The Compositional Characteristic of Uranyl Minerals in Xiazhuang Uranium Ore Field: Insight for the Oxidation Behavior of UO2 in Nuclear Waste Repository
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    Abstract:

    Xiazhuang uranium ore field is located in wet-hot climatic regions. Uraninite in this ore field is hosted in fractured zone in granite. Abundant uranyl minerals (especially, uranyl silicates and uranyl phosphates) are found because of intensive weathering of uraninite. Thus, Xiazhuang uranium ore field is an ideal site for the study of natural analogy of UO_2 oxidative corrosion with its special geochemical environment and abundant uranyl minerals. The high-level radioactive waste repository in China will be built in granite, therefore, the investigation of the behavior of uraninite weathering in this ore field is of an important role for the performance assessment of the disposal system of China. The combination of the uranyl minerals in Xiazhuang uranium ore field is comprised of uranyl oxide hydrates, uranyl silicates and uranyl phosphates, including schoepite, becquerelite, calciouranite, fourmarierite, Si-rich uranyl phase, uranophane, autunite and yingjiangite. In light of spatial relationship of these uranyl minerals, two paragensis series of uraninite weathering were identified: one is the silicate series with a mineral sequence of uraniniteuranyl oxide hydratesSi-rich uranyl phaseuranophane, and the other is the phosphate series with a mineral sequence of uraniniteuranyl oxide hydratesautuniteyingjiangite. Uranyl oxide hydrates are not stable and often substituted by stable uranyl silicates and phosphates. Consequently, uranyl silicates and phosphates are common minerals, and uranyl oxide hydrates are just found in a few samples, in this ore field. In this ore field, thermodynamic-stable uranyl silicates and phosphates are dominant uranyl minerals, and compositional characteristic of all uranyl minerals is Ca-riched, and Ca content of underground water in near-field of disposal systems is higher than in Xiazhuang ore field. These collectively foreshow that thermodynamic-stable Ca-rich uranyl silicates and phosphates should be the most common uranyl minerals and control the mobility of radionuclides, in disposal systems.

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LU Long, CHEN Fanrong, WANG Rucheng.2006. The Compositional Characteristic of Uranyl Minerals in Xiazhuang Uranium Ore Field: Insight for the Oxidation Behavior of UO2 in Nuclear Waste Repository[J]. Geological Review,52(4):562-569.

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  • Received:January 10,2006
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