Kinetics of biosorption of heavy metals by Caulerpa lentillifera

Abstract

The biosorption of heavy metals onto biomaterial derived from the marine alga, Caulerpa lentillifera, was investigated. The biosorption equilibrium was determined as a function of initial heavy metal concentration, sorbent dose, agitation rate and temperature on biosorption. The uptakes of Cu²⁺, Pb²⁺ and Cd²⁺ from aqueous solution increased with initial metal concentration and decreased with biosorbent dose. The optimal agitation rate was determined at 150 rpm for all heavy metal ions at 20 degree celsius. The biosorption of Cu²⁺, Cd²⁺ and Pb²⁺ on the biomass was correlated well (R² > 0.99) with the Langmuir isotherm as compared to Freundlich isotherm under the concentration range studied. According to Langmuir isotherm, the maximum sorption capacities were 0.19, 0.11 and 0.18 mmol g⁻¹ for Cu²⁺, Cd²⁺ and Pb²⁺ ions, respectively. The pseudo-first-order and pseudo-second-order kinetic models were applied to test the experimental data and the results were better described using the pseudo-second-order. Thermodynamic examination of the sorption (the Gibbs free energy, entropy and enthalpy) demonstrated that the biosorption process was spontaneous and endothermic under natural conditions. Ion exchange took part as a significant mechanism in the sorption of Cu²⁺ and Cd²⁺, but not for Pb²⁺. The level of ion exchange was lower with an increase in the initial metal concentration which indicated the limitation of the metals for the ion exchange process.