The effect of regrind mills on the separation of chalcopyrite from pyrite in cleaner flotation

Stirred mills have been widely used for regrinding and are more energy efficient than tumbling mills. These two types of mills present different particle breakage mechanisms and redox environments during grinding. In this study, the effect of regrinding with these two types of mills on the separation of chalcopyrite from pyrite in the cleaner stage was studied. A laboratory rod mill and a laboratory stirred mill were used to regrind rougher flotation concentrates. It was found that chalcopyrite and pyrite exhibited different flotation behavior after regrinding with the rod mill and the stirred mill, resulting in different separability of chalcopyrite from pyrite. The mechanism underpinning this phenomenon was investigated by a range of techniques including dissolved oxygen demand measurements, X-ray photoelectron spectroscopy (XPS) and Time of flight secondary ion mass spectrometry (ToF-SIMS). It was found that the two mills produced different surface oxidation and pyrite activation by copper ions which determined the separation of chalcopyrite from pyrite. This study demonstrates that the selection of a regrind mill should not only depend on its energy efficiency but also the property of surfaces produced for subsequent flotation.     

Acidic sulphate leaching of chalcopyrite concentrates in presence of pyrite

Copper concentrates with mineralogy dominated by chalcopyrite have slow leaching kinetics at atmospheric pressure in sulphate media because of the formation of passivation layer on its surface during the leaching. To enhance the leaching rate of the copper concentrate, pyrite was added to act as a catalyst. Pyrite and copper sulphide minerals then form a galvanic cell which increases both the copper leaching rate and yield. Effect of parameters such as solution redox potential, temperature, initial acid concentration, solids content, total initial iron concentration and pyrite to copper sulphide minerals mass ratio were investigated. Mineralogical analyses by XRD were performed on selected leach residues and the feed materials. A copper recovery higher than 80% in 24 h was achieved at a redox potential of 410 mV vs Ag, AgCl, a temperature of 85 °C, 15 g/L of initial acid concentration, a solid content of 7.8% (w/v), a total initial iron concentration 5 g/L and pyrite to copper sulphide minerals mass ratio 2:1. XRD patterns on leach residues showed that candidates for surface passivation, i.e. jarosite and elemental sulphur, were formed at high total initial iron concentrations.     

Formation of hydrogen peroxide by pyrite and its influence on flotation

Formation of hydrogen peroxide (H₂O₂), an oxidising agent stronger than oxygen, by pyrite (FeS₂), the most abundant metal sulphide on Earth, during grinding was investigated. It was found that pyrite generated H₂O₂ in pulp liquid during wet grinding and also the solids when placed in water immediately after dry grinding. Type of grinding medium on formation of hydrogen peroxide revealed that the mild steel produced more H₂O₂ than stainless steel grinding medium, where Fe²⁺ and/or Fe³⁺ ions played a key role in producing higher amounts of H₂O₂. The effect of grinding atmosphere of air and N₂ gas showed that nitrogen environment free from oxygen generated more H₂O₂ than air atmosphere suggesting that the oxygen in hydrogen peroxide is derived from water molecules. In addition, the solids after dry grinding producing more H₂O₂ than wet grinding indicate the role of pyrite surface or its catalytic activity in producing H₂O₂ from water. This study highlights the necessity of relooking into the electrochemical and/or galvanic interaction mechanisms between the grinding medium and pyrite in terms of its flotation behaviour.     

The separation of chalcopyrite and chalcocite from pyrite in cleaner flotation after regrinding

In this study, the differences between the separation of chalcopyrite and chalcocite from pyrite in cleaner flotation after regrinding were investigated. In the rougher flotation prior to regrinding, high chalcopyrite and chalcocite recovery were obtained in conjunction with high pyrite flotation recovery due to the activation of pyrite by copper ions during primary grinding. The rougher flotation concentrate was reground in a rod mill before cleaner flotation. It was found that chalcopyrite and chalcocite exhibited different flotation behavior and also affected pyrite flotation differently in cleaner flotation. The mechanism underpinning these phenomena was investigated by a range of techniques including the polarization of mineral electrodes, X-ray photoelectron spectroscopy (XPS) analyses and ethylene diamine tetraacetic acid (EDTA) extraction. It was found that the flotation behavior of both copper minerals and their effect on pyrite flotation after regrinding were governed by their electrochemical activities and galvanic coupling with pyrite.     

铜离子对闪锌矿、黄铁矿浮选的选择性活化机理研究

本文对铜离子活化闪锌矿(ZnS)和黄铁矿(FeS2)的表面化学、溶液化学以及两种矿物的浮选分离进行了综合评述,分析讨论了铜离子浓度、活化时间、pH值、表面电荷、表面氧化程度、矿浆电位等主要因素对闪锌矿和黄铁矿活化浮选的影响.为生产实践中闪锌矿、黄铁矿的绿色、高效浮选分离提供一定的理论及技术支撑.     

Predicting the surface chemistry contribution to the flotation recovery of chalcopyrite by ToF-SIMS

In flotation, the surface chemistry of the minerals plays a crucial role in the selectivity and recovery of valuable minerals. Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) surface analysis is used in this study to investigate the impact of surface chemistry on the flotation of chalcopyrite with dithiophosphate collector. The ToF-SIMS data corresponding to concentrate and tail particles were statistically analysed employing a combination of multivariate statistical techniques - principal components analysis and discriminant analysis - to identify the surface species that are differential in the flotation of chalcopyrite. Two models were developed to predict the concentrate and tail deportment of particles, one targeting fine and intermediate particle sizes and the other for the coarse particle size. These models were tested using cross-validation and the results showed good prediction accuracy, 88% for fine and intermediate particles and 77% for coarse particles. The models were further tested on feed samples and the results show the developed models can be used as a predictive tool that estimates the maximum recovery expected based on the surface chemistry of particles, as evidenced by ToF-SIMS, under given hydrodynamic conditions.     

Effects of free cyanide and cuprous cyanide on the flotation of gold and silver bearing pyrite

At gold and silver mineral processing plants, cyanide species are always present in the process water recycled to flotation circuits, despite the cyanide destruction process. The effect of cyanide, in particular, cuprous cyanide on gold and silver flotation has not been well understood. In the present study, free cyanide and cuprous cyanide species were isolated and their effects on the flotation of a pyritic ore were evaluated. It was found that free cyanide depressed gold and silver flotation through their carrier, pyrite. Cuprous cyanide mainly in the form of Cu(CN)₃²⁻ depressed pyrite flotation similarly as free cyanide. Electrochemical studies including open circuit potential (OCP), cyclic voltammetry and electrochemical impedance spectroscopy (EIS) techniques were carried out to understand the underpinning depression mechanism of cyanide species on pyrite flotation using xanthate as collector. It was found that all surface electrochemical reactions were inhibited by either free cyanide or cuprous cyanide. The surface layer as a result of xanthate adsorption on pyrite was completely removed in the presence of these cyanide species, which was suggested to contribute to the hydrophilic pyrite surface.     

The influence of particle shape properties and associated surface chemistry on the flotation kinetics of chalcopyrite

The role of particle shape properties in determining flotation kinetics was investigated in this study. −150/+75 μm chalcopyrite was floated in a microflotation cell, and shape properties of the timed concentrates were quantified using a mineral liberation analyser - a mineralogical characterisation system based on automated scanning electron microscopy. It was found that, when floated in the absence of collector, particles with angular shape features reported to the concentrate faster than round particles. X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (ToF-SIMS) showed that angular particles also exhibited surface chemistry characteristics favourable for flotation. When particle floatabilities were high (i.e. when floated in the presence of potassium amyl xanthate), shape properties were not found to contribute significantly to the rates at which particles floated.     

黄铜矿和黄铁矿微生物浸出差异性研究

采用搅拌浸出法,搅拌转速350 r/min、搅拌温度45℃,使用相同菌种对黄铜矿与黄铁矿浸出差异性进行了研究。结果表明,在相同生物浸出条件下,黄铁矿较黄铜矿更易浸出。黄铜矿生物浸出后期,浸出速率减慢的决定因素并非黄钾铁矾钝化层的罩盖。两种矿物浸出差异性产生的根本原因在于由其自身晶体结构所决定的生物浸出机理不同。     

Investigation on the flotation behavior and adsorption mechanism of 3-hexyl-4-amino-1,2,4-triazole-5-thione to chalcopyrite

In this paper, a novel surfactant, 3-hexyl-4-amino-1,2,4-triazole-5-thione (HATT) is first introduced as a collector for chalcopyrite flotation. Its flotation behavior and adsorption mechanism to chalcopyrite has been evaluated by micro-flotation tests, and zeta potential, FTIR spectra and adsorption quantity measurements. The results demonstrate that HATT exhibited excellent flotation performances to chalcopyrite at pH 4–8. The adsorption of HATT on to chalcopyrite agrees well with the pseudo-second-order model and Langmuir isotherm, and is a spontaneously endothermic chemisorption process. FTIR spectra and zeta potential analyses further imply that chalcopyrite might chemisorb HATT by formation of HATT–copper surface complexes.     

石英与蛇纹石异相凝聚及其对黄铁矿浮选的影响

通过单矿物和人工混合矿的浮选试验、Zeta电位测试、吸附量测试,研究了蛇纹石和石英异相凝聚的机理,以及对黄铁矿浮选的影响,以进一步探索多种矿物的体系中,蛇纹石对硫化矿物浮选影响的主要原因。结果表明:通过添加石英,可以恢复黄铁矿对捕收剂的吸附量,减弱蛇纹石的不良影响,不同粒级的石英与蛇纹石的异相凝聚作用强弱不同,粒级越细的石英,与蛇纹石的异相凝聚作用越强。     

The effect of temperature on the pulp and froth phases in the flotation of pyrite

The effect of temperature on the flotation of pyrite has been investigated. At temperatures below ambient an increase in temperature results in an increase in the rate of flotation of fast-floating particles but has a minimal effect on that for slow-floating particles. At temperatures greater than ambient the dominant effect of increasing temperature is to decrease the viscosity of the water thus increasing the rate of elutriation of the gangue back to the pulp. In general an increase in temperature resulted in an increase in the rate of pyrite recovery and the sulphur grades and a decrease in the water recovery and size of the bubbles in the pulp.     

The influence of the oxidation state of pyrite and arsenopyrite on the flotation of an auriferous sulphide ore

In this paper, the influence of the oxidation state of pyrite and arsenopyrite on the flotation of an auriferous sulphide ore was investigated by different techniques, including electrode, pulp potentials, DRIFT spectroscopy and microflotation tests. In addition, the gold and sulphide recoveries were also investigate, in a laboratory-scale cell, as a function of pulp potential and reagent concentration. It was verified that the presence of oxidation products on the sulphide mineral surface demands a higher collector concentration in order to achieve a satisfactory sulphide recovery. The electrochemical behaviour of pyrite and arsenopyrite indicated that a nitrogen atmosphere can lead to a low pulp potential, which inhibits the formation of oxidation products, enhancing both the free gold and sulphide recoveries. Although copper sulphate activates even oxidised sulphide surfaces, it does not improve free gold recovery.     

调浆气氛对黄铁矿浮选电化学性质影响研究

基于氧气在黄铁矿浮选电化学反应中的作用,考察了p H为4.00、6.86、9.18、10.01和10.96五种缓冲溶液浮选体系下,矿浆溶氧量(DO)对黄铁矿浮选矿浆电位(Eh)和回收率的影响。研究表明,五种缓冲溶液体系下,Eh均随着DO的增加而增加,碱性条件下DO对Eh的影响较小;浮选回收率随DO的增加呈下降趋势,碱性条件下回收率的变化较大。     

A comparison of the predictability of batch flotation kinetic models

Batch flotation test data of a mixture of pyrite and calcite were used to compare regression parameters of four kinetic model structures. The work included the use of unoxidized or a mixture of partially oxidized pyrite (by microwave irradiation). The objective of floating oxidized pyrite was to have mineral particles with different floatability, closer to a real situation. The models considered include: single rate constant, distributed rate constants (i.e. rectangular and gamma distributions), and a recently introduced approach based on fractional calculus. Such models were selected due to their good tradeoff between simplicity and accuracy. The regressions were performed (1) taking all the data points and comparing the mean square error (MSE) and adjusted correlation factor $\left(R_{\mathit{Adj}}^2\right)$ as indicators of the goodness of fit; and (2) taking the first data points while neglecting the last ones (from 1 to 3) and observing the variability of the model parameters and the prediction of maximum recovery (R_∞). For the latter regression scheme, besides MSE and $R_{\mathit{Adj}}^2$, a predictive factor, E, was defined by subtracting the final measured recovery from the calculation obtained by the model. This allowed to measure the ability of each model to extrapolate the omitted points on the recovery vs. time curve.Results from this study showed that the single constant model had a satisfactory performance with the advantage of having the least parameters compared to the other structures. The gamma model was effective and robust. The rectangular model gave an acceptable goodness of fit but overestimated the maximum and final recovery. Finally, the fractional calculus approach gave the best goodness of fit, overall, but failed in predicting the maximum recovery, which occurred when the derivative order was greater than 1.     

磨矿介质对黄铜矿磨矿体系矿浆电位的影响

考查了不同磨矿介质下,黄铜矿新鲜矿浆与放置24 h后矿浆pH值与矿浆电位的关系,通过测定矿浆中铁离子含量及溶氧量,分析了pH=4.67时黄铜矿磨矿体系矿浆电位变化的原因,并通过测定铁介质和黄铜矿间的迦伐尼电流,考查了黄铜矿和铁介质在不同pH条件下原电池相互作用的强弱。     

The use of canola oil as an environmentally friendly flotation collector in sulphide mineral processing

The efficiency of mineral flotation relies on the ability to selectively recover different value minerals into their respective concentrates at optimum grades and recoveries based on the differing hydrophobicities. Many of the common hydrophobizing reagents (collectors) currently used in flotation have significant occupational and environmental implications, and hence there is a quest for environmentally benign chemical additives that give similar or better performance than the more toxic conventional reagents. In this paper, we provide substantial experimental evidence that the use of edible, fatty acid-based oils (canola and palm) can foster the flotation recovery of chalcopyrite and molybdenite minerals more selectively against pyrite than the conventional collectors, sodium isopropyl, potassium amyl xanthates and diesel oil.Single and mixed chalcopyrite/pyrite minerals and plant sulphide ores’ flotation studies using canola and palm oils, in contrast with conventional collectors, are reported herein. The results indicate greater efficacy of the canola and palm oils in comparison with the conventional collectors for chalcopyrite and molybdenite recoveries and product upgrades. This is believed to be due to the edible oils’ specific interactions with iron oxides sites preferentially formed in situ on the surfaces of the chalcopyrite or molybdenite in the pulp rather than on the pyrite surfaces, causing limited recovery of the pyrite. Complementary contact angle results confirmed that more canola oil is adsorbed onto chalcopyrite surfaces than onto pyrite surfaces. For the mineral mixtures tested, the edible oil’s degree of unsaturation had a noticeable effect on its performance as a collector. A higher pyrite recovery and slightly lower chalcopyrite grade was obtained with palm oil than with canola oil. These findings suggest that the use of canola oil has a potential to add to the existing array of flotation collectors and would represent a combined opportunity for both the mining and agricultural sectors, with concomitant health, environmental and economic benefits.     

The influence of composition of nonpolar oil on flotation of molybdenite

With increasing molybdenum ore mining, the difficult to treat ores, i.e., lower-grade and fine-disseminated ores have gradually increased in importance. Kerosene was widely used as the conventional collector of molybdenum flotation all along, but it does not adapt well to the flotation of molybdenite in difficult to treat ores. Meanwhile, kerosene has been cancelled from the manufacture catalogue in China, which makes large refineries no longer produce it, and in turn makes it difficult for a molybdenum flotation plant to purchase kerosene and makes it even harder for kerosene to keep a stable composition. Therefore, many molybdenum flotation plants began to apply diesel oil instead of kerosene as collector for molybdenite. However, the flotation results reveal that diesel oil from different manufacturers or being of different specifications from the same manufacturers has a different effect on the flotation of molybdenite, and pulp temperature has an obvious effect on the flotation efficiency of diesel oil. In pulp temperatures ranging from 10 to 30 °C, the flotation recovery of molybdenite increases with increasing high-boiling component in diesel oil. When pulp temperature is below 10 °C, the flotation recovery of molybdenite is related to the dispersibility of diesel oil, i.e., the proportion of high-boiling and low-boiling component in diesel oil. Therefore, a molybdenum flotation plant should not blindly apply diesel oil instead of kerosene as the collector for molybdenite, but should select diesel oil that is suitable for the properties of its ore. This technical note is helpful to better select the proper collector for a molybdenum flotation plant.     

Decoupling rehology and slime coatings effect on the natural flotability of chalcopyrite in a clay-rich flotation pulp

Clay minerals are a commonly occurring gangue in mineral beneficiation operations and occur in a variety of ore deposits, including porphyry copper ores. The presence of clays in mineral beneficiation circuits can cause a wide range of different problems, including that of slime coatings on valuable minerals and elevated viscosities of flotation pulps. The aim of this work was to decouple and estimate the relative magnitudes of the slime coatings and pulp rheology effects on the natural floatability of chalcopyrite in a model mineral system. It was found that the two phenomena can be partially isolated and that they both have a detrimental effect on flotation performance. It was also found that the level to which these two phenomena affect chalcopyrite recovery is of a similar order of magnitude.