Adsorption of Cu(II), Cd(II), Zn(II), Mn(II) and Fe(III) ions by tannic acid immobilised activated carbon

In this study, adsorption of the toxic metal ions onto tannic acid immobilised activated carbon was investigated depending on pH, contact time, carbon dosage, adsorption capacity and adsorption isotherms by employing batch adsorption technique. In the optimum conditions, the percent adsorption of metal ions were determined for Cu(II) (23.5%), Cd(II) (17.8%), Zn(II) (14.0%), Mn(II) (11.3%) and Fe(III) (17.9%) and results were compared with that of the untreated activated carbon. The order of affinity based on uptake by tannic acid immobilised activated carbon and untreated activated carbon was the same as Cu(II)>Fe(III)>Cd(II)>Zn(II)>Mn(II), but differing in the adsorption capacities. In the studied conditions, the adsorption capacity of tannic acid immobilised activated carbon followed the order of Cu(2.23)>Fe(1.77)>Cd(1.51)>Zn(1.23)>Mn(1.13) in single systems and Fe(1.56)>Cd(1.48)>Zn(1.19)>Mn(1.11) in Cu(II) coupled competitive systems. The adsorption data was correlated to Langmuir and Freundlich isotherm for each metal ion and the data fitted better to the Langmuir isotherm model. A combined ion exchange, complex formation and surface adsorption processes were believed the major adsorption mechanisms playing role in the binding of metal ions. Adsorbed metal ions were effectively desorbed (90.2-98.4%) by using 0.1 M HCl without destroying the modified adsorbent. (C) 2005 Elsevier B.V. All rights reserved.