One-step immobilization of cesium and strontium from alkaline solutions via a facile hydrothermal route

Abstract

Hydrothermal treatment of coal fly ash cenospheres (Si/Al = 2.7) as a glassy source of Si and Al was carried out in 1.5 M NaOH at 150°C in the presence of Cs+ and Sr2+ to study the possibility of Cs+ and Sr2+ immobilization in mineral-like compounds. Systems Na2O–H2O– (SiO2–Al2O3) glass, Na2O–Cs2O–H2O– (SiO2–Al2O3) glass with Cs+/Na+ ratios of 0.05 and 0.5, and Na2O–SrO–H2O– (SiO2–Al2O3) glass with Sr2+/Na+ ratios of 0.25 and 0.025 were under study. Structure, composition and morphology of solid products were characterized by PXRD, SEM-EDS and STA methods. In the Cs+/Sr2+ free systems the deep crystallization of cenosphere glass takes place resulting in hollow polycrystalline analcime microspheres. Microsphere solids including phases of ANA topology (analcime, pollucite or analcime-pollucite solid solutions) and Cs+/Sr2+ silicates are produced as Cs+ and Sr2+ immobilized forms in the Cs+/Sr2+ bearing systems. The degree of Cs+ and Sr2+ recovery from alkaline solutions was 90–99%.