Enrichment of Uranium inside Wood: a Natural Analog from a Sandstone-hosted Roll-type Uranium Ore Deposit
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Enrichment of Uranium inside Wood: a Natural Analog from a Sandstone-hosted Roll-type Uranium Ore Deposit Huifang Xu1, Maozhong Min2, Jia Zhen2, Xinjian Peng2, Jinping Wang2, Larry Barton3, and Yifeng Wang4 1
Department of Geology and Geophysics, University of Wisconsin, Madison Wisconsin 53706, U. S. A., [email protected] 2 Department of Earth Sciences, State Key Laboratory of Mineral Deposit Research, Nanjing University, Nanjing 210093, P. R. China 3 Department of Biology, University of New Mexico, Albuquerque New Mexico 87131, U. S. A. 4 Sandia National Laboratories, Albuquerque, New Mexico 87185, U. S. A. ABSTRACT Furniture contaminated with uranium will be disposed of, together with U-bearing waste, in a geological repository such as the WIPP site in New Mexico. It is important to understand the effect of the wooden furniture on the migration of uranium in order to predict long-term behavior of uranium in a geological repository environment. In this paper, we present natural uraninite-bearing carbonized wood pieces from a sandstone-hosted roll-type uranium ore deposit in NW China. Results from SEM and TEM observations show that there are nanometer sized, and micron-sized, uraninite crystals that have accumulated on cell walls of the carbonized wood. Some uranitite crystrals display oval and round shapes that may be the result of microbial-induced reduction of uranium from groundwater. The wood carbonized fragments are the most uranium-rich “phase.” In some areas, aggregates of pyrite crystals occur with the uraninite. It is proposed that organic components from the decay of the wood cells provide nutrients for the anaerobic bacteria to grow. The wood pieces with the bacteria inside may serve as scavengers of uranium because of the local reducing chemical environment. INTRODUCTION To minimize the mobility of uranium in the environment, the reduction of U(VI) to U(IV) by microorganisms, especially bacteria, leading to U(IV) deposition has been extensively studied under experimental conditions using dilute uranium-bearing solutions [1-4]. However, there have been few direct studies of natural uranium mineralization by microorganisms [5,6]. Here, we show for the first time, using natural examples of primary uranium minerals (e.g., uraninite (UO2) and coffinite (USiO4) to demonstrate that these minerals usually adopt characteristic forms defined by the geometries of microfungi and bacteria, indicating biogenic mineralization [7] in high-grade ores (e.g., >1% U) in sandstone-hosted uranium deposits from Xinjiang in northwest China. Uranium mineralization by microorganisms reported here occurs in several sandstone-hosted uranium deposits in the YL basin area in the Xinjiang region (e.g., Wuyiyi, Wuyier and Wuyisan). These deposits are similar to the sandstone-hosted roll-type uranium deposits found in the Colorado Plateau region of the southwestern United States. The geological setting of the deposits in the YL basin has previously been described and reported elsewhere [8]. Briefly, the YL basin area is
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