Synthesis and Characterization of Chitosan/Fluorapatite Composites for the Removal of Cr (VI) from Aqueous Solutions and Optimized Parameters

In the present work, chitosan/fluorapatite composite was successfully prepared and applied for the removal of chromium (VI). The synthesized materials were characterized using X-rays diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electronic microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). The thermogravimetric analysis (TGA) and pH of the point of zero charge (pHPZC) were also considered as a part of these characterizations. A batch system was carried out to evaluate the effects of contact time, initial Cr (VI) concentration, initial pH, and adsorbent dosage on the adsorption process. The regression coefficient value showed that the experimental data best fit to pseudo-second-order model (PSO), while the Langmuir adsorption isotherms best described the equilibrium adsorption data with highest qm of 81.34 and 100.92 mg/g for CS and CS-Fa, respectively. Finally, CS-Fa was successfully reused for more than 6 cycles without severe loss in its sorption capacity. The effect of various parameters such as pH, mass, temperature, and contact time was studied using response surface methodology (RSM) and the suggested optimized values by RSM were found to be 2.54 for pH, 25.75 °C, 36.63 min, and 86.72 mg of CS-Fa adsorbent. The maximum adsorption removal efficiency of Cr (VI) was equal to 91.28% under optimum conditions.