Phosphate removal from aqueous solutions using zero valent iron (ZVI): Influence of solution composition and ZVI aging

[Display omitted] •Phosphate removal using ZVI highly affected by aging time.•Difference between reactivity of ZVI and iron oxidation products in the suspension.•Highest phosphate removal using ZVI after 8h aging time (35 mgP/gZVI).•Decrease of iron oxidation products reactivity in the suspension with time. 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 8h aging time (35 mgP/gZVI). Colloidal ZVI oxidation products showed very high phosphate removal rates especially the newly oxidized iron products (aged for 2h) 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 2h 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 0.001M to 0.5M.