An electrochemical study of the effect of lead and sulphide ions on the dissolution rate of gold in alkaline cyanide solutions

The presence of impurities in cyanide solutions may either accelerate or retard the dissolution of gold within the potential range typically encountered in conventional gold leaching, i.e. from -600 to 0 mV (SCE). By using potentiostatic and potentiodynamic techniques, it was found that lead species in solution increased the dissolution rate of gold from E-corr up to approximately -380 mV (SCE); in contrast to this, sulphide species decreased the dissolution rate of gold and also counteracted the accelerating effect of lead species. At more positive potentials, sulphide species accelerated the dissolution of gold. It is therefore possible to increase the dissolution rate of gold in cyanide solutions containing small amounts of sulphide by maintaining more oxidizing conditions on the gold surface. This finding may be put to practical use in the treatment of sulphide concentrates for which the gold leaching rate should be enhanced by increasing the oxygen concentration while the presence of sulphide ions in solution should prevent passivation of the gold at the higher potentials that would typically be obtained for these conditions. (C) 2001 Elsevier Science B.V. All rights reserved.