Crystal seed-augmented microporous cathode design for enhanced phosphorus crystallization and energy-efficient recovery.

Abstract

Addressing the dual challenges of phosphorus resource depletion and eutrophication, this study develops an innovative electrochemical phosphorus recovery system. Conventional electrochemically mediated precipitation (EMP) was significantly improved upon through synergistic combining a 200-mesh microporous cathode with acicular nano-hydroxyapatite (ANHD) crystal seeds. This system achieves triple enhancement: the microporous cathode suppressed H⁺/OH^- recombination to maintain optimal catholyte pH (10.9), while ANHD's isomorphic templating boosts phosphorus recovery by 24.3 %, and seed-induced crystallization produces high-purity hydroxyapatite. The synergistic mechanism involving a previously unreported selective bubble transport regulation of cathode, crystal engineering of nucleation site provision, morphology stabilization, and precipitation zone regulation. Through response surface optimization (3.0 mA/cm²current density, Ca/P molar ratio of 3.8, and 2.9 g/L seed dosage), the system achieves 98.4 % phosphorus recovery within 0.5 h, with ultralow energy consumption (8.10 kW·h/kg P) and strong tolerance to common interfering ions and organics. Long-term stability tests over six consecutive cycles show consistent performance (relative standard deviation of 3.52 %) without cathode scaling issues, altering the traditional cathode-dependent nucleation dogma. This work provides a breakthrough solution that simultaneously addresses phosphorus pollution control and resource recovery, offering municipalities and industries a practical, cost-effective approach for sustainable phosphorus management.