Coal Gold Agglomeration
(CGA)

In this process the liberated gold is recovered by means of coal/oil agglomerates. Such agglomerates are formed in aqueous medium when a second immiscible and hydrophobic liquid as oil, contacts a hydrophobic material (coal). Upon agitation, oil spreads on the surface of particles which after colliding form liquid bridges that lead to agglomeration.

The utilization of coal-oil agglomerates in the recovery of gold is based on the natural hydrophobicity/oleophilicity of gold, a property which according to the consensus of most surface chemistry experts is brought about by the ease by which gold surface becomes contaminated, though is possible to recover gold by agglomerating them with oil, the amount of gold in the ore is usually small that there is insufficient gold particles to form agglomerates. Thus, the need to use other hydrophobic materials (e.g. coal) to either form agglomerates together with gold or act as a carrier of gold particles.

Agglomerates are prepared in a previous step and then added to the ore pulp in a second step. The gold particles, being oilfilic, penetrate into the agglomerates. In a continuous operation the agglomerates would be maintained in contacting tanks until they reach a pre-determined gold content. The tailings are discarded by means of a screen situated at the upper part of the tanks. The recovery of gold from agglomerates is obtained in a later step by burning the agglomerates and then separating the gold from the ashes

Fig. 4.15 Layout of the CGA Process