Carbon-in-Leach Gold Recovery from Fungi-treated Carbonaceous Ore: Effect of Entrained Biomass on Activity of Activated Carbon

The ability of the fungus, Phanerochaete chrysosporium to reduce preg-robbing of carbonaceous matter (CM) in gold ores has been confirmed by many researchers, and studies are ongoing to minimize the effect of entrained biomass on subsequent gold leaching and adsorption processes. This paper presents a study on gold extraction from surrogate carbonaceous gold ore (CGO), and fungal-treated CGO to ascertain the influence of entrained biomass on the downstream carbon-in-leach (CIL) process. The surrogate CGO was prepared by adding 3% anthracite-grade CM to free-milling gold ore (FGO). The main minerals in the FGO were quartz, feldspar, and sericite, with 8.4 g/t gold, 0.18% sulphide sulphur, and 0.06% organic carbon. Aside from biotreatment of the CGO with cell-free liquor of P. chrysosporium, anthracite and activated carbon (AC) were also contacted with P. chrysosporium to confirm the direct effect of biomass on the CMs’ ability to preg-rob aurocyanide. Preg-robbing effect of the as-received anthracite and AC were 95% and 80% respectively, and these reduced to 81% and 13% respectively. Water-washing, acid-washing, and alkaline-washing of the treated CMs returned respective preg-robbing effects of 88%, 92%, and 85% for AC and 32%, 38%, and 28% for anthracite. Scanning electron microscopy and Raman spectroscopy of anthracite revealed a decrease in the degree of orderliness in the structure required for gold adsorption. The FGO and the prepared CGO gave cyanidation gold recoveries of 94.5% and 54.8% respectively. Following cell-free treatment of the CGO, direct cyanidation recorded 88.3% solution recovery, which was increased to 91.3% in CIL. The overall recovery onto activated carbon in CIL was 81%, which improved to 82% and 85% respectively after washing the fungal-treated CGO with water.