(General session) Mineral processing / Environment / Recycling

[2K0401-14-01] [Student presentation: Master’s course] Effect of coexisting metallic ions on laccase activity for enzymatic degradation of carbonaceous matter in double refractory gold ores

○Cindy -¹, Diego M. Mendoza¹, Hirofumi Ichinose¹, Kojo T. Konadu¹, Keiko Sasaki¹ (1. Kyushu University)

司会：ドドビバ　ジョルジュ（東京大学）

Keywords:double refractory gold ores, carbonaceous matter, laccase, metallic ions, Au recovery

Mining industries find difficulties in processing double refractory gold ores (DRGO) because Au(CN)₂^- ions can be adsorbed on the carbonaceous matter decreasing the gold recovery in the cyanidation step, even though higher gold contents are observed in DRGO compared to common types of gold ores. For many years, several techniques have been challenged to extract the gold like roasting, but this process leads to air pollution with SO_x and As₂O₃. Recently, the environmentally friendly biodegradation of carbonaceous matter in DRGO has been developed using lignin-degrading enzymes like lignin peroxidase and Mn peroxidase. However, laccase can be an alternative, because of higher stability and wider availability, so that it is more suitable for industrial application of mineral processing. With the presence of a mediator, such as 2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), laccase can oxidize not only phenolic compounds, but also nonphenolic compounds in carbonaceous matter. Therefore, the purpose of the present work is to investigate the effects of AsO₃^3-, AsO₄^3-, Cu²⁺ and Fe³⁺, which are commonly coexisting metallic ions in DRGO, on laccase activity through stability and kinetic studies. Based on the values of the maximum velocity (V_max) and Michaelis-Menten constant (K_m), the heavy metal effects were categorized as either competitive, non-competitive, or uncompetitive inhibition. According to the fundamental results, the positive effect was confirmed by gold recovery after laccase treatment of real DRGO in the presence of the metallic ions.