2023 Fiscal Year Research-status Report
Environmentally friendly sequential treatments for gold extraction from double refractory gold ores
| Project/Area Number |
23KJ1718
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| Research Institution | Kyushu University |
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Principal Investigator |
CINDY 九州大学, 工学府, 特別研究員(DC1)
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| Project Period (FY) |
2023-04-25 – 2026-03-31
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| Keywords | Refractory gold ore / Carbonaceous matter / Laccase-mediator system / Sequential treatment / Enzymatic degradation / Au extraction |
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| Outline of Annual Research Achievements |
Double refractory gold ores (DRGOs), in which gold (Au(0)) is encapsulated in sulfide minerals with carbonaceous matter, has generally been abandoned for economic reasons, although it has a relatively higher Au content than other types of Au ores. To enhance Au extraction from DRGOs, sulfides must be dissolved to release locked Au grains, and carbonaceous matter must be degraded to reduce Au(CN)2- adsorption during cyanidation. Laccase, aided by a mediator in a laccase-mediator system (LMS), has been applied to degrade carbonaceous matter in DRGOs. In this study, to sustain enzyme activity over 7 days treatment, LMS was added in multiple divided doses with the same final concentration. Results show decreased Au(CN)2- adsorption, leading to improved Au extraction. Characterization of solid residues using thermogravimetry/differential thermal analysis, Raman spectroscopy, three-dimensional fluorescence spectrometry, and CHN elemental analysis observed carbonaceous matter degradation. In the case of the present DRGO, the total dose of laccase was optimized to 11.87 U/100 mL, divided into four additions to treat 5 g of FW containing 5.2% C. This LMS method offers a promising, environmentally friendly approach for further exploration, particularly in advancing our understanding of carbon science in biohydrometallurgy. Some parts of this work have been presented at conferences, leading to the receipt of the CINEST Award for Best Presentation at the International Symposium on Earth Science and Technology at Kyushu University, and the Young Researcher Award from MMIJ Kyushu.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
To increase the efficiency of the biotechnological process, the study began by focusing on replacing purified laccase with laccase extracted from agricultural waste. Some agricultural waste from mushroom species may be utilizable due to its wide availability. Laccase harvested from agricultural waste underwent enzyme activity assay and was then applied for degrading carbonaceous matter in double refractory gold ores. However, the biomass of the agricultural waste itself could passivate the ore's surface, thereby hindering Au extraction. Therefore, another approach involves optimizing the laccase-mediator system by adding it in multiple divided doses with the same final concentration, while investigating the effect of different mediators in the reaction.
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| Strategy for Future Research Activity |
Numerous natural and synthetic mediators have been identified, and laccases obtained from different mushrooms have been reported to interact differently with these mediators. According to the latest research findings, the only compound applied as a mediator in the laccase-mediator system (LMS) for the biodegradation of carbonaceous matter in double refractory gold ores (DRGOs) is 1-hydroxybenzotriazole hydrate (HBT). This study examines the effects of typical mediators, specifically HBT, 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid), 2,6-dimethoxyphenol, violuric acid, and guaiacol, in LMS on degrading the carbonaceous matter in DRGOs, thus improving the extraction of Au from DRGOs.
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| Causes of Carryover |
This year, I did not attend the MMIJ Fall and MMIJ Spring conferences, but I did attend MMIJ Kyushu, which was held at Kyushu University, so the allocated travel expenses were not used. The remaining grant amount will be allocated for the next international conference that I will attend in 2024, which is the International Biohydrometallurgy Symposium (IBS) in Canada, scheduled from August 19-22. Currently, flight prices are increasing, so I anticipate spending around 600,000 JPY (100,000 JPY higher than the expected amount) to give an oral presentation about my current research at this conference.
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