Phosphate removal from aqueous solutions using zero valent iron (ZVI): Influence of solution composition and ZVI aging
Résumé
This study investigates phosphate removal from water by ZVI and its oxidation products. The effects of ZVI aging, solution ionic strength, and co-existing anions, on the removal efficiency of phosphate were evaluated. X-ray Photoelectron Spectroscopy (XPS), Raman spectroscopy, and scanning electron microscopy (SEM) were used to investigate the ZVI oxidation products and to delineate the phosphate removal mechanisms. ZVI showed the highest phosphate removal efficiency after 8 h aging time (35 mgP/gZVI). Colloidal ZVI oxidation products showed very high phosphate removal rates especially the newly oxidized iron products (aged for 2 h) with a capacity of 27.8 mgP/gFe. This capacity decreased to 2 mgP/gFe as aging time increased to 6 days. The characterization of the ZVI oxidation products revealed a mixture of crystalline lepidocrocite and goethite at the surface of ZVI however broader peaks were obtained in the supernatant fraction with aging time of 2 h indicating the presence of poorly crystalline iron products. Nitrate showed no effects on the removal efficiency, whereas ionic strength effects were critical. Phosphate maximum uptake rate (Qe) increased from 8.7 to 15.6 mgP/gFe as ionic strength increased from 0.001 M to 0.5 M.