Isotherm and Thermodynamic studies on Biosorption of Metal (II) Ions from Aqueous Solution using Calopogonium muconoides (Calopo) Seed Pod

Abstract

The potential of Calopogonium muconoides seed pods for adsorption of Pb(II), Ni(II) and Cd(II) ions from aqueous solution was investigated in a batch adsorption mode. Various physicochemical parameters such as pH, dosage, concentration and temperature were studied. The adsorbent studied exhibits high efficiency for the metal ions adsorption. The equilibrium adsorption data fitted into the Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherm models. The coefficients of determination of the four models were high with Dubinin-Radushkevich providing best data description for the adsorption of the metal ion onto activated Calopogonium muconoides seed pod powder. The maximum adsorption capacity of Ni(II), Pb(II), and Cd(II) are 43.103 mg/g, 42.373 mg/g and 32.33 mg/g respectively. Also these heavy metal ions showed maximum adsorption at pH 6. Different thermodynamic parameters, including Gibbs free energy (∆G), enthalpy (∆H) and entropy (∆S) for the adsorption process have also been evaluated. The negative value of ∆G indicates the feasibility and spontaneous nature of the process. The positive value of ∆H for the system confirms the endothermic nature of adsorption. The positive value of ∆S observed for the adsorption of metal ion molecules suggested the increased randomness at the solid-solution interface during adsorption process. These results indicated that the biosorbent studied was found to be a promising alternative for the adsorption of Pb(II), Ni(II) and Cd(II) ions from aqueous solution. The affinity of the adsorbent for the metal ions also follows the trend Ni(II) > Pb(II) >Cd(II). Therefore, Calopogonium muconoides is a promising adsorbent for adsorption of Ni(II), Pb(II) and Cd(II) ions.