Keywords: 
• Laminaria japonica /
• cadmium /
• adsorption kinetics /
• thermodynamics

Abstract: A batch method was used to investigate the kinetics and thermodynamics of cadmium(Ⅱ) biosorption onto Laminaria japonica, where the Lagrangian pseudo-first-order and pseudo-seconder-order kinetic model, Langmuir, Freundlich and DubininRadushkevich(D-R) isotherm models were applied to simulate the experimental parameters. The results show that the efficiency of biosorption is increased with the time of reaction and the maximum efficiency is attained at 60 min. The maximum efficiency of biosorption is decreased from 90.2％ to 77.5％ when the temperature is changed from 20℃ to 50℃. The biosorption of cadmium(Ⅱ) onto Laminaria japonica is found to follow pseudo-seconder-order kinetic model well. On the other hand,the biosorption of cadmium(Ⅱ) onto Laminaria japonica follows Langmuir and D-R isotherm models well, which indicates that the biosorption taken place at the functional groups/binding sites on the surface of the biosorbent which is regarded as monolayer biosorption. From the D-R isotherm model, the mean free energy is calculated as 11.4 kJ/mol, indicating that the biosorption of cadmium (Ⅱ) is taken place by chemisorption. The calculated thermodynamic parameters (ΔG°,ΔH° and ΔS°) show that the biosorption of cadmium (Ⅱ) onto Laminaria japonica is feasible, spontaneous and exothermic.