Iron Sulphurs and Oxydes

Iron Sulphurs
The pyrite, the marcasyte and the pyrrotite have the tendency of decomposing themselves with the Cyanidation.

The pyrrotite from this point of view presents the most serious problem; its dissolution drags in effect the supplementary consumption of oxygen and a diminution of the kinetic of extraction of gold.

Besides, a protective presentation of sulphur of gold, AuS, can deposit itself in the surface of the nuggets of gold and the ferrous ions re-precipitate the dissolved gold. One stage of oxidation in a basic environment in an upward movement of the Cyanidation, more often allows solving this problem.

The pyrite, very frequently associated to gold, has in fact, a different problem due to the fact that it is not so soluble. The gold can and is finely mixed as in the case of the mispickel; it has a concentration for flotation followed by one wire net and of one Cyanidation, allowing working with such minerals.

Iron Oxydes
Some hydroxides of iron can sometimes form, in the course of the Cyanidation, a protective pellicle surrounding the nuggets of gold, thus diminishing the kinetic of extraction. This pellicle of oxide of iron can also exist in a natural state. This gold type is very difficultly concentrated by flotation.

One activation by the dioxide of sulphur or a treatment of the diluted acid, sometimes allows surpassing this obstacle.