| Hajime Miki | Last modified date：2024.04.17 |
Associate Professor /
Frontier Education Center for Global Cooperation in Earth Resources Engineering /
Department of Earth Resources Engineering /
Faculty of Engineering
Papers
| 1. | HAJIME MIKI, Tsuyoshi Hirajima, Gde Pandhe Wisnu Suyantara, Keiko Sasaki, Evaluation of micro powder electrode on sulfide mineral leaching for hydrometallurgical process, The 18th International Conference on Quality in Research, 2023.10. |
| 2. | Eska Putra Dwitama, Akbarshokh Ulmaszoda, Gde Pandhe Wisnu Suyantara, Keiko Sasaki, Hajime Miki, Preliminary Evaluation of the Impact of Nanoparticles on Enargite Flotation, The 18th International Conference on Quality in Research, 2023.10. |
| 3. | HAJIME MIKI, Gde Pandhe Wisnu Suyantara, Keiko Sasaki, Arsenic removal with heat treatment - magnetic separation from dirty copper conc, The 18th International Conference on Quality in Research, 2023.10. |
| 4. | Gde Pandhe Wisnu Suyantara, Hajime Miki, Keiko Sasaki, Yuji Aoki, Daishi Ochi, Tsuyoshi Hirajima, Utilizing Oxidation Treatment for Arsenic Mineral Removal in Producing a Cleaner Copper Concentrate using Flotation, The 18th International Conference on Quality in Research, 2023.10. |
| 5. | Akbarshokh Ulmaszoda, Gde Pandhe Wisnu Suyantara, Intan Nurul Rizki, Keiko Sasaki, Hajime Miki, Investigation of Chalcopyrite Floatability in the Presence of Goethite Nanoparticles, The 18th International Conference on Quality in Research, 2023.10. |
| 6. | Ryota Nakao, Hajime Miki, Eska Putra Dwitama, Keiko Sasaki, Daishi Ochi, Yuji Aoki, Gde Pandhe Wisnu Suyantara, The Effect Of Various Reagents On Selective Flotation Of Molybdenite And Chalcocite, The 18th International Conference on Quality in Research, 2023.10. |
| 7. | Kazuto Satomura, Gde Pandhe Wisnu Suyantara, Hajime Miki, Keiko Sasaki, Study on the Effect of Iron Oxide-Hydroxide Nanoparticles on Mixed Flotation of Bornite and Molybdenite, The 18th International Conference on Quality in Research, 2023.10. |
| 8. | Berdakh Daniyarov, Miki Hajime, Suyantara Gde Pandhe Wisnu, Hirajima Tsuyoshi, Sasaki Keiko, Nakao Ryota, Ochi Daishi, Aoki Yuji, Akbarshokh Ulmaszoda, Kumika Ura, Sodium metabisulfite as a copper depressant in the selective flotation of copper-molybdenum concentrate using seawater, Advanced Powder Technology, 10.1016/j.apt.2023.104258, 34, 12, 104258, 2023.12. |
| 9. | Berdakh Daniyarov, Miki Hajime, Suyantara Gde Pandhe Wisnu, Hirajima Tsuyoshi, Sasaki Keiko, Nakao Ryota, Ochi Daishi, Aoki Yuji, Effect of oxidation treatment on the selective separation of molybdenite from chalcocite using flotation, Powder Technology, 10.1016/j.powtec.2023.119078, 431, 119078, 431, 119078, 2024.01. |
| 10. | G.P.W. SUYANTARA，H. MIKI, Y. AOKI, D. OCHI, K.SASAKI, T. HIRAJIMA, Selective Flotation of Copper Concentrates Containing Arsenic Minerals Using Potassium Amyl Xanthate and Oxidation Treatment, Materials Transactions, 10.2320/matertrans.M-M2023811, 65, 1, 27-36, 2024.01. |
| 11. | G.P.W.SUYANTARA, I.N.RIZKI, A.ULMASZODA, H.MIKI, K.SASAKI, Effect of goethite (α-FeOOH) nanoparticles on the surface properties and flotation behavior of chalcopyrite, Journal of Environmental Chemical Engineering, 10.1016/j.jece.2023.110006, 11, 3, 110006, 2023.06. |
| 12. | G.P.W.SUYANTARA, B.DANIYAROV, H.MIKI, H.TSUYOSHI, K.SASAKI, D.OCHI, Y.AOKI, Effect of hydrogen peroxide on selective flotation of chalcocite and enargite, International Journal of Mining Science and Technology, 10.1016/j.ijmst.2023.01.002, 33, 6, 703, 2023.06. |
| 13. | Y. TANAKA, H. MIKI, G.P.W. SUYANTARA，Y. AOKI, H. OKAMOTO, K. URA, T. HIRAJIMA, Effect of pH and Precipitations on Copper-Molybdenum Rougher Flotation in Seawater, Materials Transactions, 10.2320/matertrans.M-M2023805, 64, 6, 1125, 2023.06. |
| 14. | K. SASAKI, I. SUYAMA, Y. AOKI, K.T.KONADU, CINDY, C. CHUAICHAM, H. MIKI, T. HIRAJIMA, Significance of Fe contents on the surface of the gold ores in gold leaching by thiourea and ethylene thiourea, Minerals Engineering, 191, 107957, 2023.06. |
| 15. | Suyantara Gde Pandhe Wisnu、Berdakh Daniyarov、Miki Hajime、Hirajima Tsuyoshi、Sasaki Keiko、 Ochi Daishi、Aoki Yuji, Effect of hydrogen peroxide on selective flotation of chalcocite and enargite, International Journal of Mining Science and Technology, 10.1016/j.ijmst.2023.01.002, in press, , 2023.03. |
| 16. | Elmahdy Ahmed M.、Miki Hajime、Sasaki Keiko、Farahat Mohsen, The Effect of Microwave Pre-treatment on the Magnetic Properties of Enargite and Tennantite and Their Separation from Chalcopyrite, Minerals, 10.3390/min13030334, 13,334-340, 2023.03. |
| 17. | R. OGI, G.P.W. SUYANTARA, H. MIKI, T. HIRAJIMA, K. SASAKI Y. AOKI, D. OCHI , Study on the effect of sodium metabisulfite on selective flotation of chalcopyrite and molybdenite with seawater, Proc. of International Symposium on Earth Science and Technology 2022, 1, 2022.12. |
| 18. | B. DANIYAROV, G.P.W. SUYANTARA, H. MIKI, T. HIRAJIMA, K. SASAKI D. OCHI, Y. AOKI, Separation of enargite and chalcocite with H2O2 oxidation treatment using flotation method, Proc. of International Symposium on Earth Science and Technology 2022, 1, 2022.12. |
| 19. | MIKI Hajime、OKIBE Naoko、SUYANTARA Gde Pandhe Wisnu、OYAMA Keishi、SASAKI Keiko、HIRAJIMA
Tsuyoshi、NAKAMURA Takeshi、AOKI Yuji、TANAKA Yoshiyuki、SUWA Takahiro, Technical Development of Arsenic Reduction from Copper Resources by Kyushu University and Sumitomo Metal Mining Co. Ltd. , Resources Processing , 10.4144/rpsj.68.124, 68, 124-131, 2022.11. |
| 20. | H. MIKI, H. FUKUDA, G.P.W. SUYANTARA, B. DANIYAROV, T. HIRAJIMA, K. SASAKI, The estimation of microgram powder electrode system on sulfide mineral oxidation for mineral processing, Proc. of 11th Copper2022 International Conference, 1, 2022.11. |
| 21. | H. MIKI, G.P.W. SUYANTARA, K. SASAKI, T. HIRAJIMA, Y. AOKI, H. FUKUDA, Arsenic removal from arsenic containing copper concentrate with heat treatment and magnetic separation, Proc. of 11th Copper2022 International Conference, 1, 2022.11. |
| 22. | G.P.W. SUYANTARA, T. HIRAJIMA, H. MIKI, K. SASAKI, Y.TANAKA, Y. AOKI , Investigation of sodium sulfite as a selective depressant in the flotation of chalcopyrite and enargite, Proc. of 11th Copper2022 International Conference, 1, 2022.11. |
| 23. | Y. TANAKA, T. HIRAJIMA, H. MIKI, G.P.W. SUYANTARA, Estimation of Cu and Mo recoveries of five type ores composite in seawater flotation, Proc. of 11th Copper2022 International Conference, 1, 2022.11. |
| 24. | B. DANIYAROV, G.P.W. SUYANTARA, H. MIKI, T. HIRAJIMA, K. SASAKI, D. OCHI, Y. AOKI , Separation of enargite and chalcocite with H2O2 oxidation treatment using flotation method, Proceedings of the 16th International Symposium on East Asian Resources Recycling Technology (EARTH2022), 1, 2022.10. |
| 25. | Suyantara Gde Pandhe Wisnu, Semoto Yuki, Miki Hajime, Hirajima Tsuyoshi, Sasaki Keiko, Ochi Daishi, Aoki Yuji, Berdakh Daniyarov, Ura Kumika, Effect of sodium metabisulfite and slaked lime on the floatability and surface properties of chalcopyrite, Powder Technology, 10.1016/j.powtec.2022.117750, 408, 117750, 408, 117750, 2022.08. |
| 26. | Semoto Yuki、Suyantara Gde Pandhe Wisnu、Miki Hajime、Sasaki Keiko、Hirajima Tsuyoshi、Tanaka Yoshiyuki、Aoki Yuji、Ura Kumika, Effect of Sodium Metabisulfite on Selective Flotation of Chalcopyrite and Molybdenite, Minerals, 10.3390/min11121377, 1377-1390, 11，1377-1390, 2021.11. |
| 27. | Suyantara Gde Pandhe Wisnu、Hirajima Tsuyoshi、Miki Hajime、Sasaki Keiko、Kuroiwa Shigeto、Aoki Yuji, Effect of Na2SO3 on the floatability of chalcopyrite and enargite, Minerals Engineering, 10.1016/j.mineng.2021.107222, 173, 173，107222-107235, 2021.10. |
| 28. | Semoto Yuki、Suyantara Gde Pandhe Wisnu、Miki Hajime、Sasaki Keiko、Hirajima Tsuyoshi、Aoki Yuji, The study of selective flotation separation of copper-molybdenite with seawater, Proceedings of International Symposium on Earth Science and Technology 2020, 2020.11. |
| 29. | Gde Pandhe Wisnu Suyantara, Tsuyoshi Hirajima, Hajime Miki, Keiko Sasaki, Bubble interactions with chalcopyrite and molybdenite surfaces in seawater, Minerals Engineering, 10.1016/j.mineng.2020.106536, 157, 106536-106536, 2020.10, 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.. |
| 30. | Keishi Oyama, Kazuhiko Shimada, Junichiro Ishibashi, Keiko Sasaki, Hajime Miki, Naoko Okibe, Catalytic mechanism of activated carbon-assisted bioleaching of enargite concentrate, Hydrometallurgy, 10.1016/j.hydromet.2020.105417, 196, 2020.09, The catalytic mechanism of activated carbon-assisted bioleaching of enargite concentrate (enargite 37.4%; pyrite 47.3%) 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% to 53% at 0.2% (w/v) activated carbon. An excess activated carbon addition showed an adverse effect. The enargite mineral itself favored higher solution redox potential (Eh) for solubilization. However, the dissolution of co-existing pyrite, which also favors high Eh, 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 Eh level was controlled by offsetting microbial Fe3+ regeneration. As long as the Eh level was suppressed at h-control by activated carbon becomes no longer sustainable and the Eh 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% as amorphous ferric arsenate. However, the sudden initiation of pyrite dissolution also triggered the re-solubilization of ferric arsenate. Therefore, the sustainable Eh-controlling effect was shown to be critical to enable longer Cu dissolution from enargite as well as stabilization of As precipitates..  |
| 31. | Kojo T. Konadu, Ryotaro Sakai, Diego M. Mendoza, Chitiphon Chuaicham, Hajime Miki, Keiko Sasaki, Effect of carbonaceous matter on bioleaching of Cu from chalcopyrite ore, Hydrometallurgy, 10.1016/j.hydromet.2020.105363, 195, 105363-105363, 2020.08, 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.. |
| 32. | Gde Pandhe Wisnu Suyantara, Tsuyoshi Hirajima, Hajime Miki, Keiko Sasaki, Shigeto Kuroiwa, Yuji Aoki, Effect of H2O2 and potassium amyl xanthate on separation of enargite and tennantite from chalcopyrite and bornite using flotation, Minerals Engineering, 10.1016/j.mineng.2020.106371, 152, 106371-106371, 2020.06, 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.. |
| 33. | H. Miki, Tsuyoshi Hirajima, Y. Muta, G. P.W. Suyantara, K. Sasaki, Investigation of reagents for selective flotation on chalcopyrite and molybdenite, 29th International Mineral Processing Congress, IMPC 2018 IMPC 2018 - 29th International Mineral Processing Congress, 1854-1861, 2019.01, 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.. |
| 34. | Gde Pandhe Wisnu Suyantara, Tsuyoshi Hirajima, Hajime Miki, Keiko Sasaki, The use of Fenton's reagent on selective flotation of chalcopyrite and molybdenite, 29th International Mineral Processing Congress, IMPC 2018 IMPC 2018 - 29th International Mineral Processing Congress, 1862-1871, 2019.01, 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.. |
| 35. | Oyama Keishi、Miki Hajime、Okibe Naoko, Evaluation of Catalytic Effect of Activated Carbon on Enargite Bioleaching, Proceedings of International Symposium on Earth Science and Technology 2018, 2018.11. |
| 36. | Takamatsu Kyohei、Oyama Keishi、Miki Hajime、Okibe Naoko, Carbon-assisted bioleaching of chalcopyrite concentrate, Proceedings of International Symposium on Earth Science and Technology 2018, 2018.11. |
| 37. | Gde Pandhe Wisnu Suyantara, Tsuyoshi Hirajima, Hajime Miki, Keiko Sasaki, Masashi Yamane, Eri Takida, Shigeto Kuroiwa, Yuji Imaizumi, Effect of Fenton-like oxidation reagent on hydrophobicity and floatability of chalcopyrite and molybdenite, Colloids and Surfaces A: Physicochemical and Engineering Aspects, 10.1016/j.colsurfa.2018.06.029, 554, 34-48, 2018.10, 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.. |
| 38. | Miki Hajime、Hirajima Tsuyoshi、Muta Yukihiro、Suyantara Gde、Sasaki Keiko, Investigation of reagents for selective flotation on chalcopyrite and molybdenite, Proceedings of XXIV International Mineral Processing Congress (IMPC 2018), 2018.07. |
| 39. | Suyantara Gde Pandhe Wisnu、Hirajima Tsuyoshi、Miki Hajime、Sasaki Keiko, The use of Fenton’s reagent on selective flotation of chalcopyrite and molybdenite, Proceedings of XXIV International Mineral Processing Congress (IMPC 2018), 2018.07. |
| 40. | Gde Pandhe Wisnu Suyantara, Tsuyoshi Hirajima, Hajime Miki, Keiko Sasaki, Masashi Yamane, Eri Takida, Shigeto Kuroiwa, Yuji Imaizumi, Selective flotation of chalcopyrite and molybdenite using H2O2 oxidation method with the addition of ferrous sulfate, Minerals Engineering, 10.1016/j.mineng.2018.02.005, 122, 312-326, 2018.06, 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.. |
| 41. | Keishi Oyama, Kazuhiko Shimada, Junichiro Ishibashi, Hajime Miki, Naoko Okibe, Silver-catalyzed bioleaching of enargite concentrate using moderately thermophilic microorganisms, Hydrometallurgy, 10.1016/j.hydromet.2018.03.014, 177, 197-204, 2018.05, 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%, Cu recovery reached 96% while Fe dissolution was suppressed to reach only 29% 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 Eox (Cu2S) 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.. |
| 42. | Yusei Masaki, Tsuyoshi Hirajima, Keiko Sasaki, Hajime Miki, Naoko Okibe, Microbiological Redox Potential Control to Improve the Efficiency of Chalcopyrite Bioleaching, Geomicrobiology Journal, 10.1080/01490451.2018.1443170, 35, 8, 1-9, 2018.04, The effect of controlling the redox potential (Eh) 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 (Enormal) and the reaction kinetics model. Different Eh 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 Eh during the reaction. It was found that efficiency of bioleaching of chalcopyrite can be effectively evaluated on the basis of Enormal, 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 ≤ Enormal ≤ 1 (−0.35 mV optimal) at the mineral surface by employing a “weak” ion-oxidizer. This led to a copper recovery of > 75%. At higher Enormal levels (Enormal > 1 by “strong” microbial Fe2+ oxidation), Cu solubilization was slowed by diffusion through the product film at the mineral surface ( |
| 43. | Hajime Miki, Tsuyoshi Hirajima, Yukihiro Muta, Gde Pandhe Wisnu Suyantara, Keiko Sasaki, Effect of sodium sulfite on floatability of chalcopyrite and molybdenite, Minerals, 10.3390/min8040172, 8, 4, 2018.04, 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.. |
| 44. | Gde Pandhe Wisnu Suyantara, Tsuyoshi Hirajima, Hajime Miki, Keiko Sasaki, Floatability of molybdenite and chalcopyrite in artificial seawater, Minerals Engineering, 10.1016/j.mineng.2017.10.004, 115, 117-130, 2018.01, 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.. |
| 45. | Mechanism of Silver-Catalyzed Bioleaching of Enargite Concentrate, [URL]. |
| 46. | Study on the effect of a mixture of hydrogen peroxide and ferrous sulfate on the floatability of chalcopyrite and molybdenite. |
| 47. | Development of alternative additive of NaHS for selective flotation of chalcopyrite and molybdenite. |
| 48. | Michael Nicol, Hajime Miki, Suchun Zhang, The anodic behaviour of chalcopyrite in chloride solutions Voltammetry, Hydrometallurgy, 10.1016/j.hydromet.2017.05.016, 171, 198-205, 2017.08, 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.. |
| 49. | Hajime Miki, Hidekazu Matsuoka, Tsuyoshi Hirajima, Gde Pandhe Wisnu Suyantara, Keiko Sasaki, Electrolysis Oxidation of Chalcopyrite and Molybdenite for Selective Flotation, Materials Transactions, 10.2320/matertrans.M-M2017807, 58, 5, 761-767, 2017.03, 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.. |
| 50. | Tsuyoshi Hirajima, Hajime Miki, Gde Pandhe Wisnu Suyantara, Hidekazu Matsuoka, Ahmed Mohamed Elmahdy, Keiko Sasaki, Yuji Imaizumi, Shigeto Kuroiwa, Selective flotation of chalcopyrite and molybdenite with H2O2 oxidation, Minerals Engineering, 10.1016/j.mineng.2016.10.007, 100, 83-92, 2017.01, 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.. |
| 51. | Hajime Miki, Tsuyoshi Hirajima, Kazunori Oka, Keiko Sasaki, The development of fine microgram powder electrode system and its application in the analysis of chalcopyrite leaching behavior, Minerals, 10.3390/min6040103, 6, 4, 2016.12, 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.. |
| 52. | Hajime Miki, Three leading program joint field work, Evergreen, 3, 2, 68-69, 2016.12. |
| 53. | Yusei Masaki, Tsuyoshi Hirajima, Sasaki Keiko, Hajime Miki, Naoko Okibe, The Effect of Microbiological Redox Potential Control on Cu Extraction in the Chalcopyrite Bioleaching System, Proc. of International Symposium on Earth Science and Technology 2016, 2016.11. |
| 54. | Keishi Oyama, Tsuyoshi Hirajima, Sasaki Keiko, Hajime Miki, Naoko Okibe, Investigating Catalytic Effect of Silver on Bioleaching of Enargite Concentrate, Proc. of International Symposium on Earth Science and Technology 2016, 2016.11. |
| 55. | Taigen Masuyama, Tsuyoshi Hirajima, Hajime Miki, Gde Pandhe Wisnu Swantara, Ahmed Mohammed Elmardy, Sasaki Keiko, Microwave and Furnace Treatment of Sulfide Minerals, Proc. of International Symposium on Earth Science and Technology 2016, 2016.11. |
| 56. | Gde Pandhe Wisnu Swantara, Tsuyoshi Hirajima, Osamu Ichikawa, Hajime Miki, Sasaki Keiko, Ahmed Mohammed Elmardy, BUBBLE COLLISION AND ATTACHMENT ON CHALCOPYRITE AND MOLYBDENITE SURFACES, Proceedings of Copper2016 International Conference, 162-172, 2016.11. |
| 57. | Tsuyoshi Hirajima, Osamu Ichikawa, Hajime Miki, Sasaki Keiko, Gde Pandhe Wisnu Swantara, Ahmed Mohammed Elmardy, FLOATABILITY OF CHALCOPYRITE AND MOLYBDENITE IN MgCl2 SOLUTION, Proceedings of Copper2016 International Conference, 173-181, 2016.11. |
| 58. | Tsuyoshi Hirajima, Hidekazu Matsuoka, Hajime Miki, Sasaki Keiko, Yuji Imaizumi, APPLICATION OF OXIDATIVE TREATMENT ON SELECTIVE FLOTATION OF MOLYBDENITE AND CHALCOPYRITE, Proceedings of Copper2016 International Conference, 182-193, 2016.11. |
| 59. | Hajime Miki, Akinobu Iguchi, Tsuyoshi Hirajima, Sasaki Keiko, ENHANCED LEACHING OF ARSENIC CONTAINING COPPER SULFIDE WITH SILVER ADDITION IN ACID SOLUTION, Proceedings of Copper2016 International Conference, 1499-1510, 2016.11. |
| 60. | Keishi Oyama, Tsuyoshi Hirajima, Sasaki Keiko, Hajime Miki, Naoko Okibe, SELECTIVE BIOLEACHING OF ENARGITE (Cu3AsS4) OVER PYRITE (FeS2) FOR COPPER RECOVERY, Proceedings of Copper2016 International Conference, 1719-1723, 2016.11. |
| 61. | Yusei Masaki, Tsuyoshi Hirajima, Sasaki Keiko, Hajime Miki, Naoko Okibe, CHALCOPYRITE BIOLEACHING WITH REDOX POTENTIAL CONTROL, Proceedings of Copper2016 International Conference, 1724-1728, 2016.11. |
| 62. | Hajime Miki, Tsuyoshi Hirajima, Effect of Mg2+ and Ca2+ as divalent seawater cations on the floatability of molybdenite and chalcopyrite, MINERALS ENGINEERING, 10.1016/j.mineng.2016.06.023, 96-97, 83-93, 2016.10. |
| 63. | Gde Pandhe Wisnu Swantara, Tsuyoshi Hirajima, Ahmed Mohammed Elmardy, Hajime Miki, Sasaki Keiko, Effect of Kerosene on Bubble Interaction with Molybdenite and Chalcopyrite in MgCl2 Solution, Proceedings of IMPC 2016: XXVIII International Mineral Processing Congress, 2016.09. |
| 64. | Tsuyoshi Hirajima, Hidekazu Matsuoka, Hajime Miki, Gde Pandhe Wisnu Swantara, Ahmed Mohammed Elmardy, Sasaki Keiko, Comparison of Selective Flotation of Chalcopyrite and Molybdenite with Various Oxidation Techniques, Proceedings of IMPC 2016: XXVIII International Mineral Processing Congress, 2016.09. |
| 65. | Gde Pandhe Wisnu Suyantara, Tsuyoshi Hirajima, Ahmed Mohamed Elmahdy, Hajime Miki, Keiko Sasaki, Effect of kerosene emulsion in MgCl2 solution on the kinetics of bubble interactions with molybdenite and chalcopyrite, Colloids and Surfaces A: Physicochemical and Engineering Aspects, 10.1016/j.colsurfa.2016.04.039, 501, 98-113, 2016.07, 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.. |
| 66. | Hajime Miki, Akinobu Iguchi, Tsuyoshi Hirajima, Keiko Sasaki, Catalytic effect of silver on arsenic-containing copper sulfide dissolution in acidic solution, Hydrometallurgy, 10.1016/j.hydromet.2016.02.007, 162, 1-8, 2016.06, 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% copper was dissolved in 24 h at 0.750-0.850 V vs. the standard hydrogen electrode at 303 K.. |
| 67. | Keiko Sasaki, Kenta Toshiyuki, Keiko Ideta, Hajime Miki, Tsuyoshi Hirajima, Jin Miyawaki, Mitsuhiro Murayama, Ismaila Dabo, Removal mechanism of high concentration borate by co-precipitation with hydroxyapatite, Journal of Environmental Chemical Engineering, 10.1016/j.jece.2016.01.012, 4, 1, 1092-1101, 2016.03, 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.. |
| 68. | Hajime Miki, Sasaki Keiko, Tsuyoshi Hirajima, Removal mechanism of high concentration borate by co-precipitation with hydroxyapatite, Journal of Environmental Chemical Engineering, 10.1016/j.jece.2016.01.012, 4, 1, 1092-1101, 2016.01. |
| 69. | Tsuyoshi Hirajima, Gde Pandhe Wisnu Suyantara, Osamu Ichikawa, Ahmed Mohamed Elmahdy, Hajime Miki, Keiko Sasaki, Effect of Mg2+ and Ca2+ as divalent seawater cations on the floatability of molybdenite and chalcopyrite, Minerals Engineering, 10.1016/j.mineng.2016.06.023, 96-97, 83-93, 2016.01, 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.. |
| 70. | Tsuyoshi Hirajima, Hidekazu Matsuoka, Hajime Miki, Gde Pandhe Wisnu Suyantara, Ahmed Mohamed Elmahdy, Keiko Sasaki, Comparison of selective flotation of chalcopyrite and molybdenite with various oxidation techniques, 28th International Mineral Processing Congress, IMPC 2016 IMPC 2016 - 28th International Mineral Processing Congress, 2016.01, 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.. |
| 71. | Gde Pandhe Wisnu Suyantara, Tsuyoshi Hirajima, A. M. Elmahdy, Hajime Miki, Keiko Sasaki, Effect of kerosene on bubble interaction with molybdenite and chalcopyrite in MgCl2 solution, 28th International Mineral Processing Congress, IMPC 2016 IMPC 2016 - 28th International Mineral Processing Congress, 2016.01, 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.. |
| 72. | Mutia Dewi Yuniati, Keitaro Kitagawa, Tsuyoshi Hirajima, Hajime Miki, Naoko Okibe, Keiko Sasaki, Suppression of pyrite oxidation in acid mine drainage by carrier microencapsulation using liquid product of hydrothermal treatment of low-rank coal, and electrochemical behavior of resultant encapsulating coatings, Hydrometallurgy, 10.1016/j.hydromet.2015.09.028, 158, 83-93, 2015.12, 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.. |
| 73. | Tsuyoshi Hirajima, Hidekazu Matsuoka, Hajime Miki, Ahmed Mohammed Elmardy, Sasaki Keiko, Study of selective flotation of chalcopyrite and molybdenite with various oxidation techniques, Proceedings of Flotation'15, 2015.11. |
| 74. | Tsuyoshi Hirajima, Osamu Ichikawa, Gde Pandhe Wisnu Suyantara, Hajime Miki, Sasaki Keiko, Seawater divalent cations (MgCl2 and CaCl2) effect on the flotation of molybdenite and chalcopyrite, Proceedings of Flotation'15, 2015.11. |
| 75. | Hajime Miki, Review of three leading program joint fieldwork on 2014 at Beppu geothermal area, Proc. of International Forum for Green Asia 2015, Special Issue of Evergreen – Joint Journal of Novel Carbon Resource Sciences & Green Asia Strategy, 87-89, 2015.11. |
| 76. | Hajime Miki, Review of three leading program + Texas State University, joint fieldwork on 2015 at Okinoshima island, Proc. of International Forum for Green Asia 2015, Special Issue of Evergreen – Joint Journal of Novel Carbon Resource Sciences & Green Asia Strategy, 90-92, 2015.11. |
| 77. | Akinobu Iguchi, Hajime Miki, Tsuyoshi Hirajima, Sasaki Keiko, Effect of silver addition in potential controlled solution on dissolution rate of enargite, Proc. of International Symposium on Earth Science and Technology 2015, 85-97, 2015.11. |
| 78. | Hajime Miki, Sasaki Keiko, Tsuyoshi Hirajima, Hidekazu Matsuoka, Various surface treatment of molybdenite and chalcopyrite, Proc. of International Symposium on Earth Science and Technology 2015, 92-94, 2015.11. |
| 79. | Yusei Masaki, Tsuyoshi Hirajima, Sasaki Keiko, Hajime Miki, Naoko Okibe, Bioleaching of Highly Refractory Chalcopyrite in The Presence of Silver Catalyst, Proc. of International Symposium on Earth Science and Technology 2015, 189-190, 2015.11. |
| 80. | Keishi Oyama, Tsuyoshi Hirajima, Sasaki Keiko, Hajime Miki, Naoko Okibe, Selective bioleaching of enargite (Cu3AsS4) over pyrite (FeS2) for Cu recovery, Proc. of International Symposium on Earth Science and Technology 2015, 191-192, 2015.11. |
| 81. | Mutia Dewi Yuniati, Tsuyoshi Hirajima, Hajime Miki, Keiko Sasaki, Silicate covering layer on pyrite surface in the presence of siliconcatechol complex for acid mine drainage prevention, Materials Transactions, 10.2320/matertrans.M-M2015821, 56, 10, 1733-1741, 2015.10, 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.. |
| 82. | Mutia Dewi Yuniati, Tsuyoshi Hirajima, Hajime Miki, Keiko Sasaki, Silica Covering Layer on the Chalcopyrite Surface: Electrochemical Behaviors and Depression Effect on Copper-Molybdenum Flotation, Proceedings of International Symposium on Earth Science and Technology 2014, 108-111, 2014.12. |
| 83. | Hidekazu Matsuoka, Tsuyoshi Hirajima, Keiko Sasaki, Hajime Miki, Mitsuru Sawada, Electrochemical Treatment of Molybdenite and Chalcopyrite, Proceedings of International Symposium on Earth Science and Technology 2014, 320-321, 2014.12. |
| 84. | Akinobu Iguchi, Hajime Miki, Tsuyoshi Hirajima, Keiko Sasaki, Mitsuru Sawada, The Effect of Solution Potential and Silver Ion Addition on Dissolution Rate of Enargite, Proceedings of International Symposium on Earth Science and Technology 2014, 322-323, 2014.12. |
| 85. | Tsuyoshi Hirajima, Masanori Mori, Osamu Ichikawa, Keiko Sasaki, Hajime Miki, Mitsuru Sawada, Selective Flotation of Chalcopyrite and Molybdenite by surface oxidation, Proceedings of International Mineral Processing Congress (IMPC2014), 202-212, 2014.11. |
| 86. | Hajime Miki, Tsuyoshi Hirajima, Mutia Dewi Yuniati, Keiko Sasaki, Suppression of pyrite and arsenopyrite oxidation by silica coating: Electrochemical aspects and the mechanism, Proceedings of International Mineral Processing Congress (IMPC2014), 101-110, 2014.11. |
| 87. | Hajime Miki, Sasaki Keiko, Tsuyoshi Hirajima, Osamu Ichikawa, Masanori Mori, Selective flotation of chalcopyrite and molybdenite with plasma pre-treatment, MINERALS ENGINEERING, 10.1016/j.mineng.2014.07.011, 66-68, 102-111, 2014.11. |
| 88. | Hisaya Tsuji, Pilasinee Limsuwan, Tsuyoshi Hirajima, Keiko Sasaki, Hajime Miki, Satoshi Kumagai, Recovery of Furfural Produced by Hydrothermal Treatment with Biomass Charcoal, International Journal of Environment, 4, 1, 11-17, 2014.06. |
| 89. | Hajime Miki, Gamni Senanayake, Sophie Wheatley, Silica and sodium chloride assisted leaching of chalcopyrite, Proceeding of Hydrometallurgy 2014, 1, 211-224, 2014.06. |
| 90. | Osamu Ichikawa, Tsuyoshi Hirajima, Masanori Mori, Keiko Sasaki, Hajime Miki, Mitsuru Sawada, XPS and AFM Analysis of Plasma Oxidized Chalcopyrite and Molybdenite for New Selective Flotation Technique, Proceedings of International Conference on Biological, Civil and Environmental Engineering (BCEE-2014), 2014.03. |
| 91. | Tsuyoshi Hirajima, Masanori Mori, Osamu Ichikawa, Keiko Sasaki, Hajime Miki, Mohsen Farahat, Mitsuru Sawada, Selective flotation of chalcopyrite and molybdenite with plasma pre-treatment, Minerals Engineering, 10.1016/j.mineng.2014.07.011, 66, 102-111, 2014.01, 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.. |
| 92. | Hajime Miki, Tsuyoshi Hirajima, Mutia Dewi Yuniati, Keiko Sasaki, Study of Silicate Coating on Pyrite Oxidation Suppression: Fundamental Mechanism and Kinetic Analysis, Proceedings of International Symposium on Earth Science and Technology 2013, 189-192, 2013.12. |
| 93. | Mutia Dewi Yuniati, Tsuyoshi Hirajima, Hajime Miki, Keiko Sasaki, Electrochemical Study of Silicate Coating on Sulphide Minerals Oxidation Suppression, Proceedings of International Symposium on Earth Science and Technology 2013, 193-196, 2013.12. |
| 94. | Masanori Mori, Tsuyoshi Hirajima, Osamu Ichikawa, Keiko Sasaki, Hajime Miki, Mitsuru Sawada, Floatability Modification of Chalcopyrite and Molybdenite with Plasma Treatment, Proceedings of International Symposium on Earth Science and Technology 2013, 372-375, 2013.12. |
| 95. | Osamu Ichikawa, Tsuyoshi Hirajima, Masanori Mori, Keiko Sasaki, Hajime Miki, Mitsuru Sawada, Surfaces Characterization of Plasma Treated Chalcopyrite and Molybdenite, Proceedings of International Symposium on Earth Science and Technology 2013, 376-379, 2013.12. |
| 96. | Hajime Miki, Tsuyoshi Hirajima, Mutia Dewi Yuniati, Keiko Sasaki, Suppression of Pyrite Oxidation by Silicate Coating with Catechol Complex Oxidation Kinetics Estimation with Electrochemistry, The 12th International Symposium on East Asian Resources Recycling Technology, 601-604, 2013.11. |
| 97. | Tsuyoshi Hirajima, Masanori Mori, Osamu Ichikawa, Keiko Sasaki, Hajime Miki, Mitsuru Sawada, Selective Flotation of Chalcopyrite and Molybdenite with Plasma Pre-treatment, Proceedings of Flotation '13, 2013.11. |
| 98. | Hisaya Tsuji, Satoshi Kumagai, Pilasnee Limsuwan, Tsuyoshi Hirajima, Keiko Sasaki, Hajime Miki, Hydrothermal Treatment of Coconut Shell and Recovery of Furfural, Proceedings of International Conference on Green Energy and Technology, 172-175, 2013.08. |
| 99. | Michael Nicol, Hajime Miki, Petrus Basson, The effects of sulphate ions and temperature on the leaching of pyrite. 2. Dissolution rates, Hydrometallurgy, 10.1016/j.hydromet.2013.01.009, 133, 182-187, 2013.02, 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% 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.. |
| 100. | Michael J. Nicol, Hajime Miki, Suchun Zhang, Petrus Basson, The effects of sulphate ions and temperature on the leaching of pyrite. 1. Electrochemistry, Hydrometallurgy, 10.1016/j.hydromet.2013.01.010, 133, 188-196, 2013.01, 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.. |
| 101. | Michael James Nicol, Hajime Miki, Derick Rautenbach, Lilian Velasquez, C Buuren, The Development of Heap Leaching Based on Chloride for Primary and Secondary Copper Minerals, Proceedings of Percolation Leaching: The status globally and in Southern Africa 2011, 5, 2011.06. |
| 102. | Hajime Miki, Michael Nicol, The dissolution of chalcopyrite in chloride solutions. IV. the kinetics of the auto-oxidation of copper(I), Hydrometallurgy, 10.1016/j.hydromet.2010.10.009, 105, 3-4, 246-250, 2011.01, 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.. |
| 103. | Hajime Miki, Michael Nicol, Lilian Velásquez-Yévenes, The kinetics of dissolution of synthetic covellite, chalcocite and digenite in dilute chloride solutions at ambient temperatures, Hydrometallurgy, 10.1016/j.hydromet.2010.11.004, 105, 3-4, 321-327, 2011.01, 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% 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% and 45% 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.. |
| 104. | Petrus Basson, Hajime Miki, Michael James Nicol, Lilian Velasquez, Enhanced Leaching of Chalcopyrite at Low Potentials in Chloride Solutions. 2. Mechanism, Proceedings of 7th Copper2010 International Conference, 5, 1753-1770, 2010.06. |
| 105. | Petrus Basson, Hajime Miki, Michael James Nicol, Lilian Velasquez, Enhanced Leaching of Chalcopyrite at Low Potentials in Chloride Solutions. 1. Concentrates, Proceedings of 7th Copper2010 International Conference, 5, 1737-1752, 2010.06. |
| 106. | Lilian Velásquez-Yévenes, Michael Nicol, Hajime Miki, The dissolution of chalcopyrite in chloride solutions Part 1. the effect of solution potential, Hydrometallurgy, 10.1016/j.hydromet.2010.03.001, 103, 1-4, 108-113, 2010.06, 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 ( |
| 107. | Lilian Velásquez Yévenes, Hajime Miki, Michael Nicol, The dissolution of chalcopyrite in chloride solutions Part 2: Effect of various parameters on the rate, Hydrometallurgy, 10.1016/j.hydromet.2010.03.004, 103, 1-4, 80-85, 2010.06, 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% 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.. |
| 108. | Michael Nicol, Hajime Miki, Lilian Velásquez-Yévenes, The dissolution of chalcopyrite in chloride solutions Part 3. Mechanisms, Hydrometallurgy, 10.1016/j.hydromet.2010.03.003, 103, 1-4, 86-95, 2010.06, 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.. |
| 109. | Hajime Miki, Michael Nicol, The kinetics of the oxidation of iron(II) by chlorate in the leaching of uranium ores, Hydrometallurgy, 10.1016/j.hydromet.2009.10.001, 100, 1-2, 47-49, 2009.01, 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.. |
| 110. | Hajime Miki, Michael James Nicol, The kinetics of the copper-catalysed oxidation of iron(II) in chloride solutions, Hydrometallurgy 2008, Proceedings of 6th International Symposium, 971-979, 2008.10. |
| 111. | Hajime Miki, Michael James Nicol, Synergism in the oxidation of covellite and pyrite by iron(III) and copper(II) ions in chloride solutions, Hydrometallurgy 2008, Proceedings of 6th International Symposium, 646-652, 2008.10. |
| 112. | N. Hiroyoshi, S. Kuroiwa, Hajime Miki, M. Tsunekawa, Tsuyoshi Hirajima, Effects of coexisting metal ions on the redox potential dependence of chalcopyrite leaching in sulfuric acid solutions, Hydrometallurgy, 10.1016/j.hydromet.2006.07.006, 87, 1-2, 1-10, 2007.06, 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.. |
| 113. | Michael James Nicol, Hajime Miki, Applications of the Electrochemistry of Fine Mineral Sulfides, Innovations in Natural Resource Processing, Proceedings of the Jan D. Miller Symposium, 1, 179-192, 2005.02. |
| 114. | Naoki Hiroyoshi, Shigeto Kuroiwa, Hajime Miki, Masami Tsunekawa, Tsuyoshi Hirajima, Synergistic effect of cupric and ferrous ions on active-passive behavior in anodic dissolution of chalcopyrite in sulfuric acid solutions, Hydrometallurgy, 10.1016/j.hydromet.2004.01.003, 74, 1-2, 103-116, 2004.08, 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.. |
| 115. | Hajime Miki, Naoki Hiroyoshi, Shigeto Kuroiwa, Masami Tsunekawa, Tsuyoshi Hirajima, Mechanisms of Catalytic Leaching of Chalcopyrite, Proceedings of 5th Copper2003-Cobre2003 International Conference, 6, 383-394, 2003.10. |
| 116. | Naoki Hiroyoshi, Masatoshi Arai, Hajime Miki, Masami Tsunekawa, Tsuyoshi Hirajima, A new reaction model for the catalytic effect of silver ions on chalcopyrite leaching in sulfuric acid solutions, Hydrometallurgy, 10.1016/S0304-386X(01)00228-6, 63, 3, 257-267, 2002.03, 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.. |
| 117. | Naoki Hiroyoshi, Hajime Miki, Tsuyoshi Hirajima, Masami Tsunekawa, Enhancement of chalcopyrite leaching by ferrous ions in acidic ferric sulfate solutions, Hydrometallurgy, 10.1016/S0304-386X(00)00155-9, 60, 3, 185-197, 2001.05, 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.. |
| 118. | Naoki Hiroyoshi, Hajime Miki, Tsuyoshi Hirajima, Masami Tsunekawa, Model for ferrous-promoted chalcopyrite leaching, Hydrometallurgy, 10.1016/S0304-386X(00)00089-X, 57, 1, 31-38, 2000.01, 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.. |
| 119. | Naoki Hiroyoshi, Hajime Miki, Tsuyoshi Hirajima, Masami Tsunekawa, Ferrous Promoted Chalcopyrite Leaching, Proceedings of 4th Copper1999-Cobre1999 International Conference, 4, 231-243, 1999.10. |
| 120. | 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.. |
| 121. | Naoki Hiroyoshi, Hajime Miki, Tsuyoshi Hirajima, Masami Tsunekawa, Effect of Several Inhibitors to Thiobacillus ferrooxidans on Ferrous Promoted Chalcopyrite Leaching, Journal of MMIJ, 115, 172-176, 1999.03. |
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