Effect of anions and cations on cadmium sorption kinetics from aqueous solutions by chitin: experimental studies and modeling

The effect of ions, including Na+, Mg2+, Ca2+, Cl-, SO42- and CO32-, at various initial concentrations, on the kinetics of cadmium sorption by chitin was studied at 25 degreesC and free initial pH solution in batch conditions. The presence of these ions in solution was found to inhibit the uptake of cadmium by chitin to different degrees: sodium and chloride ions have no significant effect. For Mg2+, Ca2+, SO42- and CO32- ions, the effects ranged from a large inhibition of cadmium by Ca2+ and C-3(2-) to a weak inhibition by Mg2+ and SO42-. These results indicate that the uptake sites of these ions are the same. No ion was found to enhance cadmium uptake. The results also showed that the kinetics of sorption are best described by a pseudo second-order expression than a first or second-order model. (C) 2004 Elsevier Ltd. All rights reserved.