A study of the electrochemical dissolution and passivation phenomenon of roasted gold ore in cyanide solutions

• Anodic dissolution and passivation phenomenon of roasted gold ore were investigated.
• Hematite was found to promote gold dissolution whereas magnetite retarded.
• Presence of slurry resulted in lower current densities (gold corrosion rates).
• Cathodic Tafel slope only better represents practical cyanidation results.
• Fe-oxide and Au-C compound, observed by SEM, are responsible for partial passivation.

This study investigates the electrochemical interactions between gold and its associated oxide minerals either in one (OC) or two separate containers (TC) in the presence or absence of slurry. Magnetite showed negative effect on gold leaching, while maghemite and hematite demonstrated positive effect, relatively. The presence of slurry generally resulted in lower current densities. However, when the tailings of slurry was used again as a new feed in two separate containers (TC), the dissolution rate of gold was increased by 3 times (30 to 90 μA cm− 2), suggesting that the removal of detrimental ions in the first stage. Moreover, the current density of gold was enhanced up to 10 times by magnetic pre-treatment of roasted gold ore. It was found that in cyanide solutions saturated with atmospheric oxygen, cathodic Tafel slope only (8.60 × 10− 7 ± 4.56% mol m− 2 s− 1) provides close corrosion rates of gold to that in practical cyanidation (10.57 × 10− 7 ± 1.33% mol m− 2 s− 1), suggesting that cathodic polarization is the rate controlling one. Furthermore, a new electrode consisted of equal quantities of magnetite and hematite in one electrode was developed to examine the influence of these two major iron oxides on gold leaching, concurrently 0.04 M NaCN at 100 rpm agitation was found to be optimal. SEM analysis indicated the presence of Fe-oxide and Au–C compound products that could be responsible for partial passivation of gold surface.