A comprehensive study on the kinetics and thermodynamic aspects of batch and column removal of Pb(II) by the clinoptilolite–glycine adsorbent

Abstract

Natural clinoptilolite tuff was crushed to the micro (MCP) and nano (NCP) particles and then modified by Glycine (Gly). The samples were characterized by X-ray diffraction (XRD), Fourier Transformation infra-red (FT-IR), scanning electron-microscope (SEM), transmission electron microscope (TEM), Brunauer–Emmett–Teller (BET) theory and thermo-gravimetry (TG). Among the raw and modified adsorbents, the modified NCP showed better activity in Pb(II) removal (NCP: 0.292 mmol g−1, NCP-Gly: 0.553 mmol g−1, MCP: 0.263 mmol g−1, MCP-Gly: 0.372 mmol g−1) in batch experiments. Although Mn(II) had the maximum interfering effect in Pb(II) removal among the tested cations, but the adsorbent retained 50% of its initial capacity for Pb(II) removal when concentration of Mn(II) was twice greater than that of Pb(II) cations in binary solution. Adsorption isotherms of Pb(II) ions well modeled by Langmuir equation (R2 = 0.999), that indicate the monolayer sorption of Pb(II) on the surface of the modified adsorbent. A pseudo-second-order rate equation (k2 = 0.032 g/mmol min, R2 = 0.99) obtained in kinetic study of the process that indicates that the rate limiting step for the process involves a chemical reaction. The ΔH°<0 (−38.0 kJ/mol) and ΔG°<0 (−80.1 kJ/mol) indicate an exothermic spontaneous process. Applicability of the adsorbent for using in continuous systems was also tested in column studies and the breakthrough was shifted by the investigated experimental parameters. The best results obtained at flow rate of 0.25 mL min−1, bed height of 8 mm, Pb(II) concentration of 1000 mg L−1. Kinetic of the process in column experiments was followed by applying the Thomas equation and the rate constant and the qo values as the functions of the experimental variables were determined.