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

Abstract

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−, NO 3−, and SO 42− 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.