Low-cost activated carbon was prepared from Polygonum orientate Linn. (PL) by phosphoric acid activation. Its ability to adsorb Pb(II) ions from aqueous solutions was examined. Through SEM, XRD, BET, and FTIR analyses, the PL-activated carbon (PLAC) was found to have a porous structure with a surface area of about 1400 m(2)/g. Carboxyl groups played an important role in the adsorption of Pb(II) through blocking studies. The sorption system followed a pseudo second-order kinetic model, and the equilibrium time was obtained after 30 min. The adsorption isotherms were simulated well by the Langmuir model. The adsorption of Pb(II) on PLAC was strongly dependent on pH and ionic strength, indicating an ion-exchange mechanism. Regeneration studies showed that PLAC could be used several times by desorption with an HCl reagent. (C) 2010 Elsevier Ltd. All rights reserved.