Abstract: The high−value utilization of phosphorus tailings and advanced treatment of phosphorus−containing wastewater in the phosphorus chemical industry are crucial aspects of the "Three Phosphorus" governance initiative in the Yangtze River Basin. Phosphorus tailing ceramsite, as an emerging adsorption material, exhibits phosphorus removal capabilities but faces dual challenges of low removal efficiency and water turbidity due to calcium ion leaching. This study used phosphorus flotation tailings as the primary raw material, supplemented with a small amount of montmorillonite as a binder, to prepare phosphorus tailing ceramsite. Lanthanum nitrate was employed as the modifying solution, and a hydrothermal modification method was applied to construct a lanthanum−based active layer on the ceramsite surface. This approach significantly enhanced phosphorus removal efficiency while simultaneously inhibiting calcium ion leaching. Experimental results demonstrated that the modified ceramsite achieved a 99.8% phosphorus removal rate for high−concentration phosphorus wastewater (200 mg/L), representing a 17 percentage point improvement over unmodified ceramsite. Post−treatment water was clear and transparent. Multi−scale characterization (XRD, SEM, XPS) elucidated the phosphorus removal mechanism: XRD confirmed the formation of a new LaPO₄ phase; XPS revealed a binding energy shift of La 3d₅/₂ to 835.2 eV, indicating the formation of stable La³⁺–PO₄³− coordinated deposits; SEM showed a dense nanomesh membrane (2.1 ± 0.3 μm thick) formed on the ceramsite surface, effectively blocking calcium leaching channels. This successfully achieved synergistic optimization of phosphorus removal efficiency and water clarity. The research substantially enhances the comprehensive performance and application value of phosphorus tailing ceramsite, providing a valuable reference for tailing resource utilization and the design of novel, high−efficiency water treatment adsorption materials.