Cenosphere-sourced hydrothermal synthesis of pollucite-analcime solid solutions as a low-temperature method to immobilize 137Cs in a mineral-like form

Two narrow fractions of coal fly ash cenospheres with similar to 90 wt % glass phase and different Si/Al ratio (2.1 and 2.9 in the glass phase), shell porosity and thickness, globule size, and content of a mullite phase were used as a glassy source of Si and Al in the hydrothermal synthesis of pollucite-analcime solid solutions at 150 degrees C and autogenous pressure, 1.0 M NaOH, Cs/Na ratios of 0-0.25. Hollow microsphere globules of about 60-70 and 140-170 mm in sizes are produced as Cs immobilized forms in this process. The microspheres have a composite mullite/ANA wall, where ANA is analcime-pollucite solid solutions. Composition and morphology of solid products as well as composition of ANA phases were characterized by PXRD, SEM-EDS and STA methods. The influence of the mullite content and shell thickness on the preservation of the product spherical shape has been established. The degree of Cs+ recovery from alkaline solutions due to preferential involvement of cesium in the synthesis of ANA phases was up to 96%. (C) 2020 Elsevier B.V. All rights reserved.