Effects of sulfide and lead nitrate addition to a gold cyanidation circuit using potentiodynamic measurements

Corrosion potentiodynamic polarization experiments on a gold electrode in a cyanide solution with 0–30ppm lead addition and 0–20ppm sulfide were carried out. Solutions containing 300ppm NaCN, adjusted to a pH 11.1 by NaOH and bubbled with air were used at atmospheric pressure and room temperature. If the concentration of lead ions was equal or larger than the sulfide ions a change of potential towards the more negative potential (a potential drop) was observed and this was accompanied by a significant increase in the corrosion rate (up to 10mmy^-1 in certain circumstances). If lead nitrate was added to a solution with a gold electrode that had been previously passivated by sulfides, the corrosion rate typically rose from about 0.3 to 0.95mmy^-1. The addition of lead nitrate to sulfides in cyanide solution can create a synergetic effect which results in an increase in dissolution rates of gold in cyanide solutions and this is accompanied by a drop in the corrosion potential of gold and a dramatic decline in thiocyanate and free sulfide concentrations.