Highly efficient removal of phosphate by lanthanum-doped mesoporous SiO2

In this study, a series of lanthanum doped mesoporous SiO2 (La-meso-SiO2) were synthesized and characterized by X-ray diffraction, N2 adsorption–desorption, and Fourier transform infrared spectroscopy. The effects of different Si/La molar ratio, the amount of La-meso-SiO2 at different contact time, pH and initial concentration of phosphorus solution on phosphate removal have been studied. It was found that La-meso-SiO2 exhibited fast adsorption kinetics as well as high adsorption capacities. The adsorption rate and capacity of La-meso-SiO2 for removal of phosphate increase with the increasing of La/Si molar ratio. The phosphate removal would be near 100% with 0.3 g/L La-meso-SiO2 with Si/La molar ratio ≥10 after 3 h. La-meso-SiO2 with Si/La molar ratio of 10 was found to be recycled once, and 75% of phosphate was removed from this recycled adsorbent without any considerable damage to the solid. The concentrations of residual lanthanum ions in solution at different conditions were also measured. The results show that the Si/La ratio, amount of La-meso-SiO2 and initial concentration of phosphorus had little effect on the concentration of residual lanthanum ions, whereas the concentration of residual lanthanum ions decreased with increase in pH of the solution.