Removal of Pb (II) from aqueous solutions by adsorption onto modified areca waste: Kinetic and thermodynamic studies

The removal of Pb2+ in modified areca waste from aqueous solutions with the Fenton reagent was investigated. Experiments were carried out as function of contact time and initial concentration (4–12 mg/L). The equilibrium adsorption data of Pb2+ on MAW were analyzed by Langmuir and Freundlich models. The equilibrium adsorption data were well described by the Freundlich and Langmuir isotherms. The monolayer adsorption capacity was found to be 3.37 mg/g at pH 6.6 and 323 K. Adsorption data were modeled using the pseudo-first-order, pseudo-second-order and intraparticle diffusion kinetics equations. The experimental data were fitted well the pseudo-second-order kinetics. Isotherms had also been used to obtain the thermodynamic parameters such as free energy (ΔG0), enthalpy (ΔH0) and entropy (ΔS0) of adsorption. The negative value of ΔG0 indicates the feasibility and spontaneity of the adsorption process. The positive ΔH0 suggests the endothermal nature of the adsorption. The positive values of ΔS0 reflects the affinity of MAW towards Pb2+. Desorption studies revealed that the MAW can be regenerated using HNO3 by adjusting pH.