In this study, chemically modified radish cake, a by-product of biodiesel production, was used to remove Cd2+ from aqueous solutions. The chemical modification was carried out by treating the radish cake with citric acid (CRC), NaOH (NRC) or the combination of citric acid and NaOH (CNRC). The sorbents were characterized by elemental analysis, surface area analysis, infrared spectroscopy (FTIR), potentiometric titration (PT), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), and thermogravimetric analysis (TGA). The effect of the chemical treatment and contact time on cadmium sorption was evaluated. The equilibrium data were analyzed using Freundlich and Langmuir models. The maximum sorption capacity obtained by the Langmuir isotherm was 58.5 mg/g and 64.10 mg/g for the CRC, and CNRC sorbents, respectively. Complete desorption of Cd2+ was achieved using 0.1 mol/L HNO3. The results obtained demonstrate that chemically modified radish cake has potential as a sorbent for Cd2+ removal from aqueous solutions. (C) 2012 Elsevier B.V. All rights reserved.