Uranium slags

DeCaF treats soil, sludges, solids (e.g., slag), residues, and sediments contaminated with radioactive elements and other hazardous constituents. The technology has potential applications in the treatment of heavy metals. The technology can treat uranium-contaminated calcium fluoride matrices, rare-earth ore residues, and fluorspar contaminated with uranium. The technology can also extract more complex fluoride by-products. 

Melville CM, Wai CM, Collopy M, et al. 1981. Uranium dispersion along roads paved with phosphate slag. Bull Environ Cont Toxicol 27 479-473. 

The presence of uranium may be detected in ores or slags by adding an excess of zinc to a solution in nitric acid. When the reaction subsides, a yellow deposit, apparently of the hydrated trioxide, UO3.2H2O, remains on the zinc. The test is not applicable in presence of hydrochloric or sulphuric acid, and it is not successful in presence of large quantities of iron or vanadium other metals likely to be present, e.g. Au, Pt, Th, Pb, W, Ti, Cr, Hg, Cu, do not interfere. 

Reduction of halides. Table 5.30 lists pertinent properties of substances that might take part in the reduction of the uranium halides UF4 or UCI4. As this table shows, the heat available per mole of uranium produced is much higher than in the reduction of UO2. In addition, the melting point of the halide by-product is much lower than that of CaO and is near that of uranium metal. Consequently, the reaction temperature can be raised enough to melt both the uranium metal and the halide by-product, so that a clean separation between metal and slag can be obtained. 

The heat of reaction is sufficient to melt both uranium metal and CaFj slag, with reactants initially at room temperature, so that preheating is unnecessary. 

Domestic supplies of vanadium are obtained from a deposit in Arkansas that is mined for vanadium alone from some deposits in the western states that yield coproduct uranium and vanadium and from slags derived from making elemental phosphorus from phosphate rock mined in Idaho. The vanadium-production potential of these deposits does not appear to be adequate to satisfy long-range domestic requirements. 

Pyrometallurgical processes investigated include slagging of molten irradiated uranium, plutonium extraction by silver, plutonium volatilization, and fused-salt extraction (78). Interest in these approaches ended with the selection of uranium dioxide as the CANDU fuel. 

Hydratable oxides may also be present in NFS from some sources, which could potentially contribute to volumetric instability. Depending on the ore and metallurgical process, nonferrous slags produced from sulfide ores can contain leachable elemental sulfur and heavy metals, which should be investigated prior to use. Sulfurous leachate is primarily of aesthetic concern, resulting in sulfur odor and possible discoloration of water in poor drainage conditions. In addition, phosphate rocks can contain between 30-200 ppm uranium. Most of this uranium is incorporated in the phosphorus slag and results in the release of some radiation (in the form of radon gas). 

Uranium existing in coal as silicate mineral coffinite and uraninite (UOj) poses a potential environmental hazard. Following combustion of coal, the refractory coffinite remains in the bottom ash and slag while the uraninite is vaporized and is later condensed on the fly-ash particles as the flue gases cool (Chadwick et aL, 1987). Comparative radiation exposure assessment studies on coal and nuclear-based electricity generation reveal that emissions from both are very low, but dose levels from coal-fired plants are equal to or slightly lower than from a nuclear power plant (UNGA, 1980 Chadwick et al., 1987). 

The production of ingots of various rare metals, is carried out commercially on the kilogram to the ton scale. This technique is particularly valuable for uranium and beryllium, but smaller quantities of, for example, zirconium, vanadium and thorium have also been manufactured. The fluorides are generally preferred to the chlorides since they are less volatile. Oxides do not result in molten slags unless large quantities of... 

Other uses klystron and ceramic electron tube parts, radiation and antenna windows, and radar antennae. Berylha s exceptional resistance to wetting (and thus corrosion) by many molten metals and slags makes it suitable for crucibles for melting uranium, thorium and berylhum. 

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