Removal of Copper and Lead from Aqueous Solution by Adsorption onto Cross-Linked Chitosan/Montmorillonite Nanocomposites in the Presence of Hydroxyl-Aluminum Oligomeric Cations: Equilibrium, Kinetic, and Thermodynamic Studies

Adsorption removal of Cu (II) and Pb (II) on cross-linked chitosan/Al-13-pillared montmorillonite (CCPM) was examined in solutions. The chitosan dosage was drastically reduced in the new nanocomposite, which is made from the treated clay (Al-13-pillared montmorillonite). Several important parameters that influenced the adsorption of Cu (II) and Pb (II) ions, such as cross-linked chitosan-to-clay ratio, pH, temperature, initial concentration, dosage, and contact time effect, were systematically investigated. Result showed that in the nanocomposite with cross-linked chitosan-to-clay ratio of 0.45:1, the maximum removal efficiencies of Cu (II) [pH 6.5, dosage 10 g/L, initial Cu (II) concentration 100mg/L, contact time 2 h, 298 K] and Pb (II) [pH 6.0, dosage 5g/L, initial Pb (II) concentration 100mg/L, contact time 2 h, 298 K] were 96.0% and 99.5%, respectively. Kinetic and isotherm studies have indicated that the adsorption process of Cu (II) or Pb (II) nanocomposites was better fitted by the pseudo-second-order equation and the Freundlich equation, with chemical adsorptions as the rate-limiting step. The metal-ion affinity to the functional groups of CCPM followed the order Pb (II) > Cu (II). The thermodynamic parameters Delta H and Delta S values showed that the sorption process of Cu (II) or Pb (II) was spontaneous (Delta G<0), was endothermic (Delta H<0), and had decreased entropy (Delta S<0). HNO3 (0.1 M) could be a good desorbent in the recovery of metal ions after adsorption and regeneration of the adsorbent.