Although the search for new and innovative treatment technologies has focused attention on the metal binding capacities of various microorganisms, the kinetics of the metal uptake process and the description of the thermal properties of biosorption remain essentially unknown. Biosorption equilibrium, kinetics and thermodynamics of nickel(II) ions to Chlorella vulgaris were studied in a batch system with respect to temperature and initial metal ion concentration. Algal biomass exhibited the highest nickel(II) uptake capacity at 45 degreesC at an initial nickel(II) ion concentration of 250 mg l(-1) and an initial pH of 4.5. Biosorption capacity increased from 48.1 to 60.2 mg g(-1) with an increase in temperature from 15 to 45 degreesC at this initial nickel(II) concentration. Freundlich, Langmuir and Redlich-Peterson isotherm models were applied to experimental equilibrium data of nickel(11) biosorption depending on temperature. Equilibrium data fitted very well to all the equilibrium models in the studied concentration range of nickel(II) ions at all the temperatures studied. The saturation type kinetic model was applied to experimental data at different temperatures changing from 15 to 45 degreesC to describe the batch biosorption kinetics assuming that the external mass transfer limitations in the system can be neglected and biosorption is chemical sorption controlled. The activation energy of biosorption (EA) was determined as 25.92 kJ mole(-1) using the Arrhenius equation. Using the thermodynamic equilibrium coefficients obtained at different temperatures, the thermodynamic constants of biosorption (DeltaG, DeltaH and DeltaSdegrees) were also evaluated. (C) 2002 Elsevier Science Ltd. All rights reserved.