4. Investigation into the Adsorption of Cadmium and Lead by Polyaniline Grafted Cross-Linked Chitosan Beads from Aqueous Solution

This research explored the enhancement of chitosan beads by cross-linking and grafting to use the grafted beads to extract cadmium and lead from polluted water. XRD and SEM characterized the beads to bear evidence of positive cross-linking and grafting. Batch investigation was conducted with regards to the parameters of adsorption such as pH, initial concentration, contact time and adsorbent dose. Equilibrium data were collected from the adsorption investigation, and the data were compared with the isotherm models including Langmuir and Freundlich. The maximum adsorption potential for cadmium and lead ions was found to be, respectively, 145 mg/g and 114 mg/g at a temperature of 45 °C from the Langmuir model. Thermodynamic parameters such as Gibbs free energy change (ΔG^o), enthalpy change (ΔH^o) and entropy shift (ΔS^o) were subsequently determined and the findings illustrate that polyaniline adsorption of cadmium and lead ions on the produced adsorbent (GXCS) is spontaneous and endothermic in nature. The first-order pseudo- and second-order pseudo-models have been used for the study of kinetic data for both metal ions. The data match well with the second-order pseudo-model. Over five consecutive cycles of adsorption/desorption, the GXCS filled with cadmium and lead ions was measured. Nevertheless, 0.5 M HCl was successfully used among the eluents examined in desorbing the adsorbent expended and among the eluents that was investigated 0.5 M HCl was successfully used in desorbing the spent adsorbent and a percentage desorption of 98.94 and 97.50% was acquired for cadmium and lead ions correspondingly, at a desorption time of 180 min.