REVIEW OF GOLD EXTRACTION FROM ORES

Australia is now an important gold producer in the world. The nature o f Australian gold production is briefly reviewed and the hydrometallur gy of gold extraction is considered. The choice of processing routes f or free milling, complex and refractory ores is discussed. For free mi lling ores, cyanidation and recovery by the Carbon-in-Pulp/Carbon-in-L each process (CIP/CIL) is the primary and proven treatment process. Co pper 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 r efractory ores are considered in detail. These options include: ultraf ine grinding; acid and alkaline pressure oxidation; and a variety of c hemical pretreatments such as: Activox process, HMC process and Electr olytic oxidation process. In Australia, the two pre-eminent options fo r refractory gold ore pretreatment are roasting and biooxidation and t his development is reported. The trial of pressure cyanidation of stib nite concentrates at the Golden Spec mine in Australia is described. P yrolysis, the Nitrox/Redox process, the Artech/Cashman process and the Caro's acid process have not gained commercial status so far. The pot ential for resin-in-pulp (RIP) to replace CIP/CIL is discussed. The us e of cyanide has generated environmental concerns because of its toxic ity and therefore research on alternative gold recovery processes usin g non-toxic reagents is considered. The key candidates are: ammoniacal thiosulphate, thiourea and halide solutions. The chemistry of these l eaching, systems is briefly described and proposed flowsheets are refe renced. The future prospect for biohydrometallurgical gold recovery is indicated.