A Box-Behnken factorial design coupled with surface response methodology was used to evaluate the effects of temperature, pH and initial concentration in the Cu(II) sorption process onto the marine macro-algae Ascophyllum nodosum. The effect of the operating variables on metal uptake capacity was studied in a batch system and a mathematical model showing the influence of each variable and their interactions was obtained. Study ranges were 10-40 degrees C for temperature, 3.0-5.0 for pH and 50-150 mg L-1 for initial Cu(II) concentration. Within these ranges, the biosorption capacity is slightly dependent on temperature but markedly increases with pH and initial concentration of Cu(II). The uptake capacities predicted by the model are in good agreement with the experimental values. Maximum biosorption capacity of Cu(II) by A. nodosum is 70 mg g(-1) and corresponds to the following values of those variables: temperature = 40 degrees C, pH = 5.0 and initial Cu(II) concentration = 150 mg L-1. (C) 2009 Elsevier B.V. All rights reserved.