High-Temperature Cesium Sorption in Calcined Kaolin Packed Beds

Abstract

This study investigated the use of calcined kaolin particles in the size range of 300-400 μm as cesium capturing sorbents at high temperatures. Sorption tests by passing CsCl-carrying flue gas through the packed bed of calcined porous kaolin particles were performed over a temperature range of 973-1173 K and a CsCl partial pressure of 7.4-11.1 Pa. The observed structural change of the sorbent mineral at the stage of sorption revealed the characteristics of an irreversible chemical reaction as a major cesium capturing mechanism. In the fully saturated kaolin sorbent, Cs₂O · Al₂O₃ · 2SiO₂ is present as a sorption reaction product. The increase in sorbent bed temperature resulted in an increase in the rate of sorption, but it had no effect on maximum cesium uptake. The gas-phase CsCl diffusion into the macropores of calcined kaolin had a negligible effect on the overall sorption rate. The reaction between gaseous CsCl and solid Al₂O₃ · 2SiO₂ is very sensitive to the concentration of CsCl but relatively insensitive to the temperature of the sorbent bed. The order of reaction with respect to the CsCl vapor concentration was determined to be 0.75. The activation energy, E_a, was estimated as 2.86 kcal/mol according to the Arrhenius relationship.