Kinetics and Thermodynamics of Lead Adsorption from Aqueous Solutions onto Iranian Sepiolite and Zeolite

Abstract

A good understanding of adsorption equilibrium and thermodynamics is required to design and operate an adsorption process. This study was conducted to assess the adsorption percentage of Pb2+ ions as a function of contact time, solution pH and temperatures, and adsorbent dosage through a series of batch experiments. The methods including zeta potentials, specific surface area measurements and the analysis of adsorption kinetics thermodynamics were introduced to analyze the adsorption mechanisms of the Pb2+ ions on sepiolite and zeolite minerals. Results showed that the sorption of Pb2+ on Iranian sepiolite and zeolite is a relatively fast process with the equilibrium being attained within 6 hours after the sorbents application. Sepiolite and zeolite yield adsorption capacities (Qe) was found to be 30.5 and 24.4 mg/g for lead ions, respectively. The results also showed that the adsorption of lead metal ions onto sepiolite and zeolite minerals increased with contact time, solution pH, and the amount of adsorbent; but decreased as the temperature of the system increased. The experimental data fitted very well the pseudo-second- order kinetic model. The thermodynamics parameters such as Gibbs free energy, enthalpy, and entropy were also evaluated. The negative values of enthalpy (ΔH°) illustrated the exothermic nature of Pb2+ sorption. The activation energy (Ea) of Pb2+ sorption onto the sepiolite (17.00 kJ/mol) and zeolite (7.60 kJ/mol) indicated that Pb2+ ions were more strongly sorbed onto sepiolite than zeolite.