Biosorption potential of the red alga, Gracilaria verrucosa for the removal of Zn2+ ions from aqueous media: Equilibrium, kinetic and thermodynamic studies

Abstract

The aim of this study is to explore the potential of red alga, G.verrucosa as biosorbent to remove zinc (II) from aqueous solution. Experiments are carried out as a function of solution pH, biosorbent dosage, contact time and temperature. The equilibrium data were analyzed using the Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) isotherm models. The maximum biosorption capacity of G.verrucosa biomass for Zn (II) was found to be 96.1 mg/g at pH 5, biomass concentration 4 g/L, contact time 60 min, and temperature 20 ◦C. The mean free energy E (9.62 kJ/mol) got from the D-R isotherm indicated a chemical ion-exchange mechanism. Kinetic studies showed that pseudo-second order described the biosorption experimental data better than the pseudo-first order kinetic model. Thermodynamic parameters showed that the biosorption of Zn (II) onto G.verrucosa biomass was feasible, spontaneous and exothermic under examined conditions. FTIR analysis demonstrates that carboxyl and hydroxyl groups were involved in the biosorption of the metal ions.