Leaching and electrochemical dissolution of gold in the presence of iron oxide minerals associated with roasted gold ore

Abstract

This study investigates the electrochemical interactions between gold and roasted gold ore (RGO), with its associated oxide minerals serving as slurry, in an electrolyte saturated with atmospheric oxygen. Conventional cyanidation yielded a decrease of ~40% in the gold leach rate with magnetite slurry, while increases of 25% and 10% were observed for hematite and maghemite, respectively. These gold leach rates were obtained by applying cathodic Tafel slopes only. SEM-EDS, in the case of magnetite slurry, exhibited a high accumulation of iron oxides on the gold surface, which is an indication of slowdown in the gold leach rate. In the case of roasted gold ore slurry, lower amounts of iron oxides were detected with the association of calcium-magnesium coating. XPS results also exhibited a small amount of gold in the slurry of magnetite particles after leaching, i.e., suggesting the adsorption of gold by magnetite, which also justifies the slowdown in the gold leach rate. Magnetic separation tests of cyanidation tailings containing 20% Au resulted in a 4% (mass-pull) magnetic concentrate sample with 72% non-leached Au. Roasted gold ore, magnetic tailings, and synthetic maghemite electrodes exhibited a cathodic peak, suggesting the reduction of ferric to ferrous ions, which could be responsible for the slowdown of leach kinetics, whereas magnetic concentrate did not. Furthermore, when oxygen was bubbled, this peak disappeared in the case of roasted gold ore and synthetic maghemite, though magnetic tailings still exhibited the peak.