Chloride Volatilization of Cesium from Pollucite toward Dry Removal of Cesium Contained in Sewage Sludge Ash

To remove radioactive cesium (Cs) from sewage sludge ash, experiments were conducted on the chloride volatilization of Cs from pollucite, CsAlSi2O6, which may exist as a main cesium compound in such solid waste. The pollucite samples were prepared using the sol-gel method and regulated to particle sizes of 20-32 μm and 45-63 μm. They were subjected to chloride volatilization experiments, using a lab-scale electric heating apparatus, with a temperature range of 1173-1473K in a mixed N2-Cl2 (0.05-10 vol%) gas stream. Results showed that the volatilization ratio of Cs from pollucite increased as the Cl2 concentration increased up to 1 vol%. However, the ratio stayed almost the same regardless of increased Cl2 concentrations from 1 vol% to 10 vol%. Meanwhile, the volatilization ratio of Cs increased with the heating temperature. Almost all Cs could be volatilized from pollucite within 12 h when the heating temperature was raised to above 1373 K and the Cl2 concentration was 0.25 vol%. It was also found that the interparticle diffusion of the Cl2 or CsCl produced did not have an influence on the volatilization rate of Cs from pollucite with particle sizes smaller than 63 μm.