Refractory Gold Ores
Refractory gold ores resist cyanidation because gold is locked within sulphide minerals or associated with carbonaceous matter. Pre-treatment is required.
Pressure Oxidation (POX)
Autoclave POX at 180-225°C oxidizes sulphide minerals to sulphate, liberating encapsulated gold with >95% liberation from arsenopyrite and pyrite ores.
Bio-Oxidation (BIOX)
Bacteria catalyze sulphide mineral oxidation at atmospheric pressure and moderate temperatures (40-80°C). Lower capital cost than POX but requires longer residence time.
Roasting
Traditional roasting at 500-700°C burns off sulphides. Modern fluidized-bed roasters with off-gas treatment minimize emissions.