Removal of fluoride from wastewater by natural and modified nano clinoptilolite zeolite

In this study adsorption of fluoride ion from high-fluorine solutions (<2000 ppm) using the natural and modified ground clinoptilolite is investigated. These low-cost adsorbents are carefully characterized by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray fluorescence (XRF), thermos-gravimetry (TGA) and differential scanning calorimeter analysis (DSC). In order to enhance the fluoride removal capacity of natural zeolite, it is milled into nano-powders and modified using hexadecyltriammoniumions (HDTMA+ ). The kinetic, equilibrium, and thermodynamic of fluoride adsorption are measured and described by the well-known mathematical models. The Langmuir model is fitted to the experimental data of nano HDTMA-clinoptilolite with the average relative error (ARE) of 1.57%. According to Langmuir isotherm, the maximum adsorption capacity of nano clinoptilolite and nano HDTMA-clinoptilolite are determined 25.26 and 32.40 mg/g, respectively. The heat of fluoride adsorption onto the nano-clinoptilolite and nano HDTMA-clinoptilolite is calculated to equal to -82.57 and -60.46 kJ/mol, respectively. Kinetic studies indicated that fluoride adsorption rate on nano HDTMAclinoptilolite is higher than unmodified zeolite and it is modeled by the pseudo-second kinetic model.