1) fine submicroscopic gold or gold was present in the state of wrapping or disseminated sulphide minerals, usually these sulphide minerals pyrite, arsenopyrite and pyrrhotite.
2) There are sulfides of iron and base metals in the ore, and their decomposition products consume oxygen and cyanide, which adversely affects the cyanidation reaction of gold.
3) There are antimony minerals (stibnite) and arsenic minerals (realgar, orpiment) in the ore.
4) Gold and telluride symbiosis.
5) There are carbonaceous materials (ie activated carbon, graphite or humic acid) with "preemptive adsorption" properties in the ore.
6) There are clays in the ore that can adsorb gold cyanide complexes.
For such ores, some form of pre-treatment must be carried out to make the standard extraction available. The classical method is to oxidize and roast, destroy the crystal structure of the original mineral, and completely dissociate the gold. However, roasting has two disadvantages. First, the generation of flue gas containing sulfur, arsenic, antimony, and mercury is annoying, and the pollution control cost is extremely high. Second, the gold particles may be melted in the calcined product in the calcination. The oxidized base metal also reduces the cyanidation effect. In recent years, a large amount of research and experimental work has been carried out in order to find a hydrometallurgical oxidation process capable of replacing the roasting treatment which is difficult to handle gold ore. There are three general methods of wet oxidation, namely, pressurized oxidation, biological oxidation, and chemical oxidation.
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