Natural and synthetic zeolites in adsorption/oxidation processes to remove surfactant molecules from water

Iron-containing zeolites were studied as adsorbents and heterogeneous Fenton-like catalysts for the removal of the non-ionic surfactant Triton® X-100 (TX-100) from water. Adsorption tests included a variety of zeolites with different structure types (ZSM5, Beta and Y) and SiO₂/Al ₂O₃ ratios. Zeolites with 12-membered-ring channels and high molar ratio of SiO₂/Al₂O₃, indicating higher surface hydrophobicity, proved to be the most suitable adsorbents for TX-100. For preparation of iron-loaded zeolites, a Beta zeolite with a molar ratio of SiO₂/Al₂O₃ of 200 was selected, based on its excellent adsorption properties, and compared with a natural zeolite of clinoptilolite type. Batch experiments indicated that both Fe-zeolites are active in the heterogeneous Fenton-like oxidation of TX-100 at neutral pH. However, the synthetic Fe-Beta zeolite was preferable compared to the Fe-loaded natural zeolite with respect to catalytic activity and H₂O ₂ utilization efficiency, which was interpreted in terms of differences in iron speciation and adsorption properties towards TX-100. Fe-Beta (200) was successfully applied in two cycles of adsorption/oxidation steps in a column experiment. This study shows that Fe-loaded Beta zeolites with high hydrophobicity can be suitable materials for a combined approach of adsorption/wet peroxide oxidation of chemicals with relatively high molecular weight and chain-like molecule structure, such as the non-ionic surfactant TX-100.