| 研究実績の概要 |
(1)Precious metal dissolution from PCB using the novel thiourea bioleaching (TU-bioleaching) method: The potential utility of microbiologically-mediated thiourea leaching of Au was clarified for the first time, with a special focus on reducing the reagents consumption while facilitating Au dissolution. The Eh level during the reaction was first optimized by fluctuating the initial ratio of thiourea to Fe3+. The ratio precisely determined the Eh level during the TU-bioleaching and dictated the fate of thiourea decomposition and the resultant Au dissolution from PCB. Microbial contribution to Fe3+ regeneration was seen to support steady and continuous Au dissolution, enabling 98% Au dissolution while using low reagent concentrations under the microbial Eh control at around 490-545 mV. This novel TU-bioleaching process offers a new alternative approach for Au recycling from e-wastes and minimization of environmental hazards. (2)Precious metal bionanoparticles production: The acidophilic Fe(III)-reducing bacteria were successfully used for intracellular gold recovery as bio-AuNPs from highly acidic Au(III) solutions via a simple one-step reaction. It was possible to control the size of bio-AuNPs by modifying the e-donor concentration combined with a use of enzyme inhibitor: bio-AuNPs of 48 nm, 26 nm, or 13 nm. (3)Recovery of rare-earth elements from spent catalyst: By optimizing the microbial growth conditions, it was shown effective to utilize biogenic organic acids for leaching of rare earth elements such as Lanthanum (La) from spent catalysts.
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