Biosorption of Pb 2+ from aqueous solutions by Moringa oleifera bark: Equilibrium and kinetic studies

Abstract

Biosorption of Pb 2+ from aqueous solution by biomass prepared from Moringa oleifera bark (MOB), an agricultural solid waste has been studied. Parameters that influence the biosorption such as pH, biosorbent dose, contact time and concentration of metal ion were investigated. The experimental equilibrium adsorption data were tested by four widely used two-parameter equations, the Langmuir, Freundlich, Dubinin–Radushkevich (D–R) and Temkin isotherms. Results indicated that the data of Pb 2+ adsorption onto MOB were best fit by the Freundlich model. The adsorption capacity ( Q m ) calculated from the Langmuir isotherm was 34.6 mg Pb 2+ g −1 at an initial pH of 5.0. Adsorption kinetics data were analyzed using the pseudo-first-, pseudo-second-order equations and intraparticle diffusion models. The results indicated that the adsorption kinetic data were best described by pseudo-second-order model. Infrared (IR) spectral analysis revealed that the lead ions were chelated to hydroxyl and/or carboxyl functional groups present on the surface of MOB. Biosorbent was effective in removing lead in the presence of common metal ions like Na +, K +, Ca 2+ and Mg 2+ present in water. Desorption studies were carried out with dilute hydrochloric acid for quantitative recovery of the metal ion as well as to regenerate the adsorbent. Based on the results obtained such as good uptake capacity, rapid kinetics, and its low cost, M. oleifera bark appears to be a promising biosorbent material for the removal of heavy metal ions from wastewater/effluents.