Impact of gypsum supersaturated solution on surface properties of silica and sphalerite minerals

In some sulphide mineral flotation operations, the process water contains high concentrations of calcium and sulphate ions that exceed the solubility limit of gypsum. It has been speculated that the gypsum supersaturated process water would lead to precipitation of gypsum which could coat on mineral surfaces by either nucleation or coagulation, resulting in reduced flotation recovery and selectivity. In this study, a laboratory prepared gypsum supersaturated solution is used to represent the gypsum supersaturated process water, the effect of gypsum supersaturated solution on the surface properties of silica and sphalerite minerals was investigated using zeta potential distribution measurements, scanning electron microscope (SEM), X-ray photon spectroscopy (XPS), Auger electron spectroscopy (AES), and quartz crystal microbalance with dissipation (QCM-D). Our results show that silica and sphalerite minerals carry identical surface charge (−10 mV of zeta potential) in the gypsum supersaturated solution at pH 10 although they are charged differently in simple electrolyte solution at the same pH. Needle shape gypsum precipitates are found in both silica and sphalerite minerals systems conditioned with gypsum supersaturated solution. The gypsum precipitates do not grow on the minerals surfaces but form in the bulk gypsum supersaturated solution. The heterocoagulation between the examined minerals and gypsum particles is insignificant in the gypsum supersaturated solution. It is the high calcium concentration in the gypsum supersaturated solution that has significant effect on the surface properties of silica and sphalerite minerals. The zeta potentials of silica and sphalerite in a 800 ppm calcium solution (similar to the calcium concentration in the gypsum supersaturated solution) are similar to those measured in the gypsum supersaturated solutions. Both silica and sphalerite minerals surfaces are indiscriminately coated with calcium. The surface coating of calcium results in the identical surfaces between silica and sphalerite minerals, and ultimately causes problems for the flotation separation of silica and sphalerite.     

Impact of gypsum supersaturated process water on the interactions between silica and zinc sulphide minerals

Flotation recovery and selectivity problems have been reported in the flotation of fine sulphide minerals in gypsum supersaturated process water. In this study, the effect of gypsum supersaturated solution on the interactions between silica and sphalerite (ZnS) minerals was examined by observing deposition behaviour of silica nanoparticles on sphalerite surface using a quartz crystal microbalance with dissipation (QCM-D). Significant deposition of silica nanoparticles on ZnS coated sensor surface was observed in the gypsum supersaturated solution, indicating consequential slime coating of silica fines on sphalerite mineral surface. Substantial deposition of silica nanoparticles on SiO₂ coated surface was also observed suggesting strong homo-aggregation of silica fines in the gypsum supersaturated solution. The interaction behaviour between silica–sphalerite and silica–silica is mainly attributed to the high calcium concentration of the gypsum supersaturated solution. Similar deposition behaviour of silica nanoparticles onto ZnS or SiO₂ coated sensor surface was observed in 800 ppm calcium solution, which is similar to the calcium concentration of the gypsum supersaturated solution. Colloidal force measurement between a silica particle and a fractured sphalerite surface or a silica wafer surface by an atomic force microscopy (AFM) revealed attractive van der Waals force between the mineral particles in both gypsum supersaturated solution and 800 ppm calcium solution. The high calcium concentration of the gypsum supersaturated solution induced the hetero-aggregation between silica and sphalerite, accounting for the observed decrease in flotation selectivity.     

The role of calcium in xanthate adsorption onto sphalerite

This paper presents results of a laboratory study designed to look into the effect of calcium on sphalerite hydrophobization with xanthate making use of zeta potential, contact angle, microflotation and UV/vis spectrometry techniques. The experimental results show that xanthate adsorbs onto the mineral surface at neutral and slightly acid pH as reflected by contact angle, floatability (by microflotation) and xanthate adsorption (by UV/vis spectrometry) measurements. Apparently, xanthate adsorption is due to both the less negative surface charge of the mineral and to the presence of Zn²⁺ in equilibrium with the mineral, rather than Zn(OH)₂, which is the product of the mineral oxidation with dissolved oxygen at pH above 8. When calcium is present in the aqueous solution at concentrations similar to that of saturation for gypsum precipitation (e.g., about 0.017 mol/L), calcium apparently adsorbs on the sphalerite surface decreasing its negative charge (e.g., zeta potential) and promoting xanthate adsorption and hydrophobization, as reflected by contact angle and floatability measurements (ca. 30° and 33% recovery, respectively). Calcium adsorption appears to be favoured by the increase in pH, as reflected by the increased xanthate adsorption, thus suggesting that the calcium hydroxo-complex (CaOH⁺) is the adsorbing species. At pH 10 and 11, precipitation of calcium hydroxide (observed by SEM-EDS measurements at pH 11) appears to counteract xanthate adsorption, substantially decreasing mineral hydrophobicity. Calcium and xanthate appear to display some type of chemical interaction while calcium and dithiophosphinate do not.     

Adsorption of copper sulphate on PGM-bearing ores and its influence on froth stability and flotation kinetics

Copper sulphate is used as an activator in the flotation of base metal sulphides as it promotes the interaction of collector molecules with mineral surfaces. It has been used as an activator in certain platinum group mineral (PGM) flotation operations in South Africa although the mechanisms by which improvements in flotation performance are achieved are not well understood. Some investigations have suggested these changes in flotation performance are due to changes in the froth phase rather than activation of minerals by true flotation in the pulp zone. In the present study, the effect of copper sulphate on froth stability was investigated on two PGM containing ores, namely Merensky and UG2 (Upper Group 2) ores from the Bushveld Complex of South Africa. Froth stability tests were conducted using a non-overflowing froth stability column. Zeta potential tests and ethylenediaminetetraacetic acid (EDTA) tests were used to confirm the adsorption of reagents onto pure minerals commonly found in the two ores. The results of full-scale UG2 concentrator on/off copper sulphate tests are also presented. The UG2 ore showed a substantial decrease in froth stability in the order of reagent addition: no reagents > copper > xanthate > copper + xanthate, while Merensky ore showed a slight decrease. It was shown through zeta potential measurements that copper species were to be found on plagioclase, chromite, talc and pyrrhotite surfaces and through EDTA extraction that this copper was in the form of almost equal amounts of Cu(OH)₂ and chemically reacted copper ions on the Merensky and UG2 ore surfaces. In certain cases, the presence of copper sulphate and xanthate substantially increased the recovery, and therefore the implied hydrophobicity, of pure minerals in a frothless microflotation device. It was, therefore, proposed that increases in hydrophobicity beyond an optimum contact angle for froth stability, were the cause of instabilities in the froth phase and these were found to impact grade and recovery in a full-scale concentrator. Differences in the extent of froth phase effects between the different ores can be attributed to differences in mineralogy.     

Effects of salinity on xanthate adsorption on sphalerite and bubble–sphalerite interactions

The adsorption of amyl xanthate on sphalerite in NaCl solutions of different concentrations and in saline water (viz. simulated sea water) and the surface properties of treated minerals were investigated. The interactions between xanthate treated sphalerite particles and air bubbles were examined using induction time measurement, which revealed that the salt ions could inhibit the adsorption of xanthate on sphalerite due to the competitive adsorption, but also could compress the electrical double layer at mineral/water interface. The induction time of sphalerite treated in potassium amyl xanthate (PAX) with saline water was shorter than that of sphalerite treated in PAX with NaCl of the same ion concentration, which implies that the water composition (e.g. Ca²⁺, Mg²⁺) could play an important role in the bubble–particle interaction. The hydrophobicity, chemical composition, and charge property of PAX treated sphalerite surfaces were characterized using contact angle measurement, Cryo-X-ray photoelectron spectroscopy (Cryo-XPS) and zeta potential determination, respectively, which support the inhibition effect of salt ions on the xanthate adsorption on sphalerite. In the case of saline water, the xanthate decomposition products were confirmed by XPS, which could further lower the hydrophobicity of the treated sphalerite. Our results provide insights into the basic understanding of the salinity effects on the xanthate adsorption on sphalerite and the bubble–mineral interactions in flotation.     

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 250–1180 μm 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 (+425 μm), 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.     

Surface characteristics and flotation behaviour of platinum and palladium tellurides

The telluride minerals, moncheite ((Pt,Pd)(Bi,Te)₂ and PtTe₂) and merenskyite ((Pd,Pt)(Bi,Te)₂ and PdTe₂), contribute between 20% and 45% of the PGMs present in the Platreef ore which is located in the northern limb of the Bushveld Complex of South Africa. There is evidence of these minerals reporting to the tailings and the present investigation was aimed at determining their flotation behaviour and to relate this to their surface characteristics.Microflotation, zeta potential determinations, ToF-SIMS analyses (time of flight-secondary ion mass spectrometry) and X-ray photoelectron spectroscopy (XPS) were used to characterise the flotation and surface behaviour of the synthesised samples. Copper activation of both moncheite and merenskyite samples reduced the flotation response compared with xanthate on its own. When xanthate is added on its own, it is adsorbed on the mineral surfaces at a higher concentration compared to the copper activated minerals.Oxidation of the PGE telluride minerals negatively affects the flotation performance of the Pt and Pd bismuth telluride samples respectively but not the Pt and Pd telluride samples. Grinding finer reduced recoveries and increasing the calcium ion concentration from 80 ppm to 500 ppm in the synthetic water did not negatively affect the flotation response of the PdTe₂ mineral.     

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 (850–1180 μm, 425–850 μm and 250–425 μm) 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.     

Detachment of coarse composite sphalerite particles from bubbles in flotation: Influence of xanthate collector type and concentration

The force required to detach sphalerite ore particles from air bubbles has been measured in flotation concentrates, for particles in the size range of 150–300 μm and 300–600 μm with different degrees of liberation. An electro-acoustic vibrating apparatus, that produces typical force conditions experienced in a flotation cell, was used to measure particle–bubble detachment as a function of the vibrational acceleration. Sodium isopropyl xanthate (SIPX) and potassium amyl xanthate (PAX) collectors were used in flotation, at different concentrations. At a fixed frequency of 50 Hz, the maximum vibrational amplitude at which a particle detaches from bubble was used to calculate the particle detachment force. It was shown that changes in surface hydrophobicity (contact angle), due to variations in reagent conditions have significant impact on particles detaching from bubbles. On average, detachment of particles from oscillating bubble correlated well with xanthate concentration and hydrocarbon chain length of xanthate ions. Particles (300–600 μm) with high contact angle obviously required higher force to detach from bubbles than similar particles with lower contact angle. This correlated well with the flotation response at the different reagent conditions. SEM analysis of particles after detachment showed that fully liberated particles attached to bubbles more readily and also gave higher detachment force than composite particles. Moreover larger detachment forces were observed, on average, for particles with irregular shape compared to particles with rounded shape of the same size range.     

Characterisation of coarse composite sphalerite particles with respect to flotation

The flotation response of a typical zinc-lead (Zn/Pb) ore, with respect to coarse composite (sulphide/non-sulphide) particles is reported. The flotation tests were carried out on a selected feed particle size range (−600 + 75 μm, at P₈₀ of 390 μm) and the recovery of Zn composite particles analysed on a size by size basis. The best results were achieved with the use of 75 g/t sodium isopropyl xanthate (SIPX), obtaining a Zn recovery of 77%, with a significant improvement at the coarse end of the particle size distribution. Computerised scanning electron microscope (QEMSCAN) was used to characterise value mineral grain size and degree of liberation, as well as gangue and sphalerite association in particles reporting to both concentrate and tailings. A new characterisation function (Locking ratio, LR) was developed based on the data from the automated mineralogical analysis to characterise particles into two-phase composites with different degree of locking texture (simple and complex). The function, which is based on the mode of occurrence of sphalerite, grain size, proportion and composition of the constituent minerals in each particle, was used to study the flotation response of the particles with different degrees of locking. The results highlight the difference in recoverability of the sphalerite bearing particles with different degrees of locking, with simple locking texture giving higher recovery than complex locking texture, for the same overall liberation.     

Effect of Leptospirillum ferrooxidans on the flotation kinetics of sulphide ores

The objective of this work was to determine the effect of Leptospirillum ferrooxidans on the floatability of chalcopyrite, sphalerite, and pyrrhotite by using xanthate as a collector. The tests were carried out in the absence and presence of bacteria in relation to the type of ore and contact time with bacteria. The results indicate that the chalcopyrite flotation rate significantly increased in the presence of L. ferrooxidans due to the formation of hydrophobic species. The bacteria function as a weak depressant for pyrrhotite after a conditioning time ?60 min. The behaviour of sphalerite remains without changes due to its low susceptibility to oxidation. It was concluded that L. ferrooxidans brings about superficial changes mainly due to the oxidation of minerals.     

Sodium isopropyl xanthate degradation by advanced oxidation processes

This paper presents the results obtained by different oxidative processes when an aqueous solution containing sodium isopropyl xanthate is treated; this reagent is used in the flotation of copper minerals. The advanced oxidation processes used are UV photolysis, direct electrolysis and photoelectrooxidation. The solutions used containing sodium isopropyl xanthate were adjusted to the following concentrations: 6, 8, 10, 25 and 40 mg L⁻¹. The results show that the three oxidation processes proved to be suitable for the destruction of xanthate, with the following maximum destruction efficiencies: 76% for electrolysis, 95% for UV photolysis and 99% for photoelectrooxidation.     

New collectors for the flotation of unactivated marmatite

Three thiophenol collectors were tested for the flotation of marmatite without activation by copper sulfate. Flotation tests showed that marmatite flotation increased according to the following order: 2-fluoro thiophenol < 2-hydroxy thiophenol < 2-amino thiophenol. All these thiophenols exhibited a better flotation property for marmatite than butyl xanthate. Infrared spectra indicated that 2-amino thiophenol and 2-hydroxy thiophenol chemically adsorbed onto the surface of marmatite. 2-Fluoro thiophenol adsorbed physically onto the surface of marmatite. Quantum chemical calculations indicated that the energy of the highest occupied molecular orbital (HOMO) for 2-amino thiophenol was the highest among the tested collectors and we thus determined that its collecting ability should be the strongest. This agreed with the experimentally determined flotation results.     

Determination of the concentrations of calcium and magnesium released from fluid inclusions of sphalerite and quartz

This study investigates the morphology of fluid inclusions trapped within a natural sphalerite and its closely intergrown quartz, and determines the total concentrations of calcium (Ca) and magnesium (Mg) released from the inclusions after grinding. The results indicated that numerous fluid inclusions with sizes from few microns to dozens of microns exist in the sphalerite and quartz. The inclusions contain abundant Ca and Mg. However, the concentrations of Ca and Mg in the inclusions of quartz are significantly lower than those of sphalerite. The inclusions were broken during the grinding process, releasing Ca and Mg to the solution; these released concentrations increased with the increase of grinding time. The maximum concentrations of Ca and Mg released from the fluid inclusions were 61.19 ppm and 5.23 ppm for sphalerite, and 3.28 ppm and 0.21 ppm for quartz, respectively. This study provides new understanding for the source of Ca and Mg in flotation pulp.     

Decomposition of sodium butyl xanthate (SBX) in aqueous solution by means of OCF: Ozonator combined with flotator

In this study, ozonator combined with flotator (OCF) have been applied to treat the mineral processing wastewater. The process efficiency has been evaluated in the bench scale. Removing xanthate from aqueous solution was conducted by OCF. In all cases, the butyl xanthate concentration in the treated water was found to be negligible (<0.42 mg L⁻¹). The experiments were preceded under different reaction conditions to study the ozonation time and pH on the oxidation of butyl xanthate. The concentration of butyl xanthate and sulfide are analyzed at special time intervals to elucidate the decomposition of butyl xanthate. In addition, oxidation reduction potential and pH are continuously measured in the course of experiments. Chemical oxygen demand is chosen as a mineralization index of the ozonation of butyl xanthate. The degradation mechanism between butyl xanthate and ozone has been discussed. The OCF technology showed to be an efficient process, which requires ozone and flotator, and the treated water ended up with a very low residual concentration of xanthate and COD. It can be inferred from ultraviolet spectrum, HPLC-MS and COD measurement that SO₄²⁻ is produced. The COD of butyl xanthate solution declined dramatically, the removal rate of COD reached 72.21% when ozonation time is 60 min. And the biodegradability (BOD/COD) of butyl xanthate solution increased markedly and shifted from 0.251 to 0.361. It is believed that this ozonation–flotation technique, here named OCF, using ozonator and flotator has a high potential as a alternative method for pollutants removal (flotation reagents, such as butyl xanthate) form waste mining effluents.     

黄铜矿与磁黄铁矿浮选分离行为及机理研究

通过黄铜矿与磁黄铁矿的单矿物浮选试验,研究矿浆pH、捕收剂丁黄药、抑制剂石灰对其浮选行为的影响。利用红外光谱、循环伏安测试技术,研究其浮选分离的机理。单矿物浮选试验结果表明黄铜矿和磁黄铁矿浮选分离的最佳条件为pH=10,丁黄药浓度为20 mg/L,石灰浓度为300 mg/L。红外光谱测试结果表明丁黄药在矿物表面氧化生成双黄药并通过化学吸附吸附在矿物表面,石灰在磁黄铁矿表面生成氢氧化钙和硫酸钙组成的钙膜。循环伏安测试表明在未添加丁黄药时黄铜矿表面氧化生成疏水的硫单质和硫化铜,磁黄铁矿表面会生成亲水的氢氧化物。     

Influence of bromine modification on collecting property of lauric acid

Bromine atom with strong electronegativity was introduced to α-carbon position of lauric acid (LA) by solvent-free method (Hell–Volhard–Zelinski reaction) at ambient pressure in laboratory, and the synthesized product α-Bromolauric acid (CH₃(CH₂)₉CHBrCOOH, α-BLA) was used as a new type collector for the flotation of quartz mineral. The flotation properties of pure quartz using α-BLA as a collector were investigated by single mineral flotation tests. The adsorption mechanism of α-BLA collector on quartz surface was established by zeta potential measurements, Fourier transform infrared (FT-IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS), in conjunction with the results of quartz micro-flotation tests. Pure mineral flotation results showed that the collector α-BLA exhibited an excellent performance at alkaline conditions (pH ⩾ 11.50), activator CaCl₂ concentration 1.0 × 10⁻⁴ mol/L, and collector concentration 1.5 × 10⁻⁴ mol/L in a relatively lower temperature 15 °C, where about 99.8% of the quartz could be floated out. Compared with collector LA, the new synthesized collector α-BLA is more tolerant to lower pulp temperature and fluctuations of the reagents dosages. The study revealed that the α-BLA collector had adsorbed on the surface of pure quartz in the forms of chemical interaction, electrostatic adsorption and hydrogen bonding adsorption based on the results of zeta potential measurements, FT-IR spectra, and XPS.     

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.     

典型金属离子对闪锌矿浮选行为的影响及作用机制的研究进展

典型金属离子对闪锌矿浮选行为具有显著影响。总结了闪锌矿浮选矿浆体系中金属离子的来源,综述了Cu2+、Pb2+、Fe2+、Fe3+、Ca2+、Mg2+、Zn2+等金属离子对闪锌矿浮选行为的影响及其作用机制。根据金属离子本身的性质和浮选环境的不同,其作用效果和作用机制也有不同,分析表明金属离子是通过取代、吸附和覆盖的方式对闪锌矿可浮性产生影响。展望了金属离子在闪锌矿浮选中的应用前景,并提出了闪锌矿与金属离子作用机制的研究方向。      

Improved statistical methods applied to surface chemistry in minerals flotation

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.The PCA method has been applied to concentrate and tails samples collected from the Inco Matte Concentrator demonstrating extensive CuOH and NiOH transfer between the chalcocite (Cc) and heazlewoodite (Hz) minerals. Statistical differences illustrate the important discriminating depressant action of NiOH in flotation despite the activation of Hz by Cu transfer. The adsorption of the collector at specifically-identified Cu sites has been elucidated by the study. Importantly, the statistical analysis has been able to confirm some mechanisms and deny others proposed to control recovery and selectivity giving more focus on the control factors.