Synthesis, Structure Determination, and Aqueous Durability of Cs2ZrSi3O9 |
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Authors: | M Lou Balmer Yali Su Hongwu Xu Eric Bitten David McCready Alexandra Navrotsky |
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Affiliation: | Materials and Chemical Sciences and the Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington 99532 and;Thermochemistry Facility, Department of Chemical Engineering and Materials Science, University of California at Davis, Davis, California 95616 |
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Abstract: | The structure of Cs2ZrSi3O9 synthesized using a sol–gel method was determined from the Rietveld refinement of experimental powder X-ray diffraction data. The refinement confirmed that this compound was isostructural with wadeite: its structure was hexagonal (space group P 63/ m ), and its lattice parameters were a = 7.2303(2) Å and c = 10.2682(4) Å. The aqueous durability of Cs2ZrSi3O9 varied, depending on the solution conditions. In modified leach tests with buffered (pH 7) and unbuffered solutions, the 7-d cesium release rates were <1.2 × 10−4 g·(m2·day)−1, which indicated high aqueous durability. However, in unsaturated, unbuffered solutions with a pH of 9–10, the durability was much lower, with 7-d cesium release rates of 2.2 × 10−3 g·(m2·day)−1. The ability of this material to retain cesium in aqueous environments can be explained by its condensed ring structure, in which the size of the channel openings is smaller than the diameter of a Cs+ ion. However, dissolution of the network silicate occurred at high pH, which resulted in the release of cesium. |
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Keywords: | nuclear waste silicates chemical durability |
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