Abstract
Interconversion reactions among the solids SiO2 (quartz and fused), γ-AlOOH (boehmite), CsAlSiO4, CsAlSi2O6 (pollucite), and CsAlSi5O12, in contact with aqueous solutions at 200 °C, have been investigated. Results support earlier suggestions that CsAlSi5O12 is not stable with respect to CsAlSi2O6 + SiO2. CsAlSiO4 is only stable, if at all, when the activity product of dissolved Cs+ and OH−, with respect to unit molality standard states, exceeds about 10−2. CsAlSi2O6 is stable with respect to boehmite and quartz when the cesium hydroxide activity product exceeds 10−7.8±1.5. The significance of these results to the possible immobilization of radioactive cesium as a solid aluminosilicate is discussed. Based on a comparison with published estimates of enthalpies of formation, the following revised values are suggested:[Formula: see text]Keywords: cesium aluminosilicates, enthalpy of formation, hydrothermal reactions, pollucite, thermodynamic stability.
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