MECHANISMS AND KINETICS OF HIGH-TEMPERATURE CADMIUM SORPTION BY PACKED BED OF CALCINED KAOLIN

Sorption experiments by passing CdCl2-carrying flue gas through the packed bed of calcined macro-porous kaolin particles were performed over a temperature range of 973–1173 K and a CdCl2 partial pressure range of 8–16.1 Pa. The observed structural change of the sorbent mineral at the stage of sorption and the results of desorption tests revealed the characteristics of an irreversible chemical reaction as a major cadmium capturing mechanism. In the fully saturated kaolin sorbent, CdO·Al2O·2SiO2 is present as a sorption reaction product together with a smaller amount of 2CdO·Al2O·2SiO2. The increase in sorbent bed temperature resulted in an increase in the rate of sorption, but it had no effect on maximum cadmium uptake. The gas-phase CdCl2 diffusion into the macro pores of calcined kaolin had a negligible effect on the overall sorption rate. The reaction between gaseous CdCl2 and solid Al2O3.2SiO2 is very sensitive to the concentration of CdCl2 but relatively insensitive to the temperature of the sorbent b...