Enhancing the biotreatment of carbonaceous matter in double refractory gold ores: The impact of various mediators on laccase performance

Abstract

Despite their relatively higher Au content, double refractory gold ores (DRGOs) have not been developed for economic reasons, as Au grains are trapped by sulfides, and carbonaceous matter can adsorb Au(CN)₂⁻ during cyanidation. The enzymatic treatment of carbonaceous matter is gaining interest due to its eco-friendly benefits. The use of laccase, combined with an electron mediator, has been shown to enhance Au extraction from DRGOs. Although the effectiveness of mediators in improving lignin degradation has been reported, their significance in laccase-mediator system (LMS) treatment of DRGOs has yet to be thoroughly investigated. In this study, the mechanisms of various mediators in LMSs were investigated to improve Au extraction from DRGOs. To observe the degradation of the carbonaceous matter, thermogravimetry, Raman spectroscopy, three-dimensional fluorescence spectrometry, and CHN elemental analysis were utilized. The results demonstrated that the highest Au extraction was achieved after treatment with violuric acid monohydrate-mediated laccase, resulting in 92.9 ± 2.7 % Au extracted from DRGOs, which is equivalent to complete extraction when considering the 8.6 % Au locked in sulfides. The Langmuir model provided a better fit for the mediators' sorption than the Freundlich model, indicating that monolayer sorption is the predominant process in the mediators' adsorptions on pre-treated DRGOs. This proposed LMS represents a novel approach to enhancing our understanding of carbon science in biohydrometallurgy.