Efficient removal and recovery of phosphate from wastewater by nano-CaO2/BFS sorbent and its potential as a slow-release phosphate fertilizer

Abstract

Facing the dual pressure of eutrophication control and global phosphorus scarcity, the efficient removal and recovery of phosphate from wastewater has attracted growing attention in recent years. Herein, an efficient nanocomposite (nCaO₂-BFS) was successfully synthesized through a facile coprecipitation method by loading nano-calcium peroxide (nCaO₂) onto blast furnace slags (BFS) and used for phosphate removal and recovery from wastewater. Based on the preliminary screening of as-prepared nCaO₂-BFS sorbents regarding phosphate removal efficiency, the nCaO₂-BFS nanocomposite prepared with a CaCl₂-to-BFS mass ratio of 0.6:1, NH₃·H₂O amount of 20 mL, and H₂O₂ amount of 12 mL was selected for further characterization and phosphate elimination. Results showed that the developed nCaO₂-BFS sorbent exhibits a superior adsorption capacity of 67.48 mg·g^-1, a broadly applicable pH range from 4 to 10, and strong selectivity for phosphate in the presence of competing anions including Cl^-, NO₃^-, SO₄^2-, HCO₃^-, and CO₃^2-. Mechanistically, surface precipitation and inner-sphere complexation via ligand exchange were identified as the primary sorption mechanism for nCaO₂-BFS in capturing phosphate. The plant growth test confirmed that the phosphate-laden nCaO₂-BFS sorbent could be used as a slow-release fertilizer to promote the growth of Brassica rapa L. Therefore, applying nCaO₂-BFS appears to be a promising method for remediating excessive phosphate and recovering the non-renewable phosphorus resource.