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Leaching Process

Cyanide is a lixiviant, or reagent that is used to leach, often in tanks, gold from a solid matrix and form a gold cyanide complex.  The gold cyanide complex is then extracted from the pulp or slurry by adsorption onto activated carbon. CIL stands for carbon-in-leach. This is a gold extraction process called cyanidation where carbon is added to the leach tanks (or reaction vessel) so that leaching and adsorption take place in the same tanks. CIL is slightly different from another gold extraction process called CIP or carbon-in-pulp process. In the latter case leaching takes place in tanks dedicated for leaching followed by adsorption onto carbon in tanks dedicated for adsorption.




Leaching can be assimilated to the principle of preparation of tea. When we add tea in hot water, the aroma of tea will dissolve in the water and not the tea leaves. So the aromas is found in liquid form and tea leaves remains in solid form in the hot water. Thus we can separate (solid-liquid separation) tea aromas from tea leaves (filtration for example). At this stage , we have been able to extract aromas of tea from the tea leaves by changing the physical shape of the tea aromas.It is the same principle used in the leaching of gold. The gold that is in solid form in the ores turned into liquid form with cyanide in the presence of oxygen. That’s the way gold is separated from the majority of its gangue. The second step is the adsorption of gold on the surface of the activated carbon. Following a natural phenomenon known around the world (positive charges attract negative charges) Gold sticking to coal. the coal loaded with gold and some impurities is then transferred to the elution where he undergoes a cold wash which removes certain impurities and then a hot wash. The solution from the hot wash is transferred to the electrolysis where pure gold is recovered.