Biosorption of Cd(II) and Cr(III) from aqueous solution by moss (Hylocomium splendens) biomass: Equilibrium, kinetic and thermodynamic studies

The biosorption characteristics of Cd(II) and Cr(III) ions from aqueous solution using the moss (Hylocomium splendens) biomass were investigated in terms of equilibrium, kinetics and thermodynamics. Optimum biosorption conditions were determined as a function of pH, biomass dosage, contact time, and temperature. Langmuir, Freundlich and Dubinin-Radushkevich (D-R) models were applied to describe the biosorption isotherm of the metal ions by H. splendens biomass. Langmuir model fitted the equilibrium data better than the Freundlich isotherm. The maximum biosorption capacity (q_m) of H. splendens biomass was found to be 32.5 mg/g for Cd(II) ion and 42.1 mg/g for Cr(III) ion. The mean free energy values evaluated from the D-R model indicated that the biosorption of Cd(II) and Cr(III) onto H. splendens biomass was taken place by chemical ion-exchange. The calculated thermodynamic parameters, ΔG°, ΔH° and ΔS° showed that the biosorption of Cd(II) and Cr(III) ions onto H. splendens biomass was feasible, spontaneous and exothermic under examined conditions. Experimental data were also tested in terms of biosorption kinetics using pseudo-first-order and pseudo-second-order kinetic models. The results showed that the biosorption processes of both metal ions followed well pseudo-second-order kinetics.