Sample records for clarkeite

  1. X-ray diffraction and geochemical studies on uranium minerals from Jogipalle Pegmatite, Nellore Schist Belt, Andhra Pradesh: paragenetic implications

    The uranium ore sample used in this study occurs as hand - pickable lumps and grains in the Jogipalle pegmatite, Nellore Schist Belt, Andhra Pradesh. Powder X-ray diffraction (XRD) studies on separated uranium minerals (UMs) have revealed the presence of both primary (uraninite) and secondary (ianthinite, clarkeite, curite and â- uranophane) uranium minerals, which are mostly characterised by their sharply-defined reflections. The crystallographic parameters of various UMs are: Uruniuite-1 and 2 unit cell dimension (a0) =5.4758 and 5.4422 Å and unit cell volume (V) = 164.08 and 161.18 Å3; clarkeite a0=3.9473 Å, b0=3.9473 Å, c0 =17.6835 Å, α =β =900, γ=1200, V=238.628 Å3I:curite a0=12.6292 Å, b0 =13.2035 Å, c0=8.3646 Å, V = 1394.81 Å3; and β-uranophane a0= 13.9481Å, bo=15.4688 Å. C0 =6.6362 Å, α =γ =9090, β =91.30, V =1430.90 Å3. Out of two, one uraninite has ao of 5.4758 Å, which is more than the value given for the uraninite standard (5.4645 Å), suggesting its anomalous nature and formation of uraninite (primary) under high temperature condition (∼500-550℃). In contrast, another uraninite has a0=5.4422 Å, reflecting its oxidized nature. It, thus, suggests that after their formation, the uraninites have been subjected to oxidation leading to the formation of secondary uranium minerals (SUMs) with a relict core of black mineral (uraninite) encircled by successive zones of SUMs, namely. black (ianthinite, in traces), orange (clarkeite-curite) and yellow (β - uranophane). Based on available mineralogical data, the inferred paragenetic sequence of the investigated uranium minerals is: Uranium oxide (primary uraninite) > uranium oxide (altered uraninite) > uraniumoxide hydrate (ianthinite) > sodium-potassium uranium oxide (clarkeite) - lead-uraniumoxide hydrate (curite) > calcium uranyl silicate hydroxide hydrate ((β -uranophane). Uraninite-I contains high U3O8,(74.25%), ThO2 (7.96%), PbO (7.73%) and rare earth elements (16214 ppm

  2. Characterization of Solids in Residual Wastes from Underground Storage Tanks at the Hanford Site, Washington, U.S.A

    Solid phase physical and chemical characterization methods have been used in an ongoing study of residual wastes from several single-shell underground waste tanks at the U.S. Department of Energy's Hanford Site in southeastern Washington State. Because these wastes are highly-radioactive dispersible powders and are chemically-complex assemblages of crystalline and amorphous solids that contain contaminants as discrete phases and/or co-precipitated within oxide phases, their detailed characterization offers an extraordinary technical challenge. X-ray diffraction (XRD) and scanning electron microscopy/energy dispersive x-ray spectroscopy (SEM/EDS) are the two principal methods used to characterize solid phases and their contaminant associations in these wastes. Depending on the specific tank, numerous solids (such as eejkaite; Na2U2O7; clarkeite; gibbsite; boehmite; dawsonite; cancrinite; Fe oxides such as hematite, goethite, and maghemite; rhodochrosite; lindbergite; whewellite; nitratine; and several amorphous phases) have been identified in residual wastes studied to date. Because many contaminants of concern are heavy elements, SEM analysis using the backscattered electron (BSE) signal has proved invaluable in distinguishing phases containing elements, such as U and Hg, within the complex assemblage of particles that make up each waste. XRD, SEM/EDS, and synchrotron-based methods provide different, but complimentary characterization data about the morphologies, crystallinity, particle sizes, surface coatings, and compositions of phases in the wastes. The impact of these techniques is magnified when each is used in an iterative fashion to help interpret the results from the other analysis methods and identify additional, more focused analyses

  3. Thermodynamics of Uranyl Minerals: Enthalpies of Formation of Uranyl Oxide Hydrates

    K. Kubatko; K. Helean; A. Navrotsky; P.C. Burns


    The enthalpies of formation of seven uranyl oxide hydrate phases and one uranate have been determined using high-temperature oxide melt solution calorimetry: [(UO{sub 2}){sub 4}O(OH){sub 6}](H{sub 2}O){sub 5}, metaschoepite; {beta}-UO{sub 2}(OH){sub 2}; CaUO{sub 4}; Ca(UO{sub 2}){sub 6}O{sub 4}(OH){sub 6}(H{sub 2}O){sub 8}, becquerelite; Ca(UO{sub 2}){sub 4}O{sub 3}(OH){sub 4}(H{sub 2}O){sub 2}; Na(UO{sub 2})O(OH), clarkeite; Na{sub 2}(UO{sub 2}){sub 6}O{sub 4}(OH){sub 6}(H{sub 2}O){sub 7}, the sodium analogue of compreignacite and Pb{sub 3}(UO{sub 2}){sub 8}O{sub 8}(OH){sub 6}(H{sub 2}O){sub 2}, curite. The enthalpy of formation from the binary oxides, {Delta}H{sub f-ox}, at 298 K was calculated for each compound from the respective drop solution enthalpy, {Delta}H{sub ds}. The standard enthalpies of formation from the elements, {Delta}H{sub f}{sup o}, at 298 K are -1791.0 {+-} 3.2, -1536.2 {+-} 2.8, -2002.0 {+-} 3.2, -11389.2 {+-} 13.5, -6653.1 {+-} 13.8, -1724.7 {+-} 5.1, -10936.4 {+-} 14.5 and -13163.2 {+-} 34.4 kJ mol{sup -1}, respectively. These values are useful in exploring the stability of uranyl oxide hydrates in auxiliary chemical systems, such as those expected in U-contaminated environments.

  4. Residual Waste from Hanford Tanks 241-C-203 and 241-C-204. 2. Contaminant Release Model

    Fusion analyses, water leaches, selective extractions, empirical solubility measurements, and thermodynamic modeling were used with results from solid-phase characterization studies [see companion paper (1)] to determine total concentrations, contaminant-phase associations, and develop contaminant release models for residual sludge from single-shell underground waste tanks 241-C-203 and 241-C-204 at the U.S. Department of Energy?s Hanford Site in southeastern Washington state. U and Tc are primary contaminants of concern because of their long half-lives and their generally high mobility in oxidizing soil and groundwater environments. Uranium release was determined to be controlled by two phases; ?ejkaite [Na4(UO2)(CO3)3] and poorly crystalline Na2U2O7 [or clarkeite Na[(UO2)O(OH)](H2O)0-1] which were identified in C-203 and C-204 sludge samples (1). U release was determined to occur in three stages from these phases. In the first stage, U release will be controlled by the solubility of ?ejkaite, which is suppressed by high concentrations of sodium released from dissolution of NaNO3 in the residual sludges. Equilibrium solubility calculations indicate the U released during this stage will have a maximum concentration of 0.021 M. When all the NaNO3 has dissolved from the sludge, the solubility of the remaining ?ejkaite will increase to 0.28 M. After ?ejkaite has completely dissolved, the maximum concentration of U released is expected to be controlled by the solubility of Na2U2O7 at a concentration of 3.0 ? 10-5 M. For Tc, a significant fraction of its concentration in the residual sludge was determined to be relatively insoluble (20 wt% for C-203 and 80 wt% for C-204). Because of the low concentrations of Tc in these sludge materials, the characterization studies did not identify any discrete Tc solids phases. Therefore, release of the readily soluble fraction of Tc was assumed to be controlled by the solubility of NaTcO4 at 7.1 M. Selective extraction results

  5. Tank 26F Supernatant And 2F Evaporator Eductor Pump Sample Characterization Results

    In an effort to understand the reasons for system plugging problems in the SRS 2F evaporator, supernatant samples were retrieved from the evaporator feed tank (Tank 26F) and solids were collected from the evaporator eductor feed pump for characterization. The variable depth supernatant samples were retrieved from Tank 26F in early December of 2010 and samples were provided to SRNL and the F/H Area laboratories for analysis. Inspection and analysis of the samples at SRNL was initiated in early March of 2011. During the interim period, samples were frequently exposed to temperatures as low as 12 C with daily temperature fluctuations as high as 10 C. The temperature at the time of sample collection from the waste tank was 51 C. Upon opening the supernatant bottles at SRNL, many brown solids were observed in both of the Tank 26F supernatant samples. In contrast, no solids were observed in the supernatant samples sent to the F/H Area laboratories, where the analysis was completed within a few days after receipt. Based on these results, it is believed that the original Tank 26F supernatant samples did not contain solids, but solids formed during the interim period while samples were stored at ambient temperature in the SRNL shielded cells without direct climate control. Many insoluble solids (>11 wt. % for one sample) were observed in the Tank 26F supernatant samples after three months of storage at SRNL which would not dissolve in the supernatant solution in two days at 51 C. Characterization of these solids along with the eductor pump solids revealed the presence of sodium oxalate and clarkeite (uranyl oxyhydroxide) as major crystalline phases. Sodium nitrate was the dominant crystalline phase present in the unwashed Eductor Pump solids. Crystalline sodium nitrate may have formed during the drying of the solids after filtration or may have been formed in the Tank 26F supernatant during storage since the solution was found to be very concentrated (9-12 M Na