Hydrothermal Stability of Pollucite and Leachability of Cesium

The chemical stability of pollucite (CsAlSi_2O_6) has been studied under hydrothermal conditions in relation to the leachability of cesium. At room temperature, the leachability of cesium from pollucite in the neutral pH region was very low. Under hydrothermal conditions (100 and 200℃) in sodium or potassium chloride solution, cesium leached out due to an ion exchange reaction forming new phases such as analcime (NaAlSi_2O_6) and leucite (KAlSi_2O_6) through an isomorphous substitution mechanism. In the presence of calcium or magnesium chloride, the pollucite phase recrystallised with the formation of anorthite (CaAl_2Si_2O_8) and clinochlore (Mg_5Al_2Si_3O_(OH)_8) at the surface of the original pollucite and with the cesium leaching into solution. (Received November 7,1988