Synthesis and characterization of K-phillipsite (K-PHI) membrane for potassium extraction from seawater

Abstract

K-phillipsite (K-PHI) membrane was synthesized on the outer surface of a porous α-alumina tubular support by seeded hydrothermal synthesis using tetrabutylammonium bromide (TBAB) as template. The synthetic sample was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersion spectroscopy (EDS). The separation factors (α) of the sample to K+ were researched using the mixed K+–Na+, K+–Ca2+, K+–Mg2+ solutions and simulated seawater as testing media, respectively. The synthetic membrane which is mainly composed of Si, Al, K, Na and O is typical K-PHI structure. The K-PHI membrane on the tubular support is defect-free and the thickness of the membrane is about 20μm. The separation factors (α) of the sample to K+ in the mixed K+–Na+, K+–Ca2+, K+–Mg2+ solutions are 18.1, 32.1 and 118.4, respectively. And the average separation factor of K+ relative to Na+ in simulated seawater is αK+/Na+=15.7. Therefore the sample has preference selectivity to K+ and can be used as a potential inorganic membrane for potassium extraction from seawater.