The effect of ore mineralogy on the electrochemical gold dissolution behavior in various cyanide and oxygen concentrations; Effect of sulfidic ores containing heavy metals

Abstract

The effect of heavy metals-containing gold ore mineralogy on gold oxidation kinetics in solutions with various free cyanide (CN) and dissolved oxygen (DO) concentrations was studied by electrochemical tests. To effectively simulate the cyanide gold leaching conditions, the electrochemical experiments were carried out in the slurries of the ores. The results of the linear sweep voltammetry tests showed three significant gold oxidation peaks. The peak potentials and the corresponding current densities were dependent on the composition of the ores in the test slurries, and the CN and DO concentrations of the test solutions. The heavy metal concentration of the ores also effectively changed the electrochemical response of the tests.The highest gold oxidation kinetics were observed in a pyritic sample containing 1800 ppm Pb, 640 ppm Ag and 195 ppm Hg (sample 1). The fastest gold oxidation kinetics were registered at −0.2 V vs. Ag/AgCl when DO was 8.3 mg/L, and the corresponding Au oxidation peak current densities were 4.75 and 7.07 mA/cm2 at 600 and 900 mg/L free CN, respectively. The Au oxidation was assisted by cementation reaction between the aqueous Hg and/or Ag species, and metallic gold. The weak lead deposition was also observed. However, the positive effect of Hg on the gold oxidation kinetics was depressed at higher DO (37.0 mg/L) concentrations. Unlike Hg, the effect of Ag on increasing the gold oxidation kinetics was shown to be independent of the solution DO.The second sample of the study, sample 2, was a sulfidic gold ore with 0.25% galena (PbS). The results showed that the presence of galena in an electrochemical gold oxidation test could increase the gold oxidation kinetics. In tests with 8.3 mg/L DO, the current densities of 2.80 and 5.23 mA/cm2 at 600 and 900 mg/L CN solutions, respectively, were obtained at −0.4 V vs. Ag/AgCl. Increasing DO to 37.0 mg/L did not improve the gold oxidation kinetics.Based on the results of this study, the presence of the specified heavy metals is most effective in gold oxidation kinetics if the free CN concentration is high and the DO concentration is low. Besides, the electrochemical methodology introduced in this study could offer a solution for determining the leaching parameters.