Other Mineral Gravimetry

For the other minerals, due to the fact that what is essential of the treatment is the Cyanidation or the flotation, the gravimetric intervenes as an indispensable complement for a good global recuperation of gold.

Numerous reasons participate in this sense:

• The gross gold is slower in diluting in the solutions of cyanide than the fine gold, Barsky (19), for example has noted that one particle of gold of 150 microns requires more than 44 hours to be dissolved in the normal industrial conditions.
• The times of habitual remaining of the installations of Cyanidation vary from 8 to 36 hours.
• Thus it is preferable to separate the gross gold, as soon as possible to avoid its loss with the rests of the Cyanidation.
• In the same way, the gross gold floats more difficultly and maybe it gets lost in the sterile of flotation when this technique is used.
• Gold is a ductile matter which is shredded with difficulty, having the tendency of being crushed.

Besides, the gross gold, due to its strong density, is concentrated in the versants of the classifiers with which it is returned to the head of the grinding section.

To avoid that the gross gold turns for a long time in the circuits of grinding in which by segregation in the points not controlled it can be lost or stolen, it is thus a good practice to recuperate it through gravimetric, in the inside of those same circuits.

- The surface of the nuggets of gold can be naturally covered again with a layer of iron oxide (moldy gold) or of another compound.

This covering again can also come from the cementation over the surface of gold towards the grinder. It can also be accompanied by incrustations of other minerals, Feather (20).

This gold will be dissolved more slowly in the cyanide or will float more difficultly. A gravimetric separation intervening as soon as it is possible in the circuit of treatment will allow the recuperation of this molded gold and will avoid the degradation of its surface.

The advantages of the recuperation of the particles of gold which are grosser, as well as with the methods used have been discussed by Bath (21) and by Kok (22).

Their conclusions are that the advantages of recuperating the gross gold as soon as possible in the scheme of the treatment to submit it to the processes especially adapted will allow reaching elevated recuperations of the metal.

The apparatus of gravimetric used are in diverse manners, each one keeping its advantages: very elevated consumption, better adaptation to the treatment of the objects, better result in the re-washing, etc. Rotational concentrators (Johnson) dormant beds, concentrator of the belt without end, cones (Reichert), spirals, loss tables, jigs.

In certain cases the gravimetric equipment is reduced to the traps, hydraulic, prepared throughout the whole circuit: pointed boxes, elutriators.

In general rule, all of these apparatus are placed directly in the circuits of grinding, between the grinders and the classifiers. This disposition allows recuperating the gold from its liberation, thus avoiding its useless recycling in the grinders.

The concentrates of the recuperated gold by gravimetric are treated by different methods, after an eventual gravimetric re-washing the concentrates can be amalgamated, cyanided in the solutions with strong concentration in cyanide (2%) or directly sent to the melting of metals.

By the advantages which it presents, the gravimetric of the gold nowadays knows a renovation.

The statistic studies guided on the topic of the gold mines in South Africa, have shown the worldwide recuperation of gold was correlated, positively to the fraction of the gold recuperated by gravimetric.