Single-stage enrichment factor

ACS Symposium Series American Chemical Society Washington, DC, 1975. 

For many years attempts have been made to use photochemical processes for the separation of Isotopes. The basic idea is to utilize the difference in the absorption spectra of different isotopic species, and by use of sufficiently monochromatic light of an appropriate wavelength to excite only one of the species to an upper energy level. The excited species may then be separated by chemical or physical means from its isotopic partners the separating process need not have any Inherent isotopic selectivity. A particularly successful application of the method was to the separation of Hg isotopes by Gunning et al. (36,37). For example. 

The essential requirements for any photochemical isotope separation scheme follow  

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The primed or unprimed symbols refer to isotope fractions. The single stage separation factor for infinitesimal product removal (yi/zj 0), (rj)0, is given the symbol a . The i s index the stage number. Most often a is close to unity and it is convenient to define the isotope enrichment factor (the single stage enrichment factor), e, between the i th and (i + l) th stage... 

We now appreciate the reasons for the high cost of enriched uranium. The single stage separation factors are low, as is the natural abundance. This leads inexorably... 

To attain a sufficiently high degree of separation, multiplication of the single stage separation factor is needed. This can only be accomplished by providing circulation of the separated substances. With this approach most of the enriched mixture is returned to the column. 

The relationship between the separation hictor and the enrichment ratio was calculated (Figure-6). As the CO separation factor of Na-LSX at 2I3K is 1.1, it is predicted that the enrichment ratio for a single stage of this VPSA will be 2.5. 

Along the gradient of the breakthrough curve, the lithium samples were isotopically assayed by mass spectrometry. The single stage enrichment factor was determined as follows (24) ... 

Other oxides of nitrogen are present in these systems, and they affect the single stage enrichment factor a = ( N/ N)iiquid/( N/ N)gas as well as the interphase transfer rate as measured by the height of the column equivalent to a theoretical plate (HETP). 

Table I. Effect of Non-donor Solvents on the Single Stage Enrichment Factor exp for Solutions with an Initial Mole Fraction of N2O4 of Approximately 0.5 to which NO was Added until the Total Pressure in the Equilibration Vessel (146cc.) was 1 atm.

Table II. Single Stage Enrichment Factors aexp for Solutions of Com< ...

The characteristic value for a single-stage separation system is the isotopic separation factor a which is defined by Eq. (12). Because a deviates not very much from one, a number of separation stages must be connected in series for a sufficient total isotopic enrichment. The total isotopic separation factor S, using N equilibrium stages, is given by ... 

Equations (1) and (2) refer to measurements on separated Isotopes. It is also Important to develop a relation between the reduced partition function ratio (RPFR) and measured separation factors, a, referring to single stage Isotopic enrichments (on distillation) for dilute nonideal solutions. In the case of infinite dilution the molar volumes of the two Isomers are Identical (they are determined by environment) and one obtains (19)... 

Ion-exchange chromatography is able to combine the effects of many single-stage separations due to the small height of the equivalent theoretical plates, 0.1-10 mm. Hence, it can be used for the (partial) separation of isotopes for which the separation factors are of the order of 1.001 only. This method has been used for many elements, and in some cases, e.g., boron and uranium, has led to industrial isotope enrichment. 

Distillation is a countercurrent process in which equihbrium is maintained between Uquid and vapor, normally in a vertical column containing packing, thin wetted walls, or bubble cap plates. The single-stage separation factor for distillation is given by the vapor pressure isotope effect. Because mixtures of isotopic molecules show little or no nonideality in either liquid or vapor phase (Jancso et al. 1993), liquid vapor separation factors should be virtually independent of isotope enrichment (plate number), and the analysis of the distillation process is... 

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