Evaluation of Fluoride Adsorptive Removal by Metallic Phosphates

Currently, various techniques are efficient in eliminating high quantities of fluoride from water, while the deep treatment of a low concentration of fluoridated water is inadequate. In this work, four metallic phosphates were synthesized, including YP, ZrP, CeP, and LaP, to enhance the elimination of fluoride. The X-ray diffractometer data demonstrated that ZrP was amorphous, while CeP, LaP, and YP were highly crystalline. YP had a strong fluoride removal ability in a neutral environment, and ZrP exhibited a superior fluoride adsorption effect in acidic media. The adsorption kinetic results suggested that YP, CeP, and LaP could achieve the adsorption equilibrium within 150 min, which was faster than ZrP. YP had the largest fluoride adsorption capacity fitted by Langmuir of 31.61 mg/g at 298 K, followed by ZrP, which was greater than those of CeP and LaP. All four metallic phosphates showed high selectivity in the interference of competing anions and organics, with YP and ZrP exhibiting superior selectivity than CeP and LaP. The adsorption mechanism was ligand exchange between metallic phosphate particles and fluoride, which was validated by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The adsorption rate of metallic phosphates remained essentially stable in five consecutive adsorption–desorption cycles. Overall, metallic phosphates, especially YP and ZrP, have enormous potential in enhancing fluoride removal in the treatment of fluoridated water.