Cadmium removal from aqueous solutions by chitin: kinetic and equilibrium studies.

A fundamental investigation on the removal of cadmium ions from aqueous solutions by chitin was conducted in batch conditions. Kinetic data and equilibrium removal isotherms were measured. The influence of different experimental parameters such as time contact, initial concentration of cadmium, chitin mass, particles size, agitation speed, temperature and the nature of cadmium salt, on the kinetics of cadmium removal was studied. The main parameters that play an important part in removal phenomenon were initial cadmium concentration, particle size and chitin mass. Other parameters such as agitation speed, temperature and the nature of cadmium salt, showed a restricted effect on the removal kinetics. The process follows a pseudo second-order kinetics. The cadmium uptake of chitin was quantitatively evaluated using sorption isotherms. In order to describe the isotherm mathematically, the experimental data of the removal equilibrium were correlated by either the Langmuir or Freundlich equations. Results indicated that the Langmuir model gave a better fit to the experimental data than the Freundlich equation. Scanning electron microscopy coupled with a X-ray energy dispersed analysis for cadmium-equilibrated chitin, demonstrated that cadmium-containing nodules existed on the surface chitin.