Mechanisms of galvanic interactions between gold and sulfide minerals in cyanide solution

Abstract

The galvanic corrosion behavior of gold coupled with sulfide minerals was studied in order to determine the nature and mechanism of this interaction. Many sulfide minerals have sufficient conductivity to allow electron transfer reactions on their surface. Consequently, galvanic interaction between these minerals and gold may occur when such minerals and gold are coupled with each other in a medium that facilitates charge transfer. Since the free corrosion potentials of most sulfide minerals in cyanide solution are more noble than gold, an accelerated galvanic corrosion of gold is expected. However, gold anodic or sulfide mineral cathodic behavior may negatively affect the galvanic interaction. Continuous measurements of the galvanic current were used to elucidate the dominant mechanism in the galvanic interaction between sulfide minerals and gold. The galvanic currents obtained from these measurement were 85 μA, 65 μA, 35 μA, 20 μA and −60 μA respectively for pyrite (6.2 cm 2), pyrrhotite (7.03 cm 2), galena (6.7 cm 2), chalcopyrite (3.16 cm 2) and chalcocite (7.28 cm 2) coupled with gold (1.01 cm 2). Potentiodynamic and galvanodynamic methods were also used to characterize cathodic and anodic behavior, to predict the galvanic current of gold–mineral coupling and to evaluate the accuracy of such predictions. The results indicate that chalcocite and chalcopyrite exhibit negative effect on gold dissolution, whereas galena, pyrite and pyrrhotite have positive effect on gold dissolution.