The main group of sulfur content gold concentrate pyrite, pyrrhotite, arsenopyrite may also contain small amounts, by firing the concentrate can be converted to a loose and porous iron oxide calcine, and wherein the load fines and The fine-grained gold is dissociated into monomers for subsequent leaching or other methods of recovery.
According to the practice of the Kalgoorlie gold mine, pyrite is calcined in a furnace with excess air to form a pale brown calcine due to the following reaction:
4FeS 2 +11O 2 
2Fe 2 O 3 +8SO 2
When the calcination is carried out slowly at a controlled temperature (initial 550 ° C, near 700 ° C at the end), a reddish brown porous calcine in which gold is easily cyanide dissolved can be obtained. If calcined under conditions that limit the amount of air added, black magnetite calcine will be produced:
3FeS 2 +8O 2 Fe 3 O 4 +6SO 2
When fired for concentrate containing more than 0.5% of antimony, the firing process will calcine sintering, adversely affect the operation cyanide. The difficulty in the presence of lead for the calcination is well known, and when the raw material contains more than 0.2% lead, a large amount of lead remaining in the calcine is carried into the cyanidation process. Although the presence of copper has little effect on the roasting operation, it consumes a large amount of cyanide after entering the cyanidation process. Adding a small amount of sodium chloride during calcination can increase the cyanide extraction rate of gold, but may increase the volatilization loss of gold during calcination.
The roasting is usually carried out in a single Edward furnace or a boiling layer roaster, while the Campbell Red Lakc mining company uses a Dorr boiling furnace. The first crucible was supplied with a limited amount of air, calcined at 570 ° C to produce a black calcine, and then fed to a second crucible to supply excess air and calcined at 770 ° C to obtain a red calcined sand.
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