Uranium refineries

Flow patterns can be altered by change of the continuous phase and, accordingly, the tendency for the formation of emulsions or cruds is altered. At one uranium refinery, the solvent is maintained in the continuous phase to produce flow patterns to reduce emulsion tendency [57]. 

Tracy BE, Meyerhof DP. 1987. Uranium concentrations in air near a Canadian uranium refinery. Atmos Env 21 165-172. 

Concentrates are shipped from the uranium mill to a uranium refinery or conversion plant. Here chemical impurities are removed and the purified uranium is converted into the chemical form needed for the next step in the fuel cycle. Figure 1.14 shows concentrates being converted into uranium hexafluoride (UF ), the form used as process gas in the gaseous diffusion process for enriching U. Other possible products of a uranium refinery used in other fuel cycles are uranium metal, uranium dioxide, or uranium carbide. Uranium purification and conversion processes are also described in Chap. 5. 

The daughters of of principal radiological concern in uranium mills and refineries are the long-lived nuclides Th and Ra (radium) and gaseous Rn (radon). The amount of these nuclides in uranium mills and tailings piles is discussed in Sec. 8.9 their occunence in uranium refineries is discussed in Secs. 9.2 and 9.7. 

Table 5.27 lists the principal uranium refineries of the Western world and their feed and products. In all these refineries except Allied Chemical s, the sequence of operations follows some or aU of the steps shown in Fig. 5.21, in which uranium ore concentrates are first purified by solvent extraction and then converted to the materials of principal practical importance, uranium dioxide, uranium metal, or uranium hexafluoride. The steps in these refining operations will be described in process sequence in Secs. 9.2 through 9.6. 

In Allied Chemical s uranium refinery the sequence of process operations is reversed, with conversion to UF preceding purification, and with UF as the sole purified product. The Allied Chemical process will be described briefly in Sec. 9.7. 

As received by the uranium refinery, uranium ore concentrates now usually consist of uranium oxide or sodium, magnesium, or ammonium diuranate. These concentrates still contain appreciable amounts of elements other than uranium and some of uranium s radioactive decay products present in the original uranium ore, such as radium and radon. 

The next step in purification is separation of uranyl nitrate from the other metallic impurities in the dissolver solution by solvent extraction. Practically aU uranium refineries now use as solvent tributyl phosphate (TBP) dissolved in an inert hydrocarbon diluent. The first U.S. refinery used diethyl ether as solvent and later refineries have used methyl isobutyl ketone or organic amines, but practically all have now adopted TBP. It is nonvolatile, chemically stable, selective for uranium, and has a uranium distribution coefficient greater than unity when the aqueous phase contains nitric acid or inorganic nitrates. 

Althougji uranium refineries use widely different types of solvent extraction contactors, their basic process flow sheets are similar, along the lines of Fig. 5.22, hich illustrates the... 

The only Canadian uranium refinery is operated at Port Hope, Ontario by Eldorado. Tonnage quantities of oxide (U3O3) were produced first in 1942 from ore concentrates. A solvent-extraction pilot plant was operated in 1950 and 1951 to investigate methylisobutylketone (hexone) and then tributylphosphate as extractants for uranium to obtain a high-purity product. The present refinery was designed and built by the Catalytic Construction Company in 1955 (11). Yellow cake is digested in nitric acid, the resultant slurry extracted with tributylphosphate dissolved in kerosene, and the uranium, after purification, transferred back to water. This solution is decomposed thermally to UO3. Capacity is about 5 Gg U/a. 

Silver is usually found in extremely low concentrations in natural waters because of its low crustal abundance and low mobility in water (USEPA 1980). One of the highest silver concentrations recorded in freshwater (38 pg/L) occurred in the Colorado River at Loma, Colorado, downstream of an abandoned gold-copper-silver mine, an oil shale extraction plant, a gasoline and coke refinery, and a uranium processing facility (USEPA 1980). The maximum recorded value of silver in tapwater in the United States was 26 pg/L — significantly higher than finished water from the treatment plant (maximum of 5.0 pg/L) — because of the use of tin-silver solders for joining copper pipes in the home, office, or factory (USEPA 1980). 

Two epidemiology studies have examined mortality among thorium workers neither found significant excess mortality. The standard mortality ratio (SMR) for all causes of death in a cohort of 3039 male workers in a thorium processing plant was 1.05 in comparison to United States white males (Polednak et al. 1983). The estimated radiation levels to the workers for inhalation intake ranged from 0.003-0.192 nCi/m (0.001-0.007 Bq/m ) for a period of 1-33 years. No evidence of overt industrial disease was found in a cohort of 84 workers at a thorium refinery exposed to <0.045-450 nCi/m (<0.002-0.02 Bq/m ) for <1-20 years (Albert et al. 1955). In both studies, the workers were exposed to other toxic compounds (uranium dust) as well as other radioactive materials (thoron, uranium daughters, thorium daughters, cerium). 

Impoundment Detoxifier is a commercially available proprietary technology for the treatment of impoundments containing chemical, biological, or radioactive sludges or semisolid wastes. The vendor claims that Impoundment Detoxifier has successfully treated wastes from field and refinery operations, chemical operations, and uranium operations. All information is from the vendor and has not been independently verified. 

Following solvent extraction, uranium is precipitated from the solution by the addition of gaseous ammonia with the yellowcake product (Fig. 16.4) being collected, packaged in 55-gal drums, and shipped to a refinery for further purification and conversion to UF6 for enrichment. 

Following milling, the yellowcake is shipped for refining and conversion. In most refineries, the uranium ore concentrates are purified by solvent extraction and then converted to UF6 for enrichment. (A schematic diagram for this process is shown in Fig. 16.5.)... 

Uranium is also leached commercially by the same bacteria. Recently, bacterial leaching of gold in Africa has been patented by Pares and co-workers U3). Also, chemical and microbially assisted leaching has been studied and is applied to remove vanadium from by-products of coke and coke ash refinery 112). 

Other applications of this alloy are in roofs, gutters, architectural features, tubes of boiler water heaters, sheathing in seawaters, HF alkylination process, handling of HF, refining of uranium, distillation and condensation units, overhead condenser pipes in refineries and the petrochemical industry. 

BioMeteq A biological process for removing trace metals from oil refinery effluents. The effluent is passed upward through a continuous sand filter. A biofilm of bacteria on the sand particles reduces and precipitates the metals. An air blast scours the precipitates from the sand, which is washed and returned to the process. Developed by Paques BV, the Netherlands, and piloted in Germany in 2005 for removing uranium and selenium. 

Some of the important but expensive rare metals are usually extracted as by-products of other metal separation processes. Selenium and tellurium are recoverable from copper refinery slime by pressure leaching (M40), scandium from uranium plant iron sludge (R15), uranium from gold cyanida-tion residues (G3), silver from aqueous chlorination process for the treatment of slimes, and gravity concentrates from gold ores (V2). A host of other processes are in use. 

Miscellaneous applications carbon black collection catalyst recovery on refinery cat crackers penultimate gas cleaning stage on uranium... 

The ELM pertraction technology has good potential for more applications at industrial scale in the near future. The industries in question might include metal mining and refinery operations (precious metals and platinum group metals are good examples), tannery industry (recovery of hexavalent chromium), and processing of nuclear wastes (recovery of uranium, strontium, and other metals). 

Laboratory scale hoUow-fiber modules were constructed with a feed phase recycling module, and the removal efficiency of the system was tested for the treatment of synthetic and uranium bearing wastewater. The feed phase pH value was equal to 2.00. Scale-up of the system was conducted after encouraging preliminary results. During the treatment of uranium bearing wastewater, the concentration of U(VI) decreased from the initial 3.5 mg dm to below 1.0 pg din in a matter of several hours, indicating the potential apphcation of the system in the processing of metal refinery wastewaters. 

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