Uranium mineralization

Gr. helios, the sun). Janssen obtained the first evidence of helium during the solar eclipse of 1868 when he detected a new line in the solar spectrum. Lockyer and Frankland suggested the name helium for the new element. In 1895 Ramsay discovered helium in the uranium mineral clevite while it was independently discovered in cleveite by the Swedish chemists Cleve and Langlet at about the same time. Rutherford and Royds in 1907 demonstrated that alpha particles are helium nuclei. 

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. 

Gr. aktis, aktinos, beam or ray). Discovered by Andre Debierne in 1899 and independently by F. Giesel in 1902. Occurs naturally in association with uranium minerals. Actinium-227, a decay product of uranium-235, is a beta emitter with a 21.6-year half-life. Its principal decay products are thorium-227 (18.5-day half-life), radium-223 (11.4-day half-life), and a number of short-lived products including radon, bismuth, polonium, and lead isotopes. In equilibrium with its decay products, it is a powerful source of alpha rays. Actinium metal has been prepared by the reduction of actinium fluoride with lithium vapor at about 1100 to 1300-degrees G. The chemical behavior of actinium is similar to that of the rare earths, particularly lanthanum. Purified actinium comes into equilibrium with its decay products at the end of 185 days, and then decays according to its 21.6-year half-life. It is about 150 times as active as radium, making it of value in the production of neutrons. 

In 1868, within a decade of the development of the spectroscope, an orange-yeUow line was observed in the sun s chromosphere that did not exactiy coincide with the D-lines of sodium. This line was attributed to a new element which was named helium, from the Greek hellos, the sun. In 1891 an inert gas isolated from the mineral uranite showed unusual spectral lines. In 1895 a similar gas was found in cleveite, another uranium mineral. This prominent yellow spectral line was then identified as that of helium, which to that time had been thought to exist only on the sun. In 1905 it was found that natural gas from a well near Dexter, Kansas, contained nearly 2% helium (see Gas, natural). 

Radiometric ore sorting has been used successfully for some uranium ores because uranium minerals emit gamma rays which may be detected by a scintillation counter (2). In this appHcation, the distribution of uranium is such that a large fraction of the ore containing less than some specified cut-off grade can be discarded with tittle loss of uranium values. Radioactivity can also be induced in certain minerals, eg, boron and beryllium ores, by bombarding with neutrons or gamma rays. 

Vein Deposits. The vein deposits of uranium are those in which uranium minerals fill cavities such as cracks, fissures, pore spaces, breccias, and stockworks. The dimensions of the openings have a wide range, from the narrow pitchblende-fiHed cracks, faults, and fissures in some of the ore bodies in Europe, Canada, and AustraHa to the massive veins of pitchblende at Jachymov, Czech RepubHc (15). 

Plutonium occurs in natural ores in such small amounts that separation is impractical. The atomic ratio of plutonium to uranium in uranium ores is less than 1 10 however, traces of primordial plutonium-244 have been isolated from the mineral bastnasite (16). One sample contained 1 x 10 g/g ore, corresponding to a plutonium-244 [14119-34-7] Pu, terrestrial abundance of 7 x 10 to 2.8 x 10 g/g of mineral and to <10g of primordial Pu on earth. The content of plutonium-239 [15117 8-3], Pu, in uranium minerals is given in Table 2. 

ThSiO "Th and Th are present in naturally occurring uranium Th and Th occur in uranium minerals as members of the decay chain. The remaining isotopes are formed upon neutron bombardment of those isotopes discussed, or by charged particle bombardment of various targets. 

In 1896, Becquerel discovered that uranium was radioactive (3). Becquerel was studying the duorescence behavior of potassium uranyl sulfate, and observed that a photographic plate had been darkened by exposure to the uranyl salt. Further investigation showed that all uranium minerals and metallic uranium behaved in this same manner, suggesting that this new radioactivity was a property of uranium itself In 1934, Fermi bombarded uranium with neutrons to produce new radioactive elements (4). 

In 1895 Ramsay also identified helium as the gas previously found occluded in uranium minerals and mistakenly reported as nitrogen. Five years later he and Travers isolated helium from samples of atmospheric neon. 

The final member of the group, actinium, was identified in uranium minerals by A. Debieme in 1899, the year after P. and M. Curie had discovered polonium and radium in the same minerals. However, the naturally occurring isotope, Ac, is a emitter with a half-life of 21.77 y and the intense y activity of its decay products makes it difficult to study. 

Although the nucleus of the uranium atom is relatively stable, it is radioactive, and will remain that way for many years. The half-life of U-238 is over 4.5 billion years the half-life of U-235 is over 700 million years. (Half-life refers to the amount of time it takes for one half of the radioactive material to undergo radioactive decay, turning into a more stable atom.) Because of uranium radiation, and to a lesser extent other radioactive elements such as radium and radon, uranium mineral deposits emit a finite quantity of radiation that require precautions to protect workers at the mining site. Gamma radiation is the... 

What have we learned in this estimate Surely we can say the age of the earth cannot be shorter than 5 X 10s years. That was when the uranium mineral clock was wound—but the clock could be much older. To evaluate this number further, we must look for other types of data. 

In addition to meeting the foregoing requirements, a good internal standard will be easy to add uniformly and precisely, and (preferably) no appreciable amount of the element St (free or combined) will be present in the sample before the addition. Cope29 provides an excellent illustration of these points. He found that yttrium nitrate dissolved in ethyl alcohol could be added to a powdered uranium mineral in a mortar, whereupon grinding immediately to dryness dispersed the internal standard (yttrium) so uniformly that uranium could be satisfactorily determined in certain minerals. But the mineral euxenite is an exception, for it contains both yttrium and uranium, and this complicates the uranium determination with yttrium as internal standard. 

G. H. Taylor, Biogeochemistry of Uranium Minerals, in Biogeochemical Cycling of Mineral Forming Elements, P. A. Trudinger and D. J. Swaine, eds., Elsevier, Amsterdam, p. 485,1979. 

The bacterial leaching of uranium minerals is complex. This is because of the fact that uranium minerals are not sulfides and are not, therefore, directly attacked by the bacteria. However, the uranium sources usually have a substantial pyrite content which can be bac-terially oxidized to give an acidic ferric sulfate solution which is an effective leaching medium for uranium minerals. The reactions involved in the system can be shown in a simplified form as ... 

In most uranium ores the element is present in several, usually many diverse minerals. Some of these dissolve in sulfuric acid solutions under mild conditions, while others may require more aggressive conditions. Thus, while it may be comfortable to recover 90-95% of the uranium present, it may be tough or impractical to win the balance amount of a few percent economically. Some of the most difficult uranium minerals to leach are those of the multiple oxide variety, most commonly brannerite and davidite. These usually have U(IV) as well as U(VI), together with a number of other elements such as titanium, iron, vanadium, thorium, and rare earths. To extract uranium from these sources is not as easy as other relatively simpler commonly occurring sources. 

It has been seen that one set of leaching systems is that in which the reaction of H+ and OH- species are involved. In case an adequate leaching is not obtained by deploying these situations, the introduction of another anionic species may be required for the formation of new and more appropriate soluble metal species. The leaching of uranium minerals represents one of the fine examples which makes use of this stated provision. 

The dissolution of uranium minerals which may contain U(IV) and U(VI) in U-H20 systems is only achieved with the difficulty through the reactions as shown below ... 

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 ... 

Occupational studies have demonstrated an enhanced frequency of bronchial cancer among various groups of Rn-222 progeny exposed underground miners, especially uranium miners. (Archer et al, 1976 Kunz et al 1978 Kunz et al 1975 Lundin et al, 1971 Muller et al, 1983. Sevc and Placek, 1973 Seve et al, 1976 Whittmore and Mo Millan 1983.)... 

Archer V.E., Gillam J.D. and Wagoner J.K., 1976, Respiratory Disease Mortality Among Uranium Miners, Am.N.Y.Acad.Sci, 271,280-293. 

Kunz E., Sevc J. And Placek V., 1978, Lung Cancer Mortality in Uranium Miners, Health Phys., 35, 579-580. 

Sevc J., Kunz E. and Placek V., 1976, Lung Cancer in Uranium Miners and Long-Term Exposure to Radon Daughter Products, Health Phys.,... 

Whittmore A.S. and McMillan A., 1983, Lung Cancer Mortality Among U.S. Uranium Miners A Reappraisal, J.Nat.Cancer Inst. 71, 489-499. 

The histological types of lung cancer seen to excess in uranium miners reflect those in the population at large (Masse, 1984). These occur almost entirely in bronchial airways. Approximately 207 are adenocarcinomas which occur in peripheral bronchioles (Spencer, 1977) where there are no basal cells. Squamous cell cancers predominate in miners exposed early in life to relatively low concentrations of radon daughters (Saccomanno et aJL., 1982). These are considered likely to arise from the secretory small mucous granular cells which undergo cell division and extend to the epithelial surface (Masse, personal communication). Division of these cells is accelerated after irritation by toxicants such as cigarette smoke or infectious diseases (Trump et a L., 1978). 

S. Wood and R. Mick, Age Factor in Histological Type of Lung Cancer in Uranium Miners, a Preliminary Report, in Radiation Hazards in Mining (M. Gomez, ed) pp. 675-679, Society of Mining Engineers, New York (1982). 

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