Uranium minerals uraninite

In 1868, helium (He from Greek helios , the sun) was discovered due to a pale yellow line at 587.6 nm during the spectroanalytical examination of the solar prominences. In 1882, it was also detected in the spectral analysis of lava from the Vesuvius and as gas occlusion in the uranium mineral uraninite in 1889. Only in 1895, helium could be produced in its pure form in larger quantities from the mineral cleveite. And in 1908, H. Kamerlin -Onnes at Leiden succeeded for the first time in liquefying helium [4.1]. 

Alkaline leaching is carried out by using sodium carbonate solution. In this case any U(IV) present in the ore must also be oxidized to U(VI). The uranium species soluble in carbonate leach solutions in the uranyl tricarbonate ion. The formation of this ion by solubilization of a hexavalent uranium mineral such as camotite, or a tetravalent uranium mineral such as uraninite, may be represented by the following reactions ... 

Abstract uranium isotopes fractionate as a result of nuclear volume effects such that ratios vary as a funotion of uranium oxidation state, being highest in reduced species such as U"" in uraninite. The values of uranium minerals from volcanic-, metasomatic-, unconformity-,... 

Alteration at Michelin is dominated by intense soda metasomatism and potash depletion, coupled with locally intense hematization much of the mineralization consists of fine-grained uraninite within sodium-rich silicates such as aegirine and arfvedsonite. The recently discovered Jacques Lake deposit, which is an important resource in its own right (about 17 million pounds UsOs), has many similarities to Michelin, although its metavolcanic host rocks are compositionally distinct. The age of the uranium mineralization in these deposits is... 

Uranium dioxide occcurs in nature as mineral uraninite. It is used in nuclear fuel rods for reactors. Also it is used in large incandescent lamps for photography or motion pictures and is connected to the tungsten filaments to prevent sudden surges of current. 

Uranium dioxide occurs in mineral uraninite. Purified oxide may be obtained from uraninite after purification. The commercial material, however, also is recovered from other uranium sources. Uranium dioxide is obtained as an intermediate during production of uranium metal (See Uranium). Uranyl nitrate, U02(N03)2, obtained from digesting the mineral uraninite or pitchblende with concentrated nitric acid and separated by solvent extraction, is reduced with hydrogen at high temperatures to yield the dioxide. 

Uraninite crystals retain most of the actinides produced by the fission reactions and most of the fission products that have ionic radii close to that of uranium. When uraninite becomes hydrothermally altered or transformed during supergene weathering, that is, in the weathered zone of the Bangombe reactor, the reduced conditions in the close vicinity of the U ore allows its precipitation in newly formed Si-P-REE-uranium minerals (coffinite). 

Asphaltic Sandstone from Lodeve-Mas Alary, Herault, France. This rock of Permian age contains, together with uraninite, secondary uranium minerals, sulfides, molybdates, etc. (12, 15) (Figure 3). 

The concentration of uranium in the sediments of roll-front deposits is typically in the 1000 to 2000 ppm range (8). The uranium occurs as coatings on grains and as interstitial material the predominant uranium mineral is uraninite Coffinite is often... 

Uranous ion (U ) and its aqueous complexes predominate in groundwaters of low Eh. U(IV) is the major oxidation state in the most common uranium ore minerals uraninite [U02(c)]—pitchblende is roughly U02(am)—and coffinite (USi04). The U(IV) concentrations in groundwater at low... 

Uranium Dioxide. Uranous oxide black uranium oxide. 02U mol wt 270.07. O 11.85%, U 88.15%, UOj. Occurs in nature as the minerals uraninite or pitchblende. Review of uranium oxides KeUer in Comprehensive Inorganic Chemistry vol. 5, J. C. Bailar. Jr. et ai, Eds. (Pergamon Press, Oxford, 1973) pp 224-233. 

On the other hand several investigators have obtained a value of approximately 206 0 for lead extracted from pure uranium minerals. Mention may be made of the value 206 06 obtained by Hfinigschmidt and Horovitz in 1915 for lead from a sample of Norwegian brfiggerite, a variety of uraninite from Norway and 206 00 found by Baxter in 1933 for lead from Katanga pitch-blende. The atomic weight of ordinary lead is 207 22. 

Acidic and basic dissolution of uraninite (UO is depicted below as an example of U(IV) leaching. Sitmlar reactions may be written for pitchblende (UaO. Uraninite and pitchblende are the two most impoitant uranium minerals. The leaching of oxidized [U(VI)] uranium minerals such as camotite, K20 2U03 V 0) 3H20, is readily achieved in both acid and basic circuits since oxidation is not required. Oxidation-leaching processes are rate limited by the oxidation step. 

The uranium content of natural waters is generally determined by the geological conditions. The most important uranium mineral is uraninite (pitchblende, XUO3. yU02), of which there are sizeable deposits in Zaire, Canada and in Czechoslovakia (Joachimsthal), but also in Colorado (USA), North Africa (phosphate companion). South Africa (gold companion), Australia... 

There are several areas around the world where the concentration of uranium in the ground is sufficiently high that extraction of it for use as nuclear fuel is economically feasible. Such economic concentrations are called ore. When mined, it yields a mixed uranium oxide product (UjOg). Uraninite or pitchblende is the commonest uranium mineral. 

The major primary ore mineral is uraninite (basically UO2) or pitchblende (U2O5.UO3, better known as U3O8), though a range of other uranium minerals are found in particular deposits. These include camotite (uranium potassium vanadate), the davidite-brannerite-absite-type uranium titanates, and the euxenite-fergusonite-samarskite group (niobates of uranium and rare earths). 

---