Kinetics of mixed-ion metal adsorption in a packed ion-exchange column

Abstract

The adsorption kinetics of metal ions on a strong-acid cation resin (Dowex50-x8) from mixed-ion solutions of Ca2+/Mg2+/H+ were investigate in both batch and fixed-bed operations. From batch adsorption experiments, the relationship between the concentrations of metal ions on the resin (qe) and in the solution (ce) at equilibrium was developed and the adsorption rate constant (K) was determined. From column dynamic studies in the absence of metal adsrption, the packed column was found to be best as described by a small CSTR connected in series with an ideal PFR. By combining the adsorption parameters with the flow characteristics, the mathematical model was completed and then used to predict the adsorption in a mixed-ion system of Ca2+ and Mg2+ in fixed-bed operation. The model was shown to adequately describe the metal adsorption in the mixed-ion system. The competitive adsorption of Ca2+ and Mg2+ ions in a mixed-ion system was also examined. Both batch and column results revealed that Ca2+ ions were preferentially adsorbed by the Dowex50-x8 resin. The adsorption rate and adsorbed amount at equilibrium of Ca2+ ions were higher than those of Mg2+ ions while the desorption rate and desorbed amount of C12+ ions were significantly lower during regeneration.