Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Tetravalent uranium minerals

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 ... [Pg.547]

The two most important sources of uranium are the minerals carnotite, where uranium occurs in the hexavalent oxide or hydrated oxide, and pitchblende, where uranium occurs mostly in the tetravalent state as a compound salt with other metals. It also occurs as a mixed oxide with titanium, thorium, and niobium in the tetravalent form. The tetravalent uranium minerals appear to have been geologically formed in the presence of reducing agents such as hydrocarbon minerals, graphite, native metals, and sulfide minerals, while such association is rarely observed with the hexavalent uranium minerals. [Pg.8]

Minerals of the third group of Table 5.15 contain relatively small proportions of tetravalent uranium combined with a refractory oxide of titanium, niobium, or tantalum. To free the uranium from these minerals, they must be leached with hot, concentrated sulfuric acid. Davidite is one of the principal ores at Radium Hill in South Australia. Brannerite is found in the Blind River district of Ontario. Pyrochlore occurs in the Lake Nipissing district of Ontario and in Nigeria. [Pg.233]

To leach the more acid-resistant minerals containing tetravalent uranium, steam is fed to the second tank to bring the temperature to 49 to 60°C, and sodium chlorate NaQOj is added to bring the oxidation-reduction potential e, measured relative to the calomel electrode, to from —0.47 to —0.51 V. At —0.51 V, the equilibrium ratio of ferric iron to ferrous iron in the solution is 0.52. Ferric iron catalyzes the oxidation of insoluble tetravalent uranium to the soluble hexavalent uranyl form ... [Pg.243]

When iron has entered the solution, it plays a part in the oxidation of tetravalent uranium to the hexavalent uranyi sulphate and although it has been described as a catalyst, its effect is not always beneficial. The cheapest oxidants available are usually sodium chlorate or manganese dioxide. The latter may be used in the form of the mineral pyrolusite, which contains 65 to 70 per cent Mn02. Besides usually being cheaper, manganese dioxide has the advantage that it can be recovered after extraction of the mineral values, by precipitation of the hydroxide, followed by oxidation with air. [Pg.23]

Tetravalent uranium replaces calcium in the apatite structure. Hexavalent minerals (autunite, meta-autunite and torbernite) are also present. Reserves are estimated at 10 000 ton uranium. The origin of this occurrence is uncertain, so an exploration model for this type deposit has not been constructed. [Pg.127]

Geochemical Nature and Types of Deposits. The cmst of the earth contains approximately 2—3 ppm uranium. AlkaHc igneous rock tends to be more uraniferous than basic and ferromagnesian igneous rocks (10). Elemental uranium oxidizes readily. The solubiHty and distribution of uranium in rocks and ore deposits depend primarily on valence state. The hexavalent uranium ion is highly soluble, the tetravalent ion relatively insoluble. Uraninite, the most common mineral in uranium deposits, contains the tetravalent ion (II). [Pg.184]

Thorium has a wide distribution in nature and is present as a tetravalent oxide in a large number of minerals in minor or trace amounts. Thorium is significantly more common in nature than uranium, having an average content in the earth s cmst of approximately 10 ppm. By comparison, Pb is approximately 16 ppm. Thorium has a seawater concentration of <0.5 x 10 . Thorium refined from ores free of uranium would be almost... [Pg.35]

The first group, minerals containing high concentrations of uranium, mostly in the tetravalent state, can be concentrated by specific gravity methods when in massive form. Frequently, however, the particle size is so small that the uranium-bearing mineral must be dissolved in sulfuric acid or sodium carbonate leach liquors. In either case, an oxidant must be added to bring uranium to the soluble, hexavalent state. [Pg.232]

In most minerals uranium is in the tetravalent state. The most important one is uraninite 0.25), in which the uranium concentration is 50 - 90% it is foimd in Western Europe, Central Africa (e.g. Katanga, Gabon) and Canada (e.g. Cigar Lake) and Australia (e.g. Koongara). In the USA and Russia camotite (a K + U vanadate) is the most important mineral and contains 54% uranium. In the high grade ores the mineral is mixed with other minerals so the average uranium concentration in the crushed ore is much less e.g. 0.5 % on the Colorado Plateau. Uranium is often found in lower concentration, of the order of 0.01 - 0.03%, in association with other valuable minerals such as apatite, shale, peat, etc. [Pg.105]

Sedinientary rocks that contain potassium, as well as uranium and thorium and their respective radioactive daughters emit ganuna rays as the unstable atoms of these elements decay (Faure and Mensing 2005). Uranium and thorium occur in the heavy minerals that are included in sandstones and conglomerates at the time of deposition. In addition, uranium (but not thorium) may be deposited from groundwater in case the sediment contains organic matter that can reduce hexavalent uranyl ions to the tetravalent state... [Pg.356]

Direct alkali leaching of uranium alone is used in the Eldorado plant at Beaverlodge, in Canada, where the minerals are pitchblende and uraninite. Since the uranium is partially in the tetravalent state, it is not readUy leached by sodium carbonate solutions unless in the presence of an oxidant. Potassium permanganate is very efiective for this purpose< but air or oxygen under pressure are preferred on economic grounds. The reaction is essentially as follows ... [Pg.41]


See other pages where Tetravalent uranium minerals is mentioned: [Pg.8]    [Pg.8]    [Pg.75]    [Pg.75]    [Pg.76]    [Pg.35]    [Pg.95]    [Pg.498]    [Pg.232]    [Pg.237]    [Pg.24]    [Pg.440]    [Pg.443]    [Pg.219]    [Pg.534]    [Pg.788]    [Pg.4773]    [Pg.788]    [Pg.498]    [Pg.273]    [Pg.728]    [Pg.660]    [Pg.6933]    [Pg.25]    [Pg.800]    [Pg.485]    [Pg.340]    [Pg.4]    [Pg.127]    [Pg.232]   


SEARCH



Tetravalence

Tetravalent

Uranium minerals

© 2024 chempedia.info