The Experts below are selected from a list of 297 Experts worldwide ranked by ideXlab platform
Jianhua Chen - One of the best experts on this subject based on the ideXlab platform.
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dft study of coadsorption of water and oxygen on Galena pbs surface an insight into the oxidation mechanism of Galena
Applied Surface Science, 2017Co-Authors: Jianhua Chen, Ye Chen, Xianhao Long, Yu-qiong LiAbstract:Abstract Oxidation of Galena (PbS) is of crucial importance in environmental and geochemical processes. Hydrophobic nature of Galena surface hinders the adsorption of water, which involves and determines the finally oxidative product of Galena. In this work, DFT simulations of the adsorption of O2 and H2O on the hydrophobic Galena surface have been performed. Results show that the isolated O2 molecule is dissociated and adsorbed on the S atoms of Galena surface, and the isolated H2O molecule hardly interacts with the hydrophobic Galena surface. However, the dissociation of both H2O and O2 molecules occur after coadsorption, and water molecule dissociates into Ow and H radicals, which then react with surface S atom and adsorbed O2 molecule to form S Ow radical and hydrogen peroxide, respectively. Further adsorption of hydrogen peroxide on surface Pb atoms produces lead hydroxyl radicals. This work could provide microscopic insight into the mechanism of Galena oxidation.
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dft study on the galvanic interaction between pyrite 100 and Galena 100 surfaces
Applied Surface Science, 2016Co-Authors: Baolin Ke, Jianhua Chen, Yu-qiong Li, Cuihua Zhao, Ye ChenAbstract:Abstract The galvanic interaction between pyrite and Galena surface has been investigated using density functional theory (DFT) method. The calculated results show that galvanic interactions between pyrite and Galena surface are decreased with the increase of contact distance. The galvanic interactions still occurs even the distance larger than the sum of two atoms radius (≈2.8 A), and the limit distance of galvanic interaction between Galena and pyrite surface is about 10 A, which is consistent with the quantum tunneling effect. Through Mulliken charge population calculation, it is found that electrons transfer from Galena to pyrite. For Galena surface, Pb 6s and 6p states lose electrons and S 3p state loses a small amount of electrons, which causes the electron loss of Galena. For pyrite surface, Fe 4p state obtains large numbers of electrons, resulting in the decrease of positive charge of Fe atom. However, the 3p state of S atom loses a small numbers of electrons. The reactivity of mineral surface has also been studied by calculating the frontier orbitals of minerals. Results suggest that the highest occupied molecular orbital (HOMO) coefficients of Galena are increased whereas those of pyrite are decreased with the enhancing galvanic interaction, indicating that the oxidation of Galena surface would be enhanced due to the galvanic interaction. The Fukui indices and dual descriptor values of surface atoms suggest that the nucleophilicity of the Galena surface increases, meanwhile, the electrophilicity of pyrite surface increases with the decrease of the contact distance. In addition, the density of states (DOS) of atoms results show that the activity of electrons in Pb 6s and 6p orbitals enhances while the activity of electrons in Fe 3d orbitals weaken due to the galvanic contact between minerals.
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Microthermokinetic study of xanthate adsorption on impurity-doped Galena
Transactions of Nonferrous Metals Society of China, 2016Co-Authors: Jianhua Chen, Yu-qiong Li, Zhuo Yang, Guang-yong AiAbstract:Abstract Six kinds of Galena with different impurities were synthesized and the effects of impurities on the floatability of Galena were investigated. The thermodynamic and kinetic parameters on the Galena surface were measured using microcalorimetry, and the adsorption configuration and energy of butyl xanthate on the surfaces of Galena with different impurities were simulated by density functional theory. Flotation experiments showed that Ag and Bi significantly promoted the recovery of Galena, while Zn, Sb, Mn, and Cu reduced the recovery of the flotation. Microthermokinetic results indicated that the absolute value of xanthate adsorption heat was directly proportional to the flotation recovery of Galena. Adsorption heat and reaction rate coefficients of xanthate on Galena containing Ag or Bi were larger than those on pure Galena, but smaller on Galena containing Cu or Sb. Additionally, the relationship between the heat of unsaturated adsorption of xanthate and the adsorption energy of impurity atom on Galena surface was investigated.
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influence of ag sb bi and zn impurities on electrochemical and flotation behaviour of Galena
Minerals Engineering, 2015Co-Authors: Jianhua Chen, Baolin Ke, Yu-qiong LiAbstract:Abstract The influences of Ag, Bi, Sb and Zn impurities on the electrochemical adsorption of butyl xanthate on a Galena surface were investigated. The impurity-doped and pure Galena samples were synthesised by chemical precipitation and tested by X-ray diffraction (XRD) analyses. The flotation results suggest that the Ag and Bi impurities can promote the flotation of Galena, while the Zn and Sb inhibit it. Both the lead- and impurity-xanthate are observed on the Galena surface by infrared spectra, which suggests that the impurities on Galena surface also interact with xanthate. However, Ag-xanthate and Bi-xanthate at the Galena surface doped Ag or Bi may need to be further verified. The cyclic voltammetric measurements on Galena microelectrodes reveal two oxidation peaks for both the pure and impurity-doped PbS, while no obvious reduction peaks are observed. It is found that the presence of Ag and Bi enhances the oxidation of xanthate on the Galena surface, while the Zn and Sb impurities inhibit the oxidation of xanthate on the Galena surface. The amount of electrochemically adsorbed xanthate on the Galena surface varies based on the type of impurity and has a positive correlation with the flotation recovery of Galena.
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interactions of xanthate with pyrite and Galena surfaces in the presence and absence of oxygen
Journal of Industrial and Engineering Chemistry, 2014Co-Authors: Jianhua Chen, Yu-qiong LiAbstract:Abstract In this study, first-principles calculations were performed to investigate the interactions of hydrogen xanthate (HOCS2−) with pyrite (1 0 0) and Galena (1 0 0) surfaces. The calculation results suggest that strong chemisorption of HOCS2− occurs at Fe sites on the pyrite (1 0 0) surface, whereas its interaction at Pb sites on the Galena (1 0 0) surface is weak. The interaction of xanthate with oxidized pyrite surface is weakened while the interaction of xanthate with oxidized Galena surface is enhanced. The hydration of xanthate and mineral surfaces is discussed. Dixanthogen could be formed on the pyrite surface but not on the Galena surface.
Yu-qiong Li - One of the best experts on this subject based on the ideXlab platform.
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dft study of coadsorption of water and oxygen on Galena pbs surface an insight into the oxidation mechanism of Galena
Applied Surface Science, 2017Co-Authors: Jianhua Chen, Ye Chen, Xianhao Long, Yu-qiong LiAbstract:Abstract Oxidation of Galena (PbS) is of crucial importance in environmental and geochemical processes. Hydrophobic nature of Galena surface hinders the adsorption of water, which involves and determines the finally oxidative product of Galena. In this work, DFT simulations of the adsorption of O2 and H2O on the hydrophobic Galena surface have been performed. Results show that the isolated O2 molecule is dissociated and adsorbed on the S atoms of Galena surface, and the isolated H2O molecule hardly interacts with the hydrophobic Galena surface. However, the dissociation of both H2O and O2 molecules occur after coadsorption, and water molecule dissociates into Ow and H radicals, which then react with surface S atom and adsorbed O2 molecule to form S Ow radical and hydrogen peroxide, respectively. Further adsorption of hydrogen peroxide on surface Pb atoms produces lead hydroxyl radicals. This work could provide microscopic insight into the mechanism of Galena oxidation.
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dft study on the galvanic interaction between pyrite 100 and Galena 100 surfaces
Applied Surface Science, 2016Co-Authors: Baolin Ke, Jianhua Chen, Yu-qiong Li, Cuihua Zhao, Ye ChenAbstract:Abstract The galvanic interaction between pyrite and Galena surface has been investigated using density functional theory (DFT) method. The calculated results show that galvanic interactions between pyrite and Galena surface are decreased with the increase of contact distance. The galvanic interactions still occurs even the distance larger than the sum of two atoms radius (≈2.8 A), and the limit distance of galvanic interaction between Galena and pyrite surface is about 10 A, which is consistent with the quantum tunneling effect. Through Mulliken charge population calculation, it is found that electrons transfer from Galena to pyrite. For Galena surface, Pb 6s and 6p states lose electrons and S 3p state loses a small amount of electrons, which causes the electron loss of Galena. For pyrite surface, Fe 4p state obtains large numbers of electrons, resulting in the decrease of positive charge of Fe atom. However, the 3p state of S atom loses a small numbers of electrons. The reactivity of mineral surface has also been studied by calculating the frontier orbitals of minerals. Results suggest that the highest occupied molecular orbital (HOMO) coefficients of Galena are increased whereas those of pyrite are decreased with the enhancing galvanic interaction, indicating that the oxidation of Galena surface would be enhanced due to the galvanic interaction. The Fukui indices and dual descriptor values of surface atoms suggest that the nucleophilicity of the Galena surface increases, meanwhile, the electrophilicity of pyrite surface increases with the decrease of the contact distance. In addition, the density of states (DOS) of atoms results show that the activity of electrons in Pb 6s and 6p orbitals enhances while the activity of electrons in Fe 3d orbitals weaken due to the galvanic contact between minerals.
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Microthermokinetic study of xanthate adsorption on impurity-doped Galena
Transactions of Nonferrous Metals Society of China, 2016Co-Authors: Jianhua Chen, Yu-qiong Li, Zhuo Yang, Guang-yong AiAbstract:Abstract Six kinds of Galena with different impurities were synthesized and the effects of impurities on the floatability of Galena were investigated. The thermodynamic and kinetic parameters on the Galena surface were measured using microcalorimetry, and the adsorption configuration and energy of butyl xanthate on the surfaces of Galena with different impurities were simulated by density functional theory. Flotation experiments showed that Ag and Bi significantly promoted the recovery of Galena, while Zn, Sb, Mn, and Cu reduced the recovery of the flotation. Microthermokinetic results indicated that the absolute value of xanthate adsorption heat was directly proportional to the flotation recovery of Galena. Adsorption heat and reaction rate coefficients of xanthate on Galena containing Ag or Bi were larger than those on pure Galena, but smaller on Galena containing Cu or Sb. Additionally, the relationship between the heat of unsaturated adsorption of xanthate and the adsorption energy of impurity atom on Galena surface was investigated.
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influence of ag sb bi and zn impurities on electrochemical and flotation behaviour of Galena
Minerals Engineering, 2015Co-Authors: Jianhua Chen, Baolin Ke, Yu-qiong LiAbstract:Abstract The influences of Ag, Bi, Sb and Zn impurities on the electrochemical adsorption of butyl xanthate on a Galena surface were investigated. The impurity-doped and pure Galena samples were synthesised by chemical precipitation and tested by X-ray diffraction (XRD) analyses. The flotation results suggest that the Ag and Bi impurities can promote the flotation of Galena, while the Zn and Sb inhibit it. Both the lead- and impurity-xanthate are observed on the Galena surface by infrared spectra, which suggests that the impurities on Galena surface also interact with xanthate. However, Ag-xanthate and Bi-xanthate at the Galena surface doped Ag or Bi may need to be further verified. The cyclic voltammetric measurements on Galena microelectrodes reveal two oxidation peaks for both the pure and impurity-doped PbS, while no obvious reduction peaks are observed. It is found that the presence of Ag and Bi enhances the oxidation of xanthate on the Galena surface, while the Zn and Sb impurities inhibit the oxidation of xanthate on the Galena surface. The amount of electrochemically adsorbed xanthate on the Galena surface varies based on the type of impurity and has a positive correlation with the flotation recovery of Galena.
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interactions of xanthate with pyrite and Galena surfaces in the presence and absence of oxygen
Journal of Industrial and Engineering Chemistry, 2014Co-Authors: Jianhua Chen, Yu-qiong LiAbstract:Abstract In this study, first-principles calculations were performed to investigate the interactions of hydrogen xanthate (HOCS2−) with pyrite (1 0 0) and Galena (1 0 0) surfaces. The calculation results suggest that strong chemisorption of HOCS2− occurs at Fe sites on the pyrite (1 0 0) surface, whereas its interaction at Pb sites on the Galena (1 0 0) surface is weak. The interaction of xanthate with oxidized pyrite surface is weakened while the interaction of xanthate with oxidized Galena surface is enhanced. The hydration of xanthate and mineral surfaces is discussed. Dixanthogen could be formed on the pyrite surface but not on the Galena surface.
L Wang - One of the best experts on this subject based on the ideXlab platform.
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assessing the influence of humic acids on the weathering of Galena and its environmental implications
Ecotoxicology and Environmental Safety, 2018Co-Authors: Heping Li, Kai Zheng, L WangAbstract:Abstract Galena weathering often occurs in nature and releases metal ions during the process. Humic acid (HA), a critical particle of natural organic matter, binds metal ions, thus affecting metal transfer and transformation. In this work, an electrochemical method combined with spectroscopic techniques was adopted to investigate the interfacial processes involved in Galena weathering under acidic and alkaline conditions, as well as in the presence of HA. The results show that the initial step of Galena weathering involved the transformation Pb2+ and S°, regardless of whether the solution was acidic or alkaline. Under acidic conditions, S° and Pb2+ further transform into anglesite, and HA adsorbs on the Galena surface, inhibiting the transformation of sulfur. HA and Pb (II) ions form bridging complexes. Under alkaline conditions without HA, the sulfur produced undergoes no transformation, whereas Pb2+ will transform into PbO. The presence of HA changes the Galena weathering mechanism via ionization effect, and Pb2+ is ultimately converted into anglesite. Higher acidity in acidic conditions or higher alkalinity in alkaline conditions causes Galena corrosion when the electrolyte does not contain HA. Conversely, higher pH always accelerates Galena corrosion when the electrolyte contains HA, whether the electrolyte is acidic or alkaline. At the same acidity/alkalinity, increasing the concentration of HA inhibits Galena weathering. Galena will release 134.7 g m−2·y−1 Pb2+ to solution at pH 2.5, and the amount decreases to 28.09 g m−2·y−1 in the presence of 1000 mg/L HA. This study provides an in situ electrochemical method for the assessment of Galena weathering.
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Galena weathering under simulated acid rain conditions electrochemical processes and environmental assessments
Environmental Science: Processes & Impacts, 2018Co-Authors: Kai Zheng, Heping Li, L WangAbstract:Galena can be easily weathered under acid rain conditions and causes environmental issues. This process, in nature, is an electrochemical process. In situ electrochemical technology and surface analysis technology were combined to investigate this weathering process. The experimental results showed that Galena weathering under simulated acid rain (SAR) could cause an initial increase in Pb2+ ions and result in the formation of a passive S0 film, and the terminal product was SO42−. Increased acidity stimulates Galena weathering, and the promotion efficiency was 2208% as the pH of the SAR decreased from 5.2 to 4.2. The presence of pyrite is favourable for Galena weathering, and the promotion efficiency was 150% when contained 25% (wt%) pyrite. Galena will release 1.7 g per m2 per year Pb2+ to solution when the pH of acid rain is 5.2, and the released Pb2+ will reach 95.7 g per m2 per year when the pH of acid rain is 4.2 plus the galvanic effect of pyrite.
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influence of ph pb2 and temperature on the electrochemical dissolution of Galena environmental implications
Ionics, 2016Co-Authors: L Wang, Kai Zheng, Heping LiAbstract:We investigated the influence of pH, Pb 2+ , and temperature on the electrochemical dissolution of Galena. The experimental results showed the following: (1) Acidic or alkaline conditions stimulate Galena elec- trochemical dissolution. The Galena electrode corrosion current density (jcorr) increased from 0.072 to 0.143 μA· cm −2 as the pH decreased from 6.0 to 2.0 (promotion efficiency of 98.61 %) and from 0.066 to 0.132 μA· cm −2 as the pH increased from 8.0 to 12.0 (promotion efficiency of 100 %). (2) Pb(NO3)2 promotes Galena electrochemical dissolution at low concentrations ( 0.10 mol·L −1 ) because Pb 2+ has two different func- tions during Galena electrochemical dissolution. (3) Higher temperatures are favorable for Galena electro- chemical dissolution. The Galena jcorr increased from 0.143 to 0.226 μA·cm −2 as the temperature increased from 25 to 55 °C. These experimental results are of direct significance for the control of environmental pol- lution during Galena weathering and mining activities.
John Ralston - One of the best experts on this subject based on the ideXlab platform.
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control of grinding conditions in the flotation of Galena and its separation from pyrite
International Journal of Mineral Processing, 2003Co-Authors: Yongjun Peng, S R Grano, Daniel Fornasiero, John RalstonAbstract:Abstract A specially designed mill which allowed the control of pH throughout grinding was used to study the effect of grinding conditions on Galena flotation and Galena separation from pyrite. The various reactions occurring on the mineral surface were investigated by a range of techniques, including OH − addition to maintain the grinding pH, ethlenediamine tetra acetic acid disodium salt (EDTA) extraction, X-ray photoelectron spectroscopy (XPS) and Time-of-flight secondary ion mass spectrometry (TOF-SIMS) measurements. Galena flotation and Galena separation from pyrite were strongly dependent on the metal oxidation species produced on Galena and pyrite surfaces under different grinding conditions. Iron oxidation species depressed both Galena and pyrite flotation, while lead oxidation species activated pyrite but had little effect on Galena. Optimum Galena flotation and Galena selectivity against pyrite were achieved by selecting grinding conditions that enabled lead and iron oxidation to be controlled. Aeration during grinding interfered with oxygen reduction occurring on the mineral acting as the cathode, as a result of galvanic interaction, and influenced the flotation of that cathodic mineral. Oxygen purging during grinding depressed Galena flotation in single mineral experiments but increased Galena selectivity against pyrite.
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towards prediction of oxidation during grinding i Galena flotation
Minerals Engineering, 2002Co-Authors: Yongjun Peng, John Ralston, S R Grano, Daniel FornasieroAbstract:The degree of oxidation during grinding and its effect on Galena flotation were studied using a specialised mill which permitted chemical conditions during grinding to be controlled. It was found that iron oxidation species derived from the grinding medium played a dominant role in Galena flotation. The amount of hydroxide consumed to maintain the grinding pH at a constant value depended on the production of iron oxidation species. Linear relationships were obtained between the amount of hydroxide consumed to maintain a constant grinding pH and the production of iron oxidation species as well as Galena recovery. These relationships should eventually permit oxidation during grinding and Galena flotation to be predicted.
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investigating fine Galena recovery problems in the lead circuit of mount isa mines lead zinc concentrator part 1 grinding media effects
Minerals Engineering, 1999Co-Authors: V J Cullinan, C J Greet, S R Grano, N W Johnson, John RalstonAbstract:A plant survey was carried out on the lead secondary rougher and scavenger banks of the Lead/Zinc Concentrator of Mount Isa Mines Limited. Sizing analysis of the survey samples demonstrated that a major limiting factor to overall lead recovery in this section of the plant was the diminished recovery of the fine Galena in the minus 5 microns particle size fraction. Batch flotation experiments were carried out on a plant sample of lead secondary rougher feed and a sample of rod mill feed ore. Mineral recovery-size data for these tests showed similar fine Galena flotation behaviour to that observed in the plant. Increased collector addition did not improve either the maximum recovery or the flotation rate constant of the fine Galena but did reduce the selectivity of Galena against sphalerite. Changing of the grinding media used for the ore sample from a high carbon steel to a high chromium alloy steel resulted in a significant increase in the maximum recovery and flotation rate constant of the fine Galena. EDTA (ethylene diaminetetraacetic) extractable iron measured for the high carbon steel media were similar in magnitude to those measured within the plant and were higher than those measured for the high chromium alloy steel media. The increased surface concentration of hydrophilic layers of oxidised iron species on the fine Galena was a likely reason for their diminished flotation behaviour both in the laboratory and in the plant.
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Aspects of the selective flocculation and flotation of ultrafine Galena particles
1999Co-Authors: Elaine M. Wightman, Grano, John RalstonAbstract:A novel method for the selective aggregation of ultrafine Galena particles with coarse carrier Galena particles is presented. Essential differences between this approach and those conventionally employed are highlighted. The particle size - flotation rate constant dependency for Galena/quartz mixtures is examined and compared with results obtained using conventional aggregation techniques. Evidence for changes in the flotation rate of both Galena and quartz are described.
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Sulphite modification of Galena surfaces and its effect on flotation and xanthate adsorption
International Journal of Mineral Processing, 1997Co-Authors: Stephen Grano, Clive A. Prestidge, John RalstonAbstract:Abstract The effect of sulphite interaction with Galena on the mechanism of ethyl xanthate adsorption onto Galena surfaces has been studied in situ using UV spectroscopy. The influence of sulphite on Galena flotation has been studied. X-ray photoelectron spectroscopic (XPS) and dissolution studies have been used to identify the mechanism of interaction between sulphite and Galena surfaces. Metastable ethyl monothiocarbonate is a significant derivative of ethyl xanthate adsorption on Galena in the absence of sulphite. The concentration of surface sites which produce monothiocarbonate increases with the initial state of Galena oxidation, which, is in turn, apparently dependent upon Galena preconditioning time, temperature and oxygen concentration. Significantly different ethyl xanthate adsorption characteristics were found, after sulphite conditioning of the Galena surface. In this case, ethyl xanthate adsorption rate was significantly reduced, as was the formation of monothiocarbonate. Surface complexation of lead hydroxide by adsorbed sulphite decreases the rate of ethyl xanthate adsorption onto sites which, potentially, can produce monothiocarbonate. Galena dissolution studies and XPS examination of the Galena surfaces together, confirmed the formation of insoluble lead sulphite precipitates at the Galena surface. The effectiveness of sulphite depression of Galena flotation is enhanced by adsorbed lead hydrolysis products on Galena.
Alireza Javadi Nooshabadi - One of the best experts on this subject based on the ideXlab platform.
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Effect of Grinding Environment on Galena Flotation
The Open Mineral Processing Journal, 2015Co-Authors: Alireza Javadi NooshabadiAbstract:The generation of H 2 O 2 during the grinding of Galena and its effect on the oxidation of Galena particles leading to a decrease in flotation recovery has been studied. The influence of two types of grinding media in wet and dry grinding of Galena on the formation of hydrogen peroxide and its flotation response was examined. Galena ground in mild steel grinding media generated more hydrogen peroxide compared to stainless steel media. Thus, lower flotation recovery of Galena ground in mild steel could also be attributed due to the presence of higher amounts of H 2 O 2 in the pulp liquid, besides widely reported galvanic interactions between grinding medium and mineral. The extent of Galena surface oxidation because of either galvanic interactions or H 2 O 2 presence or both, is not very clear. Clearly, both mechanisms operate in Galena oxidation and needs further investigation to distinguish the predominant mechanism among the two or the extent of each contributing to surface oxidation.
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formation of hydrogen peroxide by Galena and its influence on flotation
Advanced Powder Technology, 2014Co-Authors: Alireza Javadi NooshabadiAbstract:Abstract The formation of hydrogen peroxide (H 2 O 2 ), an oxidising agent stronger than oxygen, during the grinding of Galena (PbS) was examined. It was observed that Galena generated H 2 O 2 in the pulp liquid during wet grinding and also when the freshly ground solids were placed in water immediately after dry grinding. The generation of H 2 O 2 during either wet or dry grinding was thought to be due to a reaction between Galena and water, when the mineral surface is catalytically active, to produce OH free radicals by breaking down the water molecule. It was also shown that Galena could generate H 2 O 2 in the presence or absence of dissolved oxygen in water. The concentration of H 2 O 2 formed increased with decreasing pH. The effects of using mixtures of pyrite or chalcopyrite with Galena were also investigated. In pyrite–Galena mixture, the formation of H 2 O 2 increased with an increase in the proportion of pyrite. This was also the case with an increase in the fraction of chalcopyrite in chalcopyrite–Galena mixtures. The oxidation or dissolution of one specific mineral rather than the other in a mixture can be explained better by considering the extent of H 2 O 2 formation rather than galvanic interactions. It appears that H 2 O 2 plays a greater role in the oxidation of sulphides or in aiding the extensively reported galvanic interactions. This study highlights the necessity of further study of electrochemical and/or galvanic interaction mechanisms between pyrite and Galena or chalcopyrite and Galena in terms of their flotation behaviour.
