Contamination, uranium processing

According to the vendor, full-scale processes have been employed to remediate depleted uranium and uranium process residues. Systems have also been designed for treatment of natural uranium-contaminated materials. Processes for the treatment of materials contaminated with multiple heavy metals have been designed and demonstrated. RIMS was unable to determine the commercial availability of this technology. 

Fig. 1. Schematic flowsheet of uranium processing (acid leach and ion exchange) operation. Numbers refer to the numbers that appear in the boxes on the flowsheet. Operations (3), (6), (9), and (11) may be done by thickening or filtration. Most often, thickeners are used, followed by filters. The pH of the leach slurry <4) is elevated to reduce its corrosive effect and to improve the ion-exchange operation on the uranium liquor subsequently separated, In tile ion exchange operation (7), resin contained in closed columns is alternately loaded with uranium and then eluted. The resin adsorbs the complex anions, such as UC fSO 4-. in which the uranium is present in the leach solution. Ammonium nitrate is nsed for elution, obtained by recycling the uranium filtrate liquor after pH adjustment. Iron adsoibed with the uranium is eluted with it. Iron separation operation (8) is needed inasmuch as the iron hydroxide slurry is heavily contaminated with calcium sulfate and coprecipitated uranium salts. Therefore, the slurry is recycled to the watering stage (3). Washed solids from 1,6). the waste barren liquor from (7), and the uranium filtrate from (11) are combined. The pH is elevated to 7.5 by adding lime slurry before the mixture is pumped to the tailings disposal area. (Rio Algom Mines Limited, Toronto)...

Unauthorized landfill disposal of uranium processing wastes (e.g., Shpack Landfill in Norton, Massachusetts, and the Middlesex Municipal Landfill in Middlesex, New Jersey) has resulted in soil contamination (Bechtel National 1984 Cottrell et al. 1981). Also, elevated uranium concentrations have been measured in soil samples collected at 30 of 51 hazardous waste sites and in sediment samples at 16 of 51 hazardous waste sites (HazDat 1998). The HazDat data includes both Superfund and NPL sites. Elevated concentrations of uranium have been detected in soil, in surface water, in groundwater, or in all three of these environmental media from these sites. In several cases, the uranium concentrations in soils were significantly elevated. For example, uranium concentrations from the Shpack/ALI site were found to be 16,460 pCi/g (24,000 pg/g). At the United States Radium Corporation site (New Jersey), uranium concentrahons ranged from 90 to 12,000 pCi/g (130-18,000 pg/g) for the Monticello site (Utah), uranium levels were reported to range from 1 to 24,000 pCi/g (1.5-36,000 pg/g) (HazDat 1998). 

Standards for Cleanup of Land and building Contaminated with Residual Radioactive Materials from Inactive Uranium Processing Sites... 

EPA. 1995a. U.S. Environmental Protection Agency. Standards for cleanup of land and buildings contaminated with residual radioactive materials from inactive uranium processing sites. Code of Federal Regulations. 40 CFR 192, Subpart B. 

A well-designed Purex plant aims for as complete recycle of solvent as possible, to minimize costs of solvent makeup and disposal. Solvent from the uranium purification section usually contains so few contaminants or degradation products that it can be reused a number of times without cleanup. On the other hand, solvent that has processed solutions containing hi activity of fission products and plutonium carries traces of these contaminants, uranium, nitric acid, dibutyl phosphate, and other radiolytic degradation products of TBP and dodecane. Uranium and plutonium should be recovered because of their value. Fission products should be removed to prevent product contamination in later cycles. Dibutyl phosphate should be removed because it forms strong complexes with tetravalent zirconium and plutonium that would impair ability of the solvent to reject zirconium and separate plutonium from uranium. 

The uranium content in plants can serve for monitoring contaminants in the environment (Caldwell et al. 2012). Samples of plants, soil, sediments, water, and common biota were collected from flve distinct sites in the vicinity of a uranium processing facility with the objective of studying transport pathways and selecting the plants that are efficient bioaccumulators of uranium. Plant root samples were dipped... 

Although the process requires the addition of a phosphate donor, such as glycerol-2-phosphate, it may be a valuable tool for cleaning water contaminated with radionuchdes. An alternative mode of uranium precipitation is driven by sulfate-reducing bacteria such as Desulfovibrio desulfuricans which reduce U(VI) to insoluble U(IV). When combined with bicarbonate extraction of contaminated soil, this may provide an effective treatment for removing uranium from contaminated soil (85). 

Biological activity can be used in two ways for the bioremediation of metal-contaminated soils to immobilize the contaminants in situ or to remove them permanently from the soil matrix, depending on the properties of the reduced elements. Chromium and uranium are typical candidates for in situ immobilization processes. The bioreduction of Cr(VI) and Ur(VI) transforms highly soluble ions such as CrO and UO + to insoluble solid compounds, such as Cr(OH)3 and U02. The selenate anions SeO are also reduced to insoluble elemental selenium Se°. Bioprecipitation of heavy metals, such as Pb, Cd, and Zn, in the form of sulfides, is another in situ immobilization option that exploits the metabolic activity of sulfate-reducing bacteria without altering the valence state of metals. The removal of contaminants from the soil matrix is the most appropriate remediation strategy when bioreduction results in species that are more soluble compared to the initial oxidized element. This is the case for As(V) and Pu(IV), which are transformed to the more soluble As(III) and Pu(III) forms. This treatment option presupposes an installation for the efficient recovery and treatment of the aqueous phase containing the solubilized contaminants. 

Phytoremediation methods for radionuclide decontamination do not involve hyper-aeeumulators, except possibly for uranium. Plants require a long period of eontact with a contaminant to evolve the ability to hyper-aeeumulate, and most uranium ores are located underground and so are not in eontaet with plants. Soils with high concentrations of uranium are present only where uranium is or has been mined or processed, but these have only been in existenee for a few deeades. 

Hermann, E., DulUes, F., Griebel, I., and KieBig, G., 2001, Filter material and process for the removal of heavy metals, arsenic, uranium, and radium from contaminated waters, Patents Pending DE 101 16 951, DE 101 16 953 (2001). 

Long-lived ty = 2.1 x 10 years) Tc, present as TCO4 in Purex process HNO3 feed solutions, is partially coextracted with uranium and plutonium in the first cycle. Unless separated in the Purex process, Tc contaminates the uranium product subsequent processing of the U02(N03)2 solution to UO2 can release some of the technetium to the environment. The presence of technetium in the purification steps as well as in the uranium product causes several other complications. Thus it is desirable to route all Tc into the high-level waste. Efforts in this direction have been described in some recent flow sheets [37]. 

Laboratory-scale studies indicate that the aqueous biphasic process is well suited to the recovery of ultrafine, refractory material from soils containing significant amounts of sUt and clay. The main advantages of the aqueous biphasic system in treatment of uranium-contaminated soils are that the process achieves a high removal rate for the uranium contaminant and that such removal is highly selective. Laboratory studies indicate that approximately 99% of the soil is recovered in the clean fraction. 

Preliminary estimates for full-scale treatment costs of uranium-contaminated soils were developed based on laboratory-scale studies. The process design uses polyethylene glycol (PEG) (15% solution) and sodium carbonate (10% salt solution) for the aqueous biphasic extractiou system. Uranium is recovered from the salt-rich phase by methanol precipitation. Methanol is then recovered by distillation. 

Following biological degradation, the extract is exposed to photochemical degradation, which removes uranium from solution as polyuranate. The metals and uranium are captured in separate treatment steps, allowing for the separation of wastes into radioactive and nonradioactive waste streams. This treatment process does not create additional hazardous wastes and allows for the reuse of the contaminated soil. The technology has been the subject of bench-scale tests and is not currently commercially available. 

In 1999, the SGS was used at the U.S. Department of Energy s (DOE s) Los Alamos National Laboratory (LANL) in Los Alamos, New Mexico, to sort 2526 yd of soil and debris contaminated with up to 431.46 picocuries per gram (pCi/g) of uranium from the production of nuclear weapons. The actual cost for the operation was 275,745. This figure included 6600 for predeployment activities, 46,000 for mobilization, 185,445 for processing, 35,000 for demobilization, and 2700 for the final report. LANL incurred 543,400 in additional costs for staff, the prime contractor, recharges, and soil disposal. The overall nnit cost was 109/yd of soil processed (D21040S, p. 70 D21230W, pp. 13, 14). 

An SGS was used to segregate uranium-contaminated soil at the ER Site 16 Concrete Dump Site at the DOE s Sandia National Laboratories in Albuquerque, New Mexico. The actual cost of the full-scale remediation was 164,109, including 59,326 for mobilization, 57,770 for operations, and 47,013 for demobilization. Based on the 661.8 yd of soil processed, the unit cost of the operation was 236/yd. Site preparation, crane operation, oversight labor, health physics support, water supply, sample analysis, and waste disposal were not included in the actual or unit costs (D21040S, p. 74 D21233Z, pp. 12, 13). 

Bradbury, J. W. 2002. Insights from process-level modeling of contaminant transport from uranium mill tailings. Annual Meeting Geological Society of America, Denver, CO, United States, 2002. 

RlTCEY, G. M. 1990. Weathering Processes in Uranium Tailings and the Migration of Contaminants. In The Behaviour of Radium, IAEA Technical Report Series 310, IAEA, Vienna, 27-82. 

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