Uranium in air

The only anhydrous trioxide is UO3, a common form of which (y-U03) is obtained by heating U02(N03).6H20 in air at 400°C six other forms are also known.Heating any of these, or indeed any other oxide of uranium, in air at 800-900°C yields U3O8 which contains pentagonal bipyramidal UO7 units and can be used in gravimetric determinations of uranium. Reduction with H2 or H2S leads to a series of intermediate... 

Like adults, children are exposed to small amounts of uranium in air, food, and drinking water. However, no cases have been reported where exposure to uranium is known to have caused health effects in children. It is possible that if children were exposed to very high amounts of uranium they might have damage to their kidneys like that seen in adults. We do not know whether children differ from adults in their susceptibility to health effects from uranium exposure. 

The international, national, and state regulations and guidelines regarding uranium in air, water, and other media are summarized in Table 7-1. 

PUz, N., Hoffmann, P., Lieser, K.H. et al. (1987). Determination of thorium and uranium in air filters by XRF analysis using excitation of K-lines by radionuchdes, Fresenius Z. Anal. Chem. 329, 581-583. 

The concentration of uranium in air is usually very low and this exposure pathway is negligible for the general population unless the people live in the vicinity of industrial plants or mines where uranium is processed or are employed in such facilities. The results of some studies in which the concentration of uranium in air was determined are discussed here. 

Fluorine and its compounds are used in producing uranium (from the hexafluoride) and more than 100 commercial fluorochemicals, including many well known high-temperature plastics. Hydrofluoric acid etches the glass of light bulbs, etc. Fluorochlorohydrocarbons are extensively used in air conditioning and refrigeration. 

Fig. 5.12 Oxidation rates of uranium in distilled water, air, CO2 and CO as a function of...

With the exception of iron(II) and uranium(IV), the reduced solutions are extremely unstable and readily re-oxidise upon exposure to air. They are best stabilised in a five-fold excess of a solution of 150g of ammonium iron(III) sulphate and 150 mL of concentrated sulphuric acid per litre [approximately 0.3M with respect to iron] contained in the filter flask. The iron(II) formed is then titrated with a standard solution of a suitable oxidising agent. Titanium and chromium are completely oxidised and produce an equivalent amount of iron(II) sulphate molybdenum is re-oxidised to the Mo(V) (red) stage, which is fairly stable in air, and complete oxidation is effected by the permanganate, but the net result is the same, viz. Mo(III)- Mo(VI) vanadium is re-oxidised to the V(IV), condition, which is stable in air, and the final oxidation is completed by slow titration with potassium permanganate solution or with cerium(IV) sulphate solution. 

We will use the proxy approach for all of the U-series elements, except U and Th for which there are already sufficient experimental data (Table lb). For both of these elements we will discuss 4+ cations only. U also forms 5+ and 6+ cations in oxidizing environments. These are more relevant to aqueous and hydrothermal settings and will not be considered further here. However, in some experiments run at atmospheric pressure in air (e.g., Beattie 1993b), U will occur in one of its oxidized forms. These data are excluded from discussion, although it should be noted that in all minerals discussed here, the uranium partition coefficient will be considerably smaller when uranium is dominantly 5+ and 6+ compared to when it is dominantly 4+. 

Uranium carbide emits brilliant sparks on impact, ignites on grinding in a mortar [1], or on heating in air to 400°C [2],... 

Hartmann, I. et al., Rept. Invest. No. 4835, Washington, US Bur. Mines, 1951 Thorium hydride explodes on heating in air [1], and the powdered hydride readily ignites on handling in air [2], Layers of thorium or uranium hydrides ignited spontaneously after exposure to ambient air for a few min [3],... 

Sodium hydride ignites in oxygen at 230°C, and finely divided uranium hydride ignites on contact. Lithium hydride, sodium hydride and potassium hydride react slowly in dry air, while rubidium and caesium hydrides ignite. Reaction is accelerated in moist air, and even finely divided lithium hydride ignites then [1], Finely divided magnesium hydride, prepared by pyrolysis, ignites immediately in air [2], See also COMPLEX HYDRIDES... 

Storage of uranium foil in closed containers in presence of air and water may produce a pyrophoric surface [1], Uranium must be machined in a fume hood because, apart from the radioactivity hazard, the swarf is easily ignited. The massive metal ignites at 600-700°C in air [2]. The finely divided reactive form of uranium produced by pyrolysis of the hydride is pyrophoric [3], while that produced as a slurry by reduction of uranium tetrachloride in dimethoxyethane by potassium-sodium alloy is not [4],... 

Radon-222, a decay product of the naturally occuring radioactive element uranium-238, emanates from soil and masonry materials and is released from coal-fired power plants. Even though Rn-222 is an inert gas, its decay products are chemically active. Rn-222 has a a half-life of 3.825 days and undergoes four succesive alpha and/or beta decays to Po-218 (RaA), Pb-214 (RaB), Bi-214 (RaC), and Po-214 (RaC ). These four decay products have short half-lifes and thus decay to 22.3 year Pb-210 (RaD). The radioactive decays products of Rn-222 have a tendency to attach to ambient aerosol particles. The size of the resulting radioactive particle depends on the available aerosol. The attachment of these radionuclides to small, respirable particles is an important mechanism for the retention of activity in air and the transport to people. 

Protactinium is a relatively heavy, silvery-white metal that, when freshly cut, slowly oxidizes in air. AH the isotopes of protactinium and its compounds are extremely radioactive and poisonous. Proctatinium-231, the isotope with the longest half-life, is one of the scarcest and most expensive elements known. It is found in very small quantities as a decay product of uranium mixed with pitchblende, the ore of uranium. Protactiniums odd atomic number (gjPa) supports the observation that elements having odd atomic numbers are scarcer than those with even atomic numbers. 

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