Use of surface-modified zeolite Y for extraction of metal ions from aqueous to organic phase

The surface hydroxyl groups of air-dried zeolite Y (Si/Al=2.3) were silylated using n-octadecyltrichlorosilane (OTS) as the derivatizing agent. Derivatization was confirmed by elemental analysis, infrared and nuclear magnetic resonance spectroscopies and contact angle measurements, The presence of C-18 functionalities on the surface makes the zeolite crystallites sufficiently hydrophobic such that, upon suspension in a mixture of water and an immiscible organic solvent such as toluene, the crystallites disperse into the toluene phase. We report here the ion-exchange properties of these surface-derivatized zeolites, focusing on the possibility of extracting ions from the aqueous phase into an organic phase. In order to establish the feasibility of extraction, an aqueous solution of cobaltocenium (Cp2Co+) ions was used as the model system, since its characteristic electronic spectrum can be used to estimate the loss from the aqueous phase. Although the zeolite crystallites are repelled by the aqueous solution, their ability to extract ions from the aqueous phase via ion exchange is preserved, although the rate of the ion-exchange process is considerably slower. Ion exchange of Cs+ and Sr2+ cations from aqueous solutions was also examined. In the presence of a million-fold excess of Na+ ions, concentrations typically present in radioactive waste solutions, there was no selective uptake of Cs+ and Sr2+ ions. (C) 1999 Elsevier Science B.V. All rights reserved.