Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English  

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Language：Japanese  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Powder Technology  

Molybdenite is associated with primary and secondary copper sulfide minerals. Few studies have focused on the selective flotation of molybdenite to separate it from secondary copper sulfide minerals, such as chalcocite. This study evaluated the use of oxidation treatment to separate molybdenite from chalcocite. The effects of oxidation treatment with hydrogen peroxide (H2O2) on the flotation behaviors of molybdenite and chalcocite in the presence of collectors (i.e., potassium amyl xanthate and diesel oil) were evaluated, and the impacts of H2O2 concentration, oxidation treatment duration, and pH level were assessed. Chalcocite flotation tests showed that the H2O2 treatment significantly reduced the recovery of chalcocite due to the formation of copper hydroxide and sulfate species on the chalcocite surface, which altered its surface hydrophobicity. On the other hand, the low surface oxidation of molybdenite led to high flotation recovery after the oxidation treatment. Oxidation treatment with a 10 mM H2O2 solution at a pH of 9 for 20 min resulted in a separation efficiency of 87%, with 98% molybdenite recovery and 11% chalcocite recovery. The results show that H2O2 oxidation treatment enables the selective flotation of molybdenite to separate it from chalcocite.

DOI： 10.1016/j.powtec.2023.119078

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Institute of Metals and Materials  

<p>This study investigated the effects of potassium amyl xanthate (KAX) and oxidation treatment using hydrogen peroxide (H₂O₂) on the selective flotation of copper concentrates containing arsenic-bearing copper minerals. The mineralogical analysis revealed that enargite and chalcopyrite were the main arsenic-bearing copper and copper sulfide minerals, respectively, in the copper concentrate. KAX treatment at pH 9 improved the recoveries of copper sulfide and arsenic-bearing copper minerals. However, arsenic-bearing copper minerals floated more rapidly than copper sulfide minerals, indicating better separation selectivity. The separation selectivity of the KAX treatment was significantly improved at pH 10. H₂O₂ treatment was found to selectively improve the recovery of arsenic-bearing copper minerals. A combination treatment using 0.1 M H₂O₂ and 60 g/t of KAX at pH 9 enhanced the separation selectivity in the selective flotation of copper sulfide and arsenic-bearing copper minerals by producing a copper concentrate with the lowest arsenic grade and highest copper grade in tailings compared to those obtained from separated KAX and H₂O₂ treatments.</p>

DOI： 10.2320/matertrans.M-M2023811

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CiNii Research

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Advanced Powder Technology  

The main challenge for the selective flotation of copper and molybdenum (Cu-Mo) sulfide minerals in seawater is the formation of colloidal precipitates in strongly alkaline conditions. These precipitates hinder the selective separation of copper from molybdenum minerals in seawater by lowering the floatability of Cu-Mo sulfide minerals. The present study aimed to examine the direct utilization of seawater in the selective flotation of Cu-Mo sulfides. Additionally, the effectiveness of sodium metabisulfite (Na2S2O5) as a copper depressant for selective flotation of Cu-Mo sulfides in seawater was studied under weakly acidic, neutral, and moderately alkaline conditions. A complex Cu-Mo concentrate that largely consisted of chalcopyrite and molybdenite, as well as a tiny amount of pyrite and quartz, was used in the flotation tests. The flotation results revealed that treatment with 3.6 kg/t Na2S2O5 in seawater at pH 5.5 significantly lowered the copper recovery from 97% to 11% and caused a modest reduction in the molybdenum recovery from 98% to 94% with a Cu-Mo separation efficiency of 83%. These flotation results demonstrate that Na2S2O5 treatment in seawater selectively depresses the floatability of copper minerals. Consequently, molybdenum can be separated from copper minerals under a weakly acidic condition in seawater. In addition, this study discusses the effects of various pH conditions and dosages of Na2S2O5. The surface properties of Cu-Mo minerals were studied using X-ray photoelectron and infrared spectroscopies, and a mechanism to explain the selective flotation of Cu-Mo using Na2S2O5 treatment in seawater is proposed.

DOI： 10.1016/j.apt.2023.104258

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Scopus

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Journal of Environmental Chemical Engineering  

Chalcopyrite flotation is selectively depressed by oxidation treatment. The presence of ferric oxyhydroxide on the surface of chalcopyrite after oxidation treatment is a key factor in depressing chalcopyrite flotation. However, there is no concrete evidence that ferric oxyhydroxide has a depressing effect. In addition, the effectiveness of this depressing effect could be enhanced by directly applying ferric oxyhydroxide nanoparticles. This study investigated the effect of goethite (α-FeOOH) nanoparticles on the surface properties and flotation behavior of chalcopyrite. α-FeOOH nanoparticles were produced through chemical precipitation followed by hydrothermal treatment. The crystalline structure of irregular rice grain-shaped α-FeOOH nanoparticles was confirmed by the X-ray diffraction pattern and scanning electron microscope image. Micro-flotation experiments showed that chalcopyrite recovery decreased significantly from 93 % to 13 % when 30 mg/L α-FeOOH nanoparticles was used. This flotation result demonstrated the potential of α-FeOOH nanoparticles as a nanodepressant for the flotation of chalcopyrite. These nanoparticles physically adsorbed on the chalcopyrite surface and rendered its surface hydrophilic, thereby reducing the chalcopyrite flotation recovery. The attractive electrostatic force between the positively charged α-FeOOH nanoparticles and the negatively charged chalcopyrite surface is likely responsible for the adsorption of α-FeOOH nanoparticles on chalcopyrite.

DOI： 10.1016/j.jece.2023.110006

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Scopus

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Institute of Metals and Materials  

<p>Effect of pH and precipitations on copper–molybdenum ore rougher flotation has been investigated in seawater with flotation experiments followed by precipitation estimation with thermodynamic calculations, turbidity measurements and XRD analysis. Results of flotation experiments in seawater indicated that the effect of pH on copper and molybdenum flotation maximum recovery seems limited. On the other hand, pH drastically influences copper and molybdenum flotation kinetic constant, it decreased a lot with increasing pH, and results of pH 8.5 and 9.0 is quite similar. From thermodynamic calculation, precipitation effect on seawater less than pH 9 seems limited since CaCO₃ and Mg(OH)₂ does not exist on this pH region. To estimate precipitation on pH in seawater, turbidity measurements were carried out with controlled pH and results indicated even pH is less than 9, noticeable turbidity can be seen. To confirm precipitation in seawater, precipitation was collected from controlled pH seawater solution. XRD analysis of precipitation indicated that obtained precipitation at pH 8.7 is CaCO₃, CaSO₄ and Mg(OH)₂. This result is not same as the result of thermodynamic calculation and it might be due to the activity coefficient and ionic strength effect. Although flotation kinetic is influenced with turbidity, turbidity influence on maximum recovery is limited. Effect of kinetic might be due to that precipitation exist as suspension and it prevent bubble and mineral attachments. Small effect of precipitation on maximum recovery might be due to exist of few precipitation on the surface of copper and molybdenum mineral since most of mineral in rougher flotation is gangue minerals and also most of precipitations might be on gangue minerals. These results indicated that seawater flotation have to take into account of precipitation effect more for flotation kinetic than maximum flotation recovery.</p>

DOI： 10.2320/matertrans.M-M2023805

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CiNii Research

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.ijmst.2023.01.002

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.ijmst.2023.01.002

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Minerals  

The effect of microwave pre-treatment on the magnetic properties of tennantite and enargite was investigated. Magnetic susceptibility, XRD, and XPS characterization of tennantite and enargite before and after treatment were conducted to explore the changes in their magnetic properties. Moreover, magnetic separation of chalcopyrite binary mixtures with enargite and tennantite was performed. The results showed insignificant effects on the magnetic susceptibility of the two minerals after microwave pre-treatment. Magnetic separation results showed arsenic rejection by 84.2%, and 76.3% in the case of enargite and tennantite binary mixtures with chalcopyrite; respectively.

DOI： 10.3390/min13030334

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Scopus

Publisher：Minerals Engineering  

Environmentally friendly ligands, alternatives to cyanide, are desired to extract gold for the sustainable hydrometallurgy of gold. Leaching characteristics of gold were examined using thiourea (TU) and ethylene thiourea (ETU) as ligands from three types of gold ores with different Fe contents from 2.70 to 14.09 wt% under the acidic condition. The Au recovery by TU leaching reached the extractable maximum with the lowest Fe-bearing gold ore. This type of gold ore is suitable for TU/ETU leaching. The highest Fe-bearing gold ore was the most difficult to extract Au in ETU/TU leaching. There are at least two detrimental factors in TU leaching of Fe-rich gold ores, that is (i) the oxidative decomposition of TU, and (ii) complexation of TU with Fe3+, which both cause to deduce the complexation of TU with Au+. However, adding Na2SO3 improved the Au extraction from such an ore to reduce Fe3+ to Fe2+. ETU facilitated the formation of more stable complexes with Au than TU against the coexisting Fe3+. This finding is useful when considering the cyanide-free leaching of different types of gold ores.

DOI： 10.1016/j.mineng.2022.107957

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Scopus

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Powder Technology  

In the flotation of complex copper ores containing chalcopyrite in seawater, sodium metabisulfite (SMBS) has been widely used as a pyrite depressant. Here, calcium ions in seawater or in process water because of pH control using lime (CaO) or slaked lime (Ca(OH)2) can affect the floatability of chalcopyrite. However, the effect of SMBS on the floatability of chalcopyrite in the presence of calcium ions is unknown. Therefore, the current study investigated the flotation behavior and surface properties of chalcopyrite after treatment with SMBS in the absence and presence of Ca(OH)2. The flotation experiments demonstrated that both SMBS treatment and the addition of Ca(OH)2 exhibited a depressing effect on the natural floatability of chalcopyrite. This depressing effect of SMBS and Ca(OH)2 on the floatability of chalcopyrite was significantly decreased in the presence of potassium amyl xanthate (PAX). However, the combination of SMBS treatment and Ca(OH)2 formed calcium sulfite (CaSO3) on the surface of chalcopyrite, which significantly reduced the recovery of chalcopyrite from 97% to 66% when in the presence of PAX and at a pH of 9.

DOI： 10.1016/j.powtec.2022.117750

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Scopus

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.3390/min11121377

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.mineng.2021.107222

Language：Japanese   Publishing type：Research paper (international conference proceedings)  

Language：Japanese   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：Japanese   Publishing type：Research paper (international conference proceedings)  

Language：Japanese   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (scientific journal)  

The detrimental effect of seawater on Cu-Mo flotation has attracted much attention in recent years, which has mainly been focused on altering the detrimental effect of seawater on the floatability of molybdenum ore. The interaction between bubbles and particles during flotation is a key factor in understanding the detrimental effect of seawater. Therefore, this study aimed to investigate the effect of seawater on bubble-particle interactions with chalcopyrite and molybdenite surfaces. Moreover, the effect of emulsified kerosene, a typical molybdenite collector, on bubble-particle interactions in seawater was investigated. Artificial seawater was used as a seawater model solution in this study. Flotation tests using pure chalcopyrite and molybdenite showed that the addition of emulsified kerosene to artificial seawater at a specific pH could selectively improve the floatability of molybdenite while maintaining the low floatability of chalcopyrite. A study of the bubble-particle interactions was then performed to analyze the phenomenon. It was found that the kerosene adsorbed at the air/liquid interface of the bubble improved the bubble aspect ratio and reduced the bubble rise velocity in artificial seawater. Moreover, kerosene could accelerate the formation of three-phase contact between the bubble and both mineral surfaces at the natural pH of artificial seawater. Additionally, this study showed that seawater colloidal precipitate formed under high pH conditions might be adsorbed on the mineral surfaces and might improve the stability of the intervening liquid film on the surface, thus preventing bubble-particle attachment and decreasing mineral recovery. Under these high pH conditions, the emulsified kerosene and seawater precipitate might compete in terms of adsorption on the mineral surfaces and the flotation results would most likely depend on the kerosene and hydrophilic adsorbate coverage on the mineral surfaces.

DOI： 10.1016/j.mineng.2020.106536

Language：English   Publishing type：Research paper (scientific journal)  

The catalytic mechanism of activated carbon-assisted bioleaching of enargite concentrate (enargite 37.4&#37;; pyrite 47.3&#37;) was investigated by employing microbiological, electrochemical and kinetic studies. By using moderately thermophilic microorganisms at 45 °C, the final Cu dissolution was improved from 36&#37; to 53&#37; at 0.2&#37; (w/v) activated carbon. An excess activated carbon addition showed an adverse effect. The enargite mineral itself favored higher solution redox potential (E_h) for solubilization. However, the dissolution of co-existing pyrite, which also favors high E_h, immediately hindered enargite dissolution through the passivation effect. The surface of activated carbon functioned as an electron mediator to couple RISCs oxidation and Fe³⁺ reduction, so that elevation of the E_h level was controlled by offsetting microbial Fe³⁺ regeneration. As long as the E_h level was suppressed at <700 mV, the dissolution of pyrite was largely avoided, enabling a steady and continuous dissolution of the enargite mineral through the surface chemical reaction model. When the E_h-control by activated carbon becomes no longer sustainable and the E_h hits 700 mV, rapid pyrite dissolution was initiated and the surface chemical reaction of enargite dissolution came to an end. Arsenic species dissolved from enargite was constantly immobilized with an efficiency of 75–90&#37; as amorphous ferric arsenate. However, the sudden initiation of pyrite dissolution also triggered the re-solubilization of ferric arsenate. Therefore, the sustainable E_h-controlling effect was shown to be critical to enable longer Cu dissolution from enargite as well as stabilization of As precipitates.

DOI： 10.1016/j.hydromet.2020.105417

Repository Public URL： http://hdl.handle.net/2324/4737402

Language：English   Publishing type：Research paper (scientific journal)  

Natural carbonaceous matter aided the bioleaching of Cu from chalcopyrite concentrates. The oxidative dissolution of chalcopyrite was enhanced more significantly by anthracite than carbonaceous matter in double refractory gold ore (DRGO). This was achieved through Galvanic interactions between the chalcopyrite and natural carbonaceous matter. Measurement of impedance verified that the electro-resistance is smaller in anthracite, which has a greater graphitic degree than carbonaceous matter in DRGO. The electron shuttle between chalcopyrite and the Fe³⁺ /Fe²⁺ redox couple was facilitated not only by the amounts of carbonaceous matter but also the degree of graphitization of carbonaceous matter. A higher graphitization degree increased the electron conductivity of the carbonaceous matter to help mediate Cu bioleaching while avoiding direct contact of thermophile cells with refractory copper sulfides.

DOI： 10.1016/j.hydromet.2020.105363

Language：English   Publishing type：Research paper (scientific journal)  

Effect of oxidation treatment using hydrogen peroxide (H₂O₂) on the floatability of copper sulfide minerals (i.e., chalcopyrite and bornite) and arsenic-bearing copper minerals (i.e., tennantite and enargite) is reported in this study. Pure mineral flotation shows that the floatability of each mineral significantly decreases after the oxidation treatment. Interestingly, flotation of mixed mineral of copper sulfide and arsenic-bearing copper minerals shows that enargite and tennantite exhibit a higher floatability compared to chalcopyrite and bornite after the oxidation treatment followed by the addition of potassium amyl xanthate (PAX). These flotation results indicate a possibility for selective flotation of copper sulfide and arsenic-bearing copper minerals. Indeed, bench-scale flotation tests show that the oxidation treatment using H₂O₂ and the addition of PAX can deliver a satisfying separation of copper sulfide and arsenic-bearing copper minerals. Difference oxidation products (i.e., CuO, Cu(OH)₂, CuSO₄, FeOOH, and Fe₂(SO₄)₃) on each mineral surface are likely the cause of this different flotation behavior. Furthermore, these oxidation products may affect the adsorption amount of PAX on each mineral. Indeed, the adsorption tests show that PAX is adsorbed more on tennantite, bornite, and enargite compared to chalcopyrite owing to the formation of CuSO₄ and Cu(OH)₂ on the mineral surfaces under oxidizing conditions. A possible mechanism is proposed in this study to explain the selective flotation behavior of mixed minerals.

DOI： 10.1016/j.mineng.2020.106371

Language：Japanese   Publishing type：Research paper (international conference proceedings)  

Language：Japanese   Publishing type：Research paper (international conference proceedings)  

Language：Japanese   Publishing type：Research paper (international conference proceedings)  

Language：Japanese   Publishing type：Research paper (international conference proceedings)  

Language：Japanese   Publishing type：Research paper (international conference proceedings)  

Language：Japanese   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (other academic)  

Selective flotation of chalcopyrite and molybdenite is continuing problem since its selectivity is not perfect and current NaHS process needs closed system flotation plant because of hydrogen sulfide emission on acidic condition. Some alternative additives investigated as chalcopyrite became hydrophilic and molybdenite kept hydrophobic. XPS analysis indicated chalcopyrite became hydrophilic since iron and copper sulphate, hydroxide was covered on the surface whereas molybdenite kept hydrophobic since only molybdenite can be seen. Flotation experiments of chalcopyrite and molybdenite mixture sample indicated excellent separation that 95% of molybdenite can be recovered as froth and 93% of chalcopyrite can be recovered as sink. Flotation experiments with real bulk flotation concentration indicated similar separation result compared with current NaHS additive system. Possible mechanisms and detailed phenomenon were investigated based on the surface analysis and thermodynamic calculation etc. this alternative additive is easy to handle compared with NaHS since it does not emit effluent gas and commercially preferable.

Language：English   Publishing type：Research paper (other academic)  

Hydrogen peroxide (H ₂ O ₂ ) is frequently used as an oxidizing agent in various applications. It has also been reported to reduce the recovery of sulfide minerals. Moreover, the previous work applied H ₂ O ₂ aqueous solution in selective flotation of chalcopyrite and molybdenite. However, the oxidation method suffered in pilot scale test due to too long conditioning time. Furthermore, the excessive reagent consumption increased the reagent cost, causing the method not economically feasible. Consequently, further improvement is required to reduce the conditioning time and the reagent consumption. The oxidation performance of H ₂ O ₂ can be improved by using ferrous iron as catalyst, producing a Fenton's reagent which is more powerful oxidizer than the H ₂ O ₂ itself. Therefore, the effect of Fenton's reagent on the floatability of chalcopyrite and molybdenite was investigated in this study. The flotation test results show that selective flotation of chalcopyrite and molybdenite might be possible at low concentration of H ₂ O ₂ aqueous solution by adding ferrous iron. Moreover, the conditioning time could be shortened by this improvement. To understand the phenomenon, surface characterization using atomic force microscopy (AFM) along with x-ray photoelectron spectroscopy (XPS) analysis were carried out. The AFM images show that the surface of chalcopyrite was readily covered with mountainous features which alters its hydrophobicity after the oxidation treatment. Meanwhile, the molybdenite surface remained clean and relatively hydrophobic. The XPS results indicate that the mountainous features are various oxidation products (i.e., FeOOH, Fe ₂ (SO ₄ ) ₃ , CuO, Cu(OH) ₂ ). Possible mechanisms of this phenomenon were proposed in this work.

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English  

A fundamental study is provided in this work to understand the effect of Fenton-like reagent made by the addition of FeSO₄ in H₂O₂ aqueous solution on surface hydrophobicity and floatability of chalcopyrite (CuFeS₂) and molybdenite (MoS₂). Contact angle measurements were performed to assess the surface hydrophobicity. The contact angle results showed that Fenton-like reagent could alter the surface hydrophobicity of chalcopyrite at lower concentration of H₂O₂ aqueous solution compared to that of using H₂O₂ aqueous solution. On the other hand, molybdenite surface remained hydrophobic after the oxidation treatments using Fenton-like reagent and H₂O₂ aqueous solution. Surface characterizations using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) shows that the chalcopyrite surface covered with a thicker layer of oxidation products after the oxidation treatment using Fenton-like reagent, indicating a stronger surface oxidation. Flotation results were in agreement with contact angle results, showing that Fenton-like reagent could depress the floatability of chalcopyrite at lower concentration of H₂O₂ aqueous solution. On the other hand, molybdenite recovery remained high under various oxidation treatments owing to low surface oxidation.

DOI： 10.1016/j.colsurfa.2018.06.029

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English  

Hydrogen peroxide (H₂O₂) has been used as an oxidizing agent in the selective flotation of chalcopyrite and molybdenite. However, this method required relatively high concentration of H₂O₂ to deliver flotation results (i.e., mineral grades and recoveries) comparable to those obtained by the conventional copper-molybdenum (Cu-Mo) ores flotation using sodium hydrosulfide (NaHS). Therefore, further improvements are needed to reduce the consumption of H₂O₂ reagent. In this study, ferrous sulfate (FeSO₄) was used to enhance the oxidation performance of H₂O₂ through Fenton-like reactions. Flotation results showed that the consumption of H₂O₂ reagent could be reduced by the addition of FeSO₄ without losing the flotation selectivity. The reason might be caused by increasing of oxidation performance as indicated by the increasing concentration of dissolved oxygen after the addition of FeSO₄ into the H₂O₂ aqueous solution. Surface analysis using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) images showed that the surface of chalcopyrite was covered by more hydrophilic precipitates after the oxidation treatment using H₂O₂ aqueous solution with the addition of FeSO₄, thus more hydrophilic surface and lower floatability. On the other hand, the surface of molybdenite was slightly oxidized and its surface remained hydrophobic as confirmed from contact angle results. Flotation tests using Cu-Mo bulk concentrate demonstrated that selective flotation might be possible using a mixture of FeSO₄ and H₂O₂ aqueous solution. Moreover, this new method could be used as an alternative to copper depressant in Cu-Mo selective flotation, replacing the NaHS reagent.

DOI： 10.1016/j.mineng.2018.02.005

Language：English   Publishing type：Research paper (scientific journal)  

Effect of silver (Ag) catalyst in bioleaching of enargite (Cu₃AsS₄) concentrate was studied using mixed cultures of moderately thermophilic acidophilic microorganisms at 45 °C. Addition of Ag₂S enabled selective Cu dissolution from enargite while suppressing pyrite oxidation: At the highest Ag₂S concentration of 0.04&#37;, Cu recovery reached 96&#37; while Fe dissolution was suppressed to reach only 29&#37; by day 72. Overall results from thermodynamic calculation, liquid/solid analyses and kinetic study suggested that Ag-catalyzed bioleaching of enargite concentrate proceeds via formation of at least two types of secondary products (chalcocite, Cu₂S; trisilver arsenic sulfide, Ag₃AsS₄): Addition of Ag₂S as Ag catalyst thermodynamically and microbiologically contributed to lowering solution redox potentials during bioleaching, consequently satisfying E_ox (Cu₂S) < Eh < E_c (Ag⁺) to enhance enargite dissolution via formation of chalcocite intermediate. Formation of trisilver arsenic sulfide and its intermediate layer (Cu,Ag)₃AsS₄ indicated that Cu ion in the enargite lattice is gradually substituted with Ag. Such secondary products did not impose a rate-limiting step, since the Ag-catalyzed bioleaching was shown to be controlled by a chemical surface reaction, rather than diffusion through product film which was the case in the absence of Ag₂S.

DOI： 10.1016/j.hydromet.2018.03.014

Repository Public URL： http://hdl.handle.net/2324/4737398

Language：English   Publishing type：Research paper (scientific journal)  

The effect of controlling the redox potential (E_h) on chalcopyrite bioleaching kinetics was studied as a new aspect of redox control during chalcopyrite bioleaching, and its mechanism was investigated by employing the “normalized” solution redox potential (E_normal) and the reaction kinetics model. Different E_h ranges were established by use of different acidophiles (Sulfobacillus acidophilus YTF1; Sulfobacillus sibiricus N1; Acidimicrobium ferrooxidans ICP; Acidiplasma sp. Fv-AP). Cu dissolution was very susceptible to real-time change in E_h during the reaction. It was found that efficiency of bioleaching of chalcopyrite can be effectively evaluated on the basis of E_normal, since it is normalized for real-time fluctuations of concentrations of major metal solutes during bioleaching. For steady Cu solubilization during bioleaching at a maximum rate, it was important to maintain a redox potential range of 0 ≤ E_normal ≤ 1 (−0.35 mV optimal) at the mineral surface by employing a “weak” ion-oxidizer. This led to a copper recovery of > 75&#37;. At higher E_normal levels (E_normal > 1 by “strong” microbial Fe²⁺ oxidation), Cu solubilization was slowed by diffusion through the product film at the mineral surface (< 50&#37; Cu recovery) caused by low reactivity of the chalcopyrite and by secondary passivation of the chalcopyrite surface, mainly by jarosite.

DOI： 10.1080/01490451.2018.1443170

Repository Public URL： http://hdl.handle.net/2324/4737396

Language：English  

Sodium hydrogen sulfide (NaHS) is commonly used as a copper depressant in the selective flotation of copper and molybdenum ores. However, the process is facing health and safety issues because NaHS readily yields toxic hydrogen sulfide gas (H2S) under acidic conditions. In this study, Na₂SO₃ was proposed as an alternative copper depressant. The effect of Na₂SO₃ on the surface wettability and floatability of chalcopyrite and molybdenite—typical copper and molybdenum minerals, respectively—was intensively studied using contact angle measurements and flotation tests. Contact angle readings show that the chalcopyrite surface became hydrophilic after the Na₂SO₃ treatment. Meanwhile, the molybdenite surface was relatively more hydrophobic compared with that of chalcopyrite after the treatment. Flotation tests using pure minerals of chalcopyrite and molybdenite demonstrate that the floatability of chalcopyrite decreased with increasing concentration of Na₂SO₃. On the other hand, the floatability of molybdenite gradually increased under similar conditions, suggesting that Na₂SO₃ might have the potential to be used for selective flotation of chalcopyrite and molybdenite. A possible mechanism is proposed in this study to explain the phenomenon using X-ray photoelectron spectroscopy analysis.

DOI： 10.3390/min8040172

Language：English  

Seawater has been reported to depress the floatability of molybdenum in copper-molybdenum (Cu-Mo) flotation circuits under alkaline conditions (pH > 9.5). However, the seawater used in the process contains various minerals and flotation reagents, which make it difficult to investigate the depression mechanism. This paper presents a fundamental study into the effect of artificial seawater as a seawater model solution on the floatability of molybdenite and chalcopyrite, which are the main minerals in the Cu-Mo flotation process. Floatability tests in the absence of flotation reagents (i.e., frothers and collectors) reveal that artificial seawater adversely affects the floatability of molybdenite and chalcopyrite at pH > 9. This phenomenon can be attributed to the adsorption of hydrophilic Mg(OH)₂ precipitates formed under alkaline conditions on the mineral surfaces, which increases the surface wettability of the mineral particles, as shown by contact angle measurements and atomic force microscopy (AFM) images. The effect of kerosene as a molybdenite collector has also been investigated to assess its potential in the selective flotation of molybdenite and chalcopyrite in artificial seawater.

DOI： 10.1016/j.mineng.2017.10.004

Language：Japanese   Publishing type：Research paper (scientific journal)  

Mechanism of Silver-Catalyzed Bioleaching of Enargite Concentrate

DOI： 10.4028/www.scientific.net/SSP.262.273

Other Link： 10.4028/www.scientific.net/SSP.262.273

Language：Japanese   Publishing type：Research paper (international conference proceedings)  

Development of alternative additive of NaHS for selective flotation of chalcopyrite and molybdenite

Language：Japanese   Publishing type：Research paper (international conference proceedings)  

Study on the effect of a mixture of hydrogen peroxide and ferrous sulfate on the floatability of chalcopyrite and molybdenite

Language：English  

This paper summarizes the results of a voltammetric study of the anodic characteristics of chalcopyrite in the potential region relevant to heap leaching in concentrated chloride solutions. Distinct peaks in the potential region of 0.7 to 0.85 V have been observed in the voltammograms, the magnitude of which depend on the chloride concentration and, particularly, the pH in the range 1 to 3. Three peaks are observed at low chloride concentrations that merge into one peak at higher concentrations. The anodic reactivity increases with increasing pH but shows a complex dependence on the chloride concentration while in the presence of added copper(II) ions, the mixed potential shifts to more positive potentials and only one peak is observed. Hysteresis between the forward and backward-going sweeps has confirmed the transient nature of the processes except at potentials below about 0.75 V in which region the system approaches steady-state behaviour. The voltammetric characteristics of chalcopyrite in this system appear to be very similar to those of covellite. Measurements of the initial rates of dissolution (in the range 1–5 × 10^{− 10} mol cm^{− 2} s^{− 1} depending on the conditions) have been made that confirm the voltammetric trends and compare well with previously published rates. Linear free energy relationships have been used to estimate the thermodynamic properties (Gibbs free energy − 100.7 kJ/mol) of the simplest polysulfide, namely CuS₂ and possible mechanisms for the various steps in the anodic dissolution and passivation of chalcopyrite have been suggested that are consistent with the thermodynamic predictions.

DOI： 10.1016/j.hydromet.2017.05.016

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Electrolysis oxidation of chalcopyrite and molybdenite was investigated, via various electrochemical methods, with the aim of realizing selective flotation of these minerals. Result of potential polarization indicated that oxidation via electrolysis affected only the chalcopyrite surface, owing mainly to the difference in conductivity of these minerals. Also measurements of contact angle after electrolysis indicated that contact angle of chalcopyrite selectively decreased whereas that of molybdenite did not decrease drastically. XPS analyses after electrolysis indicated that chalcopyrite peak decreased whereas iron oxyhydroxide (goethite) and iron sulfate increased, it suggests that these oxidation products covered on the surface of chalcopyrite. On the other hand, molybdenite peak is similar after electrolysis except for molybdenum oxide/oxygen with molybdenite can be seen for oxygen peak. From these results and general knowledge that sulfide hydrophobicity and sulfate/oxyhydroxide hydrophilicity, it can be explained that with electrolysis oxidation, hydrophilic oxihydroxide and sulfate covered on the surface of hydrophobic chalcopyrite then chalcopyrite surface became hydrophilic. On the other hand, molybdenite surface keep hydrophobic since its difficulty of oxidation and it is difficult to stay molybdenum oxide on the surface due to its soluble property. These results revealed that chalcopyrite was selectively oxidized and, hence, selective flotation of chalcopyrite and molybdenite was possible. This electrolysis oxidation methods were compared with those governing other oxidation treatments.

DOI： 10.2320/matertrans.M-M2017807

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The selective flotation of chalcopyrite (CuFeS₂) and molybdenite (MoS₂) was studied using surface oxidation treatments (i.e., ozone (O₃) and hydrogen peroxide (H₂O₂)). The results indicated that the oxidation treatments had different effects on the wettability of chalcopyrite and molybdenite. Single mineral flotation results showed that the H₂O₂ treatment had higher separation selectivity for molybdenite and chalcopyrite compared with that of the ozone treatment. The contact angle measurement and X-ray photoelectron spectroscopy (XPS) analysis results showed that the chalcopyrite surface became hydrophilic owing to the surface deposition of oxidized iron and copper after the H₂O₂ treatment. On the other hand, the contact angle of molybdenite slightly increased following the H₂O₂ treatment at high concentrations. Possible mechanisms of this phenomenon were proposed in this work. Moreover, the separation selectivity of each oxidation method was discussed. Flotation tests using bulk Cu-Mo concentrate showed that H₂O₂ could deliver a flotation result comparable to conventional Cu-Mo flotation using NaHS.

DOI： 10.1016/j.mineng.2016.10.007

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An electrode system to study the mechanism of fine microgram powder sulfide mineral dissolution was developed by using a relatively simple method that enables the attachment of micrograms of fine powder to a platinum plate surface. This system yields highly reproducible results and is sensitive compared with conventional electrode systems for various sulfide minerals such as pyrite, chalcopyrite, chalcocite, enargite, and tennantite. The leaching behavior of chalcopyrite was re-examined in a test of the application of this electrode system. Chalcopyrite dissolution is enhanced in specific potential regions because it is believed to be reduced to leachable chalcocite, but this result is inconclusive because it is difficult to detect the intermediate chalcocite. Powder chalcopyrite in the new powder electrode system was held at 0.45 V in the presence of copper ion and sulfuric acid media followed by an application of potential in the anodic direction. Besides the chalcopyrite oxidation peak, a small peak resulted at ~0.55 V; this peak corresponds to reduced chalcocite, because it occurs at the same potential as the chalcocite oxidation peak.

DOI： 10.3390/min6040103

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DOI： 10.1016/j.mineng.2016.06.023

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The formation of stable bubble-particle aggregates is essential to the froth flotation process. To form such aggregates, bubbles and particles must collide, the intervening liquid film must be drained below its critical rupture thickness, and three-phase contact (TPC) formation must occur. A good understanding of the interaction mechanism between bubbles and particles during collision and attachment is important. We herein investigated the effects of emulsified kerosene in a 0.01 M MgCl₂ solution (a model seawater component) on bubble interactions with pure molybdenite (MoS₂) and chalcopyrite (CuFeS₂) surfaces. In 0.01 M MgCl₂ at pH 6 and 11, kerosene retarded the bubble surface mobility and reduced the bubble rise velocity. In the presence of kerosene at pH 6, the TPC formed more rapidly on both mineral surfaces. This was due to the increase in surface hydrophobicity caused by kerosene. In addition, TPC formation was more rapid on the molybdenite surface than on the chalcopyrite surface due to the effect of the adsorbed kerosene and the low surface homogeneity of molybdenite. Finally, floatability tests demonstrated that the separation of molybdenite and chalcopyrite should be possible by adding emulsified kerosene in a 0.01 M MgCl₂ solution at pH 9.

DOI： 10.1016/j.colsurfa.2016.04.039

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Catalytic effects of silver on the dissolution of arsenic-containing copper sulfides such as enargite in acidic media were investigated. Leaching experiments showed that silver increased the enargite dissolution rate, and that the dissolution behavior was potential-dependent. The addition of silver ions and silver sulfide greatly enhanced enargite dissolution. Such behavior can be explained based on the following reaction model: enargite dissolution is enhanced by silver as the silver ions remove the hydrogen sulfide produced during enargite reduction, giving the more amenable copper sulfide. Thermodynamic calculations suggested that the addition of silver ions and controlling the potential would maintain a high enargite dissolution rate. Leaching experiments were therefore performed with the addition of silver sulfide and potential control using an automatic titration apparatus. Experimental results showed that a combination of these two factors gave high enargite dissolution; i.e., 75&#37; copper was dissolved in 24 h at 0.750-0.850 V vs. the standard hydrogen electrode at 303 K.

DOI： 10.1016/j.hydromet.2016.02.007

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Co-precipitation of borate in a wide range of concentration with hydroxyapatite (HAp) was investigated using Ca(OH)₂ as a mineralizer in the presence of phosphate. The sorption data of borate was fitted to Freundlich model. The maximum sorption density of B/Ca to maintain a mono-phase of HAp was found around 0.40. In higher B concentrations, borate was still immobilized, however, the crystalization of hydroxyapatite was inhibited, where the solid residues were accompanied with amorphous CaB₂O₄, as well as HAp. Based on ¹¹B-NMR and elemental analysis for solid residues in addition to solution chemistry, the removal mechanism of high concentration borate can be explained by the surface complexation of triborate on Ca(OH)₂, subsequently decomposition of triborate into monoborate to release [CaB(OH)₄]⁺ and B(OH)₄ ^-, followed by co-precipitation with HAp. These tetragonal B species were immobilized in the solid residues including amorphous HAp. During the process there was a trend to eliminate carbonate from the solid phase. TEM images suggested that the HAp particles precipitated at room temperatures were in a fibrous shape consisting of a number of short rods when borate species are not added. When borate species were immobilized, the HAp particles have gotten swelled with losing fibrous shapes. When further higher borate concentrations were encapsulated in co-precipitated products, the morphologies were dramatically changed, that is, nano-sized and less crystalline HAp particles were enveloped by possibly amorphous CaB₂O₄.

DOI： 10.1016/j.jece.2016.01.012

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DOI： 10.1016/j.jece.2016.01.012

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Seawater has been reported to depress molybdenite in a copper-molybdenum (Cu-Mo) flotation process at high pH due to the precipitation of Mg(OH)₂. Meanwhile, to improve mineral recoveries, collectors are usually added into the flotation cells, thus adding the complexity to the mechanism of bubble-particle interactions involved in Cu-Mo flotation. Therefore, understanding the interaction mechanism in seawater flotation and in the presence of collectors is important to explain the minerals depression. The present work investigated the effect of kerosene on the bubble collision and attachment to pure chalcopyrite and molybdenite surfaces in MgCl₂ solution as one of the seawater major components at pH 6 and 11. Mineral surfaces were characterized using atomic force microscopy (AFM). In addition, minerals floatability in the same system were tested in a column flotation. The study of bubble-particle interactions shows that following several collisions, bubble could displace the intervening liquid layer on the mineral surfaces, forming a three-phase contact (TPC). A TPC formed more rapidly in the presence of emulsified kerosene in a 0.01 M MgCl₂ solution at pH 6 for both minerals. The reason is kerosene increased the surfaces hydrophobicity and destabilized the intervening liquid layer on the surfaces. Moreover, the average time required to form a TPC was shorter on molybdenite surface. This can be attributed to the effect of adsorbed kerosene on molybdenite surface and molybdenite surface roughness.

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Selective flotation of chalcopyrite and molybdenite was studied using various surface treatment methods such as electrolysis, ozone treatment, and plasma. Oxidation via electrolysis method indicated that only chalcopyrite surface is affected by electrolysis due to conductivity difference with molybdenite. Oxidation treatments and XPS analyses indicated that chalcopyrite became hydrophilic due to deposition of oxidized iron on its surface. Various oxidizing methods also showed that chalcopyrite was selectively oxidized and this can apply selective flotation of chalcopyrite and molybdenite. The possible mechanisms are proposed in this work based on surface analyses and thermodynamic calculations.

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Seawater flotation has been applied to mineral processing in areas located far from fresh water resources. However, as seawater has a detrimental effect on molybdenite floatability under alkaline conditions (pH > 9.5), its application in the conventional copper and molybdenum (Cu-Mo) flotation circuit is hindered. A fundamental study of the effect of two divalent cations in seawater, Mg²⁺ and Ca²⁺, on the floatability of chalcopyrite and molybdenite is presented in this paper. Floatability tests showed that both MgCl₂ and CaCl₂ solutions depress the floatability of chalcopyrite and molybdenite at pH values higher than 9. Furthermore, Mg²⁺ exerts a stronger effect than Ca²⁺ owing to the adsorption of Mg(OH)₂ precipitates on the mineral surfaces, as indicated by dynamic force microscopy images. The floatability of chalcopyrite was significantly depressed compared with that of molybdenite in a 10⁻² M MgCl₂ aqueous solution at pH 11. This phenomenon is likely due to the adsorption of hydrophilic complexes on the mineral surface, which reduces the surface hydrophobicity. A reversal of the zeta potential of chalcopyrite in MgCl₂ and CaCl₂ solutions at pH 11 and 8, respectively, indicated the adsorption of precipitates onto the surface. In contrast, the zeta potential of molybdenite decreased continuously under the same conditions. The floatability test of chalcopyrite and molybdenite in mixed systems showed that selective separation of both minerals should be possible with the addition of emulsified kerosene to a 10⁻² M MgCl₂ solution at pH 11. A mechanism is proposed to explain this phenomenon.

DOI： 10.1016/j.mineng.2016.06.023

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Pyrite is a mineral sulfide found extensively in acid mine drainage; this is one of the most serious environmental problems in the mining industry. Suppression of pyrite oxidation via carrier microencapsulation (CME) with silicon (Si) and organic carriers has been proposed. In the present study, use of the hydrothermal treatment liquid (HTL) produced from low-rank coal as a carrier in CME was investigated. In dissolution tests for 51 days with pyrite and iron-oxidizing bacteria, treatment with a mixture of HTL and a silicon reagent (Si-HTL) lowered the ferric ion concentration and limited bacterial attachment compared with untreated pyrite. This might be caused by catechol present in the HTL. A mixture of catechol and a silicon reagent (Si-Cat) was also used, and the coatings obtained using Si-HTL and Si-Cat were compared. The electrochemical behavior of the treated pyrite samples showed oxidative decomposition of the Si-Cat complex and formation of an encapsulating layer at 690 mV for Si-HTL and 550 mV for Si-Cat. The two semi-circular curves in the Nyquist plot simulations showed that the total impedances of the treated pyrite samples increased. Microscopic observations showed that the oxidative layer was silica rich. These data indicate that a silica-quinone coating is created and the pyrite oxidation rate can be suppressed by pretreatment with either Si-HTL or Si-Cat for 1 h.

DOI： 10.1016/j.hydromet.2015.09.028

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In this paper, prevention of pyrite oxidation by carrier microencapsulation (CME) was investigated. A possible layer structure was suggested following analysis with electrochemical and surface analysis techniques. Electrochemical study of treated pyrite samples showed that treatment with siliconcatechol (Si-Cat) for 6 h at an initial pH of 9.5 gave the best barrier properties and suppression of the samples. Scanning electron microscopy with energy-dispersive X-ray, and Fourier transform infrared (FTIR) analyses confirmed the presence of a silicate layer on the surface of treated pyrite. X-ray photoelectron spectroscopy indicated that the coating layers on the treated pyrite samples consisted of a network of Fe-O-Si and Si-O-Si units bonded to the surface of pyrite. The Si-O-C asymmetric stretching mode was also observed in FTIR spectra. Detailed spectroscopic analyses confirmed the formation of a silicate polymer on a silicaquinone layer, which resulted in the effective suppression effect shown by Si-Cat-treated pyrite at increasing pH.

DOI： 10.2320/matertrans.M-M2015821

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DOI： 10.1016/j.mineng.2014.07.011

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For pretreatment of selective flotation, plasma treatment of chalcopyrite and molybdenite was applied then the minerals were washed by solution at pH 9 with oxygen bubbling. Surface characteristics of these minerals were investigated with AFM, XPS, zeta potential and contact angle measurements. Contact angle of chalcopyrite and molybdenite decreased a lot by plasma treatment. When they were washed with pH 9 solution with oxygen bubbling, contact angle of molybdenite increased whereas chalcopyrite one kept low. Adhesion force measurements indicated similar behavior. Result of flotation experiments indicated low recovery of both chalcopyrite and molybdenite after plasma treatment and only molybdenite recovery became higher after washing. Selective flotation of chalcopyrite and molybdenite could be achieved with this process. However, flotation of mixture of chalcopyrite and molybdenite after these treatments indicated both chalcopyrite and molybdenite were depressed. Addition of emulsified kerosene changed the flotation results where molybdenite was floated and chalcopyrite was depressed. Possible mechanism of selective flotation was proposed from the results of XPS, AFM, etc.

DOI： 10.1016/j.mineng.2014.07.011

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Part I of this series described the results of a study of the electrochemistry of pyrite under conditions similar to those encountered in acidic bioleaching of the mineral. In this paper, the electrochemical data obtained in the previous paper is used to derive estimates of the rate of leaching of pyrite based on a mixed potential model for the kinetics as a function of the solution composition and temperature. The results of the calculated rates of dissolution are compared with those obtained in a limited study of the dissolution of a milled pyrite sample at controlled potentials. It is demonstrated that the rate of dissolution calculated from the anodic current density in a solution without iron(III) when the potential is held at the mixed potential measured in the presence of iron(III) compared well with the rate predicted by the linear polarization method and that obtained from the change in the solution potential with time in a batch dissolution of a pyrite electrode in solutions containing iron(III). The dissolution rate calculated from the steady-state currents at the mixed potential in the absence of iron(III) decreased with increasing sulphate ion concentration, increased with increasing temperature and also with increasing rotation speed of the pyrite electrode. The results of leaching experiments with milled pyrite under conditions of controlled solution potential has shown that the rate of dissolution is significantly higher at a potential of 0.85 V than at 0.80 V. Approximately 90&#37; of the sulphide associated with pyrite is oxidised to elemental sulphur. The results of the leach experiments quantitatively agree well with those derived from the electrochemical measurements. The detrimental effect of high sulphate concentrations on the rate of dissolution has been confirmed by the leach tests.

DOI： 10.1016/j.hydromet.2013.01.009

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A detailed study of the electrochemical behavior of pyrite under typical bio-leaching conditions has been carried out with the focus on the effect of the concentration of sulphate ions on the mixed potential, cyclic voltammetric and potentiostatic measurements. The mixed potential decreases with increasing sulphate ion concentration and the addition of iron(II) and increases as expected with increasing iron(III) concentration and agitation at constant pH. Temperature, pH and the concentration of dissolved oxygen have minimal effects on the mixed potential in the presence of iron(III). Cyclic voltammetric and potentiostatic data confirm that the rate of anodic oxidation of pyrite decreases with increasing sulphate ion concentration and increases with increasing temperature. The pH and dissolved oxygen concentration have little effect while addition of chloride ions inhibits the anodic oxidation of pyrite. Studies of the cathodic reduction of iron(III) and dissolved oxygen have shown that the rate of the former is several orders of magnitude more reversible(rapid) than that of dissolved oxygen which only exhibits measurable reactivity at potentials well below the mixed potentials in the presence of iron(III). The reduction of iron(III) is inhibited by sulphate ions due to the formation of electrochemically less reactive sulphate complexes.

DOI： 10.1016/j.hydromet.2013.01.010

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The use of chloride in the heap leaching of sulfide minerals requires the regeneration of the oxidants copper(II) and iron(III). While this is possible in a sulfate system by the use of bacterially catalysed oxidation of iron(II), this can only economically be achieved by chemical reaction with dissolved oxygen in chloride systems due to the sensitivity of bacteria to high concentrations of chloride ions. The kinetics of the reduction of dissolved oxygen by copper(I) in acidic chloride solutions has been studied under possible heap leach conditions. The results confirm some published data that the rate is second-order in copper(I). The rate increases with increasing acid concentrations but decreases with increasing chloride and copper(II) concentrations. Peroxide has been shown to be a detectable intermediate and a modified mechanism has been proposed which is consistent with the kinetic data. The use of the derived rate equation in a modified rate expression for the copper-catalysed auto-oxidation of iron(II) has been derived.

DOI： 10.1016/j.hydromet.2010.10.009

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An experimental study of the comparative kinetics of dissolution of various synthetic copper sulphides (covellite, chalcocite, and digenite) in dilute chloride solutions has been carried out at ambient temperatures such as could be encountered in the heap leaching of secondary copper sulphide minerals. The dissolution of sized synthetic covellite particles was carried out in dilute HCl solutions containing known concentrations of copper(II) and iron(III) at controlled potentials. The results show that the rate of dissolution is similar at potentials of 600 and 650 mV, but is predictably less at a potential of 550 mV. The rate of dissolution is remarkably similar to that of chalcopyrite under similar conditions and is largely independent of Cl^- and HCl concentration in the range 0.2 to 2.5 M and 0.1 to 1 M respectively. The effect of temperature is significant and an activation energy of 71.5 kJ mol ^{- 1} was derived which confirms a chemical or electrochemical rate-determining reaction on the mineral surface. A mineralogical study of the residue after leaching shows that most of the sulphur is associated with unreacted covellite and occurs as isolated globules on the surface with over 90&#37; of the unreacted covellite surface free of sulphur. Dissolution of synthetic chalcocite and digenite is rapid compared with that of covellite under the same conditions. At a potential of 500 mV, the relatively rapid initial dissolution of chalcocite and digenite does not proceed beyond about 50&#37; and 45&#37; copper dissolution, respectively, as predicted from the thermodynamics. These results confirm the formation of a covellite-like phase as an intermediate which cannot be leached at a potential of 500 mV. An increase in the potential results in rapid dissolution of this "secondary covellite," relative to primary covellite. These results provide useful information for the conditions that should be used for the heap leaching of ores containing secondary copper sulphide minerals.

DOI： 10.1016/j.hydromet.2010.11.004

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In Parts 1 and 2 of this series, which describe the results of a study of the dissolution of chalcopyrite under conditions that could be expected in a heap leaching process for primary copper minerals, it was shown that enhanced leaching of chalcopyrite from several copper concentrates in dilute acidic chloride solutions can be achieved by controlling the potential in a "window" of 560-600 mV (SHE) in the presence of dissolved oxygen. It was also found that the rate is linear and essentially independent of the initial concentration of chloride and cupric ions under these conditions. Furthermore, the rate appears to be largely independent of the source of the mineral and is strongly dependent on the temperature (activation energy = 72 kJ mol^{- 1}). In this part, additional kinetic data on the effects of fine pyrite on the rate complemented by detailed mineralogical analysis of the residues will be used to demonstrate that sulfur forms a soluble intermediate such as H₂S in the dissolution reaction. A summary of the results of a detailed study of the kinetics of the copper ion catalysed oxidation of H ₂S by dissolved oxygen is presented which provides further support for a mechanism for the dissolution of chalcopyrite under heap leach conditions which involves an initial step involving non-oxidative dissolution to form H₂S and either cupric ions or a covellite-like surface as the initial products.

DOI： 10.1016/j.hydromet.2010.03.003

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In Part 1 of this series, which describes the results of a study of the dissolution of chalcopyrite under conditions that could be expected in a heap leaching process for primary copper minerals, it was shown that enhanced leaching of chalcopyrite from several copper concentrates in dilute acidic chloride solutions can be achieved by controlling the potential in a range of 560-600 mV (SHE) in the presence of dissolved oxygen. Based on the results of these experiments, this paper reports on an extensive study of the kinetics of the dissolution of several chalcopyrite concentrates in chloride solutions under various conditions in especially designed reactors. It will be demonstrated that the rates of dissolution at constant potential in the range of 580-600 mV by control of the oxygen supplied to the reactor are approximately constant for up to 80&#37; dissolution for sized fractions of the concentrates. The rate of dissolution of chalcopyrite under these conditions is largely independent of the pulp density, iron and copper ion concentrations which could be expected in a heap leach operation, the acidity and the chloride ion concentration. Variation of the temperature in the range 25 to 75 °C under otherwise constant conditions resulted in an activation energy for dissolution of two different concentrates of 72 kJ mol^{- 1}.

DOI： 10.1016/j.hydromet.2010.03.004

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A study of the dissolution of several copper concentrates under controlled potential conditions in chloride solutions has demonstrated that the rate of dissolution of chalcopyrite is strongly dependent on the potential of the solution. Linear rates were obtained for the dissolution of chalcopyrite in solutions containing 0.2 M HCl and 0.5 g L^{- 1} Cu(II) at 35 °C. The rate is enhanced within a range of potentials of 550 to 620 mV (versus SHE) and the presence of dissolved oxygen is essential for enhanced rates within this potential window. Even though dissolved oxygen is important in order to achieve acceptable rates of dissolution, excessive oxidation can increase the potential into a region in which passivation is possible. Reduction of the potential into the optimum region results in restoration of enhanced rates of dissolution. On the other hand, dissolution at low potentials (< 540 mV) results in reduced rates of copper dissolution which increase significantly when the potential is subsequently increased to above 580 mV. Mineralogical studies have shown that chalcopyrite remains un-leached and small amounts of covellite appear to be formed on the surface of the chalcopyrite at low potentials. All concentrates appear to dissolve at roughly the same rate under the same conditions, despite differences in the composition and mineralogy of the samples.

DOI： 10.1016/j.hydromet.2010.03.001

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The oxidation of iron(II) is an essential step in the oxidative leaching of uranium(IV) minerals such as uraninite and one of the reagents used in practice for this oxidation is sodium chlorate. This paper presents the results of an investigation into the kinetics of the oxidation of iron(II) by chlorate in solutions typical of the leaching of uranium. The results have confirmed the known form of the rate equation which is first-order in each of iron(II), chlorate and acid concentration. An overall rate equation has been derived which can be used to model the rate of iron(II) oxidation as a function of the reactant concentrations and the temperature. The half-life was found to be less than 1 min under typical leach conditions at the Olympic Dam operation in South Australia and this species cannot be considered to be the direct oxidant for uranium(IV) minerals.

DOI： 10.1016/j.hydromet.2009.10.001

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The leaching rate of chalcopyrite (CuFeS₂) in H₂SO₄ solutions depends on the redox potential determined by the concentration ratio of Fe³⁺ to Fe²⁺, and the rate is higher at redox potentials below a critical value (critical potential). In actual leaching systems, different metal ions are released from coexisting minerals to the aqueous phase. The present study investigated the effects of coexisting metal ions on the critical potential of chalcopyrite leaching. Shaking-flask leaching experiments were carried out with 0.1 g of ground chalcopyrite and 10 cm³ of 0.1 kmol m^{- 3} H₂SO₄ containing 0.1 kmol m^{- 3} Fe²⁺ and 0.001 kmol m^{- 3} of the metal ions at 298 K in air. The initial redox potential was adjusted by adding Fe³⁺, and the amount of Cu extracted after 24 h was investigated as a function of the potential. The results indicate that the critical potential increases by the addition of Ag⁺ or Bi³⁺ but is not affected by Pd²⁺, Hg²⁺, Cd²⁺, Zn²⁺, Ni²⁺, Co²⁺, or Mn²⁺. The results were interpreted by a reaction model assuming the formation of intermediate Cu₂S due to the reduction of chalcopyrite and subsequent oxidation of the Cu₂S at potentials below the critical potential. Catalytic effects of metal ions on chalcopyrite leaching are also discussed based on the experimental results and the proposed model.

DOI： 10.1016/j.hydromet.2006.07.006

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Copper extraction during the oxidative leaching of chalcopyrite (CuFeS ₂) by ferric ions or by dissolved oxygen in sulfuric acid solutions is known to be faster at low redox potentials but slower at potentials above a critical value. The present study shows that this phenomenon occurs only when cupric and ferrous ions coexist, based on electrochemical measurements. Using a chalcopyrite electrode prepared from an ore lump sample, effects of the addition of 0.1 kmol m^-3 cupric and ferrous ions on anodic polarization curves and AC impedance spectra were investigated in 0.1 kmol m^-3 sulfuric acid with stirring at 298 K in nitrogen. Without cupric and/or ferrous ions, the anodic current increased monotonically with increasing applied potential. When cupric and ferrous ions coexisted, active-passive behavior was observed, i.e., the current increased with increasing potential to reach a maximum and it suddenly decreased at a certain potential, whereby the current became less dependent on the potential. In the active region, i.e., at low potentials, the anodic current with coexisting cupric and ferrous ions was larger than that without these ions. These results agree well with the results of leaching experiments reported previously, and indicate that coexisting cupric and ferrous ions promote the anodic dissolution of chalcopyrite at low potentials. The analysis of the AC impedance spectra indicates that a high-resistance passive layer grows on the chalcopyrite surface without cupric and/or ferrous ions, and that coexistence of these ions causes a formation of another product layer and inhibits the passive layer growth in the active region. To interpret the active-passive behavior of chalcopyrite, a reaction model, assuming the formation of intermediate Cu₂S in the active region, is discussed based on the experimental results.

DOI： 10.1016/j.hydromet.2004.01.003

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Chalcopyrite leaching in sulfuric acid solutions depends on the redox potential determined by the concentration ratio of ferric to ferrous ions, and the leaching rate is higher at redox potentials below a critical value. Previously, the authors have proposed a reaction model to interpret this phenomenon. The present study applied the model to interpret the catalytic effect of silver ions on chalcopyrite leaching. The model assumes that at lower potentials, chalcopyrite leaching proceeds in two steps: first, chalcopyrite is reduced by ferrous ions to form Cu₂S that is more rapidly leached; next, the intermediate Cu₂S is oxidized by ferric and/or dissolved oxygen to release cupric ions. During the chalcopyrite reduction, hydrogen sulfide is released to the liquid phase. Silver ions react with the hydrogen sulfide to form silver sulfide precipitate and decrease the concentration of hydrogen sulfide in the liquid phase, causing a rise in the critical potential of Cu₂S formation and broadening of the potential range where rapid copper extraction takes place. To confirm the model, the redox potential dependence of chalcopyrite leaching was investigated in the presence of various concentrations of silver ions with 0.1 kmol m^-3 sulfuric acid containing known concentrations of ferrous and ferric ions at 298 K in air. The critical potential increased with increasing concentrations of silver ions. This agrees with the model proposed here but cannot be explained by the conventional model proposed by Miller et al.

DOI： 10.1016/S0304-386X(01)00228-6

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The effects of ferrous ions on chalcopyrite oxidation with ferric ions in 0.1 mol dm^-3 sulfuric acid solutions were investigated by leaching experiments at 303 K in nitrogen. With high cupric ion concentrations, the chalcopyrite oxidation was enhanced by high concentrations of ferrous ions and copper extraction was mainly controlled by the concentration ratio of ferrous to ferric ions or the redox potential of solutions. Ferrous ions, however, suppressed the chalcopyrite oxidation when cupric ion concentrations were low. A reaction model, which involves chalcopyrite reduction to intermediate Cu₂S by ferrous ions and oxidation of the Cu₂S by ferric ions, was proposed to interpret the results.

DOI： 10.1016/S0304-386X(00)00155-9

Language：English  

Oxidative leaching of chalcopyrite with dissolved oxygen and/or with ferric ions is promoted by high concentrations of ferrous ions in sulfuric acid solutions containing cupric ions. This paper proposes a reaction model to interpret this phenomenon and the thermodynamics of the leaching is discussed. The model considers the leaching to take place in two steps: (1) reduction of chalcopyrite to Cu₂S by ferrous ions in the presence of cupric ions and (2) oxidation of the Cu₂S to cupric ions and elemental sulfur by dissolved oxygen and/or by ferric ions. The intermediate Cu₂S is more amenable to oxidation than chalcopyrite, causing enhanced copper extraction. The model predicts that the formation of intermediate Cu₂S and ferrous-promoted chalcopyrite leaching occur when the redox potential of the solution is below a critical potential that is a function of the ferrous and cupric ion concentrations. To confirm this, flask-shaking leaching experiments were carried out with 0.1 mol dm^-3 sulfuric acid solutions containing known concentrations of ferrous, ferric, and cupric ions at 303 K in air. The results agreed well with the predictions, i.e. copper extraction was enhanced at solution potentials below the critical potential predicted with the model.

DOI： 10.1016/S0304-386X(00)00089-X

Language：English  

Language：English  

Language：Japanese  

Ferrous Promoted Chalcopyrite Leaching -Ferric formation and its effects on the leaching-
This paper shows that ferrous ions are more useful for leaching chalcopyrite than oxidant ferric ions in sulfuric acid solutions in air at ambient temperatures. Leaching experiments and dissolved oxygen consumption measurements were carried out with a very pure chalcopyrite and 0.001 ∼ 1 mol dm-3 sulfuric acid containing 0 ∼ 0.1 mol dm-3 ferrous or ferric ions at 303 K. Chalcopyrite oxidation with dissolved oxygen was promoted by ferrous ions and was suppressed by ferric ions. As a result, the amount of extracted copper was higher with ferrous ions than with ferric ions in air. During the ferrous promoted chalcopyrite leaching, extracted copper ions catalyzed oxidation of ferrous ions to ferric ions which suppressed copper extraction. This result indicates that higher leaching rates can be achieved by reducing the ferric ions formed during the leaching.

DOI： 10.2473/shigentosozai.114.795

Event date： 2018.6

Language：English   Presentation type：Oral presentation (general)  

Venue：サンチアゴ   Country：Chile  

Event date： 2014.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：千葉工業大学   Country：Japan  

Event date： 2014.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京大学 生産技術研究所   Country：Japan  

Event date： 2013.12

Language：English   Presentation type：Oral presentation (general)  

Venue：Inamori Foundation Memorial Hall, Kyushu University, Fukuoka   Country：Japan  

Event date： 2013.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Sunshine Hotel & Resort Zhangjiajie   Country：China  

Other Link： http://www.earth2013.org/

Event date： 2013.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：熊本大学   Country：Japan  

Event date： 2013.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：千葉工業大学   Country：Japan  

Event date： 2005.2

Language：English   Presentation type：Oral presentation (general)  

Venue：Salt lake city   Country：United States  

Event date： 2003.8 - 2003.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Santiago   Country：Chile  

Event date： 2001.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：芝浦工業大学芝浦校舎   Country：Japan  

Event date： 2000.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：千葉工業大学津田沼校舎   Country：Japan  

Event date： 1999.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：早稲田大学理工学部   Country：Japan  

Event date： 1997.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：北海道大学学術交流会館   Country：Japan  

Event date： 2021.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京   Country：Japan  

Event date： 2021.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京   Country：Japan  

Event date： 2020.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Fukuoka, Japan   Country：Japan  

Event date： 2020.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Capetown   Country：South Africa  

Event date： 2020.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Capetown   Country：South Africa  

Event date： 2020.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Capetown   Country：South Africa  

Event date： 2020.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Fukuoka, Japan   Country：Japan  

Event date： 2020.3 - 2022.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京   Country：Japan  

Event date： 2020.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京   Country：Japan  

Event date： 2019.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Fukuoka, Japan   Country：Japan  

Event date： 2019.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Capetown   Country：South Africa  

Event date： 2019.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Capetown   Country：South Africa  

Event date： 2019.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Pyongchang   Country：Korea, Republic of  

Event date： 2019.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：京都   Country：Japan  

Event date： 2019.8

Language：English   Presentation type：Oral presentation (general)  

Venue：Vancouver   Country：Canada  

Event date： 2019.8

Language：English   Presentation type：Oral presentation (general)  

Venue：Vancouver   Country：Canada  

Event date： 2019.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡   Country：Japan  

Event date： 2018.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Fukuoka, Japan   Country：Japan  

Event date： 2018.11

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2018.9

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2018.8

Language：English   Presentation type：Oral presentation (general)  

Venue：Moscow, Russia   Country：Russian Federation  

Investigation of reagents for selective flotation on chalcopyrite and molybdenite

Event date： 2018.8

Language：English   Presentation type：Oral presentation (general)  

Venue：Moscow, Russia   Country：Russian Federation  

Event date： 2018.6

Language：English   Presentation type：Oral presentation (general)  

Venue：九州大学   Country：Japan  

Event date： 2018.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：熊本大学   Country：Japan  

Event date： 2018.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：熊本大学   Country：Japan  

Event date： 2018.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：熊本大学   Country：Japan  

Event date： 2018.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：熊本大学   Country：Japan  

Event date： 2018.6

Language：English   Presentation type：Oral presentation (general)  

Venue：サンチアゴ   Country：Chile  

Event date： 2018.6

Language：English   Presentation type：Oral presentation (general)  

Venue：九州大学   Country：Japan  

Event date： 2018.6

Language：English   Presentation type：Oral presentation (general)  

Venue：九州大学   Country：Japan  

Event date： 2018.6

Language：English   Presentation type：Oral presentation (general)  

Venue：九州大学   Country：Japan  

Event date： 2018.6

Language：English   Presentation type：Oral presentation (general)  

Venue：ケープタウン   Country：South Africa  

Event date： 2018.6

Language：English   Presentation type：Oral presentation (general)  

Venue：ケープタウン   Country：South Africa  

Event date： 2018.6

Language：English   Presentation type：Oral presentation (general)  

Venue：九州大学   Country：Japan  

Event date： 2018.6

Language：English   Presentation type：Oral presentation (general)  

Venue：九州大学   Country：Japan  

Event date： 2018.6

Language：English   Presentation type：Oral presentation (general)  

Venue：九州大学   Country：Japan  

Event date： 2018.6

Language：English   Presentation type：Oral presentation (general)  

Venue：九州大学   Country：Japan  

Event date： 2018.6

Language：English   Presentation type：Oral presentation (general)  

Venue：ケベックシティ   Country：Canada  

Event date： 2018.6

Language：English   Presentation type：Oral presentation (general)  

Venue：ケベックシティ   Country：Canada  

Event date： 2018.6

Language：English   Presentation type：Oral presentation (general)  

Venue：リスボン   Country：Portugal  

Event date： 2018.6

Language：English   Presentation type：Oral presentation (general)  

Venue：フライベルグ   Country：Germany  

Event date： 2018.6

Language：English   Presentation type：Oral presentation (general)  

Venue：ケープタウン   Country：South Africa  

Event date： 2018.6

Language：English   Presentation type：Oral presentation (general)  

Venue：ケープタウン   Country：South Africa  

Event date： 2018.6

Language：English   Presentation type：Oral presentation (general)  

Venue：九州大学   Country：Japan  

Event date： 2017.9

Language：English  

Venue：Freiberg   Country：Germany  

Silver-catalyzed bioleaching of enargite concentrate with three bacteria (Acidimicrobium ferrooxidans ICP, Sulfobacillus sibiricus N1, Acidithiobacillus caldus KU) and one archaeon (Ferroplasma acidiphilum Y) was conducted in order to elucidate the catalytic mechanism of silver sulfide in enargite bioleaching. Whereas Cu recovery remained relatively low (43&#37;) and Fe dissolved completely without silver sulfide, Cu recovery was greatly enhanced (96&#37;) and Fe dissolution was suppressed (29&#37;) in the presence of 0.04&#37; silver sulfide. In the latter case, 52&#37; of the solubilized As was re-immobilized, in contrast to only 14&#37; As re-immobilization in the former. The silver-catalyzed bioleaching (at 0.04&#37; silver sulfide) proceeded at low redox potentials within the optimal range, which likely promoted enargite dissolution via formation of intermediate Cu₂ S. XAFS analysis revealed that As was mainly immobilized as As(V), which was in agreement with the EPMA results detecting ferric arsenate passivation on some enargite grains. Furthermore, formation of trisilver arsenic sulfide (Ag₃ AsS₄) was detected by XRD and EPMA, covering the surface of enargite particles. An intermediate layer, consisting of (Cu,Ag)₃ AsS₄, was also observed between the enargite grain and trisilver arsenic sulfide layer, implying that Cu in enargite may be gradually substituted by solubilized Ag. Kinetic study suggested that these secondary minerals do not rate-limit the enargite dissolution. The overall mechanism of silver-catalyzed bioleaching of enargite concentrate will be proposed.

Event date： 2014.10

Language：English  

Venue：Santiago   Country：Chile  

For pretreatment of selective flotation, surface oxidation of chalcopyrite and molybdenite was applied by oxygen plasma then the minerals were washed by solution at pH 9 with oxygen bubbling. Surface characteristics of these minerals were investigated with AFM, XPS, zeta potential and contact angle measurements. Contact angle of chalcopyrite and molybdenite decreased a lot by plasma treatment. When they were washed with pH 9 solution with oxygen bubbling, contact angle of molybdenite increased whereas chalcopyrite one kept low. Adhesion force measurements indicated similar behavior. Result of flotation experiments indicated low recovery of both chalcopyrite and molybdenite after plasma treatment and only molybdenite recovery became higher after washing. Selective flotation of chalcopyrite and molybdenite could be achieved with this process. Possible mechanism of selective flotation was proposed from the results of XPS, AFM, etc.

Event date： 2014.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：千葉工業大学   Country：Japan  

Event date： 2014.3

Language：English   Presentation type：Oral presentation (general)  

Venue：東京大学 生産技術研究所   Country：Japan  

Event date： 2014.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京大学 生産技術研究所   Country：Japan  

Event date： 2014.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：千葉工業大学   Country：Japan  

Event date： 2014.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：千葉工業大学   Country：Japan  

Event date： 2014.3

Language：English   Presentation type：Oral presentation (general)  

Venue：Holiday Inn Hotel, Dubai, United Arab Emirates   Country：United Arab Emirates  

Event date： 2013.12

Language：English   Presentation type：Oral presentation (general)  

Venue：Inamori Foundation Memorial Hall, Kyushu University, Fukuoka   Country：Japan  

Event date： 2013.12

Language：English   Presentation type：Oral presentation (general)  

Venue：Inamori Foundation Memorial Hall, Kyushu University, Fukuoka   Country：Japan  

Event date： 2013.12

Language：English   Presentation type：Oral presentation (general)  

Venue：Inamori Foundation Memorial Hall, Kyushu University, Fukuoka   Country：Japan  

Event date： 2013.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Vineyard Hotel, Cape Town, South Africa   Country：South Africa  

Other Link： http://www.min-eng.com/flotation13/

Event date： 2013.9 - 2013.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：北海道大学   Country：Japan  

Event date： 2013.9 - 2013.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：北海道大学   Country：Japan  

Event date： 2013.8

Language：English   Presentation type：Oral presentation (general)  

Venue：University of Kitakyushu   Country：Japan  

Event date： 2013.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：熊本大学   Country：Japan  

Event date： 2013.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：千葉工業大学   Country：Japan  

Event date： 2012.7

Language：English   Presentation type：Oral presentation (general)  

Venue：Santiago   Country：Chile  

Event date： 2011.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Johannesburg   Country：South Africa  

Event date： 2010.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Hamburg   Country：Germany  

Event date： 2010.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Hamburg   Country：Germany  

Event date： 2008.8

Language：English  

Venue：Phoenix, AZ   Country：United States  

An electrochemical study of the cathodic reduction of copper(II) and iron(III) ions on covellite and pyrite electrode surfaces has been carried out using rotating disk electrodes in acidic chloride solutions. The results of linear sweep voltammetric measurements have revealed that reduction of copper(II) ions on both mineral surfaces can be enhanced by a typical EC'(electrochemical/chemical) or catalytic mechanism in which the product copper(I) ions, are reoxidised in a rapid chemical reaction with iron(III) ions. Fe(III) + Cu(I) ⇆ Fe(II) + Cu(II) In the case of covellite, the catalytic effect is substantial with a significant positive shift in the mixed potential in the presence of both ions. An estimate of the magnitude of the catalytic effect using conventional EC theory for a rotating disk and published data for the rate of oxidation of copper(I) by iron(III) is consistent with the observed effect. It is suggested that the effect on the leaching rate of covellite in such solutions at ambient temperatures will not be significantly affected by the presence of this catalytic process given that the mixed potentials occur in a potential region in which the rate of anodic dissolution of the mineral is largely independent of potential. The effect is less substantial in the case of pyrite and a more extensive study of the effects of varying concentrations of chloride, copper(II) and iron(III) ions has given results which are also qualitatively consistent with those predicted from the theory in that the concentration of copper(II) has a greater effect than that of iron(III) on the catalytic currents. The practical significance is expected to be minimal in the case of pyrite for which higher potentials are required than those at which copper(II) is electrochemically active.

Event date： 2008.8

Language：English  

Venue：Phoenix, AZ   Country：United States  

An alternative approach to the heap leaching of copper sulfide minerals involves the use of chloride ions as the lixiviant. The facile oxidation of copper(I) ions in a chloride system by atmospheric oxygen offers an alternative to bio-oxidation of iron(II) in the sulfate system. In the chloride system, it is well-known that both copper(II) and iron(III) ions can act as the oxidants for these minerals. However, regeneration of these species by oxidation with dissolved oxygen is required and this is possible in a sulfate system by the use of bacterially catalysed oxidation of iron(II). However, in the chloride system, re-oxidation of copper(I) and iron(II) ions can only economically be achieved by chemical reaction with dissolved oxygen. The kinetics of the reduction of dissolved oxygen by iron(II) and copper(I) in acidic chloride solutions have been previously studied with the former being considerably slower than the latter. This paper will focus on the kinetics of the copper-catalysed reaction of iron(II) with dissolved oxygen. It will be shown that this reaction can be described in terms of the rapid equilibrium Fe(II) + Cu(II) ⇆ Fe(III) + Cu(I) followed by relatively rapid auto-oxidation of copper(I). The inhibiting effect of iron(III) ions in terms of the above equilibrium is demonstrated and the effects of acidity and chloride ion concentration on the rate described. An overall kinetic model has been developed which is consistent with the published data on the individual reactions involved in this mechanism. The application of this model to the prediction of maximum possible leach rates for copper sulfide minerals in aerated systems under ambient conditions is discussed.

Event date： 2008.8

Language：English   Presentation type：Oral presentation (general)  

Venue：Phoenix   Country：United States  

Event date： 2008.8

Language：English   Presentation type：Oral presentation (general)  

Venue：Phoenix   Country：United States  

Event date： 2005.2 - 2005.3

Language：English  

Venue：Salt Lake City, UT   Country：United States  

Relatively simple techniques have been developed which enable the electrochemistry of sulfide minerals to be studied with particles varying in size from above 100 μm to less than 1 μm. Both oxidative and reductive processes have been studied using the minerals pyrite, arsenopyrite and chalcopyrite. It has been shown that it is possible to completely oxidise or reduce the minerals during a single voltammetric sweep. The resulting voltammogram produces peaks which are characteristic of each mineral and can be used to qualitatively identify the minerals. In the case of chalcopyrite, it has been demonstrated that the charge involved in the anodic oxidation can be quantitatively related to the amount of copper dissolved. Quantitative information can be obtained using peak fitting techniques. Interesting differences in the behaviour of the minerals in sulfuric and hydrochloric acids have been observed, particularly in the case of pyrite for which a second major peak is obtained which has been attributed to the oxidation of elemental sulfur in the presence of chloride ions. The technique offers the possibility of providing mineralogical information of individual particles based on an electrochemical voltammetric fingerprint.

Event date： 2001.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：芝浦工業大学芝浦校舎   Country：Japan  

Event date： 2000.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：千葉工業大学津田沼校舎   Country：Japan  

Event date： 1999.10

Language：English  

Venue：Phoenix, AZ   Country：United States  

It is generally accepted that ferric ions are effective for leaching chalcopyrite as an oxidant and ferrous ions contribute to the leaching only as a source of the oxidant ferric ions. However, this paper shows that ferrous ions are more useful for leaching chalcopyrite than oxidant ferric ions in sulfuric acid solutions in air at ambient temperatures. Leaching experiments and dissolved oxygen consumption measurements were carried out with a very pure chalcopyrite and 0.001 - 1 mol dm^-3 sulfuric acid solutions containing 0 - 0.1 mol dm^-3 ferric or ferrous ions at 303 K. Chalcopyrite oxidation with dissolved oxygen was promoted by ferrous ions but suppressed by ferric ions. As a result, the amount of extracted copper was larger with ferrous ions than with ferric ions. Effects of Thiobacillus ferrooxidans on the ferrous promoted chalcopyrite leaching were also investigated and discussed based on the experimental data.

Event date： 1999.8 - 1999.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Pheonix   Country：United States  

Event date： 1999.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：早稲田大学理工学部   Country：Japan  

Event date： 1999.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：早稲田大学理工学部   Country：Japan  

Event date： 1999.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：早稲田大学理工学部   Country：Japan  

Type：Peer review 

Number of peer-reviewed articles in foreign language journals：3

Type：Competition, symposium, etc. 

Type：Peer review 

Number of peer-reviewed articles in foreign language journals：1

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc.