Some of the heavy metal ions such as cadmium are toxic and represent as hazardous pollutants due to their persistence in the environment. In this study the ground discarded tire rubber was used for the sorption of cadmium from aqueous solution. The batch sorption tests were conducted to investigate the sorption of Cd(II) by discarded tire rubber in the presence and absence of ultrasound. To assess the capability of sorbent, research parameters such as ultrasonic waves, solution temperature, particle size of ground tire and others were investigated. The experimental data were fitted in Langmuir model better than Freundlich one. Therefore, the former model was applied to the sorption equilibrium in order to determine the maximum metal sorption capacity in the presence and absence of ultrasound. The Langmuir constants were also obtained from the isotherms under different conditions. In the presence of ultrasound the tire rubber was a more efficient sorbent for this pollutant than its absence. According to the results, the internal porous and film diffusions were both effective in the sorption process. The porous and film diffusion coefficients of the ground tire rubber were, respectively, about 1.8 and 2.7 times more in the presence of ultrasound than its absence. The effect of ultrasound on the sorption process could be explained by the thermal and non-thermal properties of ultrasonic field. (c) 2005 Elsevier B.V. All fights reserved.