Silicates of Leucite Structure as Environmentally Safe Forms of Cesium and Strontium Immobilization

Silicates containing binary combinations of Cs cations with Mg, Sr, Cu, or Fe cations or a ternary combination of Cs, Cu, and Fe cations were prepared by the sol-gel procedure followed by heat treatment of the dried gels. Silicates of the composition Cs2MgSi5O12, Cs2SrSi5O12, Cs2CuSi5O12, CsFeSi2O6, and Cs2CuSi5O12 center dot CsFeSi2O6 (Cs3CuFeSi7O18), according to the results of X-ray phase analysis, belong to the leucite family, space group Ia3d. The temperature range of their formation is 370-450 degrees C (data of differential scanning calorimetry and X-ray phase analysis). The silicates underwent no chemical or phase transformations on heating to 900-1000 degrees C. No egress of Cs from the silicates to the gas phase was observed on heating for 4-6 h at 800 degrees C. The leaching rates of Cs and Sr at 25 degrees C on the seventh day reached 10(-7) g cm(-2) day(-1) (powdered samples, steady-state mode). The X-ray diffraction patterns of the silicates before and after hydrolytic tests were essentially similar.