Fungal-Transformation of Surrogate Sulphides and Carbonaceous Matter in Refractory Gold Ores

Abstract

Refractory gold ores contain metal sulphides that encapsulate gold and prevent its dissolution by cyanide, and carbonaceous matter (CM) that adsorbs (or preg-rob) gold cyanide complex during cyanidation. Pretreatment is therefore a necessary step to decompose the sulphides and liberate gold before cyanidation, and to deactivate CM and prevent it from adsorbing dissolved gold. To contribute to the pool of knowledge on the development of microbial-treatment techniques for refractory gold ores, this paper presents an overview of on-going research aimed at assessing the capability of the fungus, Phanerochaete chrysospo-rium, to degrade sulphides and CM. Pure pyrite and arsenopyrite, with initial sulphide sulphur content of 52% and 20% respec-tively, were used as surrogate for metal sulphides, whereas lignite, bituminous and anthracite coals were used to model the behavior of CM in refractory gold ores. The extent of biotransformation was primarily monitored by measuring sulphide sul-phur in the residual sulphidic materials, and by determining the preg-robbing effect of the treated CM. Within 21 days of treat-ment, there was 18% and 39% oxidation of sulphide sulphur in pyrite and arsenopyrite respectively. During the same period, preg-robbing effect of CM reduced by 70-95% in the order of lignite < bituminous < anthracite. Partial characterization of the treated anthracite using XRD confirmed reduction in the graphitic structure of carbon, whereas in the case of pyrite, there was a decline in the major sulphide peak after microbial pretreatment. The results indicate that the fungus biotransforms mainly by increasing the amorphous nature of the substrates through destruction of the ordered structure, followed by introduction of oxygen groups. The findings suggest a novel and technically viable alternative method for oxidative pretreatment of refractory gold ores.