Uranium chemical exchange

Nomura, M., and Suzuki, T. (2006) Temperature dependence of isotope effects in uranium chemical exchange reactions. 

M. Shimizu, S. Kiyota and R. Ninomiya, Proc, or Intern. Syinp. on Isotope Separation and Chemical Exchange Uranium Enrichment, Tokyo (1989) 56. 

Chemex [Chemical exchange] A process for separating uranium isotopes, based on the equilibrium between U3+ and U4+ in aqueous solution. U-238 concentrates in the LP+ state and U-235 in the U4+. Uranium in the two valence states is separated by solvent extraction into tributyl phosphate. Developed and piloted in France but not commercialized. 

Kitamoto, A., Shimizu, M., and Masui, T., The Advanced CECE Process for Enriching Tritium by the Chemical Exchange Method with a Hydrophobic Catalyst, in Proceedings of the International Symposium on Isotope Separation and Chemical Exchange Uranium Enrichment, Oct. 29-Nov. 1, 1990, Tokio, Yasuhiko Fuji, Takanobu Ishida, Kazuo Takeuchi, Editors, 497, 1990. 

The investigation of isotopic separations in systems with cyclic polyethers has been carried out up to now for the elements lithium, calcium and sodium, in particular. Among these elements, the enrichment of Li is of essential importance for the production of tritium and that of the heavy calcium isotopes for medical labeling experiments. An enrichment aspect does not exist for the monoisotopic element sodium. Investigations with the radioactive nuclides Na and Na are obviously of interest for fundamental investigations because these isotopes can be easily and precisely measured by their y-activity. Except for uranium, most of the investigations on other chemical exchange systems with metal ions are also based on measurements with lithium and calcium, respectively. 

A study of the kinetics of the separation of the uranium isotopes and by uranium(iv)-uranium(vi) chemical exchange on cationic exchange resins in sulphuric acid has demonstrated that large-scale uranium enrichment by this method would be uneconomical. The sorption of uranium from highly concentrated nitric acid solutions on AMP resins has been shown to be variable and dependent on concentration. 

We can not immediately conclude that we are seeing evidence for nuclear reactions. This variability was recognized years ago within the A.E.C. and it has been hypothesized that the New Mexico effect is due to chemical exchange in the oxidation-reduction cycles which are largely responsible for the formation of the large sandstone deposits of uranium in the Colorado Plateau. Now... 

This text is concerned primarily with methods used on a large industrial scale. Electrolysis, distillation, and chemical exchange, which are useful primarily for separating deuterium and isotopes of other light elements, will be described in Chap. 13. Diffusion methods, the gas centrifuge, and aerodynamic methods, which are used primarily for uranium but are applicable also to other heavy elements, will be described in Chap. 14. 

The processes used most extensively for separating isotopes of light elements, distillation and chemical exchange, become progressively less selective as the atomic weight increases and are ineffective for uranium. 

Saraceno, A. J., and C. F. Trivisonno (eds.) Uranium Isotope Separation by Chemical Exchange Reactions Between UF and UFj-Nitrogen Oxide, Report GAT-674, Feb. 4, 1972. 

Petit, J.F., Technological aspects of the historical development of EURODIF, in Proceedings of the International Symposium on Isotope Separation and Chemical Exchange Uranium Enrichment, Tokyo, Japan, October 29-November 1, Y. Fuji, T. Ishida, K. Takeuchi (eds.). Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology, 1992, p. 103. 

Marcus Y (1983) Uranium isotope separation by ion exchange. Gmelin Handbook of Inorganic Chemistry. Uranium Supplement, vol. D4. Berlin Springer. Obermoller HR and V te DA (1991) Isotope separation by chemical exchange A computer simulation. Nuclear Technology 96 337-345. 

The French did investigative work on chemical exchange in the last half of the 1970s but found the separation effect for uranium to be too small for practical application. There is no current use of this method for uranium. 

U02(C02) 3. The pregnant solution is concentrated and purified by ion exchange or solvent extraction, yielding a stripping solution of ca 50 kg/m U Og. Uranium is then precipitated chemically. Pure U Og is obtained by calcination (see Uraniumand URANIUM COMPOUNDS). 

Recovery of Uranium from Leach Solutions. The uranium can be recovered from leach solutions using a variety of approaches including ion exchange (qv), solvent extraction, and chemical precipitation. The most common methods in practice are ion exchange and solvent extraction to purify and concentrate the uranium prior to final product precipitation. 

Chemical Precipitation. The product of the extraction processes, whether derived from acid or carbonate leach, is a purified uranium solution that may or may not have been upgraded by ion exchange or solvent extraction. The uranium ia such a solution is concentrated by precipitation and must be dried before shipment. Solutions resulting from carbonate leaching are usually precipitated directly from clarified leach Hquors with caustic soda without a concentration step, as shown ia equation 9. 

The plutonium concentration in marine samples is principally due to environmental pollution caused by fallout from nuclear explosions and is generally at very low levels [75]. Environmental samples also contain microtraces of natural a emitters (uranium, thorium, and their decay products) which complicate the plutonium determinations [76]. Methods for the determination of plutonium in marine samples must therefore be very sensitive and selective. The methods reported for the chemical separation of plutonium are based on ion exchange resins [76-80] or liquid-liquid extraction with tertiary amines [81], organophosphorus compounds [82,83], and ketones [84,85]. 

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