Development of Fe⁰/Fe₃O₄ composites with tunable properties facilitated by Fe²⁺ for phosphate removal from river water

Phosphorus (P) has been overused for decades in agriculture and industry, such that excess phosphorus inevitably enters natural waters, especially river water, via runoff. Trace phosphate in natural water will cause eutrophication, and it is important to achieve low concentration phosphate removal effectively because of the increasingly stringent standards. In this study, a new technology, using Fe⁰/Fe₃O₄ composites facilitated by Fe²⁺ for low concentration phosphate removal was developed. The amount of Fe₃O₄ on the Fe⁰ surface was tuned and Fe⁰/Fe₃O₄-2 was proved to have best performance in phosphate removal and iron corrosion. The initial Fe²⁺ concentration of 0.5 mg/L was chosen for effective phosphate removal and meeting an acceptable total iron concentration below 0.3 mg/L after treatment. The generated iron corrosion products showed a high phosphate removal capacity and favorable selectivity towards phosphate in the presence of co-existing anions and NOM. The phosphate in real river water was decreased from 0.4 mg-P/L to 0.010 mg-P/L by using 0.5 g/L Fe⁰/Fe₃O₄-2 facilitated by 0.5 mg/L Fe²⁺. Adsorption, co-precipitation and precipitation contributed to phosphate removal, and the main removal mechanism was adsorption, which included electrostatic attraction and inner-sphere complexation. This study highlights a promising new method for the removal of low concentrations of phosphate from river water.