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

摘要

Novel chelating sponge (PVA-M-H) was prepared with polyvinyl alcohol by graft polymerization and nucleophilic substitution. E.A, SEM, FT-IR, ~(13)CNMR, 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 Ca~(2+) and Mg~(2+) was up to 10 mmolL~(-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.