Basically, this process can be used by small miners who are used to recover free gold particles by batch procedures. The process has been developed considering environmental aspect. It is well known that small miners employ mercury to recover free gold and part of this liquid metal is released to the environment. The process is an alternative to the amalgamation process. The agglomeration process is based on the formation of agglomerated particles with coal and is known as Coal Gold Agglomeration (CGA). This process was developed and patented by the British Petroleum research group and the key concept of the process is the formation of hydrophobic and oleophilic particles from slurries into agglomerates formed from coal and oil. The oil forms a link between gold particles and coal, and the last one act as a carrier of gold particles. Agglomerates are recycled to increase their gold recovery and once they are almost saturated are separated burned, and smelted to get a gold ingot.
The most appropriate auriferous ores for the process are placers, old tailing deposits, and some gold with easy liberation after grinding. In these deposits, the gold must be free and fine. Then, it is necessary to verify this condition by doing mineralogical studies that must cover all the deposit in order to assure its applicability in the project.
Agglomeration is a particular case of oil-agglomeration. In this case, the agglomerates are formed in an aqueous system when a second liquid contacts a hydrophobic particle like the carbon. When there is stirring and mixing, the oil is extended on the surface of hydrophobic material and creates bridges among the particles, and the hydrophilic particles stay in an aqueous suspension. The CGA process for the treatment of auriferous ores is based on the natural hydrophobicity and oleophilicity of gold. This property is considered by some researches as a form of easy superficial contamination.
Having an appropriate mixing condition and a specific oil/carbon ratio, it is possible to obtain agglomerates due to the interfacial tension of the oil and the capillary attraction of the oil bridges between particles. Next figure shows schematically the formation of coal-oil agglomerates and the contact with gold particles.
Formation of coal-oil agglomerates