Adsorption of Cadmium Ion on Activated Carbon in the Presence of Either Br^- or SCN-t

Abstract

In the presence of inorganic anion, many heavy metal ions are known to be, adsorbed on activated carbon as either [MX4]2- anions or reduced forms. In this paper, the effect of Br^- (or SCN-) concentration on the adsorption of Cd²⁺ on activated carbon was investigated in connection with the amount of [CdXn] (X=Br^-, SCN-) complexes existing in equilibrium solution. The amount of adsorbed Cd²⁺ was analyzed with Langmuir's 41sorption isotherms.
The amount of residual Cd²⁺ showed a minimum at the concentration of Br^-, (or SCN-) about 0.4 mol/l at which the distribution of [CdX2] or [CdX3]- complexes were maximum (Fig.2). The Langmuir's isotherm showed a good linearity at a constant Br^- (or SCN-) concentration (Figs.3, 4). The saturated adsorption capacities obtained from the intercept of the adsorption isotherms were constant for the same activated, carbon even if the concentration of Br^- (or SCN-) changed (Table 2), and the adsorption equilibrium constants for [CdX2] and [CdX0]- were obtained by the analysis of the slopes of adsorption isotherms using Equation (3) (Table 3, Figs.5, 6). The calculated values of residual Cd²⁺ from Equation (4) using these equilibrium constants are in fair agreement with the experimental values on adsorption of Cd²⁺ in the presence of Br^- (or SCN-) (Fig.7). From these results, it is concluded that [CdX2] and [CdX3]- (X=Br^-, SCN-) complexes play an important role in the adsorption of Cd²⁺ on activated carbon.