Abstract: A process for treating refractory ores combines pressure oxidation treatment of the ore with cyanidation and carbon-in-pulp recovery. Pressure oxidation is carried out under acidic conditions, at elevated temperatures and pressure. Before cyanidation, the oxidized slurry is subjected to a multiple stage washing operation to remove excess acid and heavy metals generated during the pressure oxidation. Such heavy metal removal lowers the subsequent cyanide usage and makes the process more economical. Cyanidation is carried out in a conventional manner, and it has been found that carbon-in-pulp recovery leads to greatly enhanced recovery of gold when compared to other conventional methods, such as zinc precipitation.

Abstract: A process for pretreating refractory ores improves the recovery of gold from such ores upon subsequent cyanidation. After comminuting the ore and forming an aqueous slurry, the ore is subjected to pressurized oxidation at an elevated temperature. By adjusting the pH to below about 1.85 and maintaining the pressure and temperature above 300 psig and 160.degree. C., respectively, very high recovery of gold can be achieved. Additionally, by maintaining a preselected soluble iron concentration in the slurry, the oxidation of the ore is promoted and proceeds at a more rapid rate.