Investigation of gold dissolution in cyanide solutions using cyclic voltammetry methods

The study presents the results of gold dissolution in cyanide solutions using the cyclic voltammetry method. A methodology was developed to investigate the mechanism of gold leaching in cyanide solutions by determining the relationship between current and potential under varying cyanide and oxygen concentrations. It is known that as the electrode potential increases, the gold dissolution current rises until the passivation potential is reached, after which it sharply decreases due to the formation of an oxide film, resulting in gold passivation. It was established that the maximum passivation current is achieved at oxygen and sodium cyanide concentrations of 7.5 mg/dm³ and 300– 400 mg/dm³, respectively. Mathematical relationships for the passivation potential and current as functions of sodium cyanide and oxygen concentrations were determined, described by polynomial equations with approximation coefficients R₂ > 0.7. When the polarization direction is reversed, the current polarity changes, producing a cathodic curve with a peak at the depassivation potential, corresponding to the dissolution of the passive gold film. The depassivation potential and current show weak dependence on sodium cyanide concentration. The cyclic voltammetric curve terminates at the initial point with the same current and potential values, indicating the complete removal of the oxide film from the gold surface. The oxide film thickness, calculated based on the amount of passed charge, was found to be 0.007 μm. Metallographic studies demonstrated that the film thickness could not be determined by this method. A gold surface diffractogram revealed that the passive film formed after heating to 125 °C has the crystallochemical formula Na_0.66Au_2.66O₄. The study highlights the potential for enhancing gold recovery from refractory ores through electrochemical treatment in alkaline conditions.

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