The adsorption of metallic ions on the surface of activated carbons is the result of the interactions between the aqueous solution and the different active sites on the carbon surface. The presence of different surface functional groups with either acid or basic properties is responsible for the surface hydrolysis of the activated carbons in aqueous solutions and for the preferential interaction with cations and anions, respectively. These structures are generically denoted as COxHy and are mainly originated by the activation process of the raw material [15]. The presence of surface heteroatoms and the structure of the graphitic layer itself, as well as the ash properties, determine the occurrence of active sites acting either as Lewis acids or as bases, able to capture ions with base or acid character, or as nucleophilic/electrophilic active sites [15] and [16]. Furthermore, some of these groups, such as lactonic and phenolic, exploit reducing properties, which are also observed for the same graphitic layer. Lakatos et al. [17] pointed out the role of surface functional groups with reducing properties in determining the adsorption of chromium ions. During an adsorption experiment, the occurrence of surface reduction reactions can be observed by measuring Cr(VI) and total chromium in solution.