Zeolite W was synthesized by hydrothermal method using sodium aluminate and soluble glass as the raw materials in the absence of organic template. The ion-exchange equilibrium and ion-exchange capacity of the synthetic sample to K+ in seawater, as well as the selectivity coefficient to K+ in the mixed K+-Na+ solution were investigated. The sample was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS) and Fourier transform infrared spectroscopy (FT-IR). Based on the ion-exchange equilibrium curve, it shows that the ion-exchange velocity of the sample to K+ is a rapid process and reaches leveling within 20 min. The ion-exchange capacity of the sample to K+ is 54.9 mg/g in seawater, and the selectivity coefficient to K+ is 85.6 in the mixed K+-Na+ solution. The sample has high selectivity to K+, and therefore it can be used to extract potassium selectively from seawater. The sample, which is mainly composed of Si, Al, K and O, exhibits a bouquet-like shape and is zeolite W verified by its XRD pattern. (C) 2012 Elsevier B.V. All rights reserved.