Phosphate adsorption using modified iron oxide-based sorbents in lake water: Kinetics, equilibrium, and column tests

Adsorption behavior of Bayoxide® E33 (E33) and three E33-modified sorbents for the removal of phosphate from lake water was investigated in this study. E33-modified sorbents were synthesized by coating with manganese (E33/Mn) and silver (E33/AgI and E33/AgII) nanoparticles. Adsorbent characterization was done by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), surface area analyzer (BET), transmission electron microscopy (TEM), and high resolution TEM (HR-TEM) analysis. Batch, equilibrium, and column experiments were conducted to determine various adsorption parameters. Equilibrium data were fitted to different adsorption isotherms and the Langmuir isotherm provided the best fit. Based on the Langmuir model, it was found that E33/AgII had a slightly higher maximum monolayer adsorption capacity (38.8 mg g−1) when compared to unmodified E33 (37.7 mg g−1). Data for adsorption kinetics were found to best fit with the pseudo-second-order model, suggesting chemisorption is the mechanism of sorption. Intra-particle diffusion studies indicated that the rate-limiting step for phosphate sorption onto E33 and modified E33 was intra-particle diffusion. Although limited improvements were seen, the results of this study suggest that the surface of E33 can be modified with nanoparticles to enhance the adsorption of phosphate from aqueous solutions and may give other advantages such as limiting biofouling over an extended lifetime of numerous recovery/regeneration steps.