Core–shell functional material from phosphate tailings for phosphate removal and potential slow-release fertilizer application

Phosphorus recovery and reutilization are essential for sustainable resource management, while the efficient utilization of reactive phases in phosphate tailing-derived adsorbents remains challenging. In this study, a core-shell structured phosphate tailing-derived ceramsite (CS-PTCA) was developed through functional zoning of different flotation tailing fractions. The silica-rich direct flotation tailings were used as the structural core, whereas the Ca/Mg-rich reverse flotation tailings were concentrated in the outer shell as the primary reactive region. This design aimed to regulate the accessibility of reactive phases and thereby influence both phosphate capture and subsequent nutrient release behavior. Compared with homogeneous ceramsite of identical composition, CS-PTCA achieved effective phosphate capture through shell-regulated diffusion and Ca-mediated fixation, achieving a Langmuir-fitted maximum adsorption capacity of 7.10 mg·g −1 . Characterization results revealed that the porous shell structure enhanced the accessibility and utilization of reactive Ca/Mg phases, promoting phosphate immobilization through surface-induced calcium phosphate precipitation. Phosphate fixation extended from the outer shell toward the inner shell region, indicating progressive inward immobilization enabled by the core-shell architecture. Furthermore, phosphorus-loaded CS-PTCA exhibited a more regulated nutrient release behavior than the homogeneous counterpart, providing sustained release of available phosphorus together with calcium and magnesium under soil conditions. Pot experiments confirmed that the recovered phosphorus effectively promoted plant growth and biomass accumulation. Overall, the core-shell architecture enabled the regulation of phosphate capture and nutrient release within a single material, establishing a dual-mode utilization pathway that integrates wastewater phosphorus removal with agricultural phosphorus recycling. This study provides a sustainable strategy for the high-value utilization of phosphate tailings.