A review of pretreatment methods to separate the different types of pyrites in gold processing

Sulfide associated refractory gold ores hold a majority of the gold within the pyrite, which has several forms. The high proportion of the gold atomically dispersed in the pyrite has been confirmed by various mineralogy techniques such as optical microscopy, scanning electron microscopy and secondary ion mass spectrometry. There are different types of pyrite that exist within a refractory orebody. Some types possess a relative abundance of gold compared to other forms.The low gold pyrite influences the rate at which the concentrate can be processed by any particular route. If the different types of pyrite could be separated by flotation, then the gold grade of the final concentrate can be improved and the invisible gold could be recovered by downstream processing. This separation of low gold pyrite from the gold rich pyrite would increase the Au:S (gold:sulfur) ratio to the autoclave feed, thereby maximising the autoclave throughput and gold production per tonne.Different methods of extraction such as chemical oxidation, thermal oxidation and biological oxidation liberate gold from refractory ores. However, such oxidation methods have not been reported yet to be successful to allow separation of the low gold pyrite from the gold rich pyrite. This review is an evaluation of the separation processes of different sulfides available in the recent literature for refractory gold ores. All major pretreatment processes have been analysed and recommendations have been put forward for further research and development.