[en] Clarkeite crystallizes during metasomatic replacement of pegmatitic uraninite by latestage, oxidizing hydrothermal fluids. Samples are zoned compositionally: Clarkeite, which is Na rich, surrounds a K-rich core (commonly with remnant uraninite) and is surrounded by more Ca-rich material-volumetrically, clarkeite is most abundant. Clarkeite is hexagonal (space group R3m) a = 3.954(4), c = 17.73(1) Angstrom (Z = 3). The structure of clarkeite is based on anionic sheets of the form [(UO₂)(O,OH)₂]. The sheets are bonded to each other through interlayer cations and H₂O molecules. The empirical formula for clarkeite from the Fanny Gouge mine near Spruce Pine, North Carolina, is: (Na_0.733K_0.029Ca_0.021Sr_0.009Y_0.024Th_0.006Pb_0.058) Σ_0.88 [(UO₂)_0.942O_0.918(OH)_1.082] (H₂O)_0.069 Na predominates and the Pb is radiogenic. The general formula for clarkeite is ((Na,K)_pM_q²⁺ M_r³⁺ M_s⁴⁺ Pb_x)[(UO₂)_1-xO_1-y(OH)_1+y] (H₂O)_z where Na >> K and p > (q + r + s). The number of O^2- ions and OH groups in the structural unit is determined by the net charge of the interlayer cations (except Pb): y = 1 - (p + 2q + 3r + 4s). This suggests that the ideal formula for ideal end-member clarkeite is Na[(UO₂)O(OH)](H₂O)_0-1. The structural sheets are destabilized as U decays to Pb (increasing x), and Pb enters vacant interlayer cation sites. Clarkeite eventually recrystallizes to lead uranyl oxide hydrates such as woelsendorfite or curite. 45 refs., 5 figs., 7 tabs

[en] 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 (a_0) =5.4758 and 5.4422 Å and unit cell volume (V) = 164.08 and 161.18 Å"3; clarkeite a_0=3.9473 Å, b_0=3.9473 Å, c_0 =17.6835 Å, α =β =90"0, γ=120"0, V=238.628 Å"3I:curite a_0=12.6292 Å, b_0 =13.2035 Å, c_0=8.3646 Å, V = 1394.81 Å"3; and β-uranophane a_0= 13.9481Å, b_o=15.4688 Å. C_0 =6.6362 Å, α =γ =90"9"0, β =91.3"0, V =1430.90 Å"3. Out of two, one uraninite has a_o 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 a_0=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 U_3O_8,(74.25%), ThO_2 (7.96%), PbO (7.73%) and rare earth elements (16214 ppm), whereas, SiO_2 (1.03%), CaO (0.82%) and Fe_2.O_3 (0.33%) contents are low. Chemically, â-uranophane analysed 47.42% U_3O_8, 4.75% CaO, and 19.15% SiO_2. (author)

[en] The work shows many-year experimental materials on the content of chemical elements in underground waters of Semipalatinsk Priirtyshye of the Republic of Kazakhstan depending on various factors (chemical type of water, water-in-taking rocks and their age, natural geomorphologic zonality and others)

[en] Specimens from five sections of mountain brown grounds have been studied. Determination of uranium content in the specimens has been carried out by the luminescence method (sensitivity n x 10^-8), ZrOCl₂ being used as a carrier. The uranium content in the specimens studied is found to be within the range 1.0 x 10^-4 - 2.5 x 10^-4 %, i.e. it is not much greater that one clark (n x 10^-4%). Investigations indicate that the uranium content in mountain brown grounds of the Khanlar district does not exceed one clark and is closely connected with their mechanical composition, medium reaction and content of organic substance. No regularity can be observed in uranium distribution across the ground section in the similar grounds studied

[en] The exploration activities carried out by the nuclear materials corporation in gebel gattar area revealed the presence of some uranium mineralizations within the gattar granite. The present work deals with the mineralogic studies of some mineralized surface samples of this granite. X-ray diffraction indicated the presence of a wide variety of uranium minerals, namely uraninite, clarkeite, zippeite, umohoite, carnotite as well as uranophane, soddyite, kasolite and becquerelite. Further more detailed work concerning the mineralogy of deeper samples from this promising uranium occurrence is recommended

[en] At present the groundwater quality undergo a considerable changes under the influence of intensive man's impact and natural factors. The aim of this investigation is to reveal a generic geochemical aspects of content and migration of heavy metals and radionuclides in underground waters and water-in-taking rocks by open coal mining on the Karazhyra coal deposit. The average concentration of heavy metals in underground waters of coal deposit exceed 4-124 times than their clarkes and maximum permissible concentration: Fe - 16 times; Pb - 6 times; Mn, Cd, Ti - 4 times; As - 3 times and Sr - 2 times

[en] Bulk X-ray diffraction (XRD), synchrotron X-ray microdiffraction (microXRD), and scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) were used to identify the individual phases, phase associations, morphologies, particle sizes, and compositions of solids in residual sludge from single-shell underground waste tanks C-203 and C-204 at the U.S. Department of Energy's Hanford Site in southeastern Washington state. Cejkaite [Na4(UO2)(CO3)3] was determined to be the dominant crystalline phase in the C-203 and C-204 sludges. This is only the second documented occurrence of cejkaite reported in the literature, and the first documented occurrence of this phase in radioactive wastes from DOE sites. XRD and SEM/EDS analyses of cejkaite found in the sludge solids are consistent with analyses of a natural mineral specimen of cejkaite. Characterization of residual solids from water leach and selective extraction tests indicates that cejkaite has a high solubility and a rapid rate of dissolution in water at ambient temperature, and that these sludges may also contain poorly crystalline Na2U2O7 [or clarkeite Na[(UO2)O(OH)](H2O)0-1], as well as nitratine (soda niter, NaNO3), goethite [FeO(OH)], and maghemite (Fe2O3). SEM/EDS analysis also shows that the C-204 sludge contains a solid composed of Na, Al, P, O, and possibly C that is likely amorphous. Other identified solids include Fe oxides that often also contain Cr and Ni and occur as individual particles, coatings on particles and botryoidal aggregates; a porous-looking material (or an aggregate of sub-micrometer particles) that typically contained Al, Cr, Fe, Na, Ni, Si, U, P, O, and C; Si oxide (probably quartz); and Na-Al silicate(s). The latter two solids probably represent minerals from Hanford sediment that were introduced into the tank during prior sampling campaigns or other tank-related activities. Preferential dissolution cavities were found on the surfaces of some of the Fe oxide particles present in residual solids from the water leach and selective extraction tests. If these solids contain contaminants, then their release into infiltrating water would be limited by dissolution of the low solubility Fe oxides. This process may account for at least some of the slow release of recalcitrant Tc-99 found in these sludges as discussed in the companion Part II paper by Cantrell and others

[en] Five actual Savannah River Site tank waste samples and three chemically-modified samples were tested to determine solubility limits for uranium and plutonium over a one year time period. Observed final uranium concentrations ranged from 7 mg U/L to 4.5 g U/L. Final plutonium concentrations ranged from 4 (micro)g Pu/L to 12 mg Pu/L. Actinide carbonate complexation is believed to result in the dramatic solubility increases observed for one sample over long time periods. Clarkeite, NaUO₂(O)OH · H₂O, was found to be the dominant uranium solid phase in equilibrium with the waste supernate in most cases.

[en] The oxidative alteration of uraninite by alkali-bearing, hydrothermal (200-400 degrees C) solutions in granitic rocks produces the rare mineral clarkeite. The general formula for Na-clarkeite is {(Na,K)_6-y-z(M²⁺_pM³⁺_qM⁴⁺_r)_y(□_1+z-xPb_x)}[(UO₂)_7-xO₁₀]·nH₂O z = p+2q+3r. The terms in square brackets designate the sheet structure; the other elements and vacancies (□) occur in interlayer sites. Clarkeite can accommodate Ca, Sr, Ba, Y, Th, and lanthanides. Thus, clarkeite is a potential actinide and fission product host. The replacement of uraninite by clarkeite occurs in the solid state and results in the loss of one-half of the uranium from uraninite. As U decays to Pb, the radiogenic Pb enters interlayer vacancies in clarkeite. This destabilizes the structure and clarkeite eventually decomposes to woelsendorfite, (Pb,Ca)₂U₂O₇·2H₂O, or curite, Pb₃U₈O₂₇·3H₂O

[en] Multi-metal Big Kanimansur Deposit host rocks contain high averages of uranium and thorium which are more than clark averages by 7 and 2.5 times accordingly. The second property of radio-active elements distribution are low ratio of thorium to uranium. That criteria can be used as prospecting sings for flanks and depth of know ore fields as well as for new squares of multi-metal mineralisation