Sr(Ⅱ) Sorption by Nano Clinoptilolites, (Afrazand, Abyaneh, Toska and Neginpowder): Kinetic, Thermodynamic and Mechanism Studies

摘要

Different samples of natural zeolites were collected from Iranian mines. They were characterized using X-ray diffraction, Fourier Transform Infrared, X-ray fluorescence, Transmission-Electron Microscopy and Scanning-Electron Microscopy techniques. The TEM images showed that the zeolite particle sizes are reduced into the size range of less than 80 nm by means of ball milling. After pre-treatment they were considered for Sr(Ⅱ) removal from wastewater by using a batch-type method. The results clarified that the crystalline clinoptilolite has a poor adsorption performance for Sr(Ⅱ) compared with amorphous samples. The results demonstrated that the natural zeolites contained a complement of exchangeable Na, K, metal ions, functional groups, and channels and cavities as well as network charges for adsorption of metal ions. The adsorption mechanisms (chemisorption, physisorption, ion-exchange and trapping) regarding the structure and chemical composition of zeolite were proposed for the adsorption of metal ions based on the zeolite. The sample (Afrazand) with high adsorption capacity was selected and experiments were carried out using batch method as a function of the initial concentration, shaking time, and temperature. The maximum adsorption capacity (q) for Sr(Ⅱ) ions obtained from the experimental data at room temperature was 78.5 mg g~(-1). The results indicated that the pseudo-second-order model gives a better description of the Sr(Ⅱ) ions sorption kinetics as judged by the R2 value. Equilibrium modelling data were fitted to linear Langmuir and Freundlich models. Thermodynamics parameters such as change in free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) were also calculated. The negative ΔG° value indicated that the sorption of Sr(Ⅱ) ions was spontaneous at all studied concentrations. The reasons of positive ΔS° are the liberation of more ions when one Sr(Ⅱ) ion is bound to the sorbent and increasing of randomness at the solid-solution interface during the fixation of ion on the adsorbent surface.