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Activated carbon can be used 8 to 10 times. The best way to assure a good period of life for activated carbon is not only avoiding losses by attrition
during absorption else effecting thermic regeneration. Once carbon has been stripped of its mineral it has one more process to go through before it is ready to be put back into service. This is regeneration.
Carbon is not selective. It adsorbs other substances very readily. As the cyanide solution percolates through the ore mass it will pick up other elements that it is compatible with. These are often organic in nature. The stripping process regularly leaves these substances behind in the carbon. After a time they restrict the carbon's ability to adsorb.
When this occurs, the carbon must be refreshed by having the stray substances removed. To do this the carbon is heated to above 700°C. The problem is that the carbon will burn away at that temperature. To prevent this from happening, heat is applied in a negative oxygen atmosphere. In other words, there can't be enough oxygen with the carbon to support combustion. A common way of doing this is by having fans pull the air out of a rotary kiln. However it doesn't stop there. After the carbon has gone through this heat treatment two or three times, leftover ash material will begin to interfere with the adsorption process. This is eliminated by acid washing the carbon.
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