Water Washing of Fungal-treated Carbonaceous Ores: Effect on Aurocyanide Adsorption by Activated Carbon in CIL Circuit

A typical challenge encountered on most gold processing plants during leaching of refractory ores is the reduction in recovery due to the presence of carbonaceous matter which preg-robs dissolved gold. To reduce preg-robbing during cyanidation, carbonaceous matter has to undergo pretreatment to passivate the active surface. The fungus, Phanerochaete chrysosporium has been shown to biotransform carbonaceous matter, thus reducing its ability to preg-rob gold. However, the possible transfer of entrained fungal biomass into Carbon-In-Leach (CIL) circuits has been reported to decrease the activity of activated carbon, and a proposed solution to this was to wash the fungal-treated material thoroughly with water before CIL operation. This paper therefore set out to assess the effect of water-washing on aurocyanide adsorption by activated carbon in CIL following fungal pretreatment of carbonaceous ores. To realise the objective, activated carbon was contacted with cell-free extract of P. chrysosporium under varying conditions of pH and time, after which it was washed with different volumes of water, and its gold-adsorption ability assessed.  The results revealed a decrease in the activity of activated carbon as a function of increasing contact time with the cell-free extract. The percentage decrease was higher after treatment in the acidic medium (13%) than the basic medium (9%). After washing the carbon (treated in acidic medium), gold adsorption was found to increase directly with the volume of water used from 64% at 0 mL to 84% at 500 mL and 91% at 1000 mL. Correspondingly, the carbon treated in basic medium recorded 69% at 0 mL to 87% at 500 mL and 93% at 1000 mL. This paper thus concludes that, sufficient water washing should be employed after fungal-biotransformation of refractory ores before CIL operation to decrease the effect of entrained biomass on the adsorption capacity of activated carbon. Keywords: Carbonaceous Gold Ore, Activated Carbon, Carbon-In-Leach, Cell-Free Extracts