Removal of Ni(II) and Co(II) ions from aqueous solution using teak (Tectona grandis) leaves powder: adsorption kinetics, equilibrium and thermodynamics study

In the present study, batch experiments were carried out to elucidate the potential of teak leaves powder (TLP) to remove Ni(II) and Co(II) ions from aqueous solution. The TLP was characterized by Bruanauer, Emmett and Teller surface area, Fourier transform infrared spectroscopy and scanning electron microscopy. Effects of various process parameters such as initial pH (2-8), adsorbent dose (1-10gL(-1)), initial metal ion concentration (25-200mgL(-1)), contact time (5-120min) and temperature (303-323K) were investigated in their respective range and their optimum conditions were ascertained. Maximum percentage removal of 75.64 and 76.04% was achieved for Ni(II) and Co(II) ions, respectively, at an initial concentration of 50mgL(-1), at their respective optimum pH of 6 and 5, adsorbent dose of 8 and 6gL(-1) in an equilibrium time of 30 and 60min at 303K. Adsorption kinetics was analyzed by pseudo-first-order, pseudo-second-order, Elovich and intraparticle diffusion kinetic models. It was found that the adsorption of both the metal ions followed pseudo-second-order kinetic model. Adsorption isotherms were modelled with Langmuir, Freundlich, Tempkin and Dubinin-Raduskevich models and their isotherm constants were calculated. The equilibrium data fitted well to the Langmuir isotherm model for adsorption of both Ni(II) and Co(II) ions on TLP. Thermodynamic parameters such as change in Gibb's free energy, change in enthalpy and change in entropy were calculated to predict the nature of adsorption process. The calculated thermodynamic parameters showed that the adsorption of Ni(II) and Co(II) ions on TLP were feasible, spontaneous and endothermic in nature.