Phosphate removal by ex situ generated Fe (hydr)oxides from scrap iron electrocoagulation: the critical role of coprecipitation

Abstract

The immobilization of phosphate by Fe (hydr)oxides is a promising method with low cost and high efficiency. However, the complicated synthesis process and particle aggregation limited their application. In this study, we utilized electrocoagulation with a scrap iron anode to generate Fe (hydr)oxides in the prepared NaCl electrolyte, which are ready to use for phosphate removal on-site. The Fe (hydr)oxides generated via scrap iron electrocoagulation without aeration removed 86.7% of phosphate and showed an energy cost of 35.9 W h g⁻¹ P. The structure and morphology of Fe precipitates containing phosphate were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The results showed that vivianite, strengite, and amorphous Fe–P precipitates were formed immediately after the mixing of Fe (hydr)oxides with phosphate. Compared to coprecipitation, adsorption by Fe (hydr)oxides (e.g., lepidocrocite) plays a minor role in phosphate removal. The findings gained from this study shed light on the feasibility and mechanism of scrap iron materials in the immobilization of phosphate through on-site electrocoagulation.