Reactivity of sulfide minerals and its effect on gold dissolution and its electrochemical behaviour in cyanide solution

The effects of sulfide minerals on gold dissolution in atmospheric and oxygen enriched solution was studied by using rotating disc method. This research was divided into four sections: Direct leaching of gold in cyanide solution in the presence of sulfide minerals in air and oxygen saturated solutions; Direct leaching of gold in the presence of metallic and non-metallic ions; Anodic dissolution of gold; and finally, Cathodic reduction of oxygen on gold and mineral surfaces followed by galvanic interaction between gold and those minerals.; Chalcocite and stibnite exhibited a very intensive negative effect on the gold dissolution. Pyrrhotite had slightly less negative effect which were maximize at the certain concentration. Galena on the other hand indicated significant positive effect on the gold dissolution. The study of metal ions effect on the gold dissolution demonstrated that lead ions at low concentration, and ferro-cyanide ions at moderate concentration enhanced the gold dissolution. Antimony ions and especially the sulfide ions had intensive deleterious effects on the gold dissolution.; The anodic dissolution of gold was studied in the pure cyanide solution and in the cyanide solution containing various ions and sulfide minerals. The potentiodynamic method was used to study the anodic dissolution reaction. It was found that the anodic reaction of pure gold was inhibited due to the passivation from various ions and sulfide minerals. Minor amount of silver in gold disturbed the passivation mechanism and the mass-transfer controlled the reaction rate. The results of this investigation indicate that sulfide ions had the most serious negative effects on the gold anodic dissolution followed by antimony ions. Metal ions such as copper, iron and lead, did not have significant negative or positive effect on the gold anodic reaction. The effect of sulfide minerals indicated that stibnite had a very strong deleterious effect on the gold anodic behavior. Gold anodic reaction in the low overpotential range was almost intact in the presence of galena. Under the same conditions, pyrite, pyrrhotite and chalcopyrite decrease the activity of gold toward the anodic reaction. Gold cathodic reaction was also affected by the presence of sulfide minerals. Chalcopyrite and pyrite did not indicate any significant negative effect on gold cathodic behavior. Whereas galena enhances oxygen reduction kinetics, in the presence of stibnite oxygen reduction was substantially retarded at relatively low and moderate overpotentials. Pyrrhotite, however, performed a negative effect on the gold cathodic reaction at all overpotentials.; Potentiodynamic and galvanodynamic methods were also used to characterize the oxygen reduction on sulfide minerals and gold anodic behavior, to predict the galvanic current of gold-mineral coupling and to evaluate the accuracy of such predictions. Pyrite and pyrrhotite both indicated a most active substrate for oxygen reduction. Galena yielded the lowest activity, followed by chalcopyrite. The results of galvanic corrosion experiments indicate that chalcocite and chalcopyrite exhibited negative effects on gold dissolotion, whereas galena, pyrite and a pyrrhotite had a positive effect on gold dissolution due to galvanic interaction.