Use of dry grinding process to increase the leaching of gold from a roasted concentrate containing hematite in the thiosulfate system

Abstract

Iron-containing oxides are the main minerals associated with roasted gold concentrates. The influence of different iron-containing oxides on the gold thiosulfate leaching process is very complex. In this study, we found the use of dry grinding methods can considerably eliminate the adverse effects on gold thiosulfate leaching under wet grinding conditions for a roasted gold concentrate containing hematite. The leaching results of gold ore showed that the gold leaching percentage was significantly improved from only 35% in 8 h under wet grinding conditions to 85% under dry grinding conditions. Using dry grinding to replace wet grinding, the loss of copper ions in the solution is much lower, and the diffusion coefficient of copper ions in the slurry is higher. Scanning electron microscopy (SEM) characterization shows that the passivation of the gold surface is much reduced. X-ray photoelectron spectroscopy (XPS) detection shows that the material adsorbed on the gold surface is mainly FeOOH. In addition, X-Ray diffraction (XRD) analysis results indicate that under wet grinding conditions, part of the hematite is transformed into goethite. Combined with the leaching results of gold powder, it is confirmed that the formed goethite during wet grinding is the cause of the deterioration of the gold leaching. Dry grinding can effectively avoid the formation of goethite and thus is a useful method to increase the gold leaching rate.