Layered lanthanum hydroxycarbonate turns phosphate pollution into slow-release fertilizer

Mismanagement of Phosphorus (P) depletes phosphate finite rock reserves and exacerbates widespread aquatic eutrophication, driving an urgent demand for integrated strategies that simultaneously remove and recover phosphate (PO₄^3-). Herein, we show that rough-surfaced oblate La(OH)CO₃ particles capture PO₄^3- with exceptional efficiency, and the spent one can serve as a slow-release P fertilizer, enabling full pollutant-to-resource conversion. The material achieves a maximum adsorption capacity of 211.59 mg_P g^-1, rapid chemisorption-dominated kinetics, a broad pH window (3-7), and strong selectivity against competing anions and natural organic matters. In fixed-bed column tests, effluent P concentrations stayed below 0.2 mg L^-1 discharge threshold for a breakthrough time of 84 h and > 90% P recovery was achieved. When evaluated as a fertilizer in hydroponic cultivation of Pisum sativum, the spent adsorbent produced plant height and biomass that matched or exceeded those from a conventional soluble P source at the optimal dosage. Mechanistic and comparative studies with La(OH)₃ and La₂(CO₃)₃ reveal that the superior performance originates from the synergy of electrostatic attraction, surface OH^- ligand exchange, interlayer CO₃^2- anion exchange (facilitated by favorable size matching), and inner-sphere complexation, all enabled by the unique layered structure of La(OH)CO₃ ([La(OH)]²⁺ framework layers and interlayer CO₃^2-). This work reports a high-performance La-based adsorbent for efficient P control and establishes a broadly applicable pollutant-to-resource paradigm that bridges environmental remediation with circular nutrient economies.