The role of oxidants in the intensive cyanidation of gold. II. Sulfide mineral oxidation.

In the intensive cyanidation of gravity gold concentrates, sodium m-nitrobenzene sulfonate (NBS) is often used to supplement dissolved oxygen as the oxidant in the process. A previous paper presented the results of a largely electrochemical study of the behaviour of NBS during cyanidation of gold. The results confirmed that NBS acts as an oxidant in the cyanidation of gold and that the mixed potential model can be applied to describe the mechanism of its action. This paper explores the corresponding oxidation of sulfide minerals, that inevitably are contained in gold concentrates, by either dissolved oxygen or NBS. Using electrochemical techniques it was found that dissolved oxygen is effective in the oxidation of several sulfide minerals at pH values between 9 and 11. The effect of cyanide on both the anodic and cathodic processes has been studied. NBS has been found to be ineffective as an oxidant for all minerals tested except galena, even in the presence of cyanide. • Effect of oxygen and NBS on mineral mixed potential good indicator of the rate of mineral oxidation. • Cathodic reduction of NBS occurs at potentials too negative to oxidise the sulfide minerals. • Relative rates of oxidation of minerals by dissolved oxygen in absence and presence of cyanide. • The presence of cyanide results in reduced rates of oxidation of most minerals except chalcopyrite and galena. [ABSTRACT FROM AUTHOR]