Design of zeolite ion-exchangers for selective and fast removal of radioactive strontium

Abstract

To eliminate the radioisotope ${90}$Sr${2+}$ from contaminated water, various inorganic ion-exchange materials have been developed. LTA zeolite has been widely used for Sr${2+}$ capture adsorbent to get rid of Sr${2+}$ ion under contaminated water due to the high Sr${2+}$ removal at equilibrium state. Due to the small micropores of LTA zeolite, however, LTA zeolite has low adsorption kinetics, which is a weakness for continuous flow removal system. To remove Sr${2+}$ diffusion limitation through zeolite micropore, we synthesized mesoporous-sodalite (Meso-SOD), so that Sr${2+}$ ions can diffuse through only mesopores. Various experimental analyses exhibit that Meso-SOD zeolite has enough adsorption site to capture 1 ppm Sr${2+}$ ion under presence of competing cations. Pseudo-second order fitting analysis exhibits that FAU zeolite which has larger micropore (12 MR) showed 7.6 times higher kinetic value and Meso-SOD has 33 times higher that conventionally used LTA (8MR) zeolite respectively. Additionally, Sr${2+}$ removal under simulated ground and sea water, which includes competing cations (e.g., Na$^+$, K$^+$, Ca${2+}$, Mg${2+}$) are comparable or even better than LTA and FAU zeolite. We anticipate that Meso-SOD zeolite will demonstrate a sharp S-shape curve in breakthrough column experiment because of high Sr${2+}$ adsorption kinetics.