Multiple laccase-mediator system treatments for carbonaceous matter degradation in double refractory gold ore

Abstract

Double refractory gold ore contains a higher level of gold than general ore but has been ignored in industry due to economic reasons. To improve gold recovery from double refractory gold ore (DRGO), the sulfides must be oxidized to release gold grains and the carbonaceous matter must be degraded to minimize “preg-robbing” during cyanidation. Recently, the degradation of carbonaceous matter in DRGO by enzymatic reactions has gained extensive interest owing to its environmental friendliness. Reportedly, laccase using 1-hydroxybenzotriazole hydrate (HBT) as an electron mediator can improve gold extraction from DRGO. In the present study, multiple-divided additions of the laccase-mediator system (LMS) are performed to maintain the enzyme activity, thus resulting in an improvement of gold extraction to 86.1%, compared with performing single addition with the same final dose, which yields a gold extraction of only 67.0%. However, multiple-divided additions of a higher dose of LMS decrease the gold extraction. The total dose of laccase is optimized to 11.87 U/100 mL of 5.0 g pretreated DRGO with a C content of 5.2%. These interesting results are comprehensively interpreted by combining different characterization methods for natural carbonaceous matter, including thermogravimetry-differential thermal analysis, Raman spectroscopy, and three-dimensional fluorescence spectrometry. This LMS proposed represents a novel approach worthy of further attention, especially in understanding carbon science in hydrometallurgy.