Design and Synthesis of a Novel Silicate Material from Red Mud for Simultaneous Removal of Nitrogen and Phosphorus in Wastewater

This study reports on a material (CSH@SiO₂@MgO) that is formed by calcium silicate hydrate (CSH) and silicon dioxide (SiO₂), and then coated with magnesium oxide (MgO) on the surface. CSH@SiO₂@MgO can simultaneously remove ammonia nitrogen (NH₄⁺) and phosphate (PO₄^3-) in water. The raw material SiO₂ is extracted from the red mud by acid leaching. A simple preparation method is employed to synthesize CSH@SiO₂@MgO composite material by using CSH@SiO₂ with core-layer structure doped with MgO. The removal process of NH₄⁺ and PO₄^3- is as follows: First, the struvite precipitation method was used to remove NH₄⁺ and a part of PO₄^3-, and then the CSH@SiO₂ was used to remove the residual part of PO₄^3- through chemical precipitation reaction. The CSH@SiO₂@MgO automatically regulated pH in water, and the removal rate of NH₄⁺ and PO₄^3- could reach 83.88% and 93.87%. Also, the CSH@SiO₂@MgO was recycled five times, and the removal rate of NH₄⁺ and PO₄^3- was maintained at about 73.51% and 80.86%. It was characterized by XRD, XPS, SEM, S_BET, and FTIR, and the effects of reaction time, pH value, and dosage on removal rate were investigated. This Article aims to present a new material (CSH@SiO₂@MgO), which can remove the NH₄⁺ and PO₄^3- effectively and simultaneously.