(Poster session & Short presentation) Environment & Recycling Group

[1105-25-11] [Student presentation: Master’s course]Improvement of gold extraction from double refractory gold ore by multiple laccase-mediator system treatments

○Cindy¹, Hirofumi Ichinose¹, Keiko Sasaki¹ (1. Kyushu University)

Chairman: Kazutoshi Haga (Akita University)

Keywords:laccase, carbonaceous matter, double refractory gold ore, enzymatic degradation, gold extraction

Sequential treatment of double refractory gold ore (DRGO) basically consists of the oxidative dissolution of sulfides and the degradation of carbonaceous matter prior to the extraction of gold. Environmentally friendly treatment of DRGO to degrade carbonaceous matter for improving gold extraction remains challenging. Recent studies showed that laccase showed several advantages over lignin peroxidase and manganese peroxidase, including higher stability, broader availability, easier handling, and shorter reaction time, so that laccase is more suitable for industrial application. In accompany with 1-hydroxybenzotriazole (HBT) as a mediator, laccase can degrade not only phenolic compounds, but also non-phenolic compounds. In this study, laccase-mediator system treatments were conducted by single, double, and quadruple additions, keeping the total laccase activity 152.6 U/L and mediator concentration 2 mM in all cases, within 7 days. The results revealed that multiple additions of laccase-mediator could enhance gold extraction compared to the single addition. In parallel, the activity of laccase and concentration of mediator were doubled (305.2 U/L and 4 mM) with twice additions, but the gold extraction was not improved. The three-dimensional fluorescence spectra for the alkaline washing solution of the solid residues after the above LMS treatments revealed that carbonaceous matter was degraded to smaller molecular sizes of humic substances and degraded more intensively by multiple additions of laccase-mediator. To improve the gold extraction after doubled laccase activity and mediator concentration with twice additions, some countermeasures should be taken.