Uranium minerals carnotite

Originally, radium was obtained from the rich pitchblende ore found in Joachimsthal, Bohemia. The carnotite sands of Colorado furnish some radium, but richer ores are found in the Republic of Zaire and the Great Lake region of Canada. Radium is present in all uranium minerals, and could be extracted, if desired, from the extensive wastes of uranium processing. Large uranium deposits are located in Ontario, New Mexico, Utah, Australia, and elsewhere. 

The discovery of the calcrete hosted surfical uranium deposits of Namibia demonstrated the presence of widespread uranium in calcrete filled palaeochannels (Hambleton-Jones 1984) and similar mineral deposits have been observed elsewhere in Southern Africa, USA and Australia (Carlisle 1978 Hambleton-Jones 1978 Mann Deutscher 1978). The host rocks are typically lenticular bodies of alluvium, soil or detritus material cemented by calcite, gypsum, palygorskite, and other mineral phases. Uranium mineralogy is dominated by the mineral Carnotite [K2(U02)2(V04)2.3(H20)] as the main mineral in these channels. However other phases such as andersonite (Na2K3U03(C03)3(H20)6), liebigite (Ca2U02(C03)3(H20)io ... 

Uranium occurs in nature in many rocks, minerals and sediments. The principal uranium minerals are pitchblende, carnotite, uranitite, tobernite, uranophane, autunite, and davidite. Uranium also is found in very small quantities in monazite sand, phosphate rock, and lignite. Although uranium is present in very smaU quantites, these sources also are used for commercial recovery of the metal. 

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. 

Canada, South Africa, and the United States. The two most important oxide minerals of uranium are uraninite (UsOg 50-90% uranium), a variety of which is called pitchblende, and carnotite (K2(U02)(V04)2 3H2O 54% uranium). A very common uranium mineral is autu-nite (Ca(U02)2(P04)2 H20, n = 8-12). Natural uranium consists of 99.3% U and 0.72% of the fissionable... 

Dominant ore minerals in the reduced zone are pitchblende and coffinite and, in some deposits, associated primary vanadium oxides—for example, montroseite. In oxidized zones the important uranium minerals are the uranyl vanadates (carnotite, tyuyamunite or francevillite). Accessory elements include Mo, Se and Cu. Average uranium content ranges from 0.01 to 0.40 7o U3O8. 

Uranium, not as rare as once thought, is now considered to be more plentiful than mercury, antimony, silver, or cadmium, and is about as abundant as molybdenum or arsenic. It occurs in numerous minerals such as pitchblende, uraninite, carnotite, autunite, uranophane, and tobernite. It is also found in phosphate rock, lignite, monazite sands, and can be recovered commercially from these sources. 

Thorium is widely but rather sparsely distributed its only commercial sources are monazite (together with the rare earths) and uranothorite (a mixed Th, U silicate). Uranium is surprisingly common and more abundant than mercury, silver or cadmium in the earth s crust. It is widely distributed and it is found scattered in the faults of old igneous rocks. Concentration by leaching followed by re-precipitation has produced a number of oxide minerals of which the most important are uranite (also called pitchblende) U308 and carnotite, K UC HVO -SF O. 

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. 

Vanadium is not found in its pure state. Small amounts of vanadium can be found in phosphate rocks and some iron ores. Most of it is recovered from two minerals vanadinite, which is a compound of lead and chlorine plus some vanadium oxide, and carnotite, a mineral containing uranium, potassium, and an oxide of vanadium. Because of its four oxidation states and its ability to act as both a metal and a nonmetal, vanadium is known to chemically combine with over 55 different elements. 

Where uranium and vanadium concentrations are in pg/L and potassium and bi-carbonate are in mg/L. Where the CSI is equal to zero then groundwater chemistry and carnotite saturation are in equilibrium and the mineral has the potential to be present. The assessment of groundwater chemistry in the vicinity of calcrete-hosted carnotite deposits indicates that a wide geochemical halo exists and that this halo can be identified during exploration. In Australia direct analysis of groundwater and the CSI have been demonstrated as suitable methods for exploration. In Namibia, in reality although the approach may be useful for... 

Characterization of carnotite uranium deposit in calcrete channels, Trekkopje, Namibia. In Proceedings of Africa Uncovered Mineral Resources for the future. SEG-GSSA 2008 Conference, 7 -1 o" July 2008, 114-121. Boyle, D.R. 1984. The genesis of surficial uranium deposits. In Toen, P.D. (ed) Surficial Uranium Deposits. lAEA-Tecdoc-322. Vienna, 45-52. 

CARNOTITE, This mineral is a vanadate of potassium and uranium with small amounts of radium. Its formula may be written K (UCL) (VOah JHsO. The amount of water, however, seems to be variable. It occurs as a lemon-yellow earthy powder disseminated through cross-bedded sandstones with rich concentrations around petrified and carbonized trees. Soft sp gr 4.7. It was mined in Colorado and Utah as a source of radium. Other localities are in Arizona. Pennsylvania, and Zaire. 

Only thorium and uranium have half-lives long enough to survive since the formation of the Earth. Thorium is found together with lanthanides in the phosphate mineral monazite (LnP04), and uranium occurs as pitchblende U303 and carnotite K2(U02)2(V04 )2.3H20. Uranium is principally used as a... 

Butler (B39) described the leaching of carnotite ores that contained high-vanadium-low-lime and low-vanadium-asphaltic-type minerals. The high-vanadium-low-lime ore (less than 2%) is roasted with 6-9 wt. % salt at 850°C and is immediately quenched in 3% hot sodium carbonate solution. The calcine is ground to 65 mesh and uranium and vanadium are dissolved by agitation leaching at 92-96°C. 93% of the uranium and 85% of the vanadium are extracted from the ore. The asphaltic tjq>e ore is roasted at 550°C and 80-85% of the uranium and 35-40% of the vanadium are extracted. The leach solution concentration was maintained between 7 and 9% sodium carbonate. The pulp density was between 45 and 50% solids. 

Carnotite is a double vanadate of potassium and uranium, of probable composition K2(U02)2(V04)2.8H30,2 but generally very impure with silica. It occurs as a yellow crystalline powder, or in loosely cohering masses, chiefl in Colorado and Utah, but also in South Australia and Portugal. The mineral has attained considerable importance in America as a source of uranium and radium. 

Uranium is a moderately rare element. Its abundance is estimated to be about 1 to 2 parts per million, making it about as abundant as bromine or tin. The most common ore of uranium is pitchblende, although it also occurs in other minerals, such as uraninite, carnotite, uranophane, and coffinite. 

Uranium U(VI) minerals are most often products of the oxidation and weathering of nearby primary U(IV) ore minerals such as uraninite [U02(c)I and coffinite [USi04(c)l (cf. Pearcy et al. 1994). They also form by evaporative concentration of dissolved U(VI), particulary under arid conditions. Schoepite (/J-UOj 2H2O) is fairly soluble and, therefore, is a rare mineral, whereas carnotite K2(U02)2(V04)2j and tyuyamunite (Ca(U02)2(V04)2j, which have lower solubilities (particularly above pH 5) are the chief oxidized ore minerals of uranium. The plots in Figs. 13.5 and 13.6 indicate that uranyl minerals are least soluble in I0W-CO2 waters, and, therefore, are most likely to precipitate from such waters. This is con.sistent with the occurrence of carnotite and tyuyamunite in oxidized arid environments with poor. soil development (Chap. 7), such as in the calcrete deposits in Western Australia (cf. Mann 1974 Dall Aglio et al. 1974), and in the sandstone-hosted uranium deposits of the arid southwestern United States (cf. Hostetler and Carrels 1962 Nash et al. 1981). The... 

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