Without any doubt, activated carbon plays an important role in many gold operations and there are some economical considerations associated to its use in gold recovery systems. The technical aspects associated to selection and handling of activated carbon are key factors in the operating cost of the operation. It well known that carbon is used to adsorb from cyanide solutions or slurries. Basically activated carbon is prepared from several sources such as coconut shell, fruit pit or wood. El activation process is performed chemically or physically. In the first case a chemical reagents such as phosphoric acid is employed to activate carbon, and in the second case, a gas in a vapor phase in employed in the manufacturing process.
Gold operations employ activated carbon manufactured with coconut shell and the surface area of this carbon is 1,000-1,500 m2/g and the porous structure of the carbon is an important factor. It is possible to distinguish three types of porous according to the radius size: macropore (> 25 nm), mesopores (1-25nm) and micropore (< 1nm). Activated carbon can be used in three modes: carbon-in-pulp (CIP), carbon-in-leach (CIL) and carbon-in-column (CIC). During the adsorption process carbon is subjected to some losses related to attrition, abrasion, and mechanical losses. Then, it is important to reduce the losses in order o extend the life of the carbon and the adsorption efficiency.
Gold recovery processes with activated carbon comprises the following stages: adsorption, elution or stripping, acid washing, reactivation and classification. It has been noted in several operations that reactivation is important to reduce and minimize costs. It is important to select the appropriate reactivation kiln and to optimize the operation of reactivation; otherwise the carbon recycled to the process will not have appropriate properties to adsorb gold. Essentially, cost optimization is directly related to the basic operating parameters and the variability of the aspects considered during the engineering design. Most the time, parameters experiment almost immediate change due to ore variations, processing rate, operator’s skills and reagent quality.
It has been detected in several gold operations that carbon is considered as a simple element or part of the recovery process and its optimization is not necessary. Nevertheless, when gold operations invested time trying to identify losses and how to solve problems, the benefits associated to metallurgical performance and operating costs were significantly important. For example, some plant metallurgists overlook the design of the adsorption tanks or the classification of the carbon. There are potential savings for each gold operation.