Poly(N-vinyl-2-pyrrolidone-g-dtric acid) [P(VP-g-CA)] hydrogels were prepared for the removal of U(VI), Pb(II), and Cd(II) from aqueous solutions containing different amounts of these ions (2.5-10 mg/L). Different pHs (1-13), temperatures (20-40degreesC), and ionic strengths (0.5M) were also tried for the adsorption behavior of these ions. The competitive adsorption values of U(VI), Pb(II), and Cd(II) ions on pure poly(N-vinyl-2-pyrrolidone) were low [0.71-2.03 mg of U(VI)/g of dry gel, 0.15-1.58 mg of Pb(II)/g of dry gel, and 0.10-0.68 mg of Cd(II)/g of dry gel]. The incorporation of citric acid significantly increased the adsorption of these ions [0.67-2.12 mg of U(VI)/g of dry gel, 0.44-1.88 mg of Pb(II)/g of dry gel, and 0.04-0.92 mg of Cd(II)/g of dry gel for P(VP-g-CA)-1; 0.71-2.36 mg of U(VI)/g of dry gel, 0.60-2.16 mg of Pb(II)/g of dry gel, and 0.14-0.80 mg of Cd(II)/g of dry gel for P(VP-g-CA)-2; and 0.79-2.47 mg of U(VI)/g of dry gel, 0.70-2.30 mg of Pb(II)/g of dry gel, and 0.20-0.86 mg of Cd(II)/g of dry gel for P(VP-g-CA)-3]. The observed affinity order of adsorption was U(VI) > Pb(II) > Cd(II) for competitive conditions. The optimal pH range for the removal of these ions was 5-9. Competitive adsorption studies showed that other stimuli, such as the temperature and ionic strength of the solution, also influenced the U(VI), Pb(II), and Cd(II) adsorption capacity of P(VP-g-CA) hydrogels. (C) 2003 Wiley Periodicals, Inc.