Enhancing Phosphorus Removal Using Fe-Modified Granular Activated Carbon: Influence of Impregnation Method and Storage Conditions

Abstract

This study investigates the phosphorus adsorption performance of Fe-impregnated granular activated carbon (GAC-Fe), focusing on improvements in the impregnation procedure and the influence of post-synthesis storage conditions on adsorbent efficiency. Commercial granular activated carbon was modified with iron hydroxides using different impregnation approaches, and the resulting materials were evaluated through batch kinetic experiments using a pseudo-second-order model. Three preparation strategies were compared: a standard impregnation procedure, an increased iron-reagent concentration, and a sequential double-impregnation process. Results demonstrated that sequential impregnation significantly enhanced adsorption performance, increasing the equilibrium adsorption capacity by approximately 50%–80% compared with single-step methods. Statistical analysis confirmed that the double-impregnation strategy produced a significant improvement in adsorption capacity without affecting adsorption kinetics. In addition, storage conditions were found to strongly influence the long-term performance of the material. Adsorbents stored under non-inert conditions exhibited a progressive reduction in adsorption capacity over time, whereas samples maintained under an inert atmosphere preserved their adsorption efficiency. Iron leaching during adsorption experiments remained negligible, indicating minimal risk of secondary contamination. Overall, the findings demonstrate that both impregnation strategy and storage environment play critical roles in optimizing the performance and stability of Fe-modified activated carbon for phosphorus removal from aqueous systems.