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

摘要

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 Cs_(2)MgSi_(5)O_(12), Cs_(2)SrSi_(5)O_(12), Cs_(2)CuSi_(5)O_(12), CsFeSi_(2)O_(6), and Cs_(2)CuSi_(5)O_(12)(centre dot)CsFeSi_(2)O_(6) (Cs_(3)CuFeSi_(7)O_(18)), 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 deg C (data of differential scanning calorimetry and X-ray phase analysis). The silicates underwent no chemical or phase transformations on heating to 900-1000 deg C. No egress of Cs from the silicates to the gas phase was observed on heating for 4-6 h at 800 deg C. The leaching rates of Cs and Sr at 25 deg 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.