Separation of uranium

Many challenging industrial and military applications utilize polychlorotriduoroethylene [9002-83-9] (PCTFE) where, ia addition to thermal and chemical resistance, other unique properties are requited ia a thermoplastic polymer. Such has been the destiny of the polymer siace PCTFE was initially synthesized and disclosed ia 1937 (1). The synthesis and characterization of this high molecular weight thermoplastic were researched and utilized duting the Manhattan Project (2). The unique comhination of chemical iaertness, radiation resistance, low vapor permeabiUty, electrical iasulation properties, and thermal stabiUty of this polymer filled an urgent need for a thermoplastic material for use ia the gaseous UF diffusion process for the separation of uranium isotopes (see Diffusion separation methods). 

The need for a large number of stages and for the special equipment makes gaseous diffusion an expensive process. The three United States gaseous diffusion plants represent a capital expenditure of close to 2.5 x 10 dollars (17). However, the gaseous diffusion process is one of the more economical processes yet devised for the separation of uranium isotopes on a large scale. 

UFe is important in the separation of uranium isotopes by gaseous diffusion (p. 1259). 

The last paragraph in this extract refers to work on the separation of uranium by ether extraction as a step toward obtaining a plutonium concentrate from a large sample of neutron-irradiated uranyl nitrate. 

Figure 1. Schematic diagram showing a TRU-spec extraction chromatography method for separation of uranium, thorium, protactinium, and radium from a single rock aliquot. Further purification for each element is normally necessary for mass spectrometric analysis. Analysis of a single aliquot reduces sample size requirements and facilitates evaluation of uranium-series dating concordance for volcanic rocks and carbonates. For TIMS work where ionization is negatively influenced by the presence of residual extractant, inert beads are used to help remove dissolved extractant from the eluant.

Chalov PI, Merkulova KI (1968) Effects of oxidation on the separation of uranium isotopes during leaching from minerals. Geochem Int 5 (Suppl) 391-397... 

One of the most important examples of the fluorination of oxides is the fluorination of uranium dioxide. Uranium tetrafluoride (UF4) is the intermediate compound which is reduced to uranium metal. The gaseous higher fluoride, uranium hexafluoride (UF6) is used for the separation of uranium isotopes to obtain enriched uranium (i.e., uranium containing a higher proportion of the isotope, U235, than natural uranium). 

The development and mass production of membranes for the separation of uranium isotopes by the process of gaseous diffusion applied to UF. ... 

Subsequently, solvent extraction was applied to recover the fission product technetium from the residue remaining after the fluorination of irradiated uranium fuel elements . The residue was leached with concentrated aluminum nitrate solution, which was extracted by 0.3 M trilaurylamine in a hydrocarbon diluent. After separation of uranium, neptunium, and aluminum nitrate, technetium was back extracted into a 4 N sodium hydroxide solution. 

Burnett WC. n.d. US-New Zealand cooperative research into the development and application of a new method for separation of uranium-series isotopes. National Science Foundation, Division of International Programs, Washington, DC. 

Fluorine is used in the separation of uranium, neptunium and plutonium isotopes by converting them into hexafluorides followed by gaseous diffusion then recovering these elements from nuclear reactors. It is used also as an oxidizer in rocket-fuel mixtures. Other applications are production of many fluo-ro compounds of commercial importance, such as sulfur hexafluoride, chlorine trifluoride and various fluorocarbons. 

The Simons Process or Electrochemical Fluorination (ECF) was devised during the 1940s, as part of the Manhattan Project, with a view to synthesising perfluo-rinated materials capable of tolerating the aggressive conditions encountered in the uranium hexafluoride diffusion process for the preparation and separation of uranium isotopes. 

Nier s instrumentation, in comparison to the mass spectrometers existing at that time in 1934, was well developed and was extensively used for a quite different application during the Manhattan Project (1940-1945) for separation of uranium isotopes. It is well known that the 235U isotope... 

VOIDS. Empty spaces of molecular dimensions occurring between closely packed solid particles, as in powder metallurgy. Their presence permits barriers made by powder metallurgy techniques to act as diffusion membranes for separation of uranium isotopes in the gaseous diffusion process. 

In spite of its toxicity and extreme reactivity, fluorine is widely used for the manufacture of polymers such as Teflon, (C2F4) . Fluorine is also important in the production of UF6, used in the separation of uranium isotopes for nuclear power plants, and fluoride ion is added to toothpaste in the form of NaF to help prevent tooth decay. 

Suzuki, S., Sasaki, Y., Yaita, T., Kimura, T. 2004. Study on selective separation of uranium by N,N-dialkylamide in ARTIST process. Proc. ATALANTE 2004, Nimes, France, June 21-25. 

Pathak, P.N. Veeraraghavan, R. Manchanda, V.K. Separation of uranium and thorium using tris(2-ethylhexyl) phosphate as extractant, J. Radioanal. Nucl. Chem. 240 (1999) 15-18. 

The flowsheet of the UREX process, developed in the United States, includes the following extraction cycles (1) separation of uranium and technetium, (2) separation of plutonium, (3) separation of cesium and strontium, (4) separation of MAs and Rare Earth Elements (REE), and (5) group separation of MA from REE metals.9,10 Flowsheet development in Europe11 includes a modified PUREX process and, after that, the DIAMEX process for separation of MAs and lanthanides, the SANEX process for separation of MAs from lanthanides, and a special cycle for Am/Cm separation. Cesium and strontium will be in the raffinate of the DIAMEX process, and this raffinate will be vitrified, or cesium can be preliminarily extracted.12... 

Apostolidis, C., Molinet, R., Richir, P., Ougier, M., and Mayer, K., Development and validation of a simple, rapid, and robust method for the chemical separation of uranium and plutonium, Radiochim. Acta, 83, 21-25, 1998. 

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