Amalgamation Base Techniques

The superficial tension to the interaction of gold and mercury is very inferior to that of water with gold and allows a preferential contact and favors the combination of the two metals that form in that way, groups of metallic composites called amalgams. There will be a whole composite of alloys of AuHg2 with Au8Hg. In effect, from the point of view of the treatment, it can be seen that a mixture consists of: A liquid solution of the gold in the mercury (0.1 percent of gold) or one or several solid composites of gold and mercury. 

The superficial tension to the interaction of gold and mercury is very inferior to that of water with gold and allows preferential contact and favors the combination of the two metals that then form a group of metallic composites that is known as amalgam. There would exist therefore a whole series of alloys of AuHg2 with Au8Hg. In effect, from the point of view of the treatment, we can observe a mixture that comprises: A liquid solution of the gold in the mercury (0.1 percent of gold), one or several solid composites of gold and mercury, and the particles of solid natural gold, recovered and cemented by the other two composites.

The limits of amalgamation are mainly the following: it does not concern more than the natural gold; this natural gold needs to be freed; have a clean surface and extent of layers of oxides or of hydrophobic reagents (grease, flotation reagents etc); if the gold is very fine it can have a tendency of floating on the surface of the water or the mercury; the presence of certain sulphides of arsenic mainly that is somewhat soluble in the water, can bring about difficulties in the amalgamation, especially in the formation of very fine drops of mercury that are impossible to recover. The application of these techniques on minerals, is in these days something that is no longer done due to the dangers presented by the manipulation of mercury, the important side of labor that it requires and in the fact that it can cause gold to be lost. Amalgamation is no longer practiced on gravimetric or flotation concentrations. The technique that is generally employed is the discontinuation of a load of concentrate in a sort of grinder. After the gravimetric separation and the step of the plaques of copper, the amalgam is pressed with a chamois skin to get rid of the residual mercury, and then distilled to 350 degrees C. to 450 degrees C. The concentrated mercury is recycled. The gold that is left on the bottom is sent to be refined. We will point out, that there is a tendency that is pretty clear these days to replace amalgamation of the concentrates due an intense cyanidation through sending it to be smelted.