Biosorption of Fe (II) and Pb (II) on unmodified Senna tora: Isotherm and kinetic modeling

Contamination of environment by heavy metals has become a major concern worldwide. The role of conventional methods in remediating heavy metals has become ineffective and costly. Therefore, it becomes imperative to explore bioremediation using a cost effective, efficient and environmentally friendly alternative method of removing heavy metals. In this study, the adsorption behaviour of Senna tora, a low-cost adsorbents, with respect to Fe(II) and Pb(II) ions, has been studied in order to consider its application to the treatment of wastewater. The physicochemical properties of the unmodified Senna tora were predetermined. The batch experimental method was employed: parameters such as pH, contact time, dosage and initial metal concentration were studied. The influence of the pH of the metal ion solutions on the uptake levels of the metal ions by the adsorbent used was carried out between pH 4 and 10. The optimum pH for both Fe (II) and Pb(II) removals by Senna tora was 7. An equilibrium contact time of 60 min was required for the adsorption of Pb(II) ions onto Senna tora. Percentage sorption of Fe(II) increased from 94 to 99% and that of Pb (II) from 94.4 to 96% as adsorbent dose was increased from 2 to 10 g. The isotherms data provide information on the capacity of the adsorbent or the amount required to remove a unit mass of pollutant under the operating conditions. The equilibrium data of Fe(II) and Pb(II) adsorbed onto Senna tora pods were fitted by the Langmuir, Freundlich, and Temkin isotherms. On the basis of correlation coefficients R2, it is concluded that the Fe(II) and Pb(II) biosorption is better fitted to the Freundlich model. This suggests that the biosorption of Fe(II) and Pb(II) on the surface of Senna tora pods occurs on heterogeneous binding sites with equivalent adsorption energies and multilayer coverage. The results demonstrated that Senna tora pod holds potential to remove cationic heavy metal species from industrial wastewater.