Batch Equilibrium and Kinetics Studies of Cd (II) Ion Removal from Aqueous Solution Using Porous Chitosan Hydrogel Beads

In this study chitosan hydrogel beads with porosity ~ ۰.۸۶ and diameter ~ ۲۰.۰۷ mm were prepared from ۸۵ % deacetylated chitosan for removal of Cd۲+ ions from aqueous solutions.  Chitosan powder was dissolved into dilute acetic acid as solvent and formed into spherical beads using a phase inversion technique. The effect of temperature, initial concentration of Cd۲+ ions, and the period of agitation were perused to achieve the best isotherm model. Freundlich model was better fitted than Langmuir model (R۲ > ۰.۹۹ and R۲> ۰.۹۳ respectively, at pH of ۶.۳, and shaker speed of ۲۰۰ rpm), the constants of Langmuir and Freundlich models were calculated, which RL value and qmax (mg/g wet weight) at ۳۰ °C, ۴۰ °C, ۵۰ °C showed maximum uptake capacity of ۶۱.۳۵ (mg/g wet weight) obtained at ۳۰ °C. The calculated heat of adsorption was -۸.۶۹,-۷.۰۵۱, -۵.۵۱۳ kJ mol-۱ at ۳۰, ۴۰, ۵۰ °C respectively which verified an exothermic process. Kinetic studies of the adsorption phenomena were conducted in a batch system by initial concentrations from ۱۰۰ to ۵۰۰ mgL-۱ until the equilibrium concentration Ce (mgL-۱) was reached. First-order, and second-order kinetic models were used; the experimental data were in reliable compliance with second-order kinetic model with R۲ value greater than ۰.۹۷. The rate constants of the kinetic models were also calculated and tabulated. To investigate the surface morphology of the chitosan beads before and after adsorption process, they were observed by the use of Scanning Electron Microscopy (SEM). The surface characterization of the beads in both cases showed metal ions binding toward the surface of porous chitosan beads. All of the experiments carried out at pH of ۶.۳ and agitation rate of ۲۰۰ rpm, which were opted according to optimum status of previous researcher’s reports.

کلیدواژه ها:

Chitosan ، Hydrogel beads ، Adsorption ، Cd ۲+ ، Kinetics