Magnetic Fe3O4@MgAl-LDH@La(OH)3 composites with a hierarchical core-shell structure for phosphate removal from wastewater and inhibition of labile sedimentary phosphorus release

In order to facilitate recovery and enhance phosphate adsorption capacity of lanthanum (La)-based materials, magnetic Fe3O4@[email protected](OH)3 (MMAL) composites with a hierarchical core-shell structure were synthesized. In the preparation process, citric acid played a vital role in the morphology control of La(OH)3, deciding the La content and phosphate adsorption capacity of materials. MMAL composites with a citric acid-to-La molar ratio of 0.375 (MMAL-0.375) exhibited a high adsorption capacity of 66.5 mg P/g, fast adsorption kinetics of 30 min, widely applicable pH range of 4.0–10.0, outstanding selective adsorption performance, and superior reusability in batch adsorption experiments. Moreover, the phosphate in the desorption solution could be concentrated by repeated use of desorption solution and recovered by using CaCl2. When the obtained composites were used for the sedimentary phosphorus sequestration and recovery, the results showed that the addition of MMAL-0.375 effectively reduced the concentration of soluble reactive phosphorus (SRP) in the overlying water. Accompanied by an evident increase in HCl-extractable phosphorus (HCl–P), mobile phosphorus (Pmob) in sediments was effectively reduced. This work indicates that the MMAL-0.375 composites can serve as an effective tool for the removal of phosphate from wastewater and the control of sedimentary phosphorus.