Uranium concentration, particle size

Cardiovascular Effects. No cardiovascular effects have been reported in humans after inhalation exposure to uranium. No effect on blood pressure or pulse rate was observed in a man accidentally exposed to powdered uranium tetrafluoride for 5 minutes (Zhao and Zhao 1990). Air concentration and mean particle size of the powder were not determined. Electrocardiograms and chest X-rays were normal shortly after the accident and over a 7.5-year follow-up period. 

Uranium becomes airborne due to direct releases into the air from these processes. Deposition of atmospheric uranium may occur by wet (rain, sleet, or snow) or dry (gravitation or wind turbulence) processes. The rate of uranium deposition is dependent upon such factors as particle size, particle density, particle concentration, wind turbulence, and chemical form. Data are lacking on residence times of particulate uranium in the atmosphere, although UNSCEAR (1988) assumed that it behaves like atmospheric dust, for which meteorological models exist. 

While entrained in the air, particulate uranium represents an inhalation source for humans, the extent of which is dependent upon concentration and particle size. For particulate uranium to be an inhalation hazard to humans, the particulates must be in the size range of 1-10 pm (Bigu and Duport 1992 ICRP 1979). In some cases, the solid tailings have been removed from the site for use as fill or construction material, which can lead to external radiation exposures primarily from the uranium progeny. 

The mobility of uranium in soil and its vertical transport (leaching) to groundwater depend on properties of the soil such as pH, oxidation-reduction potential, concentration of complexing anions, porosity of the soil, soil particle size, and sorption properties, as well as the amount of water available (Allard et al. 

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. 

Concentration by leaching. The powdered ore is concentrated in uranium by means of classical ore-benefidation processes. Although several powdered metallic ores are easily concentrated by a common froth flotation process, this operation unit is seldom applicable to uranium ores because relatively few uranium minerals can be selectively floated. Therefore, after particle size reduction, because of the unsuitability of operation units such as... 

Megumi, K. and Mamuro, T., 1977. Concentration of uranium scries nuclides in soil particles in relation to their size. J. Gcophys. Res., 82 353-356. 

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