Pressure chloride leaching of a refractory gold ore

Abstract A series of metallurgical methods were employed to recover gold contained in a pyrite matrix. Direct cyanidation of the ore at P80 = 75 μ m yielded only 33% recovery after 24 hours leach time. Efforts to improve this level of recovery by finer grinding to 53μm and 38 μm followed by subsequent cyanidation were fruitless. A maximum of 35% Au recovery was realised. The ore was then roasted at 650°C and the calcine was subsequently leached with cyanide. After 24 hours of leaching, 98% of the gold was recovered. Finally, the ore was treated by simultaneous oxidation and gold dissolution within an autoclave using a O 2 /H 2 SO 4 /HCl/NaCl system. The results revealed that at temperatures between 180–200 °C, between 1.5 to 2 hours was required to attain sulphide oxidation and attendant gold recoveries in excess of 90%. This system indicated the potential for direct dissolution of gold within the autoclave thus avoiding the need for cyanidation treatment of the autoclave discharge as is currently done.