Equilibrium and Kinetic Study of Congo Red Adsorption onto Lignin-Based Activated Carbons

The adsorption of Congo Red (CR) from aqueous solutions has been studied using various activated carbons prepared by us from eucalyptus kraft lignin. The adsorption isotherms were complex; nevertheless their data were fitted to the Langmuir and BET models. Delta G values suggested spontaneous nature of the adsorption processes. The high amounts adsorbed were studied as a function of the operating variables (pH, temperature) as well as the specific surface properties (zero-point charge, burn-off, and porosity) of the activated carbons. The diffusion coefficients have been estimated on the basis of an internal diffusion controlling mechanism for the net adsorption rate. Therefore, the obtained results in the present study should be of utility for the preparation of new adsorbents and they should make a contribution to design the adsorption equipment. Technical, economical, and environmental concerns have been considered in the purpose of the present study for water purification where that is polluted by anionic dyes.