Cyanidation of gold ores containing copper, silver, lead, arsenic and antimony

Cyanidation tests on two ore samples from two different gold deposits are reported. The first sample contained 10.5 ppm gold with high arsenic and antimony. The second sample had a low gold content (2.5 ppm) but a high silver content (160 ppm). The first series of test work focused on the determination of conditions for extracting gold from the samples ground to - 75 μm. The optimum parameters were 4000 mg/L for cyanide concentration, pH = 11.1 and 24-h cyanidation time for the first sample; and 2500 mg/L, pH = 10.5 and 24 h for the second sample. Silver and gold recoveries were 94.91% and 28.2% respectively for the first sample and 92.5% and 93.5% for the second sample.

In the second series of test work, H ₂O ₂ (0.015 M), air (0.15 L/min) and a mixture of H ₂O ₂ and air were used as oxidizing agents to improve the gold extraction kinetics of the first sample. It was found that gold leaching recovery followed first order kinetics and that the injection of air had the maximum beneficial effect on the leaching kinetics. In the third series of test work, acid pretreatment (HNO ₃ and HCl) and roasting (600-1000 °C) from 0.5 to 2 h were carried out before cyanidation. Acid pretreatment reduced cyanide consumption by 340 and 210 mg/L respectively and the corresponding gold recoveries increased to 98.87% and 95.11%. Cyanidation results on roasted samples showed that cyanide consumption was drastically reduced by 1150 mg/L and gold recovery increased by 5.2%. Furthermore, arsenic, antimony, cadmium and mercury contents were considerably reduced in the roasted sample (2 h at 1000 °C).