Comparison of lead removal from aqueous solution between natural-, sodium-, and acid-modified clinoptilolite-rich tuffs

• Published in: Desalination and water treatment 2017-04, Vol.72, p.318-327
• Main Authors: Abatal, M., Olguin, M.T.
• Format: Article
• Language: English
• Subjects: Adsorption capacity; Kinetic; Lead; Natural zeolites; Sorption
• ISSN: 1944-3986
• DOI: 10.5004/dwt.2017.20433

In this paper, the sorption behavior of lead by unmodified and modified natural zeolites is discussed considering, the structural characteristics of each zeolitic material, the contact time, the initial concentration of Pb (II) in solution, the dosage of the adsorbents and the initial pH value. The characterization of all sorbents was performed using X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The surface area (BET) and the pHpzc measurements were also determined. The contact between the Pb(II) solutions and the zeolites were done in a batch system. Mathematical models (pseudo-first and pseudo-second-order) were employed to describe the Pb(II) kinetic adsorption by natural, sodium, and acid-modified clinoptilolite-rich tuffs as well as Langmuir and Freundlich models to analyze the adsorption isotherms. It was found that the percentage of extra red cations from natural zeolite (Nat-CL) changes after contact with NaCl and H2SO4 solutions to obtain the sodium and acid forms (Na-CL and H-CL). The acid treatments of the natural zeolite promote the dealuminization of the material and the pH pzc drastically varied. The pseudo-second-order kinetic model best describes the sorption behavior and the k2 diminished when the concentration of the lead in solution increases from 10 to 100 mg/L. The experimental data of the isotherms fitted to the Langmuir and Freundlich isotherms and the qm and KF are 2.6 and 15.2 times higher for Na-CL than for H-CL, respectively. The variation of kinetic rate constant k2 (g/mg min) as a function of the adsorbent mass presents an exponential behavior for Nat-CL and Na-CL, whereas for H-CL, k2 increase linearly with amount of adsorbent. The initial pH of the Pb solutions affect on the time to reach the Pb2+ sorption equilibrium, the percentage of Pb sorbed in this condition. The mechanism involved on the sorption of Pb(II) by the Nat-CL and Na-CL are ion exchange and precipitation on the surface. In the case of H-CL, only an ion exchange could be possible.