Base Techniques

Amalgamation
The superficial tension to the gold-mercury interaction is very inferior to the one of water with gold; it allows a preferential contact and favors the combination of the two metals which afterwards, form conjunctions of metallic compounds called amalgamate.

There would exist as a matter of fact, a whole series of aleations of AuHg2 with Au8Hg (15).

In effect, from the point of view of the treatment, one can observe a mix which comprehends:

• A liquid solution of gold in the mercury (0.1% of gold)
• One or various solid compounds of gold-mercury.

Dissolution of Copper Minerals & Zinc in Cyanide Solution To 0,1% During 24 Hours, To 23°C

MINERAL: Chalcopyrite
FORMULA: Cu Fe S2  
DISSOLUTION IN %: 5,6

MINERAL: Chrysocola 
FORMULA: Cu Si O3  
DISSOLUTION IN %: 11,8

MINERAL: Tetraedrite 
FORMULA: 4Cu2S – Cus 
DISSOLUTION IN %: 21,9

MINERAL: Enargite 
FORMULA: 3CuS – As2S5 
DISSOLUTION IN %: 65,8

MINERAL: Bornite 
FORMULA: FeS – 2Cu2S – CuS 
DISSOLUTION IN %: 70,0

MINERAL: Cuprites
FORMULA: Cu2 O  
DISSOLUTION IN %: 85,5

MINERAL: Copper
FORMULA: Cu  
DISSOLUTION IN %: 90,0

MINERAL: Calcosite
FORMULA: Cu2 S  
DISSOLUTION IN %: 90,2

MINERAL: Malachite
FORMULA: Cu Co3 Cu(OH)2  
DISSOLUTION IN %: 90,2

MINERAL: Azurite 
FORMULA: 2CuCo3-Cu(OH)2  
DISSOLUTION IN %: 94,5

MINERAL: Wilemite 
FORMULA: Zn2 SiO4  
DISSOLUTION IN %: 13,1

MINERAL: Esphalerite 
FORMULA: Zn S  
DISSOLUTION IN %: 18,4

MINERAL: Hydrozincite
FORMULA: 2ZnCo3 – 3Zn (OS)2  
DISSOLUTION IN %: 35,1

MINERAL: Zincite
FORMULA: Zn O 
DISSOLUTION IN %: 35,2

MINERAL: Smithsonite 
FORMULA: Zn CO3  
DISSOLUTION IN %: 40,2

The superficial tension to the interaction gold-mercury is very inferior to that of water with gold, it allows a preferential contact and favors the combination of the two metals, which then form a conjunction of metallic compounds, called amalgam.

As a matter of fact there would exist, a complete series of aleations of AuHg2 with Au8Hg (15).

In effect, from the point of view of the treatment, one can observe a mix which comprehends:

• A liquid solution of gold in the mercury (0.1% of gold)
• One or various solid compounds of gold-mercury.
• The particles of natural solid gold re-covered and refined by the other two compounds.
• The limits of the amalgamation are mainly the following:
• It does not concern more than the natural gold.
• This natural gold must be well liberated, its surface clean and extent of layers of oxide of iron or of hydrophobic reactive (greases, reactive of flotation).
• If the gold is very fine, it can have the tendency to float in the surface of the water or of the mercury.
• The presence of certain sulphurs, of arsenic in particular more or less soluble in water, can provoke difficulties in the amalgamation, in particular in the formation of ultra fine drops of mercury which are impossible of recuperating.

The putting in action of the techniques of amalgamation is well described in works as those of Taggar or the Techniques of the Engineer.

The application of these techniques above minerals which have, it is nowadays almost abandoned due to the dangers presented by the manipulation of the mercury, the important part of handwork which need and the facilities which offer to the theft of the precious metal. The amalgamation is not practiced today more than above the gravimetric or flotation of concentrates.

The technique generally used is the amalgamation in discontinuity of a load of the concentrate in a type of grinder.      

After the separation by gravimetric and the passing above the plaques of copper, the amalgam is pressed with a skin of chamois to eliminate the residual mercury, after distilled towards 350°C to 450°C. The concentrated mercury is recycled, the remaining gold is in the bottom is sent to the affination.

We will finally point out that a recent tendency is shown clearly today, to replace the amalgamation of the concentrates by an intense Cyanidation for the direct sending to the melting and joining.