Uranium selenates

The phase diagram studies by Serezhkina et al. show that the stable solid phase in contact with water at 298.15 K is U02Se04-4H20. The solubility is  

A phase diagram and related information are available for the system U02Se04-H2Se04-H20 at 298.15 K in [88SER/BLA] U02Se04-BeSe04-H20 at 

The value of the solubility product of U02Se04-4H20(cr), U02Se04-4H20(cr) UOf + SeOj + 4H20(1) 

Complex formation in the dioxouranium(Vl)-selenate system has been studied by Lubal and Havel [97LUB/HAV] by spectrophotometric and potentiometric methods at (298.2 + 0.5) K. The evidence for the formation of U02Se04(aq) and U02(Se04)2 is convincing, see Appendix A. The following equilibrium constants of Reactions (V. 168) and (V.169)  

The correspondingly extrapolated value of pi is logij, PI = (3.1010.50). This value cannot be selected due to lack of data supporting the long extrapolation. The potentiometric data in [97LUB/HAV] indicated that logn.yffj does not exceed 3.4. This selection yields  

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Biological activity can be used in two ways for the bioremediation of metal-contaminated soils to immobilize the contaminants in situ or to remove them permanently from the soil matrix, depending on the properties of the reduced elements. Chromium and uranium are typical candidates for in situ immobilization processes. The bioreduction of Cr(VI) and Ur(VI) transforms highly soluble ions such as CrO and UO + to insoluble solid compounds, such as Cr(OH)3 and U02. The selenate anions SeO are also reduced to insoluble elemental selenium Se°. Bioprecipitation of heavy metals, such as Pb, Cd, and Zn, in the form of sulfides, is another in situ immobilization option that exploits the metabolic activity of sulfate-reducing bacteria without altering the valence state of metals. The removal of contaminants from the soil matrix is the most appropriate remediation strategy when bioreduction results in species that are more soluble compared to the initial oxidized element. This is the case for As(V) and Pu(IV), which are transformed to the more soluble As(III) and Pu(III) forms. This treatment option presupposes an installation for the efficient recovery and treatment of the aqueous phase containing the solubilized contaminants. 

LUB/HAV] Lubal, P., Flavel, J., The study of complex equilibria of uranium(Vl) with selenate, Talanta, 44, (1997), 457-466. Cited on pages 390,391,579. 

EXPLOSION and FIRE CONCERNS combustible solid NFPA rating (NA) reacts to form explosive products with metal amides contact with acids may cause formation of poisonous hydrogen selenide gas incompatible or reacts violently with barium carbide, bromine pen-tafluoride, chromic oxide, fluorine, lithium carbide, lithium silicon, metals, nickel, sodium, nitric acid, nitrogen trichloride, oxygen, potassium, potassium bromate, rubidium carbide, zinc, silver bromate, uranium, strontium carbide, and thorium carbide toxic gases and vapors may be released in a fire involving selenium, sodium selenite, sodium selenate, and selenium dioxide use water for firefighting purposes. 

The order of presentation of the uranium minerals will follow chemical groups. The U minerals are discussed first, followed by the niobates, tantalates and titanates. These two groups include the primary reduced minerals. The uranyl minerals are considered in the order hydrated oxides, silicates, phosphates and arsenates, vanadates, molybdates, sulphates, carbonates, and selenates and tellurates. Each section includes an evaluation of the known crystal chemistry and its effect on chemical variability and occurrence of mineral species. 

A totally new group of minerals, all of which have been described since Frondel, comprises the uranyl selenates and tellurates. Although other selenate and tellurate minerals have been reported as occurring in many types of uranium deposits, the uranyl compounds have only been recognized at two rather different localities. A Au-Te deposit near Moctezuma, Mexico, has yielded moctezumite, cliffordite and schmit-terite and the Musonoi Cu-Co deposit at Katanga, Zaire, has produced the other minerals. Schmitterite has also been found at the Shinkolobwe uranium deposit in Katanga. All the minerals are secondary. 

Zinc Hydrosulfite Zinc Nitrate Fluorine Graphite Oxygen Chlorine Nitrous Acid Sulfurous Acid Hydrogen Sulfide Selenic Acid Ammonium Hyposulfite Ammonium Thiosulfate Ammonium Sulfate Ammonium Phosphate Dibasic Diammonium Phosphate Hexafluorouranium Uranium Hexafluoride Silver Chloride Aluminum Fluoride Aluminum Trifluoride Aluminum Ammonium Sulfate Ammonium Alum Silver Bromide Magnesium Chloride Magnogene Barium Sulfite Bismuth Trichloride Cesium Bromide... 

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