Adsorption of Cr(VI) and As(III) on coaly activated carbon in single and binary systems

In single component system, the adsorption of Cr(VI) and As(III) increase with contact time. Solution pH is found influencing the adsorption. Cr(VI) removal is found to be maximum (98%) at pH = 2. While, As(III) removal is found to be maximum at pH = 6 (77.2%). The adsorption capacity of Cr(VI) is greater than that of As(III) in single component system. Several adsorption isotherms were used to fit the equilibrium data. The adsorption kinetic data of Cr(VI) and As(III) were analyzed and is found fitting well in a pseudo-second-order equation both in single and binary systems. In binary system, the adsorption of As(III) is generally higher than that in single system. The pseudo-second-order rate constant k2 is 0.5037 g/mg min in binary system larger than 0.0782 g/mg min in single system. However, the presence of As(III) in solution does not significantly influence the capacity of Cr(VI) adsorption on coaly activated carbon (CAC). The complexation between Cr(VI) and As(III) influence the adsorption, resulting in increased adsorption of As(III). The complexation structure of As(III), Cr(VI) and CAC was proposed as A–Cr(VI)–As(III) (A represents the adsorption site on the CAC).