Nanoscale Zero-Valent Iron Confined in Anion Exchange Resins to Enhance Selective Adsorption of Phosphate from Wastewater

The removal and recovery of phosphorus from wastewater are crucial for reducing eutrophication and alleviating phosphate rock depletion. In this study, nanoscale zero-valent iron (nZVI) confined in Alfa Aesar Amberlite IRA-402 (Cl) anion exchange resin composite adsorbents was developed by in situ reduction and deposition (denoted as nZVI-402-Cl) to remove phosphate from simulated and real wastewater. Surface and structure characterizations revealed that nZVI particles with a partially oxidized surface were loaded on the surface and inside the anion exchange resin. The phosphate adsorption capacity of nZVI-402-Cl was found to be high over a wide pH range (3.0-11.0), with a maximum adsorption capacity of 56.27 mg P/g at pH 7.2. Despite the presence of interfering sulfate and nitrate anions, nZVI-402-Cl maintained its high phosphate adsorption capacity owing to its excellent selectivity. The confinement of nZVI in anion exchange resins, in particular, could reduce the negative effects of humic acid on phosphate removal. After five regeneration/use cycles, the phosphate removal of nZVI-402-Cl was maintained close to 95%. In column mode tests, the nZVI-402-Cl column process generates -1850 bed volume (BY) clean water ([phosphorus] < 0.1 mg/L) from the wastewater treatment plant effluents. In contrast, the value of the IRA-402 column is only -900 By. nZVI-402-Cl has proven to be an efficient and selective adsorbent for practical phosphate removal and recovery in different water environments.