Absorption Above Active Carbon

The principle of the recuperation of gold by the active carbon rests in the property that the active carbonized matter has of absorbing the gold contained in cyanide. This property is recognized since the past century, particularly by the negative effects which presents in the cyanidation of the carbonized minerals.

Its use and effective development are, nonetheless, recent and are due in large part to the focus of an effective economic process of the elusion of gold from the carbon, Zadra, thus allowing its reclining in the installation in place of its burning.

The active carbon used is prepared starting from the vegetable carbon naturally hardened (stone of pulpy fruit, coconut nut), worked especially for developing its capacity of absorption and its porosity.

A granulometric set immediately allows to prepare an active carbon of tight granulometry, generally understood between 0,8 and 3 mm.

One of the decisive advantages of the active carbon, is that it can work not only with auriferous solutions, but also directly with the pulps pf minerals after attacked by cyanide.

Such is the process of carbon in pulp whose development is well described by Laxen.

At the exit of the cyanidation, the pulp of the mineral finely grinded, is sent in a series of reactors of the pachuca type, or more commonly with mechanical agitation.

From the active carbon, this pulp is mixed in each scale and is retained in the reactor by a system of cribbage. The carbon is advanced periodically in the system, in a counter-current of the pulp, one final cribbage allows to separate the pulp from the sterile mineral of the loaded carbon.

This process of the carbon in pulp avoids all solid/liquid separation, with the intention of the cyanidation and is, therefore, particularly adapted to the case of the minerals difficultly filtered or exagerated.

In the case of the cyanidation in piles, the absorbing over carbon is effectuated in the columns in fixed or pulsed beds, according to an analogical procedure to the use for the absorbing over resins.

At the end of the absorption the carbon is recuperated and treated by elusion. There are various processes of elusion.

The first one applied is of Zadra, which uses a solution of 1% of glasswort and 0,1% of cyanide of sodium to the temperature of ebullition, at atmospheric pressure or under pressure.

One bettering of this process consists in introducing 10% approximately of ethanol in a solution of 2% of glasswort which accelerates the cynetic of elusion of gold.

Finally, a process developed in South Africa, used pure water after a drenching of the charged carbon in a solution of 5% cyanide of sodium and 1% glasswort.

The auriferous solutions are immediately treated by electrolisis, the gold is deposited above the wool of iron cathodes. The eluded gold can more rarely be precipitated sbove zinc dust.

The techno-economical comparisons of the procedures of the carbon in pulp and precipitation above zinc have been done recently. It is to stand out that the procedures of the carbon in pulp is particularly well adapted when the liquid/solids separations are difficult, in the case of the presence of copper in a mother solution (the carbon is partially selective for the couple gold-copper) or when the mineral has a weak content.

The operational costs or of blockage are generally less elevated for the carbon in pulp than for the precipitation over zinc.

Another use of the technique of carbon in pulp is actually done in the case of the minerals which contain carbonized matter, the introduction of carbon in the pulp at the moment of lixiviation, allows to contrary the absorption of gold over a natural carbon, favoring its absorption over the increased active carbon, whose activation is very important.

This procedure is proceeded immediately as the present.