A new type of adsorbent which is capable of selectively adsorbing lead(II) ions (Pb2+) was developed. The adsorbent was generated by reaction of sodium alginate with NB-9000B, a polyisocyanate type of prepolymer of polyurethane. The adsorbent was a hydrophilic and flexible alginate/polyurethane composite foam (ALG/PUCF) with the alginate chemically immobilized in the cell walls of the foam. Acid-base titration was used to quantify the concentration of carboxyl groups, which are present on the alginate molecules of the ALG/PUCF, functioning as the essential sites for binding Pb2+. For the optimized ALG/PUCF, the carboxyl was found to be 38.2 +/- 1.2 mu mol/g of dry weight. The capacity for adsorbing Pb2+ ions in 1.0 g of dry weight of the optimized ALG/PUCF was found to be 16.0 +/- 2.1 mu mol, indicating that ion exchange was the essential mechanism for adsorbing Pb2+ ions. The adsorption capacity was found to be highly sensitive to the pH of the sample solution; lower pH (< 3) significantly decreased the adsorption. Competing ions such as Mg2+, Ca2+, and Cd2+ also caused a decrease in selectivity and capacity for Pb2+ adsorption, although the effect was less pronounced than the effect of pH. The ALG/PUCF is highly stable, flexible and easy to use. ALG/PUCF is also reusable after regeneration with ethylenediamine-N,N,N',N'-tetraacetic acid, disodium salt (EDTA-2Na). Due to these features, this adsorbent may be highly useful for elimination of Pb2+ ions from contaminated water. (c) 2008 Elsevier B.V. All rights reserved.