Adsorption of fluoride, phosphate, and arsenate ions on lanthanum impregnated silica gel

A lanthanum-impregnated silica gel has been developed for the removal of fluoride, phosphate, and arsenate ions by adsorption. The interaction between silica gel and lanthanum ion was maximum at a final pH of 6. The removal of fluoride and arsenate ions by adsorption on the lanthanum-impregnated silica gel was more than 99.9% at neutral pH from initial concentration of 0.55 and 0.2 mmol/L, respectively. The removal of phosphate ion was 95% at an initial concentration of 0.5 mmol/L at neutral pH. Arsenite ion was not adsorbed on the material. The rate of adsorption of the anions followed the first-order reaction and fit in the Lagergren equation. The adsorption of each anion followed the Langmuir isotherm. Other anions such as Cl- Br-, I-, NO3-, and SO42- did not interfere with the adsorption. A column study was conducted for the removal of these anions at a fixed flow rate of 0.5 mL/min at pH approximately 7. These anions were removed by more than 99.9% at initial first or second fraction, and the column was regenerated at pH 8.5. The method was applied for the removal of these anions from synthetic and high-tech industrial wastewaters.