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Adsorption of lead(II) ions from simulated wastewater using natural waste: A kinetic, thermodynamic and equilibrium study



Locally available natural waste such as cashew nut shell (CNS), a byproduct of cashew nut industry, was found to be a low-cost material and also a promising adsorbent for removing lead(II) ions from simulated wastewater. A batch adsorption study was carried out with various adsorption parameters, such as solution pH, CNS dose, contact time, initial lead(II) ion concentration, and temperature. The kinetic data were analyzed using four adsorption kinetic models: the pseudo-first-order and pseudo-second-order equations, intraparticle diffusion, and Boyd kinetic equation to determine the best fit equation for the adsorption of lead(II) ions onto CNS. Kinetics of lead(II) ions adsorption by CNS is better described by the pseudo-second-order equation. Various thermodynamic parameters, such as ΔG°, ΔH°, and ΔS°, have also been evaluated and it has been found that the adsorption process was feasible, spontaneous, and exothermic in nature. The experimental data were analyzed using the Freundlich, Langmuir, and Dubinin–Radushkevich adsorption isotherm equations. The equilibrium data were found to fit well in the Freundlich isotherm, which confirmed the multilayer coverage of lead(II) ions onto CNS. The Langmuir monolayer adsorption capacity of the CNS was found to be 17.82 mg/g. A single-state batch adsorber system was designed to estimate the amount of adsorbent required to treat the known volume of the effluent using the Freundlich adsorption isotherm model. The results indicate that the CNS can be used to effectively adsorb lead(II) from wastewater. © 2013 American Institute of Chemical Engineers Environ Prog, 33: 55–64, 2014