Adsorption of heavy-metal ions on poly(ethylene imine)-immobilized poly(methyl methacrylate) microspheres

Poly(methyl methacrylate) (PMMA) microspheres carrying poly(ethylene imine) (PEI) were prepared for the removal of heavy-metal ions (copper, cadmium, and lead) from aqueous solutions with different amounts of these ions (50-600 mg/L) and different pH values (3.0-7.0). Ester groups in the PMMA structures were converted to imine groups in a reaction with PEI as a metal-chelating ligand in the presence of NaH. The adsorption of heavy-metal ions on the unmodified PMMA microspheres was very low [3.6 mu mol/g for Cu(III, 4.6 mu mol/g for Cd(II), and 4.2 mu mol/g for Pb(II)I. PEI immobilization significantly increased the heavy-metal adsorption [0.224 mmol/g far Cu(II), 0.276 mmol/g for Cd(II), and 0.126 mmol/g for Pb(II)]. The affinity order of adsorption (in moles) was Cd(II) > Cu(II) > Pb(II). The adsorption of heavy-metal ions increased with increasing pH and reached a plateau value around pH 5.5. Their adsorption behavior was approximately described with the Langmuir equation. (C) 2001 John Wiley & Sons, Inc.