

Zinc sulfate is a well-known selective depressant for zinc sulfide minerals such as sphalerite during the flotation of complex Cu–Pb–Zn sulfide ores. It deactivates sphalerite flotation by substituting the activating metal ions, and depresses sphalerite flotation by forming hydrophilic coatings of zinc hydroxyl species on sphalerite surfaces. However, we recently observed that zinc sulfate could also induce coagulation of fine sphalerite particles and such coagulation significantly reduced the mechanical entrainment of the fine sphalerite. Therefore, it seems that the effectiveness of zinc sulfate as a selective sphalerite depressant is not only due to its ability to make mineral surface hydrophilic, which reduces genuine flotation, but also due to its ability to coagulate the mineral, which reduces mechanical entrainment. Zinc sulfate is a “dual function” selective flotation depressant.

Depression mechanisms of sodium bisulphite in the xanthate-induced flotation of copper activated sphalerite

The effect of sodium bisulphite on the xanthate-induced flotation of copper-activated sphalerite has been studied using batch flotation testing, surface analysis techniques (XPS and ToF-SIMS), and FTIR. The various techniques have been used to identify the mechanisms of interaction of sulphite ions with both collector and the sphalerite surface. The results indicate that sodium bisulphite depressed the flotation of sphalerite particles pre-treated with copper and xanthate at pH 9 with nitrogen and air purging. It was found that sodium bisulphite interacts with the sphalerite surface, as well as with xanthate in its adsorbed state. Based on the evidence obtained in the present study, and in conjunction with previous work, the mechanisms involved in the depression of the xanthate-induced flotation of copper-activated sphalerite by sulphite are proposed. It is suggested that copper xanthate decomposition on the surface of the activated sphalerite and the decomposition of the hydrophobic copper-sulphide-like species on the sphalerite surface are the active mechanisms for sphalerite depression by sodium bisulphite.

Surface modification of sphalerite with sodium alginate

In order to prevent sphalerite particles from aggregating in leaching solution, and to reduce the loss of organic solvent, the surface modification of sphalerite with sodium alginate was investigated. The modified sphalerite particles were characterized by dispersion experiments, determination of adsorption rate of oil, FT-IR spectra and X-ray photoelectron spectra. The results showed that the modified sphalerite particles exhibited good dispersibility in water. The contact angle between sphalerite particles and water changed from 86.9° before modification to 0° after modification with sodium alginate. The sedimentation volume reduced from 0.85 ml/g to 0.70 ml/g. The adsorption rate of oil reduced from 0.15 ml/g to 0.07 ml/g. The checking results of FT-IR and XPS spectra indicated that some modification reagents were coated on the particle surface. The modifier combined to sphalerite particle surface through the chemical bond, resulting in the comprehensive stability action of static and steric effect.

Size-Dependent Phase Transformation Kinetics in Nanocrystalline ZnS

Nanocrystalline ZnS was coarsened under hydrothermal conditions to investigate the effect of particle size on phase transformation kinetics. Although bulk wurtzite is metastable relative to sphalerite below 1020 degrees C at low pressure, sphalerite transforms to wurtzite at 225 degrees C in the hydrothermal experiments. This indicates that nanocrystalline wurtzite is stable at low temperature. High-resolution transmission electron microscope data indicate there are no pure wurtzite particles in the coarsened samples and that wurtzite only grows on the surface of coarsened sphalerite particles. Crystal growth of wurtzite stops when the diameter of the sphalerite-wurtzite interface reaches approximately 22 nm. We infer that crystal growth of wurtzite is kinetically controlled by the radius of the sphalerite-wurtzite interface. A new phase transformation kinetic model based on collective movement of atoms across the interface is developed to explain the experimental results.

Depressing mechanisms of sodium bisulphite in the collectorless flotation of copper-activated sphalerite

The effect of sodium bisulphite on the collectorless flotation of copper-activated sphalerite has been studied at pH 9 with nitrogen purging. X-ray photoelectron spectroscopy (XPS), time of flight secondary ion mass spectroscopy (ToF-SIMS) and ion chromatography (IC) have been used to identify a mechanism of interaction of sulphite ions with sphalerite particles. The results indicate that sodium bisulphite acts as an effective depressant for the collectorless flotation of copper-activated sphalerite and has a specific effect on the surface chemistry of sphalerite particles under the experimental conditions studied. It is suggested that sulphite ions react with the surface of copper-activated sphalerite and subsequently decompose the hydrophobic sulphur-like species responsible for flotation. Most likely, sulphite ions specifically interact with the reduced coordination sulphur atoms associated with copper activation and report into solution as a thiosulphate, which is then oxidised to sulphate. At the same time, zinc hydroxide is formed at the sphalerite surface. The consequent reduction in surface hydrophobicity explains the depression of copper-activated sphalerite in the presence of sulphite.

Transformation of sphalerite particles into copper sulfide particles by hydrothermal treatment with Cu(II) ions

The nature of the hydrothermal reaction between sphalerite and copper solutions was investigated in the range 160–225 °C. Digenite (Cu 1.8S) was the main reaction product at 160–212 °C, and chalcocite (Cu 2S) at 225 °C. The reaction was characterized by the formation of a compact layer of copper sulfide around the sphalerite nuclei. Final particles retained the size and shape of the original ZnS. Reaction rate followed a parabolic kinetic law. No significant effect of aqueous copper concentration was observed in the range 1–10 g/L. An activation energy of 147 kJ/mol was obtained, indicating kinetic control by solid-state counter diffusion of Cu + and Zn 2+ ions through the copper sulfide layer. A possible electrochemical mechanism is discussed. The removal of zinc from digenite or chalcocite bearing copper concentrates is effective at ∼225 °C, in which a high sphalerite conversion can be achieved in times allowing autoclave processing (∼1 h).

Aggregation, Coarsening, and Phase Transformation in ZnS Nanoparticles Studied by Molecular Dynamics Simulations

Molecular dynamics simulations at 300 K in vacuum were used to study nanoparticle motion and structural changes during aggregation and coarsening of 3 nm sphalerite (ZnS) particles and atomic diffusion during the subsequent phase transformation. Interaction forces between atoms in different nanoparticles can induce translational and rotational movements of the nanoparticles, driving them to find appropriate locations and orientations for aggregation. Following aggregation, the coarsened particle adopts a near-amorphous structure that transforms rapidly to wurtzite. Atomic diffusion is faster on the surface than in the bulk. Transient episodes of very fast atomic diffusion occur locally on the surface. Diffusion plays significant roles in nanoparticle structural change, aggregation, coarsening, and surface nucleation.