Phosphorus removal by Magnesium‐based Cementitious Material: Performance and mechanisms

The green synthesis and mass production of cost-effective substrates with high phosphorus adsorption capacity and good application feasibility is crucial for the efficient removal and recovering of phosphorus from aquatic environments. In this study, eco-friendly Magnesium-based Cementitious Material (MCM) was prepared and its phosphate adsorption performance was thoroughly investigated. The MCM exhibited a significant phosphorus adsorption capacity of 42 mg/g. Phosphate adsorption on MCM was well fitted by the Redlich-Langmuir isotherm and pseudo first-order models. The intra-particle diffusion model indicated that phosphate adsorption was governed by surface reactions and diffusion processes. Scanning Electron Microscopy, Fourier Transform Infrared Spectroscopy, and X-ray Photoelectron Spectroscopy analyses revealed that phosphate removal mechanisms involved electrostatic attraction, inner sphere complexation, ligand exchange, crystal nucleation and crystallization, and precipitation. Density Functional Theory (DFT) calculations confirmed that the -OH groups provided by Mg(OH)2 and Mg3(OH)5Cl·4H2O were active sites capable of chemically adsorbing HPO42− anions, forming surface complexes. In addition, plant available Mg-P precipitates were observed on the surface of MCM, indicating that postsorption MCM might be used as phosphate and magnesium fertilizer. MCM showed great application prospects with the advantages of being non-toxic, economical, and easy to prepare.