| 1. |
Keishi Oyama, Tsuyoshi Hirajima, Keiko Sasaki, Hajime Miki, Naoko Okibe, Mechanism of silver-catalyzed bioleaching of enargite concentrate, Solid State Phenomena, 10.4028/www.scientific.net/SSP.262.273, 262 SSP, 273-276, 2017.08, 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 Cu 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 (Ag AsS ) was detected by XRD and EPMA, covering the surface of enargite particles. An intermediate layer, consisting of (Cu,Ag) AsS , 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. 2 3 4 3 4. |
| 2. |
佐藤 啓太, 小山 恵史, 小板 丈敏, 久保田 明紀子, 所 千晴, 接着接合の易解体における浸漬前処理の有効性評価, 環境資源工学, 70, 2, 65-72, 2024.02. |
| 3. |
Keishi Oyama, Kazuhiko Shimada, Jun-ichiro Ishibashi, Hajime Miki, Naoko Okib, 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 degrees 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 E-ox (Cu2S) |
| 4. |
Keishi Oyama, Kazuhiko Shimada, Jun-ichiro 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 degrees 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 (E-h) for solubilization. However, the dissolution of co-existing pyrite, which also favors high E-h, immediately hindered enargite dissolution through the passivation effect. The surface of activated carbon functioned as an electron mediator to couple RISCs oxidation and Fe3+ reduction, so that elevation of the E-h level was controlled by offsetting microbial Fe3+ regeneration. As long as the E-h level was suppressed at |
| 5. |
Keishi Oyama, Applicability estimation of bioleaching into copper mining industry: Comparison between mining-developed and developing countries, Evergreen, 7, 2, 195-201, 2020.06, Chile and Indonesia, as a mining-developed country and a mining-developing country, respectively, are compared to estimate the future applicability of bioleaching technique into real operation. Chilean copper industry has improved via the following steps: (i) domination by foreign capitals, (ii) resource nationalization, (Chilenization), (iii) lost competitiveness due to the decrease in the ore-grade, (iv) the invitation of foreign capitals to regain the competitiveness. Indonesia takes the same path and it was easily predicted that Indonesian copper mining industry is also likely to loose the competitiveness due to the decrease in ore-grade. Therefore, the installation of bioleaching would be proposed for further development of Indonesian copper industry.. |
| 6. |
Keishi Oyama, Kyohei Takamatsu, Kaito Hayashi, Yuji Aoki, Shigeto Kuroiwa, Tsuyoshi Hirajima, Naoko Okibe, Carbon-Assisted Bioleaching of Chalcopyrite and Three Chalcopyrite/Enargite-Bearing Complex Concentrates, MINERALS, 10.3390/min11040432, 11, 4, 2021.04, Overcoming the slow-leaching kinetics of refractory primary copper sulfides is crucial to secure future copper sources. Here, the effect of carbon was investigated as a catalyst for a bioleaching reaction. First, the mechanism of carbon-assisted bioleaching was elucidated using the model chalcopyrite mineral, under specified low-redox potentials, by considering the concept of E-normal. The carbon catalyst effectively controlled the E-h level in bioleaching liquors, which would otherwise exceed its optimal range (0 |
| 7. |
Naoko Okibe, Kaito Hayashi, Keishi Oyama, Kazuhiko Shimada, Yuji Aoki, Takahiro Suwa, Tsuyoshi Hirajima, Bioleaching of Enargite/Pyrite-rich "Dirty" Concentrate and Arsenic Immobilization, MINERALS, 10.3390/min12040449, 12, 4, 2022.04, Bioleaching of arsenic (As)-rich, so-called "dirty" concentrates can produce additional Cu value from the flotation waste while simultaneously releasing toxic As. This study bioleached three such concentrates of varying pyrite/enargite ratios ([Py]/[Ena] = 0.7, 1.3 and 2.4) at a pulp density of 20%. The dissolution behavior of Cu and As in relation to the solution redox potential (Eh) was studied with and without activated carbon (AC) as a potential Eh-controlling catalyst. At this high pulp density, Eh was naturally suppressed, without a need for AC dosing, to |
| 8. |
岩井 久典, 石井 駿, 小山 恵史, 淵田 茂司, 横田 尚樹, 高橋 優子, 所 千晴, 酸性触媒廃液からの硫化物法によるNi回収プロセスと硫化沈殿物の化学特性, 粉体工学会誌, 10.4164/sptj.60.600, 60, 10, 600-606, 2023.10. |
| 9. |
辰本拓也, 綱澤有輝, 小板丈敏, 高谷雄太郎, 小山恵史, 所千晴, 衝撃試験とD E M シミュレーションによる電子スクラップの単体分離機構の考察, Journal of MMIJ, 10.2473/journalofmmij.139.52, 139, 11_12, 52-62, 2023.12. |
| 10. |
Juan Qin, Yeting Fang, Jian Shi, Chiharu Tokoro, Mauricio Córdova-Udaeta, Keishi Oyama, Juncheng Zhang, Waste-Based Ceramsite for the Efficient Removal of Ciprofloxacin in Aqueous Solutions, International Journal of Environmental Research and Public Health, 10.3390/ijerph20065042, 20, 6, 5042-5042, 2023.03, Ciprofloxacin (CIP), a compound with bioaccumulation toxicity and antibiotic resistance, is frequently detected in water at alarming concentrations, which is becoming an increasing concern. In this study, a low-cost ceramsite was developed from industrial solid wastes through sintering to remove CIP from wastewater. The effects of adsorbent dosage, initial pH, contact time, initial CIP concentration, and temperature were explored. More than 99% of CIP (20–60 mg/L) was removed at around pH 2–4 by the ceramsite. The kinetic data fitted well with the pseudo-second-order model, revealing that chemisorption was the main rate-determining step. The isotherm data was better described by the Freundlich model, suggesting that CIP was removed by the formation of multiple layers on the heterogeneous surface. Moreover, the removal efficiency was practically higher than 95% during five regeneration cycles, when different regeneration methods were used, including calcination, HCl, and NaOH washing, indicating that the ceramsite exhibited outstanding reusability in removing CIP. The primary mechanism of CIP removal by the ceramsite was found to be the synergism of adsorption and flocculation, both of which depended on the release of Ca2+ from the ceramsite. In addition, strong Ca-CIP complexes could be formed through surface complexation and metal cation bridging between Ca2+ and different functional groups in CIP.. |
| 11. |
Jifeng Xue, Keishi Oyama, Shigeshi Fuchida, Chiharu Tokoro, Improving Flotation Separation of Mg(OH)2-Depressed Chalcopyrite and Pyrite by EDTA Modification: A Promising Method for Sustainable Cu Production, Journal of Sustainable Metallurgy, 10.1007/s40831-023-00754-6, 2023.10. |
| 12. |
Juan Qin, Sujuan Yuan, Mauricio Córdova-Udaeta, Keishi Oyama, Chiharu Tokoro, Highly Efficient Cd2+ Removal Using Tobermorite with pH Self-Adjustment Ability from Aqueous Solution, Materials, 10.3390/ma16031314, 16, 3, 1314-1314, 2023.02, Cadmium (Cd), as a type of heavy metal, can increase the incidence of many diseases, even in low concentrations. In this study, tobermorite was hydrothermally synthesized and then applied to adsorb Cd2+ from an aqueous solution. The physicochemical characteristics of the synthesized tobermorite were detected, and the results indicated that the well-crystallized tobermorite had a lot of mesopores and a large specific surface area of 140.92 m2/g. It acquired a pH self-adjustment ability via spontaneously releasing Ca2+ and OH- into the aqueous solution. The effects of different factors on Cd2+ removal were investigated. For Cd2+, the removal efficiency could reach 99.71% and the maximum adsorption capacity was 39.18 mg/g using tobermorite. The adsorption data was best fitted with the pseudo-second-order kinetic and Langmuir isotherm models. In addition, there was no strict limit on the solution pH in Cd2+ adsorption because the tobermorite could adjust the solution pH to an alkaline atmosphere spontaneously. The efficient removal of Cd2+ using tobermorite was a result of surface complexation and ion exchange.. |
| 13. |
Keishi Oyama, Kentaro Hayashi, Yusei Masaki, Takaya Hamai, Shigeshi Fuchida, Yutaro Takaya, Chiharu Tokoro, Geochemical Modeling of Heavy Metal Removal from Acid Mine Drainage in an Ethanol-Supplemented Sulfate-Reducing Column Test, Materials, 10.3390/ma16030928, 16, 3, 928-928, 2023.01, A passive treatment process using sulfate-reducing bacteria (SRB) is known to be effective in removing heavy metals from acid mine drainage (AMD), though there has been little discussion of the mechanism involved to date. In this work, a sulfate-reducing column test was carried out using supplementary ethanol as an electron donor for microorganisms, and the reaction mechanism was examined using geochemical modeling and X-ray absorption fine structure (XAFS) analysis. The results showed that Cu was readily removed from the AMD on the top surface of the column (0–0.2 m), while Zn and Cd depletion was initiated in the middle of the column (0.2–0.4 m), where sulfide formation by SRB became noticeable. Calculations by a developed geochemical model suggested that ethanol decomposition by aerobic microbes contributed to the reduction of Cu, while sulfide produced by SRB was the major cause of Zn and Cd removal. XAFS analysis of column residue detected ZnS, ZnSO4 (ZnS oxidized by atmospheric exposure during the drying process), and CuCO3, thus confirming the validity of the developed geochemical model. Based on these results, the application of the constructed geochemical model to AMD treatment with SRB could be a useful approach in predicting the behavior of heavy metal removal.. |
| 14. |
Taketoshi Koita, Yoshiki Egawa, Yutaro Takaya, Keishi Oyama, Soowon Lim, Takao Namihira, Chiharu Tokoro, Comparison of size distributions of recovered particles generated from Ag wire in air by pulsed wire discharge and electric explosion of wire methods, Advanced Powder Technology, 10.1016/j.apt.2023.104227, 34, 11, 104227-104227, 2023.11. |
| 15. |
Keishi Oyama, Shun Ishii, Shigeshi Fuchida, Chiharu Tokoro, Chemical stability of Hg-adsorbed pyrite under different pH and redox conditions: A fundamental study for stable management of Hg-bearing wastes, Journal of Environmental Chemical Engineering, 10.1016/j.jece.2024.112053, 112053-112053, 2024.01. |
| 16. |
Yusuf Olalekan Zubair, Shigeshi Fuchida, Keishi Oyama, Chiharu Tokoro, Morphologically controlled synthesis of MgFe-LDH using MgO and succinic acid for enhanced arsenic adsorption: Kinetics, equilibrium, and mechanism studies, Journal of Environmental Sciences, 10.1016/j.jes.2024.01.049, 148, 637-649, 2025.02. |
