CS214905B1 - Method of Isotope Separation by Controlled Distribution Method Using Particularly Balanced Concentration Effect - Google Patents

Abstract

The purpose of the invention is to significantly increase the value of the elementary separation factor, namely to the level of 1.10 ± 0.4, which represents specifically for the separation of uranium isotopes a reduction in the total number of separation stages by 1 to 1.5 orders of magnitude, a reduction in the time for establishing a stationary state and a reduction in the enriched uranium tank in the device also by about 1 order of magnitude. The separation of isotopes is controlled by the duration and hydrodynamic parameters of phase contact, temperature, illumination and phase composition in the sense that when an equilibrium state of the transport process is reached, such as the process of isotope sorption and desorption, the concentrations of individual isotopes in the phases due to the retardation of isotope exchange correspond with maximum approximation to the shape of the equilibrium isotherm of the relevant transport process.

Description

Isotope separation is controlled by the duration and hydrodynamic parameters of the phase contact, temperature, illumination and phase composition in such a way that when reaching the equilibrium state of the transport process, such as isotope sorption and desorption, the concentration of individual isotopes in phases due to maximum approximation of the shape of the equilibrium isotherm of the respective transport process.

The invention is a method of isotope separation in two-phase systems such as solid-liquid phase, solid-gas phase, liquid-phase liquid phase, based on the recognition that it is possible to retard the isotopic exchange process and by selecting phase composition that higher sorption selectivity can be achieved , or desorption, respectively extraction, or reextraction, for one of the isotopic components. The isotopes of uranium, nitrogen and others from their aqueous and non-aqueous solutions and possibly gaseous mixtures can be separated with high efficiency by the process according to the invention. It is basically a chemical separation method.

Previously published and used chemical methods of isotope separation (see, for example: Laskorin BN et al.: Uspechi chimii, Vol. XVIV, No. 5, 761-780 [1975]; Garman de J. et al., Report AAEC / LIB / BIB-273 (1970)) are based on isotope exchange reactions whose equilibrium constants, i.e., typically elemental separation factors, depending on the mass numbers of the isotopes in question, are in the range of about 1.01 to 1.0001; lower values refer to isotopes of heavy elements such as uranium. In recent years, much attention has been paid to the separation of uranium isotopes on solid sorbents and liquid extraction agents. In particular, patents and patent applications can be cited Japanese in the Federal Republic of Germany (eg: DOS 2,235,603 (1973); DOS 2,349,595 (1973); DOS 2,623.891 [1977]), French (eg: Franc, patent 1,600.437 [1968]) and Romanian publications (eg: Ponta A., Calusaru A .: Isotopenpraxis 13, No. 6, 214-216 [1977]; ibid 11, No. 12, 422-426 [1975]). The common feature of all published procedures is the maximum effort to comply with the conditions for the course of the isotope exchange reaction of:

238uj + 235u _n 238v _n + 235u _b where Roman numerals indicate the phase.

However, the initial work on the separation of U (VI) isotopes was unsuccessful because it was not possible to reproducibly obtain a separation factor greater than about 1,000,009 using ion exchangers and chromatographic techniques. Therefore, attention was turned to systems in which uranium is present. They are present in different valence states, namely: U (VI) - U (IV), U (IV-U (III). At the same time, an electron exchange reaction occurs in which the higher valence grade of uranium is always enriched by a lighter isotope. In connection with the isotopic effect of the complexing reactions and the use of a suitable type of sorbent or extraction agent selective for one of the valency forms of uranium, a significant increase in the separation efficiency has indeed been achieved.

It is apparent from the published data that the value of the elementary separation factor has been shifted to the level of about 1.001, which is said to be the limit of economic usability of the process. (For example, the actual separation factor of the gas diffusion process used on an industrial scale for the separation of uranium is about 1.0027.) It can therefore be stated that the results achieved are already economically and technologically interesting. However, operational applicability is not unambiguous, mainly because of the elemental separation factor limit associated with the need for a plant with a large number of separation stages, a large containment of enriched uranium and a relatively long time to achieve a stationary process state. Also, the need for multiple repetitions of the uranium reduction and oxidation process is associated with considerable demands on the respective reducing and oxidizing agents, respectively on the energy of these reactions.

These disadvantages are overcome by the novel method of isotope separation according to the invention, based on the controlled distribution method, using in particular the equilibrium concentration effect and isotopic exchange retardation in two-phase systems. The process according to the invention is characterized in that one of the phases is an aqueous or non-aqueous solution of isotopic components and a ligand at a concentration of 10 ^-6 M to a saturated solution, or is a gaseous mixture of isotopic components or a gaseous mixture of isotopic components and an inert gas. a solid sorbent such as styrene-divinylbenzene ion exchangers, lower fungal mycelia biosorbents and cellulose sorbents, or is an extraction agent such as tributyl phosphate and trioctylamine, optionally supported on a carrier such as teflon, silica gel and cellulose, and a two-phase system exhibits a non-linear equilibrium isotherm for spp. carboxylic, hydroxyl, phosphorous, nitrogen and sulfur-based pins, or washing in the dark, or under light at a wavelength in the range of 250 nm to 1 m, isotopic exchange retardation occurs, with a temperature in the range of -173 to 727 ° C; a sorbent particle size in the range of 1 μΐη to 0.01 m; furthermore, solutions of compounds such as sodium carbonate, ammonium nitrate, sodium chloride, sodium sulfate, sulfuric acid, nitric acid and hydrochloric acid are used for desorption or reextraction of the isotopic components, and compounds containing ligand complexing agents, such as citrate, ethylenediaminetetraacetic and isobutyric ions, alone or in admixture with a total concentration of 10 ^-3 M to a saturated solution. For example, an aqueous solution of isotopic components such as ²³⁵ U (VI) and ²³⁸ U (VI) and a ligand such as nitrate, sulfate and carbonate ions at a total concentration of 0.01 M to 0.1 M in which the isotopes ²³⁵ U and ²³⁸ U are in the starting mixture in a molar ratio of 1: 500 to 1: 100. As a solid sorbent, strongly acidic cation exchangers based on styrene-divinylbenzene copolymer or mycelium lower fungi of P. chrysogenum can be used. Phase contact duration is chosen in the range of 100 s to 167 min., Working in the dark or under light with a wavelength of 250 to 650 nm, further with the stirrer speed in the range of 0.8 to 12.0 s ^-1 , or s flow rate at the column arrangement in the range of 10 ~ ^{_1 3-10} m / s and a solid sorbent having a particle size range of 0.1 to 1 mm and at a temperature in the range 0-100 ° C, 273-373 Κ. for desorption solutions may be used sodium chloride + sodium carbonate, or uh sodium methoxide or hydrochloric acid at a concentration between 0,1 M and

1,5 M.

The process according to the invention is characterized by considerably higher separation factors than hitherto achieved in isotopic exchange reactions. A significant increase in the value of the elemental separation factor, namely to the level of 1.10 ± 0.4, represents, in particular for the separation of uranium isotopes, a reduction of the total number of separation steps by 1 to

1.5 order, the reduction of the stationary time and the enrichment of the enriched uranium in the plant also by about 1 order. It is possible to work with solutions of hexavalent uranium, it is not necessary to change its valency state and it is not necessary to convert uranium to UF ₆ prior to enrichment, as is the case with the previously used enrichment processes. Another economically and technologically significant moment is the fact that depleted uranium can be used as input U-material, which is “produced” by existing processes and it is realistic to reduce the content of isotope ²³⁵ U in this waste by at least half.

The essence of the isotope separation according to the invention is further described by the example of sorption:

a) By contacting the solid sorbent with an aqueous isotope solution, e.g. ²³⁵ U (VI) + 4- ²³⁸ U (VIJ), in which the concentration of one of the isotopes is at least half to one order higher than the other, both isotopes are sorbed virtually simultaneously. The contact time is chosen to be sufficient to achieve the initial phase of the equilibrium sorption state.

bj In view of the concentration of isotopes in the solution, it is necessary to select a sorbent which exhibits, in the area of concentration changes which occur during the sorption, as much as possible different slopes of the equilibrium isotherms of the respective isotopes. It is preferable that the part of the sorption isotherm that belongs to the lower concentration isotope has a slope of about 10 ² to 10 ³ and the part corresponding to the higher concentration isotope is about 10.

c) Since the choice of sorbent has its limitations on the properties of the sorbent itself, it is also possible to adapt the composition of the solution to the properties of the sorbent. In this sense, it is possible to change the absolute isotope concentration, for example by dilution, while maintaining the isotopic ratio at the original level, and to adjust the composition of the solution by adding other components, including complexing agents.

d) For example, so-called biosorbents can be used as sorbents of the above-mentioned properties (cf. art. no. 184 471 and art. no. 189198), as well as ion exchangers based on styrene-divinylbenzene copolymers; such as teflon, cellulose and silica gel and the like.

If there is no isotopic exchange, then the amount of each isotope that corresponds to the corresponding point on the equilibrium sorption isotherm would be trapped on the sorbent. In fact, however, the isotopic exchange proceeds and the consequence is that the differences in the adsorbed amounts of isotopes resulting from the non-linear course of the equilibrium isotherm are simultaneously or gradually reduced to a level corresponding to the equilibrium constant value of the respective isotopic exchange reaction. The retardation of the isotopic exchange is, together with the non-linear course of the equilibrium isotherm, the basic and unconditional condition of this method of separation. This can be achieved (retardation) by selecting and selecting the sorbent type, composition of the solution, lowering the temperature, reducing light access and interrupting the process in time, or selecting the phase contact time, respectively. It is a particularly advantageous measure to complex the isotopic component in one of the phases, either by adding a suitable ligand to the solution or by using a sorbent with complexing functional groups.

f) The same as mentioned above as an example of the sorption process also applies in its principle to desorption and its accompanying isotopic exchange.

Example 1 g of the sorbent of the brand Ostsorb MV 6/5 (sorbent based on the fungus of the P. chrysogenum strain), in the H ⁺ form, swollen and centrifuged, was stirred at a stirrer speed of 5 s ^-1 at 20 ° C and contacted with 50 ml of a 0.01 M uranylnitrate solution in the presence of daylight. The isotope ratio of ²³⁵ U: ²³⁸ U in the starting solution was 0.725. ÍO ^-2 . After 3 hours, the two phases were separated and the solution, in the second step, contacted with fresh 2 g of the same sorbent again for 3 hours. A total of four such sorption steps were performed. After each step, the total uranium concentration was determined in the liquid phase (by arsenazo I spectrophotometric method) and after the last step, in the sorbent phase, an isotope ratio of ²³⁵ U: ²³⁸ U (using an Aldermaston-Micromass mass spectrometer model 30). The elemental separation factor of one degree was calculated from the results. Result: 1,020.

The separation factor is defined as the ratio of isotope ratios of ² ' ⁵ U: ^{3 3?} U in the sorbent phase to the same isotopic ratio in the liquid phase - in our case after 3 hours of phase contact.

Example 2

Using the same procedure as in Example 1, except that the titanium dioxide activated Ostsorb MV 6/5 sorbent was used, four sorption steps were performed. The elemental separation factor of one stage was calculated from the result. Result: 1,025.

Example 3 g of a sorbent of the brand Ostsorb MV 6/5 in H ⁺ form (swollen and centrifuged) saturated with uranium to a capacity of 4.10 ~ ⁵ MU / g, with stirring, at a stirrer speed of 5 s ^-1 , at 20 ° C and 20 ml of 1 M sodium chloride + 0.1 M sodium carbonate solution in the presence of daylight. The isotope ratio of ²³⁵ U: ²³⁸ U in the sorbent at the start of the experiment was 0.725.10 ^-2 .

After 1 hour, the two phases were separated and a new solution of the above composition was added to the sorbent. A total of 4 such desorption steps were performed. After each step, the total uranium concentration in the solution was determined and after the last step, in the sorbent phase, an isotope ratio of ²³⁵ U: ²³⁸ U. The elemental separation factor of one step was calculated from the results. Result: 1,150.

Example 4

Using the same procedure as in Example 3, except that a 0.1 M sodium carbonate solution was used for desorption, four desorption steps were performed. The elemental separation factor of one degree was calculated from the results.

Result: 1.120.

Example 5

By the same procedure as in Example 3, except that a 0.1 M hydrochloric acid solution was used for desorption, 4 desorption steps were performed. The elemental separation factor of one degree was calculated from the results. Result: 0.980.

The principle of the controlled distribution method using the equilibrium concentration effect is applicable to the separation of components in general. This includes, for example, the separation of substances of close properties, such as rare earths, Zr - Hf, Ra 226 - Ba, etc. Also, the preparation of pure substances, such as semiconductor, nuclear and analytical purity materials, can be advantageously realized by this method.

Claims (9)

A method of isotope separation by a controlled distribution method using in particular an equilibrium concentration effect and isotopic exchange retardation in two-phase systems, characterized in that one of the phases is an aqueous or non-aqueous solution of isotopic constituents and 10 ^-6 M to a saturated solution, or is a gaseous mixture of isotopic constituents or a gaseous mixture of isotopic constituents and an inert gas, and the second phase is a solid sorbent such as styrene-divinylbenzene ion exchangers, lower fungal mycelia biosorbents and cellulose sorbents, or is an extraction agent such as tributyl phosphate and trioctylamine optionally supported on a carrier such as teflon, silica gel and cellulose, and the biphasic system exhibits a non-linear equilibrium isotherm for sorption and / or desorption, optionally for extraction and / or reextraction, isotopic components and ligand isotope complexes such as OF THE INVENTION are carbonate, sulfate, chloride, citrate and ethylenediaminetetraacetic ions, or by the use of sorbents and extracting agents with chelating functional groups such as carboxyl, hydroxyl, phosphorus, nitrogen and sulfur based groups and / or in the dark or in the light. a wavelength in the range of 250 nm to 1 m, isotopic exchange retardation occurs, with a temperature in the range of -173 ° C to 727 ° C and a sorbent particle size in the range of 1 μια to 0.01 m, isotopic desorption or reextraction components of compounds such as sodium carbonate, ammonium nitrate, sodium chloride, sodium sulphate, sulfuric acid, nitric acid and hydrochloric acid, and compounds containing complexing ligands such as citrate, ethylenediaminetetraacetic and isobutyric ions alone or in a mixture of a total concentration of 10 ^-3 M to a saturated solution. 2. The method of claim 1, wherein an aqueous solution of isotopic components such as ²³⁵ U (VI) and ²³⁸ U (VI) and a ligand such as nitrate, sulfate and carbonate ions are used at a total concentration of 0.01 M to 0.1 M. 3. The process of claim 1 wherein the separated isotopes, such as ²³⁵ U and ²³⁸ U, are in the starting mixture in a molar ratio of 1: 500 to 1: 100. 4. A process according to claim 1, wherein solid sorbents based on the lower fungus of the P. chrysogenum strain or strongly acidic cation exchangers based on styrene-divinylbenzene copolymer are used. 5. The method of claim 1, wherein the contact time of the phases is selected in the range of 100 s to 167 min. . 6. The method according to claim 1, characterized in that it is operated in the dark or in light with a wavelength of 250 to 650 nm. 7. A method according to claim 1, wherein the agitator speed is operated in the range of 0.80 to 12.0 s ^-1 , with a column flow rate in the range of 10 ^-3 to 10 ^-1 m / s and fixed. a sorbent having a particle size in the range of 0.1 to 1 millimeter. 8. The process of claim 1 wherein the temperature is between about 0 ° C and about 100 ° C. 9. The process of claim 1 wherein the desorption is a sodium chloride / sodium carbonate solution or a hydrochloric acid solution having a concentration of 0.1 to