Biosorption of palladium(II) from aqueous solution by moss (Racomitrium lanuginosum) biomass: Equilibrium, kinetic and thermodynamic studies

The biosorption potential of Racomitrium lanuginosum as aquatic moss biosorbent for the removal of Pd(II) from aqueous solution was investigated. The effects of pH, biomass dosage, contact time, and temperature on the biosorption processes were systematically studied. Experimental data were modeled by Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherms. Langmuir isotherm model (R² = 0.994) fitted the equilibrium data better than the Freundlich isotherm model (R² = 0.935). The monolayer biosorption capacity of R. lanuginosum biomass for Pd(II) was found to be 37.2 mg/g at pH 5. The mean free energy was calculated as 9.2 kJ/mol using the D-R isotherm model (R² = 0.996). This result indicated that the biosorption of Pd(II) was taken place by chemical ion-exchange. The calculated thermodynamic parameters, ΔG°, ΔH° and ΔS° showed that the biosorption of Pd(II) on R. lanuginosum biomass was feasible, spontaneous and exothermic under examined conditions. Experimental data were also tested using the biosorption kinetic models. The results showed that the biosorption processes of Pd(II) on R. lanuginosum followed well pseudo-second-order kinetics at 20-50 °C (R² = 0.999).