Modification of Diatomite by Zirconium and Its Performance in Phosphate Removal from Water

Abstract

Zirconium modified diatomite was obtained by modifying raw diatomite with zirconium and the mass fraction of zirconia was 12.39% in the obtained material, which was proved to be amorphous via XRD. SEM images showed that porous floccules covered the surface of diatomite after modification and the specific surface area of the zirconium modified diatomite was 75.22 m2·g-1, larger than that of raw diatomite (14.00 m2·g-1). XPS spectra indicated that zirconia and diatomite were bonded together through chemical linkage, rather than physical deposition. The adsorption isotherm of phosphate by zirconium modified diatomite was fitted better to the Langmuir model with a calculated maximum adsorption capacity reaching 10.56 mg·g-1. The adsorption amount of zirconium oxide component in the material was estimated to be 81.67 mg·g-1 ZrO2, which was higher than that of pure zirconium oxides reported in previous studies. The adsorption amount of phosphate by zirconium modified diatomite decreased with the increase of pH. The adsorption was proved to be a ligand exchange process, supported by the XPS spectra of Zr3d region before and after adsorption. Chloride ion, sulfate ion and nitrate ion did not inhibit the adsorption of phosphate on the material, whereas coexistence of bicarbonate ions competed with phosphate ions to a certain extent. When treating eutrophic lake water with a phosphate concentration of 2 mg·L-1, the phosphate concentration level could meet the Ⅲ rank of Surface Water Environment Quality Standard of China by adopting the dosage of zirconium modified diatomite ≥1.25 g·L-1.