Adsorption kinetics of an ion-exchange column in fixed-bed operation : a simple model approach

Abstract

The adsorption kinetics of Ca2+ and Mg2+ ions on a strongly acid cation resin (Dowex50-X8) in packed-bed column were studied at room temperature. Prior to the column studies, the adsorption of the metal ions from single-ion and mixed-ion solutions was carried out in batch operation in order to develop a correlation between equilibrium adsorption capacity (qe) and equilibrium metal concentration (ce). The correlation was then incorporated into a simple expression for the adsorption rate which, subsequently, was shown to predict the adsorption of metal ions in fixed-bed operation reasonably well. In addition, the no adsorption experiment was performed so as to investigate the flow characteristics of the ion-exchange column. It was found that the column could be modelled by one CSTR and one ideal PFR connected in series with a CSTR volume of 2.5 ml. Lastly, the competitive adsorption of Ca2+ and Mg2+ in mixed-ion system was examined. The results strongly suggested that Ca2+ was preferentially adsorbed by the Dowex50-X8 resin than Mg2+. The adsorption rate and adsorbed amount at equilibrium of Ca2+ were higher than those of Mg2+. This preferential adsorption was also supported by the results obtained from the desorption studie