Adsorption of Ni(II) and Cd(II) from water by novel chelating sponge and the effect of alkali-earth metal ions on the adsorption

Novel chelating sponge (PVA-M-H) was prepared with polyvinyl alcohol by graft polymerization and nucleophilic substitution. E.A, SEM, FT-IR, (CNMR)-C-13, and XPS analyses were used to characterize PVA-M-H. The equilibrium adsorption capacities of PVA-M-H for Ni(II) and Cd(II) were 65.39 and 125.11 mg g(-1), respectively. Within the range of 278-308 K, the adsorption enthalpy changes of Ni(II) and Cd(II) on PVA-M-H were about 36.39-37.72 kJ mol(-1), and the free energy were about -13.27 to -1.7 kJ mol(-1). Both pseudo-first- and -second-order equations fit the adsorption kinetic curves well, and the initial adsorption rates of Ni(II) and Cd(II) onto PVA-M-H were 17.83 and 34.81 mg (g min)(-1), respectively. Although the presence of alkali-earth metal ions in solution decreased Ni(II) and Cd(II) removal, PVA-M-H still retained more than 60 and 80% of its adsorption capacity even as the concentration of Ca2+ and Mg2+ was up to 10 mmol L-1, respectively. Both 0.1 M HCl and 0.1 M EDTA solution could desorb Ni(II) and Cd(II) from PVA-M-H effectively, and the adsorption capacity of PVA-M-H for Ni(II) and Cd(II) could still maintain more than 90% level without any obvious decrease at the fifth cycle. (C) 2013 Elsevier B.V. All rights reserved.