First successful synthesis of an Al-rich mesoporous aluminosilicate for fast radioactive strontium capture

Abstract

Al-rich zeolites such as NaA (Si/Al = 1.00) have been widely applied to remove radioactive ⁹⁰Sr²⁺ because of their high surface charge density enabling efficient ion-exchange of multivalent cations. However, due to the small micropore diameters of zeolites and large molecular size of strongly hydrated Sr²⁺, Sr²⁺-exchange with zeolites suffers from very slow kinetics. In principle, mesoporous aluminosilicates with low Si/Al ratios close to unity and tetrahedrally coordinated Al sites can exhibit both high capacity and fast kinetics in Sr²⁺-exchange. Nonetheless, the synthesis of such materials has not been realized yet. In this study, we demonstrate the first successful synthesis of an Al-rich mesoporous silicate (ARMS) using a cationic organosilane surfactant as an efficient mesoporogen. The material exhibited a wormhole-like mesoporous structure with a high surface area (851 m² g^-1) and pore volume (0.77 cm³ g^-1), and an Al-rich framework (Si/Al = 1.08) with most Al sites tetrahedrally coordinated. Compared to commercially applied NaA, ARMS exhibited a dramatically improved Sr²⁺-exchange kinetics (>33-fold larger rate constant) in batch adsorption while showing similarly high Sr²⁺ capture capacity and selectivity. Due to the fast Sr²⁺-exchange kinetics, the material also exhibited 3.3-fold larger breakthrough volume than NaA in fixed-bed continuous adsorption.

Keywords: Ion-exchange; Kinetics; Mesoporous; Organosilane surfactant; Strontium.