Synthesis of magnesium-modified ceramsite from iron tailings as efficient adsorbent for phosphorus removal

The preparation of ceramsite from iron tailings to remove phosphate can reduce environmental pollution and realize the sustainable development of “treating waste with waste”. This study prepared a modified ceramsite for phosphate removal in water bodies,with iron tailings as the main raw material and magnesium chloride as the modification agent. The optimal preparation conditions for the modified ceramsite were determined as follows: iron tailings: MgCl2 = 50:15, pre-heating at 300 °C for 10 min, and sintering at 800 °C for 60 min. The effects of factors such as adsorbent dosing, contact time, temperature, pH, NH4+ concentration, and coexisting ions were investigated, and the slow-release ability of modified ceramsite after phosphate adsorption was explored. The results show that the adsorption process best fit the pseudo-second-order model and the Sips model at a dose of 1 g/L and an initial phosphorus concentration of 100 mg/L, belonging to multilayer chemical adsorption. The phosphate adsorption was influenced significantly by pH, and the adsorption capacity reached the maximum of 10.24 mg/g at pH 6. The NH4+ concentration of 100 mg/L was favorable for the simultaneous removal of phosphorus and nitrogen. Coexisting anions in water have a minor effect on the adsorption process, while coexisting cations promote adsorption. The XRD, FTIR and XPS characterization results indicate that electrostatic attraction, internal complexation and chemical precipitation are the main mechanisms of action.