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. This study successfully synthesized a novel and highly efficient nanocomposite (nCaO2-BFS) through a coprecipitation method by anchoring 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 adsorbents 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 evaluation. The 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-, SO42-, HCO3-, and CO32-. Through surface precipitation, inner-sphere complexation between nCaO2 and phosphate 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 and mixed with soil to promote the growth of Brassica rapa L. Therefore, applying nCaO2-BFS appears to be a promising method for remediating excessive phosphate and recovering non-renewable phosphorus resources.