Preparation of Hangjin clay-supported sulfidated zero-valent iron and its performance on phosphate removal

Natural Hangjin clay with large specific surface area and excellent adsorption properties was used as a carrier to synthesize Hangjin clay-supported sulfidated zero-valent iron (HJ@S-nZVI). Preparation conditions such as the iron loading ratio, the molar ratio of sulfide iron (S/Fe) and the aging time were optimized. Scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and specific surface area (SSA) and other methods were utilized to comprehensively characterize and analyze the characteristics of HJ@S-nZVI. The effects of the dosage, initial pH, and co-existing ions on the phosphate removal efficiency were investigated, and the adsorption performance and adsorption mechanism of phosphate removal by HJ@S-nZVI were studied based on the adsorption isotherms and adsorption kinetics. The results showed that the optimized preparation conditions of HJ@S-nZVI were: iron loading ratio was 0.25, S/Fe was 0.01, and aging time was 10 d. SEM, EDS and element distribution map analysis manifested that sulfidated zero-valent iron was successfully loaded on the surface of Hangjin clay in the form of spherical particles. XPS analysis showed that the main existing forms of iron on the surface of HJ@S-nZVI were FeS and FeOOH. The dosage, initial pH and SiO₃ ²⁻ had a greater influence on phosphate removal, while SO₄ ²⁻, CO₃ ²⁻ and Cl⁻ had no obvious competitive influence. The adsorption process of phosphate by HJ@S-nZVI conformed to Freundlich isotherm model (R²=0.992). Under different initial concentrations, the quasi-second-order kinetic model could better describe the phosphate removal process（R²>0.995）.