17α-Ethinylestradiol removal from water by magnetic ion exchange resin

Magnetic ion exchange (MIEX) resins have received considerable attention in drinking water treatment due to their fast and efficient removal of dissolved organic carbon (DOC). Two types of mechanisms, i.e., ion exchange, reversible and irreversible adsorption, may occur during pollutants removal by MIEX. This work examined the removal mechanism of 17α-Ethinylestradiol (EE2) by MIEX. As one of typical estrogen micro-pollutants, EE2 existed as neutral molecule in natural water, and its charge density was close to zero [(0.00000219 ± 0.00000015) meq·(μg EE2)− 1] based on the potentiometric titration method. However, the removal of EE2 by MIEX was much higher than that of other micro-pollutants previously reported. Multi-cycle adsorption-regeneration experiments and ion exchange stoichiometry analysis were conducted to elucidate the removal mechanism of EE2 by MIEX resin. The results suggested that the main removal mechanism of EE2 by MIEX was ion exchange instead of reversible micro-pore adsorption. The experimental analysis based on Donnan theory indicated that the internal micro-environment of resin beads was alkaline, in the alkaline environment EE2 would be ionized into negatively charged groups. As a result, ion exchange reaction occurred inside the pore of MIEX resin, and the removal process of EE2 by MIEX was dominated by the ion exchange reaction.