Comparison of different kinetic models for adsorption of heavy metals onto activated carbon from apricot stones

In this work single and four-component adsorption kinetics was studied for removal of Pb(2+), Cd(2+), Cu(2+) and Zn(2+) from aqueous solutions with activated carbon from apricot stones. The adsorption equilibrium was calculated by the Langmuir model for single- and multi-component systems. Comparison of three kinetic models for internal diffusion control was performed. The steep initial part of the kinetic curve was accounted for by an intercept term in the linear representation of the models of Weber and Morris, Boyd and the moment method. The Weber and Morris model was found to correlate best with the experimental data. The intraparticle diffusion coefficients for the individual ions are in the range 1-3x10(-8)cm(2)/s. Similar results were obtained by the moment method applied to homogeneous solid phase diffusion control. Lower values of the kinetic parameters were obtained in four-component solutions. The calculated summary diffusion coefficient in the multi-component system is close to that obtained for single-component solutions with the same total initial ion concentration.