Reduction of preg-robbing by biomodified carbonaceous matter-A proposed mechanism

The carbonaceous matter (CM) in gold ores behaves similarly to activated carbon in its ability to adsorb aurocyanide ions. This phenomenon is termed preg-robbing as the adsorbed gold cannot be recovered from the CM. The mechanism of gold adsorption depends, among other things, on the surface functional groups, pore structure and maturity of CM, and hence the development of graphitic structure. In this study, the fungus Phanerochaete chrysosporium was used to biomodify the surface and alter the gold adsorption ability of anthracite coal, which was used as surrogate for CM. Characterization, employing FTIR, XANES, Raman and TEM analyses, showed more oxygen-containing groups and enhancement in the amorphous nature of carbon, following fungal transformation. As well, pore structure measurement indicated drastic reduction in surface area and micro pore volume, and enlargement in average pore diameter. The results suggest a number of theories by which P. chrysosporium biotransforms CM: (a) surface oxidation, which disrupts the continuous graphitic structure, thus decreasing the active sites necessary for adsorption; and (b) reduction in surface area via (i) plugging of pores possibly by fungal biomass and/or slimy substances formed through fungal interaction with the growth medium, and hence decreasing accessibility of gold to the adsorption sites, and (ii) cleavage of bonds leading to pore enlargement, thus rendering the pores too large for adsorption of the aurocyanide ion which are known to adsorb into micropores.