Removal of chromate by Amberlite A21: kinetics and equilibrium studies

In the present study, batch experiments were performed to characterize the effectiveness of Amberlite A21 in the removal of Cr(VI) ions from aqueous solutions. The retention by the resin is studied as a function of pH, temperature, chromate concentration and the presence of foreign ions. The exchange kinetics and isotherms are evaluated in the absence and in the presence of foreign ions at different pH. The obtained results show that the highest removal efficiency occurs in the pH range 3-5. The chromate removal increases with the increase in temperature. The calculated thermodynamic data imply that the process is endothermic. Whatever the pH and the competitive ion, the chromate removal kinetics is well described by the first-order model. Both Langmuir and Freudlich isotherms can describe the experimental data. At pH 3.3, the exchange capacity calculated by the Langmuir equation is estimated to 106 mg (Cr(VI)/g (resin)) in single system, 118 mg/g in the presence of chloride and 105 mg/g in the presence of sulfate.