Metal recovery or concentration by adsorption on activated carbon has been the dominant process for gold extraction after leaching by cyanide in aerated alkaline slurry. The continuous processes of gold recovery by adsorption on activated carbon in agitated tanks, namely the carbon-in-pulp (CIP) and the carbon-in-leach (CIL) processes, have been widely used since the 1970s.
Carbon-in-pulp (CIP) is the sequential leach then absorption of gold from ore. During the CIP stage, pulp flows through several agitated tanks where sodium cyanide and oxygen have been added to dissolve gold into solution. In the absorption stage, this solution flows through several agitated tanks containing activated carbon. Gold absorbs on to the activated carbon, which flows counter-current to the pulp, while screens separate the barren pulp from the gold-loaded carbon.
Carbon-in-leach (CIL) is a simultaneous leach and absorption process. The simultaneous leach and absorption phases of the CIL process were developed for processing gold ores that contain preg-robbing materials such as natural absorptive carbon.These reduce the gold yield by attracting gold meant for the activated carbon. Simultaneous leaching and absorption help minimize the problem.
In the CIL (Carbon in Leach) or CIP (Carbon in Pulp) plants while the precious metals are being dissolved by the cyanide solution in the large volume tanks the dissolved metals are adsorbed by the active carbon. These processes are generally preferred for the relatively high grade and lower reserve ore types with very fine graded precious metals.
The major difference between the CIL and CIP processes is; during the CIL process both cyanide leaching and carbon adsorption take place in the same tanks but in the CIP process first leaching occurs in the first couple of tanks then carbon adsorption take place in the following tanks while leaching continues. In all of these tanks agitation and air sparging is available.