Process optimization and modeling research for the defluoridation of water using a novel adsorbent of cellulose and hydroxyapatite nanocomposite

According to world health organization fluoride ion concentration in the drinking water greater than 1.5 mg/L results in humans healthy risks. In this research, a cellulose/hydroxyapatite nanocomposite was produced and used for fluoride ions removal from water by adsorption. To synthesize the nanocomposite, cellulose of African alpine bamboo (Yushuania alpina) and (ii) hydroxyapatite of chicken eggshells were used. The adsorbent characteristics were determined based on dynamic light scattering, Brunauer-Emmett-Teller, scanning electron microscopy, Fourier transform infrared spectroscopy, x-ray diffraction, thermogravimetric analysis and derivative thermogravimetric analysis. Adsorption experiments were designed by the central composite design approach. The influence of an adsorbent dose (0.075-1.75 g/L), pH (5-9), contact time (40-80 min) and initial fluoride ion concentration (20-40 mg/L) were investigated. The highest adsorption capacity of the adsorbent was 23.02 mg/g. The highest removal efficiency of 98.68% was attained by employing dosage of 1.43 g/L for 77 min, at a pH of 5.24, and with an initial concentration of 24.43 mg/L. Thermodynamic analysis shows that the process is spontaneous and endothermic, as confirmed by the positive values of ΔH° and ΔS°, and the negative values of ΔG°. The adsorption process can be described the pseudo-second-order kinetic model and the Langmuir isotherm. The study showed that the cellulose/hydroxyapatite nanocomposite is an environmentally friendly and effective adsorbent for fluoride ion removal.