REVIEW OF GOLD EXTRACTION FROM ORES

Australia is now an important gold producer in the world. The nature of Australian gold production is briefly reviewed and the hydrometallurgy of gold extraction is considered. The choice of processing routes for free milling, complex and refractory ores is discussed. For free milling ores, cyanidation and recovery by the Carbon-in-Pulp/Carbon-in-Leach process (CIP/CIL) is the primary and proven treatment process. Copper containing ores are discussed in some detail as they interfere in the CIP/CIL process. Oxygen consuming and preg-robbing ores are also described. Five different classes of process options for pretreating refractory ores are considered in detail. These options include: ultrafine grinding; acid and alkaline pressure oxidation; and a variety of chemical pretreatments such as: Activox process, HMC process and Electrolytic oxidation process. In Australia, the two pre-eminent options for refractory gold ore pretreatment are roasting and biooxidation and this development is reported. The trial of pressure cyanidation of stibnite concentrates at the Golden Spec mine in Australia is described. Pyrolysis, the Nitrox/Redox process, the Artech/Cashman process and the Caro's acid process have not gained commercial status so far. The potential for resin-in-pulp (RIP) to replace CIP/CIL is discussed. The use of cyanide has generated environmental concerns because of its toxicity and therefore research on alternative gold recovery processes using non-toxic reagents is considered. The key candidates are: ammoniacal thiosulphate, thiourea and halide solutions. The chemistry of these leaching, systems is briefly described and proposed flowsheets are referenced. The future prospect for biohydrometallurgical gold recovery is indicated.