Thermodynamic studies on the bioadsorption of Cr(III) onto Agave lechuguilla biomass were conduced. The experimental results at different temperatures were modeled using the Langmuir and Freundlich isotherms to obtain the characteristic parameters of each model. Both the Freundlich and Langmuir models were found to represent the bioadsorption process. The average adsorption capacities calculated from Freundlich (4.7 mg/g) and Langmuir (14.2 mg/g) isotherms showed A. lechuguilla to be an effective biomass in the removal of Cr(III) from an aqueous solution. Thermodynamic parameters (Delta G(0), Delta H-0 and Delta S-0) determined in the temperature range from 10 to 40 degrees C along with the parameters of the Dubinin-Radushkevick equation support the idea that the binding of Cr(III) may be caused by interactions with functional groups such as carboxyl groups located on the outer surface of the cell tissue of the bioadsorbent. (c) 2005 Elsevier Ltd. All rights reserved.