Evaluation of Pb2+ ion adsorption by roasted and grounded barley (Hordeum vulgare L.) waste

Abstract

This work was carried out with the objective of studying the process of adsorption of Pb2+ ions by barley dust, Hordeum vulgare L. The adsorbent material was prepared by boiling in water with consequent sedimentation, drying, grinding and sieving. Kinetic, isothermal and thermodynamic studies were carried out in the adsorption processes. Factors such as contact time (1–128 min), initial concentration (20–400 mg.L-1) and temperature (288–298, 308 and 318 K) were considered. Mathematical models were applied and satisfactorily demonstrated the adsorptive process. The pseudo-first order models, pseudo-second order models Elovich and Boyd showed that equilibrium was reached within the first 40 min, with the pseudo-second order model as the most suitable to describe the process, as well as adsorption by external diffusion was demonstrated from the model of Boyd. The adsorption isotherm was evaluated using the Langmuir, Freundlich and Temkin models, demonstrating great applicability to the adsorptive process. The maximum adsorption capacity obtained in the Langmuir model was in the order of 25.76 mg.g−1. The Freundlich model indicated that the process is favorable. The thermodynamic parameters were calculated, demonstrating that the adsorption is endothermic and favorable. Therefore, the results obtained showed that the waste of roasted and ground barley powder can be used as an alternative, viable and low-cost adsorbent for use in processes aimed at decontaminating effluents containing Pb2+ ions.