The thermal decomposition of potassium titanium hexacyanoferrate(II) (KTiFC) loaded with cesium (referred to as Used Exchanger, or UE) was studied at different flow rate of air in a fixed bed calciner. The calcination process consisted of four stages: ambient temperature- 180 degrees C (stage I), 180-250 degrees C (stage II), 250-400 degrees C (stage III), and constant 400 degrees C (stage IV). The most intense reaction occurred in stage II. The rate of thermal decomposition was controlled, depending on the O-2 flux, by O-2 or CN concentration in different stages. Results from differential thermal analysis (DTA) showed that the calcination reaction of the anhydrous UE was exothermic, with an approximate heat output of 4.6kJ center dot g(-1) which was so large to cause the possible agglomeration of calcined residues. The agglomeration could be avoided by enhancing heat transfer and controlling the O-2 flux. It was found that there was no cyanides in the calcined residues and no CN-bearing gases such as HCN and (CN)(2) in the off-gas. It seemed that the catalytic oxidation furnace behind the fixed bed calciner could be cancelled.