Combined adsorption and ion exchange equilibrium of phenol on Amberlite IRA-420

Phenol can be efficiently removed from polluted wastewaters by using a strong-base anion exchanger. It was observed that its removal capacity was higher than that of other known adsorbents. This high capacity of anion exchangers for the removal of phenolic compounds has been previously observed but the reason for so high capacity has not been suitably explained yet. For that reason, isotherms of phenol removal on Amberlite IRA-420 were reproduced by both empirical and theoretical treatments. A simple empirical model was able to reproduce the measured total uptake of phenol. The pH dependent equilibrium isotherms can be explained assuming that the uptake of phenol in the resin is accomplished by two ways: ion exchange and molecular adsorption. The theoretical treatment allowed us to verify that the adsorption capacity does not depend on pH and to obtain the parameter values required for both adsorption and ion exchange isotherms. The importance of each phenomenon in the process is analyzed. Adsorption of phenol onto IRA-420 is predominant at acidic pH, whereas both adsorption and ion exchange are important at alkaline pH. The theoretical model developed herein enables the relation between phenol removal, pH and amount of resin to be determined.