JPH0253087B2 - - Google Patents

Description

[Detailed description of the invention]

The subject of the invention is a two-phase system, for example a solid-liquid phase,
A method of separating isotopes in liquid-liquid or solid-gas phase, in which the distribution of isotopes into each set is determined by the selection of the composition of the phases, that is, their structural and material properties. controllable and further by the choice of isotope and ligand concentrations, by the choice of temperature, light irradiation, hydrodynamic parameters, and by the choice of the length of time the phases are in contact. This method is based on the knowledge that it can be controlled. For example, isotopes of uranium, lithium and nitrogen are brought into contact with solid adsorbents or liquid extractants from aqueous and non-aqueous solutions (if necessary from gaseous mixtures thereof) by the method according to the invention, It is possible to separate with high efficiency. In principle, this is a problem with chemical separation methods. The chemical methods of isotope separation that have been published and used so far (e.g. Laskorin BNand cow.
Uspechi Khimii, band XLIV.No.5, 761-780,
1975; Carman de J. and cow., Report
AAEC/LIB/BIB-273, 1970), which is based on isotope exchange reactions, whose equilibrium constant (i.e., typically the elemental separation factor) is approximately 1.0001 to 1.01, depending on the masses of the isotopes involved. The lower value is related to the isotope of the heavier element (e.g. uranium). In recent years, much attention has been paid to separating isotopes of uranium with solid adsorbents and liquid extractants. i.e. West German patents and patent applications (e.g. DOS 2235603, 1973;
DOS 2349595, 1973; DOS 2623891, 1977
), French patents (e.g. no. 1600437, 1968),
and Romanian national publications (e.g. Ponta
A., Calusaru A., Isotopenpraxis 13, No.6,
214-216, 1977; ibid 11, No. 12, 422-426,
1975). Formula: ²³⁸ U〓 + ²³⁵ U〓 ²³⁸ U〓 + ²³⁵ U〓 [In the formula, the Roman numerals (,) represent the phase. ] The effort to ensure conditions for the process of isotope exchange in the form of is a common feature of all published methods. Nevertheless, due to the fact that it has not been possible to reproducibly achieve separation factors higher than about 1.00009 using ion-exchange and chromatographic methods, the separation of uranium () isotopes has Early efforts toward this goal were unsuccessful. This is because uranium has various valence states [i.e. U
This is why attention has been paid to the systems existing in ( ) to U() and U() to U()].
In these systems, electron-exchange reactions occur simultaneously, always enriching lighter isotopes with higher valence states of uranium. Moreover, in connection with complexation reactions and isotopic effects by using a suitable type of adsorbent (and, if necessary, extractant) selective for one of the valence states of uranium, substantially enhanced The efficiency of separation was actually achieved. Published data (e.g. M. Seko, T. Miyake, K. Inada,
Nucl.Technology 50, 178−186, 1980;
Report INFEC/DEP/WG.2/31, On the
Thechnical, Economical and Safeguard
Information of the Different Enrichment
Thechniques, March 15, 1979), it is clear that we have succeeded in moving the value of the element separation factor to about 1.001, which is said to be the lower limit for the economical use of this process. For example, the elemental separation factor for gas diffusion processing, which is used as an operating standard for the separation of uranium isotopes, is approximately 1.0027. Therefore, the obtained results can already be said to be economically and technically advantageous. Nevertheless, operational applications are not obvious, mainly due to the limited value of the element separation factor, which requires a large number of stages, large amounts of enriched uranium hold-up, and processing. This is associated with necessitating the fabrication of devices with a relatively long time required to reach a stable state. The need to repeat the redox treatment of uranium many times is due to the redox agent involved (as well as the energy of the reaction, if necessary).
related to the substantive requirements of These defects are eliminated by a new method of separating isotopes according to the invention, which is based on a controlled distribution approach that takes advantage of isotope effects on concentration in a two-phase system. The method according to the invention is characterized in that the first phase is an aqueous or non-aqueous solution of the isotope and the ligand at a concentration from 10 ^-6 M up to a saturation concentration, or a gaseous mixture of the isotopic components or the isotope and an inert gas. and the molar ratio between the isotopes to be separated is from 1: ¹⁰⁵ to 1: ^10-5 in the starting mixture (or solution if necessary); Solid adsorbents such as benzene ion exchangers or biosorbents based on mycelium of lower fungi (if necessary, such as Teflon (a trade name for materials based on polytetrafluoroethylene), silica gel and cellulose) an extractant such as tributyl phosphate and trioctylamine (retained on a carrier); said two-phase system is used in the sorption and/or desorption (if necessary in the extraction and/or re-extraction); nonlinear isotherm
It is advantageous to indicate; and the carbonate ion,
by isotopic complexation with ligands such as sulfate, titanate, chloride and ethylenediaminetetraacetate or with carboxyl and hydroxyl groups and phosphorous, nitrogen and sulfur based groups. By using adsorbents and extractants with chelating functional groups and/or even in the dark or under light with a wavelength between 2.5 x 10 ² and ^{10 9} nm, both phases can be isolated. contact time from 10 ^-2 to 10 ⁶ seconds,
The temperature was 10 ² to 10 ³ K, the stirring speed was 10 ^-2 to ^{10 4} revolutions per second, and the flow rate in the column device was 10 ^-6 to 10 ^-1.
m/s and the particle size of the absorbent from 10 ^-6 to 10 ^-2 m.
and even for the desorption or re-extraction of isotopic components, compounds such as sodium carbonate, ammonium nitrate, sodium chloride, sodium sulfate, sulfuric acid, nitric acid and hydrochloric acid, as well as titanate ion, ethylenediaminetetraacetic acid. ions and solutions of compounds containing complexing ligands such as isobutyrate ions, alone or
When the two phases are brought into contact using a mixture with a total concentration from 10 ^-3 M to a saturated solution, the rates of isotope transfer from one phase to the other are unequal and the suppression of isotope exchange (retardation) occurs; In the method according to the invention, an aqueous solution of isotopic components such as ²³⁵ U () and ²³⁸ U () and ligands such as nitrate ions, sulfate ions and carbonate ions, the total concentration of which is 10 ^{- 2} to 10 ^-1 M and the dissolved isotopes ²³⁵ U and ²³⁸ U in the starting mixture are 1:500 to 1:100.
It is possible to use, for example, a molar ratio of . It is possible to use ion exchangers based on styrene-divinylbenzene copolymers or adsorbents based on the mycelium of the lower fungus P. Chrysogenum as solid adsorbents. in the dark or
The operation was carried out under light with a wavelength of 250 to 650 nm, and the stirring rotational speed was 0.800 to 12.00 revolutions per second, and the flow rate in the column was 10 ^-4 to ^{10 -1} m/s, and the rotation speed was 10 -4 to 10 ^-4 m/s.
A solid adsorbent with a particle size of 10 ^-3 m was used at a temperature of 273 m.
~373K, and the phase contact time length is ¹⁰² ~
10 to ⁴ seconds can be selected. Sodium chloride + sodium carbonate, with a concentration of 10 ^-1 to 1.5M,
Alternatively, solutions of sodium carbonate or hydrochloric acid can be used for desorption. The process according to the invention is characterized by a substantially higher separation factor than previously achieved in isotope exchange reactions. The maximum value of the element separation factor varies between 1.02 and 1.10 in the process of sorption (and also desorption, if desired) of uranium isotopes. It is particularly advantageous to use solid adsorbents with uranium () solutions as well as with high selectivity of the sorption process (followed by the desorption process if necessary) but with not too fast reaction rates. The economic and technical importance of the isotope separation method according to the invention is considerable. exhibiting substantially increased elemental separation factor values, i.e. in the separation of uranium isotopes;
This shows a reduction in the total number of separation stages by an order of 1 to 1.5, a reduction in the hold-up of enriched uranium in the device by almost the same order, and a reduction in the time required to achieve a stable state. It is possible to operate with an emulsion of hexavalent uranium, without having to change its valence and without converting the uranium to UF ₆ before enrichment, as in conventionally employed enrichment steps. Another important point is that the depleted uranium generated in this process can be used as input U material, and the content of ²³⁵ U isotope in this waste is actually reduced by half. The new method of isotope separation (i.e. in the example of sorption) can be further explained as follows: (a) an aqueous solution of the isotope, e.g. ²³⁵ U() + ²³⁸ U
When a solid adsorbent or a liquid extractant is brought into contact with a solution in which the concentration of one isotope is at least 0.5 to 1 order of magnitude higher than that of the other, the sorption of both isotopes occurs simultaneously. However, the rate of sorption of each isotope is proportional to the driving force of this process, ie, the relative deviation from equilibrium and the value of the mass transfer coefficient. This generally different rate of isotope component sorption, conditioned by the suppression of isotope exchange (see (g) below), is the property of an effect called the isotope effect of concentration.
The sorption rate can be determined, for example, by the relation: R = K _q Δ _q = K _c Δ _c [where R is the respective sorption of isotope transfer from one phase to the other (if necessary K _q , K _c are the mass transfer coefficients, and Δ _q , Δ _c represent the driving forces of the process, the respective concentration gradients in phases “q” and “c”. ] It is possible to express it as follows. (b) The driving force for isotope transfer from one phase (here the aqueous phase) to the other is a function of the initial concentration of the isotope in both phases, on the one hand, and as the isotope concentration changes on the other hand. It depends on the shape of the equilibrium curve (a curve that graphs the isotope concentration in the sorbent with respect to the isotope concentration in the solution; the same applies hereafter) in the region (this change occurs during the sorption process). (c) in the region of concentration changes, in relation to the isotope concentration in solution and how the sorption process is limited;
It is advantageous to select sorbents which exhibit as different slopes of the equilibrium curve as possible, corresponding to a single isotope if possible. The portion of the sorption equilibrium curve corresponding to lower concentration isotopes is approximately 10 ²
It appears advantageous to have a slope of ˜10 ³ and the portions corresponding to high concentrations of isotopes have a slope of about 10. (d) The choice of adsorbent is limited by the properties of the adsorbent alone, so it is likewise possible to adjust the composition of the solution to the properties of the solvent. In this sense, the isotope ratios are kept at their initial values and the absolute concentration of the isotopes can be adjusted, for example by dilution or even by adjusting the solution composition by adding further components, including complexing agents. Take changes into account. (e) The mass transfer coefficient is a function of the solution composition (isotope concentration) and the type of adsorbent (extractant if necessary) on the one hand, and the temperature and hydrodynamic parameters, stirring rate, flow rate, adsorption on the other hand. the particle size of the agent; although these mass transfer coefficients generally have different values for each isotope, with concentration dependence being one of the most important, their absolute values are primarily a function of adsorption. Depends on the type of agent. The inventors found that the mass transfer coefficient was between 10 ^-5 and ^{10 -3}
We have found it advantageous to operate with such adsorbents per second. (f) For example, so-called biosorbents (Chieco Inventor Certificate No. 155833 and Chieco Inventor Certificate No. 184471 and 189198 (PV1867-75 and PV588-76)
), as well as ion exchangers based on styrene-divinylbenzene copolymers, alone or supported on carriers such as Teflon, cellulose, silica gel, etc., can be used as adsorbents with the above-mentioned equilibrium and kinetic properties. It is. (g) Simultaneously with isotope sorption (and if necessary extraction), isotope exchange begins to occur practically immediately;
This isotope exchange suppresses differences in the sorption amount of a single isotope that result from different sorption rates. The negative effects of the isotope exchange process (the rate of which is approximately equal to the sorption rate of isotopes at higher concentrations) can be suppressed on the one hand by the selection of the type of sorbent and the solution composition and by the appropriate Compensation can be made by suitable selection, on the one hand, and by operating at low temperatures and limited light irradiation. Interference with isotopic exchange can be achieved as well by complexing the isotopic components in one phase, either by adding suitable ligands to the solution or by complexing functional groups. Either by using a sorbent (and if necessary an extractant) with a (h) The same statements made above by way of example regarding the rate of isotope sorption are also true in principle regarding the rate of desorption (and re-extraction if desired) and the rates associated with isotope exchange. Example 1 Ostsorb trademark MV6/5 in Na form activated with hydrated titanium oxide (), swollen and centrifuged
Adsorbent (P. chrysozenum)
2 g of an adsorbent based on a fungus (chrysogenum) was mixed at a temperature of 293 K without exposure to light, with a stirring speed of 5 revolutions per second, while the PH
It was brought into contact with 60 ml of 0.01 M uranyl nitrate solution adjusted to 3.5. ^{The 235} U: ²³⁸ U isotope ratio in the initial solution was 0.725×10 ^-2 (we were dealing with a compound prepared from natural uranium). During the process of the sorption reaction, a sample of the liquid phase was taken out, and the total concentration of uranium in the sample was measured by spectroscopic analysis using the reagent arsenazo, and the ²³⁵ U: ²³⁸ U isotope ratio was determined.
Measurement was performed using an Aldermaston-Micromass model 30 mass spectrometer. Based on the results obtained, the value of the separation factor was calculated as a function of time:

[Table] Separation factor is defined as the ratio of ^{the 235} U: ²³⁸ U isotope ratio in the adsorbent to the same isotope ratio in the liquid phase. Example 2 The same procedure as in Example 1 was carried out, except that the experiment was carried out in daylight, and the time evolution of the total uranium concentration and isotopic ratio in the liquid phase was measured. The time dependence of the separation factor was calculated based on the obtained results:

[Table] Example 3 The same treatment as in Example 1 was carried out, except that a strongly acidic cation exchanger with the trademark Amberlite IR-120 in the H ⁺ form was used, and the total uranium concentration and isotope ratio in the liquid phase were determined. Changes over time were measured. The time dependence of the separation factor was calculated from the obtained results:

[Table] Example 4 Trademark Ostsorb saturated with uranium to a capacity of 4×10 ^-5 M/g of uranium, swollen and centrifuged.
5g of adsorbent MV6/5 was heated under light irradiation to
At 293K, while stirring at a stirring speed of 5 revolutions per second,
It was brought into contact with 20 ml of a solution of 1M NaCl + 0.1M Na ₂ CO ₃ . The uranium isotope ratio of the adsorbent at the beginning of the experiment was 0.725×10 ^-2 . During the sorption process, a liquid phase sample was taken and the total uranium concentration and ²³⁵ U: ²³⁸ U isotope ratio were measured. The time dependence of the separation factor was calculated from the results:

[Table] Example 5 Example 4 except that the experiment was conducted without light irradiation
The same treatment as in was carried out, and the temporal changes in the total uranium concentration and isotope ratio in the liquid phase were measured. The time dependence of the separation factor was calculated from the obtained results.

[Table] Example 6 Trademark in H ⁺ form, swollen and centrifuged
Ostsorb MV6/5 adsorbent (P. chrysogenum
2 g of an adsorbent based on fungal mycelia) were brought into contact with 50 ml of a 0.01 M uranyl nitrate solution at a temperature of 293 K under daylight irradiation and with stirring at a rotational speed of 5 revolutions per second. ^{The 235} U: ²³⁸ U isotope ratio in the starting solution was 0.725×10 ⁻² . After 3 hours the two phases were separated and in a second step the solution was again contacted with 2 g of fresh same adsorbent for 3 hours.
In total, four such sorption steps were performed.
The total uranium concentration in the liquid phase is determined after each step by spectrometry using the arsenazo reagent, and
^{The 235} U: ²³⁸ U isotope ratio in the adsorbent phase was measured after the final stage using an Aldermaston-Micromass model 30 mass spectrometer. From the results, the element separation coefficient of one stage was calculated. The result was 1.020. The separation factor is defined as the ratio of ^{the 235} U: ²³⁸ U isotope ratio in the adsorbent to the same isotope ratio in the liquid phase - in our example after 3 hours of phase contact. Example 7 Trademark Ostsord activated with titanium oxide ()
Example 1 except that an adsorbent called MV6/5 was used.
Four sorption steps were carried out using the same treatment as in . A one-stage element separation factor was calculated from the results. 1.025 was obtained. Example 8 Trade name for swollen and centrifuged H ⁺ form saturated with uranium to a capacity of 4×10 ^-5 M/g of uranium
5 g of Ostsord MV6/5 adsorbent was added to a solution of 1 M NaCl + 0.1 M Na ₂ CO ₃ at a temperature of 293 K under daylight irradiation and with stirring at a rotational speed of 5 revolutions per second.
It was brought into contact with 20 ml. The isotope ratio ²³⁵ U: ²³⁸ U in the adsorbent at the beginning of the experiment was 0.725×10 ^-2 .
After 1 hour the two phases were separated and a fresh solution of the above composition was added to the adsorbent. A total of four such desorption steps were performed. Measure the total uranium concentration of the solution after each step and determine the isotope ratio in the adsorbent phase.
²³⁵ U: ²³⁸ U was measured after the last stage. A single-stage element separation factor was calculated from the results. 1.150 was obtained. Example 9 Four desorption steps were carried out using the same procedure as in Example 3, except that a 0.1M sodium carbonate solution was used for the desorption. A single-stage element separation factor was calculated from the results. 1.120 was obtained. Example 10 The same procedure as in Example 3 was carried out, except that a 0.1M hydrochloric acid solution was used for desorption, and four desorption steps were carried out. A single-stage element separation factor was calculated from the results. 0.980 was obtained. Example 11 20.0 ml of a 0.1 M tri-n-octylamine solution in the base form is mixed with 0.01 M−UO ₂ SO ₄ +0.1 M− while stirring on a laboratory shaker at a temperature of 293 K.
It was contacted with 100.0 ml of a solution of Na ₂ SO ₄ . The isotope ratio of the starting solution ²³⁵ U: ²³⁸ U was 0.725×10 ^-2 (we were dealing with a compound prepared from natural uranium).
During the extraction process, a sample of the aqueous phase is taken, in which the total concentration of uranium is determined by spectrometry using the reagent arsenazo, and
Isotope ratios were measured using a mass spectrometer model 30 manufactured by Aldermaston-Micromass. From the results, the value of the separation coefficient as a function of time was calculated.

[Table] The principle of controlled partitioning is applied more generally to the separation of components that either have different concentrations or different migration rates between phases, i.e. the rate of sorption (and desorption if necessary). It can be used for component separation when one component is different. In addition to mixtures of isotopes, rare earths and even
This involves the separation of substances with similar properties such as Zr~Hf, ²²⁶ Ra~Ba and the like. The preparation of semiconductors, nuclear reactions and pure substances of analytical purity can likewise be advantageously realized with the present method.

Claims (1)

[Claims] While stirring at a speed of 1 10 ^-2 to 10 ⁴ revolutions per second.
contacting the first and second phases at a temperature of 10 ² to 10 ³ K for ^{10 -2} to ^{10 6} seconds, followed by separating these phases and recovering the desired uranium isotope; and the first phase consists of a solution of a ligand selected from nitrate ions, sulfate ions, hydrochloride ions, and carbonate ions and two or more uranium isotopes at a concentration from 10 ^-6 M to a saturation concentration; The phase may consist of a solid adsorbent consisting of a styrene-divinylbenzene ion exchanger or a bioadsorbent based on mycelium of lower fungi, or an extractant consisting of tributyl phosphate or trioctylamine alone or supported on a carrier. A method for separating uranium isotopes in a characterized two-phase system. 2. The method according to claim 1, wherein the first phase consists of a solution of U ₂₃₅ (), U ₂₃₈ () and a ligand at a concentration of 0.01 to 2.0 M, and the ligand is a nitrate or a sulfate. Method. 3 The second phase is P. chrysozenum (P.
2. A method according to claim 1, comprising a solid adsorbent based on the mycelium of a lower fungus, A. chrysogenum. 4. The method of claim 1, wherein said second phase comprises a strongly acidic solid adsorbent cation exchanger based on a styrene-divinylbenzene copolymer. 5. The method according to claim 1, wherein the contact between the first phase and the second phase is performed in a dark place. 6 The contact between the first phase and the second phase is 250 to 650 nm.
2. The method according to claim 1, which is carried out in the presence of light having a wavelength of . 7. The second phase consists of a solid adsorbent having a particle size of 10 ^-4 to ^{10 -3} m, the stirring speed is 0.80 to 12.0 revolutions per second, and the flow rate of the phase in the column is 10 ^-4 to 10 -3 m ^{. 1}
2. A method according to claim 1, wherein the speed is m/sec. 8. The method according to claim 1, wherein the contact temperature is between 273 and 373. 9 Compounds consisting of sodium carbonate, sodium sulfate, sulfuric acid, nitric acid or hydrochloric acid alone or as a mixture with a ligand consisting of titanate ion, ethylenediaminetetraacetate ion or isobutyrate ion from 10 ^-3 M to saturation concentration 2. The method according to claim 1, wherein the uranium isotope is desorbed or re-extracted with a solution having a concentration of . 10 Sodium carbonate; a mixture of sodium chloride and sodium carbonate; or 10 ^-1 consisting of hydrochloric acid
2. The method according to claim 1, wherein the adsorbent is eluted with a solution having a concentration of 1.5M. 11. The method of claim 1, wherein the second phase is an extractant. 12. Process according to claim 2, wherein the isotopes U ₂₃₅ and U ₂₃₈ are present in the starting mixture in a molar ratio of 1:500 to 1:100. 13. The method of claim 11, wherein the extractant is tributyl phosphate. 14. The method of claim 11, wherein the extractant is trioctylamine.