Abstract
The paper presents new polyphase ceramic waste forms (matrices) of aluminosilicate-phosphate type synthesized from natural bauxites and apatite ore tailings. This ceramic material is named “geoceramics” by the authors. The optimum composition of the waste matrix is selected (Cs2O, P2O5, SiO2, and Al2O3) and a cost-saving method for synthesis of matrices capable to accommodate up to 12 wt. % of cesium and 6 wt. % of strontium isotopes is developed. Phases which immobilize cesium isotopes are identified. It is shown that waste forms which are close in stoichiometric composition to pollucite (CsAlSi2O6) have the best resistance to water. The rate of cesium leaching (R) from these waste forms is 2.10-6 g/cm2day in the kinetic region. Heat treatment and cooling of the matrix material does not affect the immobilization performance of the proposed waste forms. In some cases, a positive effect is achieved by using the sol-gel method which can reduce the grain sizes, resulting in a decrease in the leach rate of cesium to 1.10-6 g/cm2 day. The leach rate of strontium is below the detection limit of atomic absorption spectrophotometers (0.3 .10-6 g/cm2day).
Keywords: Aluminosilicate-phosphate polyphase ceramics, apatite ore tailings, bauxite, Cs-Sr-fraction of HLW, corrosion resistance of matrices, geoceramic matrices (geoceramics), high level radioactive waste (HLW), immobilization of HLW.
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