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 ~ 0.86 and diameter ~ 20.07 mm were prepared from 85 % deacetylated chitosan for removal of Cd2+ 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 Cd2+ ions, and the period of agitation were perused to achieve the best isotherm model. Freundlich model was better fitted than Langmuir model (R2 > 0.99 and R2> 0.93 respectively, at pH of 6.3, and shaker speed of 200 rpm), the constants of Langmuir and Freundlich models were calculated, which RL value and qmax (mg/g wet weight) at 30 °C, 40 °C, 50 °C showed maximum uptake capacity of 61.35 (mg/g wet weight) obtained at 30 °C. The calculated heat of adsorption was -8.69,-7.051, -5.513 kJ mol-1 at 30, 40, 50 °C respectively which verified an exothermic process. Kinetic studies of the adsorption phenomena were conducted in a batch system by initial concentrations from 100 to 500 mgL-1 until the equilibrium concentration Ce (mgL-1) was reached. First-order, and second-order kinetic models were used; the experimental data were in reliable compliance with second-order kinetic model with R2 value greater than 0.97. 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 6.3 and agitation rate of 200 rpm, which were opted according to optimum status of previous researcher’s reports.