Adsorption of Cu(II), Cd(II) and Ni(II) ions from aqueous solution by unmodified Strychnos potatorum seeds

Abstract

In this study, the unmodified Strychnos potatorum seeds were examined as an adsorbent to remove the metal ions such as Cu(II), Cd(II) and Ni(II) ions from their aqueous solutions. The surface properties of the adsorbent were analysed by FTIR and scanning electron microscopy analyses. The adsorption experimental parameters which affect the adsorption process such as pH, adsorbent dose, initial metal ions concentration, contact time and temperature were studied. Adsorption isotherm experiments indicated that the Freundlich adsorption isotherm model displayed the best coefficient of determination values. A single-stage batch adsorber was designed to estimate the amount of adsorbent required to treat the known volume of the wastewater by using the Freundlich adsorption isotherm model. From the Langmuir adsorption isotherm model, the maximum monolayer adsorption capacity of the adsorbent for Cu(II), Cd(II) and Ni(II) ions was found to be: 8.649, 7.023 and 5.140 mg/g, respectively. The adsorption kinetic results showed the pseudo-second-order model was more suitable to describe the adsorption process. Adsorption mechanism was explained with the intraparticle diffusion and Boyd kinetic models. The thermodynamic parameters such as free energy change (ΔG ^°), enthalpy change (ΔH ^°) and entropy change (ΔS°) indicate the effectiveness of the adsorbent to remove the metal ions from the aqueous solution.

Keywords:

• adsorption
• isotherms
• kinetics
• metal ions
• process design
• thermodynamics

Acknowledgement

The authors are grateful for the financial support from the SSN Trust, Chennai.