Uranium sulphides

Z 1 Niobium 1 Nitrate 1 Osmium 73 a. I Perchlorate Phenols u a o Platinum o 0. 1 5 u 1 Rhodium 1 Rubidium Ruthenium Scandium 1 Selenium Silver I Sodium 1 Strontium 1 Sulphate Sulphides, organic Sulphur dioxide 1 Tantalum 1 Tellurium 1 Thallium Thorium e H 1 Titanium a u ab a 1- I Uranium 1 Vanadium 1 Yttrium 1 Zinc Zirconium... 

Potassium sulphide Rhenium (VII) sulphide Silver sulphide Sodium disulphide Sodium polysulphide Sodium sulphide Tin (II) sulphide Tin (IV) sulphide Titanium (IV) sulphide Uranium (IV) sulphide... 

Occurrence. Important minerals are carnotite K(U02)V04 3/2 H20, more important as a uranium ore, vanadinite Pb5(V04)3Cl and some complex sulphides. It occurs also in certain crude oils and may be recovered from dusts after combustion. 

The size of the reactors is quite variable. In length, the biggest reactor has dimensions of 12 x 18 m and has a thickness of 20 to 50 cm (Fig. la). The core of the reactors consists of a 5 to 20 cm thick layer of uraninite embedded in clays (illite and chlorite). Clays around the reactors result from the hydrothermal alteration of the host sandstone during the fission reactions. This alteration occurred at a temperature close to 400 °C in the core. Temperature decreased drastically toward the vicinity with a thermal gradient of 100 °C/m (Pourcelot Gauthier-Lafaye 1999). The uranium content of the core ranges between 40 and 60%. Accessory minerals are mainly sulphides (pyrite and galena), hematite and phosphates (mainly hydroxyapatite). 

U-bearing minerals and adsorption processes (Salah et al. 2000 Perez del Villar et al. 2000). The vertical and lateral flow of groundwater is responsible for the oxidation and dissolution of primary sulphides, leading to acidic solutions that facilitated the oxidation and dissolution of uraninite. The resulting uranyl cations migrated and precipitated as uranyl minerals, mainly phosphates, silicates, silico-phosphates. In certain local conditions, reduction of these uranyl cations allowed precipitation of coffinite with a high content of P and LREE. Adsorption of uranium, together with P, mainly occurs on Fe-oxyhydroxides, but this kind of uranium retention seems less efficient than the precipitation, at least in the close vicinity to the... 

Aluminium and magnesium selenides are very similar light brown powders, unstable in air. Zinc and iron (ferrous) selenides are more stable in air, the zinc compound being citron-yellow and the iron compound black and metallic in appearance.8 The latter becomes brown in air owing to oxidation. Ferric selenide is difficult to obtain pure. Cadmium selenide, which is dark brown, is very stable in colour and is used as a pigment. With thallium, selenium is said to form three distinct compounds,9 but analyses of these compounds have led to discordant results. The selenides of aluminium, chromium and uranium cannot be prepared in the wet way. Nickel selenide, unlike the sulphide, shows no tendency to form a colloidal solution. 

That the atomic weight of uranium lead is extremely variable has already been shown. In order to interpret this variability its sources must be studied both geologically and mineralogically. On the geologic side of the question the uranium ore can be divided in to three principal classes, which are sharply distinct. The definitely crystallized varieties of uraninite occur in coarse pegmatites, associated with feldspar, quartz, mica, beryl, and other minor accessories. The massive pitchblende is found in metalliferous veins, together with sulphide ores of copper, lead, iron, zinc, and so forth. As for camotite, that is a secondary mineral, found commonly as an incrustation on sandstone, and often, also upon fossil wood. There may be other modes of occurrence, but these are the most distinctive. 

The other determinations of the atomic weight of uranium lead give values much above 206, and even approaching 207. This is especially true of the lead from pitchblende, which contains no thorium and little if any helium. Its association with sulphide ores, however, leads to the suspicion that it may contain ordinary lead, perhaps in the form of occluded or dissolved galena. The atomic weight of the lead derived from it would, therefore, be that of a mixture, and not of the isotope alone. The carnotite lead would also seem to be a mixture, but of what kind is not clear. 

Phillips and Timms [599] described a less general method. They converted germanium and silicon in alloys into hydrides and further into chlorides by contact with gold trichloride. They performed GC on a column packed with 13% of silicone 702 on Celite with the use of a gas-density balance for detection. Juvet and Fischer [600] developed a special reactor coupled directly to the chromatographic column, in which they fluorinated metals in alloys, carbides, oxides, sulphides and salts. In these samples, they determined quantitatively uranium, sulphur, selenium, technetium, tungsten, molybdenum, rhenium, silicon, boron, osmium, vanadium, iridium and platinum as fluorides. They performed the analysis on a PTFE column packed with 15% of Kel-F oil No. 10 on Chromosorb T. Prior to analysis the column was conditioned with fluorine and chlorine trifluoride in order to remove moisture and reactive organic compounds. The thermal conductivity detector was equipped with nickel-coated filaments resistant to corrosion with metal fluorides. Fig. 5.34 illustrates the analysis of tungsten, rhenium and osmium fluorides by this method. 

Compounds Bis-dimethylstibinyl oxide Bis(dimethylthallium) acetylide Butyllithium Nonacarbonyldiiron Octacarbonyldicobalt Pentacarbonyliron Tetracarbonylnickel Dibismuth trisulphide Dicaesium selenide Dicerium trisulphide Digold trisulphide Europium (II) sulphide Germanium (II) sulphide Iron disulphide Iron (II) sulphide Manganese (II) sulphide Mercury (II) sulphide Molybdenum (IV) sulphide Potassium sulphide Rhenium (VII) sulphide Silver sulphide Sodium disulphide Sodium polysulphide Sodium sulphide Tin (11) sulphide Tin (IV) sulphide Titanium (IV) sulphide Uranium (IV) sulphide ... 

Three well-defined sulphides of uranium are known ... 

Uranium Oxysulphide, U3O2S4 or UO3.2US2, is formed when uranous oxide, urano-uranic oxide, or ammonium uranate is heated in a stream of hydrogen sulphide or carbon disulphide vapour when one of the oxides is heated with a mixture of ammonium chloride and sulphur or when uranyl sulphate is heated in hydrogen or with potassium pentasulphide. It is a greyish-black powder, which is decomposed by nitric acid %vith deposition of sulphur. 

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