Cadmium biosorption was evaluated in 15 samples of heat-inactivated seaweeds collected from the coast of Rio de Janeiro State; Brazil. The classical Langmuir and Freundlich sorption models were fitted to the results in order to test whether these equations could appropriately describe the process of passive biosorption uptake. Depending on the algal sample and on some assumptions, both models could be applied to this study. The possible ion-exchange mechanism associated with the adsorption process was also investigated, as well as the effect of pH on biosorption and re-use of the different biomasses through several biosorption/desorption cycles.