Pigeon pea (Cajanus cajan) pod as a novel eco-friendly biosorbent: a study on equilibrium and kinetics of Ni(II) biosorption

Abstract

Background: Pod of pigeon pea (Cajanus cajan) was used as a novel eco-friendly material to investigate its nickel binding efficiency. The influence of key physicochemical parameters such as contact time, initial metal ion concentration, adsorbent dosage, and pH on Ni(II) removal was studied. Optimum Ni(II) removal was obtained with a contact time of 45 min, pH of 8.0, and an adsorbent dose of 0.4. Results: The removal of Ni(II) decreased from 95% to 85% as the initial metal concentration increased from 20 to 100 mg L �1 . Under the optimal conditions selected, metal ion adsorption equilibrium was very well represented by the Freundlich isotherm model followed by the Langmuir isotherm and Temkin isotherm models. The adsorption process followed second-order kinetics, and the corresponding rate constants for initial Ni(II) concentration ranging from 20 to 100 mg L �1 were found to be 0.179 to 0.0035 g mg �1 min �1 . Various thermodynamic parameters such as standard enthalpy (ΔH°), standard entropy (ΔS°), and standard free energy (ΔG°) were evaluated to predict the nature of adsorption. Conclusions: The adsorbent prepared from the pod of pigeon pea appears to be a promising adsorbent for the removal of Ni(II) ions from aqueous solution. The study indicated that the pretreated adsorbent produced through chemical activation using NaOH is an effective material for the removal of Ni(II). Hence, the adsorbent prepared from the pigeon pea pod would be an economically useful tool and alternative to the commercially available activated carbon in the treatment of effluent containing Ni(II) ions.