EQUILIBRIUM ISOTHERM, KINETIC MODELING, AND CHARACTERIZATION STUDIES OF CADMIUM ADSORPTION IN AN AQUEOUS SOLUTION BY ACTIVATED CARBON PREPARED FROM BAUHINIA PURPUREA LEAVES

摘要

Cadmium is the toxic metal selected for adsorption in this study and adsorbent of interest was activated carbons prepared from Bauhinia Purpurea leaves as a plant biomass. Batch experimental studies conducted for the given adsorbent imparted that the experimental data were fitted very well with the Freundlich isotherm for the Cadmium adsorption process. The sorption kinetic studies for a given adsorbent indicated that the adsorption tends to follow the pseudo-second order. The suitability of kinetic models followed in the order by Second - order kinetic model > First - order model >Elovich model > Intra-particle diffusion model.The mean adsorption energy E value of Cadmium adsorption was decreased with increasing isothermal temperature (303–323K) from 1.936 to 1.79 kJ/mole. It was observed that the scope of an ordinary free energy credited to physical adsorption and the force of attraction between the adsorbate and adsorbent is very weak, therefore this type of adsorption can be easily reversed by heating or by decreasing the pressure. The characterization of metal-adsorbent interactions before and after adsorption was studied using SEM, FTIR and XRD techniques. FTIR spectrum of raw activated carbon of Bauhinia Purpurea leaves reveals that there were a large number of hydroxyl and carboxyl groups present on the surface of the adsorbent, which possibly reacted with metal ions in aqueous solution.