Removal of heavy metal ions from aqueous solutions using carbon aerogel as an adsorbent

The removal of Cd(II), Pb(II), Hg(II), Cu(II), Ni(II), Mn(II) and Zn(II) by carbon aerogel has been found to be concentration, pH, contact time, adsorbent dose and temperature dependent. The adsorption parameters were determined using both Langmuir and Freundlich isotherm models. Surface complexation and ion exchange are the major removal mechanisms involved. The adsorption isotherm studies clearly indicated that the adsorptive behaviour of metal ions on carbon aerogel satisfies not only the Langmuir assumptions but also the Freundlich assumptions, i.e. multilayer formation on the surface of the adsorbent with an exponential distribution of site energy. The applicability of the Lagergren kinetic model has also been investigated. Thermodynamic constant (K-ad), standard free energy (Delta G(0)), enthalpy (Delta H-0) and entropy (Delta S-0) were calculated for predicting the nature of adsorption. The results indicate the potential application of this method for effluent treatment in industries and also provide strong evidence to support the adsorption mechanism proposed. (c) 2005 Elsevier B.V. All rights reserved.