Kinetic and mass transfer analyses of metal biosorption by Caulerpa lentillifera

This study examined kinetics and mass transfer in the biosorption of heavy metals onto Caulerpa lentillifera. The sorption capacity of Cu2+, Pb2+ and Cd2+ from aqueous solution increased with initial metal concentration and decreased with biosorbent dose. Kinetic data were well described using the pseudo-second-order model. Results showed that both external mass transfer and intraparticle diffusion were rate limiting steps in the biosorption process. Activation energy of biosorption kinetics fell in the range of 3–13 kJ/mol. The biosorption of Cu2+, Cd2+ and Pb2+ on the biomass correlated well with the Langmuir isotherm (R2 > 0.99) with maximum sorption capacities at 293 K of 0.169, 0.085 and 0.177 mol/kg for Cu2+, Cd2+ and Pb2+ ions, respectively. Thermodynamic studies demonstrated that the biosorption process was spontaneous and endothermic under conditions. The results were analyzed to determine external mass transfer coefficient which was proved to be related to the rate constant of Langmuirian kinetic model.

Research Highlights
► Pseudo 1st and 2nd order models are used to determine mass transfer coefficient.
► External mass transfer and intraparticle diffusion were rate limiting steps.
► External mass transfer coefficient relates to Langmuirian kinetic constants.
► Kinetic data of sorbent dose can be predicted from initial concentration.
► Biosorption process was spontaneous and endothermic under thermodynamic conditions.