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.