The effect of pyrite particle size on the electrochemical dissolution of gold during cyanidation

Abstract

Pyrite is considered as the most common sulphide mineral that carries gold in refractory gold ores. In these ores, pyrite can be found in different particle sizes. Following flotation process, the flotation tailings is sent to the cyanidation circuit for gold extraction that may contain appreciable amounts of pyrite. Until now, the effect of pyrite on gold dissolution was reported to be either positive or negative in the open literature. This current research examines the effect of particle size and amount of pyrite on gold dissolution in a packed bed leach reactor (PBLR). Electrochemical characterization as a function of pyrite particle size on gold dissolution was tested. It was found that pyrite (4g) has positive galvanic effect on gold dissolution especially in the presence of fine particles, −106μm (i.e., 54% Au in the absence of pyrite vs. 95% with +20–53μm pyrite). On the other hand, gold dissolution showed a sharp decrease when particle size was coarser than +106μm. Highest gold extraction, 98%, was achieved when gold particles are in contact with +75–106μm pyrite particles. When the pyrite amount was doubled (8g of +75–106μm), gold dissolution was decreased to 35% due to the partial passivation of gold. If the pyrite amount were reduced by half (2g of +75–106μm), gold dissolution increased by 30% as compared to the case without pyrite. Different scenarios were also considered regarding to activation and passivation of gold. For instance, when gold was split and dispersed equally within the pyrite layer and within the adjacent quartz layer, gold dissolution was found to be around 35%, suggesting a negative effect of released species from pyrite. Cyclic voltammetry and potentiodynamic polarization findings are in line with the cyanide leaching results. The shift in open circuit potential in presence of pyrite is in support of observed leach kinetics. SEM-EDS results have confirmed the decrease in gold dissolution in the presence of coarse particles. These findings have revealed that pyrite particle size and its amount have significant impact on gold dissolution.