Fungal biotransformation of anthracite-grade carbonaceous matter: Effect on gold cyanide uptake

摘要

Carbonaceous matter ( CM) present in refractory carbonaceous gold ores adsorbs dissolved gold during cyanidation, leading to a decrease in gold recovery. In an on-going study the fungus Phanerochaete chrysosporium has been shown to reduce the gold adsorption ability of anthracite-grade CM by more than 90% in a mixture of millet and wheat bran medium. The present study thus focused on establishing the set of incubation parameters responsible for maximum reduction in gold adsorption by anthracite-grade CM. Anthracite coal was used as surrogate for CM, and the results indicate that P. chrysosporium deactivates anthracite within a wide range of time, pulp density, temperature, pH, and level of agitation. A processing time of 4 -7 days at pH 4 and 371 gave the best conditions. The best pulp densities for stationary and shake culturing respectively were 60% and 25% . Analyses of the anthracite material using XANES spectroscopy showed an increase in the amount of oxygen-containing groups such as carboxyls and carbonyls. In addition, BET surface area and micropore volume decreased by 76% and 80% respectively, whereas average pore diameter increased by 65%. The results suggest that P. chrysosporium biotransforms anthracite by surface oxidation, which leads to a decrease in C/0 ratio and disruption of the continuous graphitic structure, thus decreasing the active sites necessary for adsorption.