Performance and characteristics of fluoride adsorption using nanomagnetite graphite–La adsorbent

Abstract

Excessive fluoride in water can cause a series of health problems. In this study, a three-element adsorbent (γ-Fe₂O₃–graphite–La, MGLNP) was successfully developed for fluoride adsorption. Magnetic graphite nanoparticles (MGNP) were synthesized through the chemical deposition of Fe₃O₄ nanoparticles onto nanographite powder (NG) under alkaline conditions. The MGLNP was synthesized by immersing the MGNP in a saturated solution of La(NO₃)₃·6H₂O and calcining at 300 °C for 3 h in a muffle furnace. These nanoparticles featured a quick and easy separation process with the saturation magnetization of 26.66 emu g⁻¹. The surface charge of the MGLNP was highly pH-dependent, the corresponding pH_pzc was approximately 7.9. The fluoride adsorption isotherm of the MGLNP could be well described by the Langmuir equation, and the maximum adsorption capacity was about 77.12 mg g⁻¹ at 25 °C and pH = 7 ± 0.1. The kinetics of the fluoride adsorption was described by a pseudo first-order rate law. As the pH decreased, the fluoride adsorption capacity of the MGLNP continuously increased. The effects of the co-existing anions indicated that the anions had minimal effect on the fluoride adsorption. After six cycles of reuse, the MGLNP could still maintain 77.54% adsorption capacity. On the basis of the zeta potential analyses, FTIR spectroscopy, and XPS measurements, ion exchange, combination of La³⁺ and F⁻, as well as electrostatic attraction could be observed in the fluoride adsorption process.