Kyushu University Academic Staff Educational and Research Activities Database
List of Presentations
Hajime Miki Last modified date:2023.06.28

Associate Professor / Frontier Education Center for Global Cooperation in Earth Resources Engineering / Department of Earth Resources Engineering / Faculty of Engineering


Presentations
1. 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, The 16th International Symposium on East Asian Resources Recycling Technology, (EARTH2021), 2021.11.
2. Y. TANAKA, T. HIRAJIMA, H. MIKI, G.P.W. SUYANTARA, Estimation of Cu and Mo recoveries of five type ores composite in seawater flotation, Copper2022 International Conference, 2022.11.
3. 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, Copper2022 International Conference, 2022.11.
4. 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, Copper2022 International Conference, 2022.11.
5. 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, Copper2022 International Conference, 2022.11, Electrochemistry with powder sample is essential for hydrometallurgy since in many case sample can obtain only with powder form such as ground mineral or precipitations. However, powder electrode system is not well developed since it is difficult to obtain reproducibility and sensitivity with current carbon paste electrode. Authors has developed its well sensitivity and reproducibility with relative simple method for powder sample electrode. This system yields highly reproducible results and is sensitive compared with conventional electrode systems for various sulfide minerals. Authors estimate this method to apply oxidation behavior on various sulfide minerals. These results can be utilized with sulfide oxidation leaching or mineral processing method. From this method, results of various primary copper sulfide and secondary sulfide minerals will be indicated and reaction model will be discussed on this research..
6. 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, International Symposium on Earth Science and Technology 2020, 2020.11.
7. Suyantara Gde Pandhe Wisnu、Hirajima Tsuyoshi、Orii Yuta、Miki Hajime、Sasaki Keiko、Kuroiwa Shigeto、Aoki Yuji, Effect of a sulfite reagent on floatability of chalcopyrite and enargite, IMPC 2020:XXX International Mineral Processing Congress, 2020.10.
8. Tanaka Yoshiyuki、Miki Hajime、Suyantara Gde Pandhe Wisnu、Hirajima Tsuyoshi、Aoki Yuji、Okamoto Hideyuki, Effect of seawater and process water on copper-molybdenum rougher flotation in batch and pilot test, IMPC 2020:XXX International Mineral Processing Congress, 2020.10.
9. Miki Hajime、Hirajima Tsuyoshi、Suyantara Gde Pandhe Wisnu、Orii Yuta、Sasaki Keiko、Kuroiwa Shigeto、Aoki Yuji, Selective flotation for removal of impurities on copper concentrates with various redox reactions, IMPC 2020:XXX International Mineral Processing Congress, 2020.10.
10. Yuta Orii, Gde Pandhe Wisnu Suyantara, Hajime Miki, Keiko Sasaki, Tsuyoshi Hirajima, Shigeto Kuroiwa, Yuji Aoki, Study of selective flotation of copper sulfide and As containing copper minerals, International Symposium on Earth Science and Technology 2019, 2019.11.
11. Gde Pandhe Wisnu Suyantara, Tsuyoshi Hirajima, Hajime Miki, Keiko Sasaki, Shigeto Kuroiwa, Yuji Aoki, Effect of hydrogen peroxide on the separation of copper sulfide minerals and arsenic-bearing copper minerals using flotation, Flotation'19 International Conference, 2019.10.
12. Gde Pandhe Wisnu Suyantara, Tsuyoshi Hirajima, Hajime Miki, Keiko Sasaki, Shigeto Kuroiwa, Yuji Aoki, Effect of seawater on bubble interactions with chalcopyrite and molybdenite surfaces, Flotation'19 International Conference, 2019.10.
13. Hajime Miki, Tsuyoshi Hirajima, Gde Pandhe Wisnu Suyantara, Keiko Sasaki, Selective Flotation on Chalcopyrite and Molybdenite with Various Redox Reactions, The 15th Internatonal Symposium on East Asian Resources Recycling Technology, 2019.09.
14. Gde Pandhe Wisnu Suyantara, Tsuyoshi Hirajima, Hajime Miki, Keiko Sasaki, Masashi Yamane, Eri Takida, Shigeto Kuroiwa, Yuji Imaizumi, Mitsuru Sawada, Separation of molybdenite and chalcopyrite using various oxidation treatments, 10th Copper International Conference, 2019.08.
15. Hajime Miki, Tsuyoshi Hirajima, Gde Pandhe Wisnu Suyantara, Keiko Sasaki, Effect of Heating Treatment on Magnetic Properties, 10th Copper International Conference, 2019.08.
16. Oyama Keishi、Miki Hajime、Okibe Naoko, Evaluation of Catalytic Effect of Activated Carbon on Enargite Bioleaching
, International Symposium on Earth Science and Technology 2018, Fukuoka, Japan, 2018.11.
17. Takamatsu Kyohei、Oyama Keishi、Miki Hajime、Okibe Naoko, Carbon-assisted bioleaching of chalcopyrite concentrate, International Symposium on Earth Science and Technology 2018, Fukuoka, Japan, 2018.11.
18. Miki Hajime、Hirajima Tsuyoshi、Muta Yukihiro、Suyantara Gde、Sasaki Keiko, Investigation of reagents for selective flotation on chalcopyrite and molybdenite, XXIV International Mineral Processing Congress (IMPC 2018), Moscow, Russia, 2018.08.
19. Suyantara Gde Pandhe Wisnu、Hirajima Tsuyoshi、Miki Hajime、Sasaki Keiko, The use of Fenton’s reagent on selective flotation of chalcopyrite and molybdenite, XXIV International Mineral Processing Congress (IMPC 2018), Moscow, Russia, 2018.08.
20. Gde Pandhe Wisnu SUYANTARA, Tsuyoshi HIRAJIMA, Hajime MIKI, Keiko SASAKI, Effect of Seawater on Selective Flotation of Chalcopyrite and Molybdenite, International Symposium on Earth Science and Technology 2017 (CINEST), 2017.12.
21. Keishi Oyama, Haruki NOGUCHI, Tsuyoshi HIRAJIMA, Keiko SASAKI, Hajime MIKI, Naoko OKIBE, Catalytic Effect of Activated Carbon on Bioleaching of Enargite Concentrate, International Symposium on Earth Science and Technology 2017 (CINEST), 2017.12.
22. G.P.W. SUYANTARA, Tsuyoshi HIRAJIMA, Hajime MIKI, Keiko SASAKI, Study on the Effect of a Mixture of Hydrogen Peroxide and Ferrous Sulfate on the Floatability of Chalcopyrite and Molybdenite, Flotation ‘17, 2017.11.
23. Tsuyoshi HIRAJIMA, Hajime MIKI, Y. MUTA, G.P.W. SUYANTARA, Keiko SASAKI, Development of Alternative Additive of NaHS for Selective Flotation of Chalcopyrite and Molybdenite, Flotation ‘17, 2017.11.
24. Keishi OYAMA, Tsuyoshi HIRAJIMA, Keiko SASAKI, Hajime MIKI, Naoko OKIBE, Mechanism of Silver-Catalyzed Bioleaching of Enargite Concentrate, IBS 2017, 2017.09.
25. Tsuyoshi HIRAJIMA, Hajime MIKI, G.P.W. SUYANTARA, Hidekazu MATSUOKA, Keiko SASAKI, Oxidation of Chalcopyrite and Molybdenite with Hydrogen Peroxide and its Application to Their Separation, Fifth International conference on Multifunctional, Hybrid and Nanomaterials, 2017.03.
26. Keishi Oyama, Tsuyoshi Hirajima, Keiko Sasaki, Hajime Miki, Naoko Okibe, Mechanism of silver-catalyzed bioleaching of enargite concentrate, 22nd International Biohydrometallurgy Symposium, 2017, 2017.01, 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%) and Fe dissolved completely without silver sulfide, Cu recovery was greatly enhanced (96%) and Fe dissolution was suppressed (29%) in the presence of 0.04% silver sulfide. In the latter case, 52% of the solubilized As was re-immobilized, in contrast to only 14% As re-immobilization in the former. The silver-catalyzed bioleaching (at 0.04% 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..
27. 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, XXVIII International Mineral Processing Congress (IMPC 2016), 2016.10.
28. 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, XXVIII International Mineral Processing Congress (IMPC 2016), 2016.10.
29. Hidekazu MATSUOKA, Tsuyoshi Hirajima, Sasaki Keiko, Hajime Miki, Various Surface Treatment Techniques of Molybdenite and Chalcopyrite, International Symposium on Earth Science and Technology 2015 (CINEST), 2015.12.
30. Akinobu IGUCHI, Hajime Miki, Tsuyoshi Hirajima, Sasaki Keiko, Effect of Silver Addition in Potential Controlled Solution on Dissolution Rate of Enargite, International Symposium on Earth Science and Technology 2015 (CINEST), 2015.12.
31. Keishi OYAMA, Tsuyoshi Hirajima, Sasaki Keiko, Hajime Miki, Naoko Okibe, Selective Bioleaching of Enargite (Cu3AsS4) over Pyrite (FeS2) for Cu Recovery, International Symposium on Earth Science and Technology 2015 (CINEST), 2015.12.
32. Yusei MASAKI, Tsuyoshi Hirajima, Sasaki Keiko, Hajime Miki, Naoko Okibe, Bioleaching of Highly Refractory Chalcopyrite in The Presence of Silver Catalyst, International Symposium on Earth Science and Technology 2015 (CINEST), 2015.12.
33. Tsuyoshi Hirajima, Hidekazu MATSUOKA, Hajime Miki, Ahmed Mohamed Elmahdy Ahmed MOHAMED, Sasaki Keiko, Study of Selective Flotation of Chalcopyrite and Molybdenite with Various Oxidation, Flotation ‘15, 2015.11.
34. Tsuyoshi Hirajima, Osamu ICHIKAWA, G.P.W. SUYANTARA, Hajime Miki, Sasaki Keiko, Ahmed Mohamed Elmahdy Ahmed MOHAMED, Seawater Divalent Cations (MgCl2 and CaCl2) Effect on the Flotation of Molybdenite and Chalcopyrite, Flotation ‘15, 2015.11.
35. Hidekazu MATSUOKA, Tsuyoshi HIRAJIMA, Keiko SASAKI, Hajime MIKI, Mitsuru SAWADA, Electrochemical Treatment of Molybdenite and Chalcopyrite, International Symposium on Earth Science and Technology 2014 (CINEST), 2014.12.
36. 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, International Symposium on Earth Science and Technology 2014 (CINEST), 2014.12.
37. Akinobu IGUCHI, Hajime MIKI, Tsuyoshi HIRAJIMA, Keiko SASAKI, Mitsuru SAWADA, The Effect of Solution Potential and Silver Ion Addition on Dissolution Rate of Enargite, International Symposium on Earth Science and Technology 2014 (CINEST), 2014.12.
38. Tsuyoshi HIRAJIMA, Masanori MORI, Osamu ICHIKAWA, Keiko SASAKI, Hajime MIKI, Mitsuru SAWADA, Selective Flotation of Chalcopyrite and Molybdenite by Surface Oxidation, XXVII International Mineral Processing Congress (IMPC 2014), 2014.10.
39. Hajime MIKI, Tsuyoshi HIRAJIMA, Mutia Dewi YUNIATI, Keiko SASAKI, Suppression of Pyrite and Arsenopyrite Oxidation by Silica Coating: Electrochemical aspects and the mechanism, XXVII International Mineral Processing Congress (IMPC 2014), 2014.10.
40. 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, International Conference on Biological, Civil and Environmental Engineering (BCEE-2014), 2014.03.
41. Mutia Dewi Yuniati, 平島 剛, 三木 一, 笹木 圭子, シリカコーティングによる硫化鉱の酸化挙動, 資源・素材学会 春季大会, 2014.03.
42. Masanori Mori, Tsuyoshi Hirajima, Osamu Ichikawa, Keiko Sasaki, Hajime Miki, Mitsuru Sawada, Floatability Modification of Chalcopyrite and Molybdenite with Plasma Treatment, International Symposium on Earth Science and Technology 2013, 2013.12.
43. Osamu Ichikawa, Tsuyoshi Hirajima, Masanori Mori, Keiko Sasaki, Hajime Miki, Mitsuru Sawada, Surfaces Characterization of Plasma Treated Chalcopyrite and Molybdenite, International Symposium on Earth Science and Technology 2013, 2013.12.
44. Hajime Miki, Tsuyoshi Hirajima, Mutia Dewi Yuniati, Keiko Sasaki, Study of Silicate Coating on Pyrite Oxidation Suppression: Fundamental Mechanism and Kinetic Analysis, International Symposium on Earth Science and Technology 2013, 2013.12.
45. Mutia Dewi Yuniati, Tsuyoshi Hirajima, Hajime Miki, Keiko Sasaki, Electrochemical Study of Silicate Coating on Sulphide Minerals Oxidation, International Symposium on Earth Science and Technology 2013, 2013.12.
46. 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 Internatonal Symposium on East Asian Resources Recycling Technology, 2013.11, [URL].
47. Tsuyoshi Hirajima, Masanori Mori, Osamu Ichikawa, Keiko Sasaki, Hajime Miki, Mitsuru Sawada, Selective flotation of chalcopyrite and molybdenite with plasma pre-treatment, Flotation '13, 2013.11, [URL].
48. Hisaya Tsuji, Satoshi Kumagai, Pilasnee Limsuwan, 平島 剛, 笹木 圭子, 三木 一, Hydrothermal Treatment of Coconut Shell and Recovery of Furfural, International Conference on Green Energy and Technologies (ICGET), 2013.08.
49. Michael James Nicol, Hajime Miki, Derick Rautenbach, Craig van Buuren, Norma Hoyos, Lilian Velasquez, The Development of Heap Leaching Based on Chloride for Primary and Secondary Copper Minerals, Hydroprocess2012, 2012.07.
50. Hajime Miki, Michael James Nicol, Rautenbach Derick, Lilian Velasquez, Craig van Buuren, The Development of Heap Leaching Based on Chloride for Primary and Secondary Copper Minerals, Percolation Leaching: The status globally and in Southern Africa 2011, 2011.11.
51. Petrus Basson, Hajime Miki, Michael James Nicol, Lilian Velasquez, Enhanced Leaching of Chalcopyrite at Low Potentials in Chloride Solutions. 1. Concentrates, Copper2010 International Conference, 2010.06.
52. Petrus Basson, Hajime Miki, Michael James Nicol, Lilian Velasquez, Enhanced Leaching of Chalcopyrite at Low Potentials in Chloride Solutions. 1. Mechanisms, Copper2010 International Conference, 2010.06.
53. Hajime Miki, Michael James Nicol, The Kinetics of the Copper-catalysed Oxidation of Iron(II) in Chloride Solutions, Hydrometallurgy 2008, 2008.08.
54. Hajime Miki, Michael James Nicol, Synergism in the oxidation of covellite and pyrite in chloride solutions containing iron(III) and copper(II), Hydrometallurgy 2008, 2008.08.
55. Michael James Nicol, Hajime Miki, Applications of the electrochemistry of fine mineral sulfides, Innovations in Natural Resource Processing, 2005.02.
56. Hajime Miki, Naoki Hiroyoshi, Shigeto Kuroiwa, Masami Tsunekawa, Tsuyoshi Hirajima, Mechanisms of Catalytic Leaching of Chalcopyrite, Copper2003 International Conference, 2003.09.
57. Naoki Hiroyoshi, Hajime Miki, Tsuyoshi Hirajima, Masami Tsunekawa, Ferrous Promoted Chalcopyrite Leaching, Copper1999 International Conference, 1999.09.
58. Tsuyoshi Hirajima, Masanori Mori, Osamu Ichikawa, Keiko Sasaki, Hajime Miki, Mitsuru Sawada, Selective flotation of chalcopyrite and molybdenite by surface oxidation, 27th International Mineral Processing Congress, IMPC 2014, 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..
59. Hajime Miki, Michael Nicol, Synergism in the oxidation of covellite and pyrite by iron(III) and copper(II) ions in chloride solutions, Hydrometallurgy 2008: 6th International Symposium, 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..
60. Hajime Miki, Michael Nicol, The kinetics of the copper-catalysed oxidation of iron(II) in chloride solutions, Hydrometallurgy 2008: 6th International Symposium, 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..
61. Michael J. Nicol, Hajime Miki, Applications of the electrochemistry of fine mineral sulfides, Proceedings of the Jan D. Miller Symposium - Innovations in Natural Resource Processing, 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..
62. Naoki Hiroyoshi, Hajime Miki, Tsuyoshi Hirajima, Masami Tsunekawa, Ferrous promoted chalcopyrite leaching, Fourth International Conference COPPER 99 - COBRE 99, 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..