Biosorption of Ni(II) from aqueous phase by Moringa oleifera bark, a low cost biosorbent

Moringa oleifera bark (MOB), an agricultural solid waste by-product has been developed into an effective and efficient biosorbent for the removal of Ni(II) from aqua solutions. The biosorbent was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), elemental analysis and FTIR analyses. The experimental equilibrium adsorption data were analyzed by four widely used two-parameter equations – Langmuir, Freundlich, Dubinin–Radushkevich (D–R), and Temkin isotherms. Among the four isotherm models Langmuir model provided a better fit with the experimental data than others as revealed by high correlation coefficients, low chi-square values. The kinetics data fitted well into the pseudo-second-order model with correlation coefficient greater than 0.99. Desorption experiments were carried out to explore the feasibility of regenerating the biosorbent and the biosorbed Ni(II) from MOB was desorbed using 0.2 M HCl with an efficiency of 98.02% recovery. The thermodynamic parameters (∆H, ∆S and ∆G) of the nickel ion uptake onto MOB indicated that, the process is endothermic and proceeds spontaneously. The findings of the present study indicates that MOB can be successfully used for separation of Ni(II) from aqueous solutions.

Research Highlights
► The FTIR spectral results indicated that the biosorption of Ni(II) occurs at hydroxyl, carboxyl, and carbonyl functional groups present on the surface of MOB.
► The biosorption process follows pseudo- second order kinetic model.
► The calculated thermodynamic parameters showed the feasibility, endothermic and spontaneous nature of the biosorption of Ni(II) onto MOB biomass.
► The reusability of the biosorbent was good after six consecutive biosorption–desorption cycles.