The Biooxidation of Refractory Gold Ores

This involves the production of a sulfide concentrate by froth flotation to remove oxides and gangue minerals. The concentrate is roasted at 600-800°C to oxidize sulfide and arsenic, if present, to sulfur dioxide and arsenious oxide. The product is cyanided to recover the gold. 

The biooxidation of refractory gold concentrates has been studied by several groups using stirred tank reactors and small-scale continuous systems, usually with T. ferrooxidans. Significant improvement in gold recovery has been achieved (6-8,26, 41, 69, 72,122). 

A major problem in extending laboratory-scale experiments to large pilot plants is associated with the prevalent use of T. ferrooxidans. This mesophile has an optimum temperature for growth of around 30-35°C. The oxidation of pyrite is exothermic, so that cooling of the reactor is often necessary to maintain the optimum temperature. This problem is particularly serious in operations in deserts, where water may be unavailable or prohibitively expensive. One solution involves 

There has also been some interest in heap leaching of low-quality refractory ores. This is a two-stage process, as bacterial leaching of the ore must be followed by leaching with alkaline cyanide to solubilize the gold. The heap must also be washed and neutralized before the cyanide leach can be applied (103). 

Bacterial Oxidation of Refractory Gold-Bearing Concentrates 

---