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

Excessive fluoride in water can cause a series of health problems. In this study, a three-element adsorbent (γ-FeO-graphite-La, MGLNP) was successfully developed for fluoride adsorption. Magnetic graphite nanoparticles (MGNP) were synthesized through the chemical deposition of FeO nanoparticles onto nanographite powder (NG) under alkaline conditions. The MGLNP was synthesized by immersing the MGNP in a saturated solution of La(NO)·6HO 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. The surface charge of the MGLNP was highly pH-dependent, the corresponding pH 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 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 La and F, as well as electrostatic attraction could be observed in the fluoride adsorption process.