Sources of Uranium

At current prices of uranium ( 30 to 50/lb U30g) ores containing around 0.1 percent UgOg or more are being mined pritrrarily for their uranium content. The principal uranium-bearing minerals found in such ores are listed in Table 5.15, classified according to the type of treatment needed to extract the uranium. 

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. 

Uraninite, or pitchblende as it is more commonly known, is the form in which uranium was first discovered, at Joachimsthal, Czechoslovakia. Later, very rich deposits of massive uraninite were discovered at the Shinkolobwe mine in the Belgian Congo (Zaire) and were the principal source of uranium for the Manhattan Project. Leaner ores containing finely divided 

Coffinite is a major mineral in the important Ambrosia Lake district of New Mexico. Uranothoiite is mined in the Bancroft district of Ontario. 

Camotite is a major ore of the Colorado plateau. Tyuyamunite occurs near Grants, New Mexico, in Utah, and in the Soviet Union. Autunite is found near Marysvale, Utah, and in Washington and Wyoming, Torbemite is found in the White Canyon district of Utah and in the upper zones of ore bodies in Zaire. 

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Global uranium flux calculations have typically been based on the following two assumptions (a) riverine-end member concentrations of dissolved uranium are relatively constant, and (b) no significant input or removal of uranium occurs in coastal environments. Other sources of uranium to the ocean may include mantle emanations, diffusion through pore waters of deep-sea sediments, leaching of river-borne sediments by seawater," and remobilization through reduction of a Fe-Mn carrier phase. However, there is still considerable debate... 

Today, phosphoric acid for use in the pharmaceutical or food industry must be free from uranium and other harmful metals. In the future, the processing of phosphate rock for production of fertilizers may be an important source of uranium because uranium removal may become compulsory to avoid its dissemination into the environment from the use of phosphate-based fertilizers. 

At the same time it is quite obvious that most mantle material cannot be the source of uranium, because it was not... 

Euxenite (Loranskite). (Y, Ca, Ce, U, Th)-(Nb, Ta, Ti)20. A rare-earth mineral, occurring in Norway, Madagascar, Canada Pennsylvania. It is brownish-black, brilliant to vitreous sp gr 5.0—5.9 and hardness 5— 6. Used as a source of uranium, niobium and tantalum... 

The downside of breeder reactors is their enormous complexity. The United States gave up on breeders more than a decade ago, and only France and Germany are still investing in them. Officials in these countries point out that supplies of naturally occurring uranium-235 are limited. At present rates of consumption, all natural sources of uranium-235 may be depleted within a century. If countries then decide to turn to breeder reactors, they may well find themselves digging up the radioactive wastes they once buried. 

IJmnate. Sodium uranate, uranium yellow, Na2U04, yellow solid, insoluble, formed by reaction of soluble uranyl salt solution and excess sodium carbonate solution. Used (1) in the manufacture of yellowish-green fluorescent glass, (2) in ceramic enamels, (3) as a source of uranium for chemical reactions. 

Uranium levels have been measured in tissues from humans, with no occupational exposure where the source of uranium was assumed to be dietary and environmental. 

The uranium content of food has been studied extensively human daily intake has been estimated to range from 0.6 to 1.0 (0.9-1.5 ig/day) pCi/day of natural uranium. Uranium is adsorbed onto the roots of plants thus unwashed potatoes, radishes, and other root vegetables which retain their surface membrane are a primary source of uranium in the diet. Based on consumption rates, potatoes constitute the highest dietary intake of uranium (EPA 1985). One study showed that the concentration of uranium in plant roots was proportional to the uranium concentration in the soil (NCRP 1984a), while a second study did not support a linear relationship (Mortvedt 1994). 

Uranium releases occur as a result of phosphate mining for production of phosphorous, which is used in phosphoric acid and phosphate fertilizers (NCRP 1984a). Phosphate rock from Florida, Texas, and southeastern Idaho contains as much as 120 ppm (80 pCi/g) uranium, a concentration sufficiently high to be considered as a commercial source of uranium (NCRP 1975). 

Low bioconcentration factors for uranium were observed in fish. The highest bioconcentration factors observed in fillet of rainbow trout (Salmo gairdneri), white and finescale suckers (Castastomus catactomus), and lake whitefish (C. clupeaformis) did not exceed a value of 38 (Mahon 1982 Poston 1982 Swanson 1983, 1985). Ahsanullah and Williams (1989) concluded that the primary source of uranium for crab (Pachygrapsus laevimanus) and zebra winkle (Austrocochlea constricta) was from water since both fed and starved animals took up uranium at the same rate. 

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. 

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. 

Treatment of Uranium Minerals.—The chief source of uranium compounds is uraiiinite, but at the present time the working up of all uranium minerals has for its main object the extraction of radium, and the uranium salts are merely produced as by-products. The methods in use ary according to the nature of the desired product, which may be ammonium or sodium diuranate, or iiranyl nitrate. 

A calutron consists essentially of an intense source of uranium ions, a way to accelerate the ions to high energy within a vacuum system, and a way to collect the uranium-235 and uranium-238 ions after they have moved in separate arcs between the poles of a very large electromagnet. The components at the heart of the system are ion sources, collectors, and high-voltage, regulated direct-current power supplies (Lore, 1973 London, 1961 USDoE, 1980). 

Use Source of uranium dioxide, extraction of uranium into nonaqueous solvents. 

The background concentrations of radium in the subsurface material, before creation of the phosphogypsum piles, can be accurately estimated since longterm data are available 14.6], Interest in radioactivity in Florida dates back to 1942 through 1948, when there was an urgent need to find domestic sources of uranium. In addition, there has been environmental concern about radium in Florida for the last 20 years, and considerable data have been published, some of which are shown in Table 9. 

The Witwatersrand Basin The best known late Archaean sedimentary basin is the Witwatersrand Basin, for it hosts the world s richest gold province and is also an important source of uranium. For these reasons the geology of this basin is known in considerable detail. The Witwatersrand basin contains a 7 km-thick succession of terrigenous sediments and volcanic rocks, formed between 3.074 and 2.714 Ga ago. 

All isotopes of radium are radioactive and occur naturally in very small quantities. In their studies of radioactive elements, husband and wife Pierre (1859-1906) and Marie (1867-1934) Curie discovered that pitchblende—the mineral that was their source of uranium—was more radioactive than its uranium and thorium content alone could explain. Therefore, they suspected that a new, undiscovered element... 

In addition to the well-characterized minerals containing uranium listed in Table 5.15, uranium occurs as a minor constituent of many other materials, some of which have been used as commercial sources. Table 5.16 lists low-grade sources of uranium and gives the range of their uranium content. Uranium from the five commercial sources is being produced as a by-product or co-product of other materials n4iose value helps pay for the cost of producing the uranium. 

Some lignites contain sufficient uranium so that they can be mined for the uranium alone most are so lean that they must be used as fuel as well as a source of uranium. 

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