Decomposition of sulfides and carbonaceous matters in double refractory gold ores by fungal-released enzymes

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Double refractory gold ore containing gold-bearing sulfides and carbonaceous matter was sequentially treated with iron and sulfur oxidising archaea Acidianus brierleyi and lignin-degrading enzymes from Phanerochaete chrysosporium. This treatment resulted in an increase in gold recovery from 24% to 92%. Biooxidation of the sulfide minerals is already known, and therefore, the secondary focus, after improving the gold recovery, was characterising the carbonaceous matter. The transformation of the carbonaceous matter during the sequential treatment was investigated using QEMSCAN analysis, Raman and 3D fluorescence spectroscopy. The results show that the carbonaceous matter was initially hosted in illite, a silicate mineral, and the amount of carbon to illite affected the texture of the carbonaceous illite mineral. The enzymatic decomposition of the carbonaceous matter was found to be accelerated if the sample had undergone a prior treatment to decompose sulfide minerals. This is because the enzymes are susceptible to arsenic poisoning and therefore, the oxidative dissolution of arsenopyrite aided the enzymatic reaction. The lignin-degrading enzymes preferentially attacked the defects in the graphitic structure of carbonaceous matter and in the process, produced humic-like substances. The humic-like substances that are produced by the enzyme treatment acted as one of the binding agents in the agglomeration of the carbonaceous aluminosilicate residue (C-Si-Al). This new C-Si-Al was partially removed by alkaline washing step to improve gold recovery from DAC from 76% to 92%.