Graft copolymerization of acrylic acid (AA) onto starch was carried out with ceric ammonium nitrate as initiator under nitrogen atmosphere. The grafting percentages (GP%) of starch-graft-acrylic acid (St-g-AA) copolymers were determined. The effect of GP% of St-g-AA copolymers on the competitive removal of CO2+, Ni2+, Zn (2+) ions from aqueous solution was investigated at different pH (2, 4, 6). The concentrations of each ion in aqueous solution 5 mmol/ L. Effects of various parameters such as treatment time, initial pH of the solution and grafting percentage of starch graft copolymers were investigated. Metal ion removal capacities of St-g-AA copolymers increased with Gp%. of the copolymers and pH. The results show that the removal of metal ions followed as given in the order Co2+ > Ni2+ > Zn2+. In this study, metal ion removal capacities were determined by atomic absorption spectrophotometer (AAS). (C) 2007 Wiley Periodicals, Inc.