RU2753033C1 - Method for separating isotopes of lanthanides and thorium using gas centrifuge method - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention can be used in obtaining highly enriched isotopes of lanthanides or thorium. The method for separating isotopes of lanthanides and thorium by separating molecules of a gaseous metal compound by the molecular weight thereof in a field of centrifugal forces in a cascade of separating elements includes synthesising a volatile metal compound - metal tetraborohydride or metal tetramethyl borohydride. Said compound is supplied to a cascade of separating elements and a gas fraction enriched by the target isotope is isolated. A cascade of gas centrifuges is used as the cascade of separating elements. The gas fractions obtained during separation in the cascade of separating elements is processed using a chlorinating reagent. Hydrogen chloride is used as the chlorinating agent for the purpose of recycling lithium borohydride or lithium methyl borohydride used in synthesising the volatile metal compound.

EFFECT: invention allows improving efficiency of separation of isotopes of lanthanides and thorium and providing recycling of reagents used in the process.

3 cl, 2 ex

Description

The technical solution relates to technologies for the separation of isotopes of lanthanides and thorium by gas centrifugation. Isotopes of lanthanides and thorium are used in nuclear medicine, for example, ytterbium-168, lutetium-176, erbium-167, thorium-229, in nuclear technology, for example, europium-151, gadolium-157, erbium-167 and nuclear physics research, for example, erbium-162, neodymium-150 and others.

Various methods of isotopic separation of lanthanides are known from the prior art (La - lanthanum, Ce - cerium, Pr - prazedim, Nd - neodymium, Pm - promethium, Sm - samarium, Eu - europium, Gd - gadolinium, Tb - terbium, Dy - dysprosium, But - holmium, Er - erbium, Tm - thulium, Yb - ytterbium, Lu - lutetium) and thorium.

For example, the separation of isotopes of lanthanides in the liquid phase by ion exchange chromatography (US Patent 4711768 from 08.12.1987. Process for the separation of gadolinium isotopes) or chemical isotope exchange (US Patent 7318899 from 15.01.2008. Method of separating isotopes). The disadvantage of these methods is a low isotope separation factor (separation factor α = 1.001-1.005), which leads to high energy and capital costs for the separation process. In addition, it is technically extremely difficult to ensure the multiplication of the separation effect achieved in a single stage, which is necessary to obtain an isotope with high enrichment. Therefore, these physicochemical methods are not used in industrial practice.

A wider group of methods for the separation of isotopes of lanthanides and thorium is based on technologies for the separation of isotopes in the gas or vapor phase by molecular kinetic, laser and electromagnetic methods.

For example, the method of electromagnetic separation (Isotopes. Properties, production, application. Volume 1, ed. Baranov V.Yu. M .: Fizmatlit, 2005, p. 290-338), based on the ionization of atoms of the separated element by an electron beam with subsequent splitting into the electromagnetic field of the initial beam into a number of beams depending on the molecular weight of the ion, that is, depending on the molecular weight of the corresponding isotope of the element. At the outlet of the installation, these beams are selectively deposited or captured. The disadvantage of this method is the relatively small number of elements with which electromagnetic separation units can operate, the permissible density of the ion beam in a vacuum is limited, the amount of isotopes obtained is hundreds of milligrams - grams per year even in the largest separation plants. This determines the extremely high cost of the obtained isotopes, which often makes their use economically unfeasible.

A similar order of complexity occurs in the case of using the AVLIS method - “laser selective photoionization of atomic vapors” and the ion-cyclotron resonance ICR method.

The use of the AVLIS method has been described for the separation of isotopes of neodymium (I.S. Grigoriev, A.B. Diachkov, S.K. Kovalevich, et al "AVLIS of neodymium", Proc. SPIE Vol. 5121, p. 406-410, 2003). In this method, a flux of evaporated atoms passes through the region of laser radiation, where selective photoionization of atoms occurs. Photo ions of the required isotope (Nd-150) are drawn by the electric field to the product collector, while the atoms of other isotopes, remaining neutral, continue their path in a straight line to the waste collector. Difficulties in the implementation of the process are associated with the high evaporation temperature of the metal (3341 K for neodymium) and the need to use simultaneously intense radiation in the infrared and ultraviolet regions for photoionization.

Application of the ICR method is described for the separation of gadolinium isotopes (US Patent 5422481 dated 06.06.1995. Device for isotope separation by on cyclotron resonance). The essence of the method consists in selective heating of resonant ions of a multi-isotopic plasma obtained in a plasma source and transported in a uniform magnetic field, followed by the separation of hot and cold ions. To implement the method, the following operations are carried out sequentially: evaporation and ionization of element vapors, creation of a flow of calm plasma with magnetized ions in a sufficiently extended uniform magnetic field; selective acceleration of ions of the released isotope, separation and collection of accelerated ions. In sum, all this requires high energy costs for separation.

Thus, the disadvantages of the methods using atomic vapors - AVLIS and ICR are high energy costs for separation and specific technical difficulties associated with the high temperature of evaporation of lanthanides and thorium. This makes production by these methods economically ineffective, as established by the example of uranium isotope separation (AVLIS Production Plant Project Schedule and Milestones. APP-030. 11/15/1984. Lawrence Livermore National Laboratory).

Molecular kinetic methods of isotope separation, such as gas centrifugation and separation in an aerodynamic nozzle, are more productive and efficient, ultimately based on the separation of molecules with different isotopic compositions in the field of centrifugal forces due to the difference in molecular weights of molecules. A limitation in the use of these methods is the presence of a stable gaseous compound of the corresponding element. Lanthanides and thorium in their chemical compounds have a predominantly ionic nature of the bond, therefore their compounds, including complex and organometallic ones, are distinguished by low vapor pressure in the temperature range of 20 ° -100 ° C that is technically acceptable for these methods (Drozdov A., Kuzmina N. Volatile compounds of lanthanides. Comprehensive Inorganic Chemistry. II. Elsevier, 2012. p. 511-534; Suglobov D.N., Sidorenko G.V., Legin E.K. Volatile organic and complex compounds of f-elements. Energoatomizdat, 1987.208 p.).

For example, for the separation of neodymium isotopes, a method is proposed using gas centrifuges, in which modified neodymium beta-diketonates are used as gaseous neodymium compounds (RU 2638858 from 05.10.2015. Method for producing neodymium isotopes). The disadvantage of this method is the need to maintain a high temperature (more than 80 ° -100 ° C) throughout the production complex, the complexity of the synthesis of the initial gaseous neodymium compounds and a very high molecular weight of the resulting compounds (more than 1000 AU). The latter requires the development of special gas centrifuges to handle compounds of a similar molecular weight.

The borohydride compounds of lanthanides and thorium have a significantly lower molecular weight and higher volatility; erbium using volatile Gd and Er species using an aerodynamic process).

This method, which is the closest to the claimed one and was chosen by us as a prototype, is based on the separation of molecules with different molecular weights in the field of centrifugal forces arising in a gas flow in an aerodynamic nozzle of a special design, and by its physical principle is similar to the separation of molecules in a gas centrifuge , where the field of centrifugal forces is realized due to the rotation of the rotor. The method includes the interaction of a metal chloride MCl _n , where M is lanthanide or thorium, n = 3 for lanthanides or n = 4 for thorium with lithium borohydride LiBH ₄ or lithium methyl borohydride Li (CH ₃ ) H ₃ to obtain the corresponding volatile borohydride M ( ВН ₄ ) _n or metal methyl borohydride М [В (СН ₃ ) Н ₃ ] _n , supply of the obtained gaseous compound with the carrier gas flow to the aerodynamic nozzle, selection of fractions enriched in heavy and light isotopes at the outlet of the nozzle, separation of gaseous compounds from gas carrier and their conversion into the chemical form of chlorides during the treatment of compounds with molecular chlorine:

For the recycling of lithium borohydride, an expensive and scarce reagent, the preparation of diborane В ₂ Н ₆ by the interaction of boron chloride with hydrogen is used:

with the subsequent interaction of diborane with lithium hydride:

Recycling of lithium methyl borohydride is carried out in a similar manner.

The main disadvantage of the method, according to the prototype, is the use of an aerodynamic nozzle, which requires the use of large volumes of carrier gas and is not mastered in industrial practice, as a separating element that separates molecules with different masses in the field of centrifugal forces. In addition, it is extremely difficult to construct a cascade of aerodynamic nozzles (cascading) to achieve a high degree of isotope enrichment. In the chemical part of the process, a disadvantage is the proposed method for recycling lithium borohydride, based on the treatment of metal borohydride or metal methylborohydride with molecular chlorine. As a result of this reaction, boron trichloride is formed, which is technically extremely difficult to convert into diborane.

The task of the technical solution is to create a process for obtaining isotopes of lanthanides and thorium using standard high-performance separation equipment - gas centrifuges - with the achievement of the possibility of efficient recycling of expensive reagents used in the process - lithium borohydride and lithium methyl borohydride.

The technical result of the above problem is achieved by creating a method for producing isotopes of lanthanides and thorium by separating molecules of a gaseous metal compound in the field of centrifugal forces, including the synthesis of a volatile metal compound - metal tetrabohydride or metal tetra-methylborohydride from metal chloride and borohydride or lithium methyl borohydride, supplying said compound metal into the cascade of separating elements, the separation of a gas fraction enriched in the target isotope at the outlet of the cascade of separation elements, the treatment of the obtained gas fractions with a chlorinating reagent and the recycle of lithium borohydride or methyl borohydride, forces, gas centrifuges are used, and hydrogen chloride is used as a chlorinating reagent when recycling lithium borohydride or methyl lithium borohydride.

The specified technical result provides the production of isotopes of lanthanides and thorium on standard separation equipment - gas centrifuges designed to work with gaseous compounds of average molecular weight (no more than 350 a.u.), and recycle reagents according to a technically and economically efficient scheme.

The method of separating isotopes of lanthanides and thorium using the method of gas centrifuges consists in using volatile borohydride M (BH ₄ ) _n and methyl borohydride M [(CH ₃ ) ₃ H ₃ ] ₄ compounds, similar to the prototype. The compounds are prepared by reacting the corresponding metal chlorides MCl _n with lithium borohydride LiBH ₄ or lithium methyl borohydride Li [(CH ₃ ) BH ₄ :

where M is lanthanide or thorium at n = 3, if M is lanthanide and n = 4, if M is thorium.

The resulting gaseous compounds are fed into the separating elements, which ensure the separation of the molecules of the gaseous compound in the field of centrifugal forces by their mass. At the outlet of the separating element, or cascade of separating elements, fraction No. 1 of gas with molecules of higher molecular weight, containing heavy isotopes of element M, and fraction No. 2 of gas with molecules of lower molecular weight, containing light isotopes of the element are obtained. According to the prototype, an aerodynamic nozzle is used as separating elements ensuring the separation of gas molecules by their molecular weight in the field of centrifugal forces, and gas M (VN ₄ ) _n or M [(CH ₃ ) VN ₄ ] _n is fed into the separating elements in a gas flow - carrier: hydrogen or helium. According to the claimed technical solution, gas centrifuges of standard design are used as separating elements, which increases the efficiency and economy of the separation process. In addition, the use of gas centrifuges as separating elements simplifies the implementation of a scheme with a large number of separating elements (cascade) required to obtain a highly enriched product.

Gas fractions No. 1 and No. 2, obtained at the outlet of the separating elements, are treated with a chlorinating agent, which is used in the claimed technical solution as hydrogen chloride, in contrast to the use of chlorine according to the prototype equation 1.

According to the stated solution:

In accordance with the above equations (6) and (7), when processing gas fractions with a chlorinating reagent - hydrogen chloride, diborane В ₂ Н ₆ or, respectively, dimethyl diborane [(CH ₃ ) BH ₂ ] ₂ are obtained.

The obtained reagents - diborane B ₂ H ₆ or dimethyl diborane [(CH ₃ ) BH ₂ ] ₂ treat lithium hydride to synthesize a new portion of lithium borohydride or lithium methyl borohydride according to equations (8) and (9):

This allows expensive lithium borohydride or lithium methyl borohydride to be recycled. The synthesis according to equations (8), (9) is carried out according to the described method [Review: Comparison of the LiBH ₄ Material Synthesis Method and its Application as Hydrogen Energy Storage J. Appl. Sci. Envir. Stud. 3 (4) (2020) 232-253].

Lithium hydride is obtained similarly to the prototype according to the general scheme:

from commercially available lithium metal and hydrogen, or use a commercially available reagent.

Thus, obtaining isotopes of lanthanides and thorium in the task at hand is solved by enriching gaseous compounds of these elements in a separating element or a cascade of separating elements, which are used as gas centrifuges. The advantages of the centrifugal method are lower energy consumption, significantly higher plant productivity and the possibility of multiplying the separation effect on a single gas centrifuge by connecting individual centrifuges into a coordinated cascade of a large number of centrifuges. By choosing the length of the cascade, the ratio of the fraction collection flows, and the value of the cascade feed flow, it is possible to ensure that the lightest components of the working gas with concentrations up to 100% are obtained in the selection of the light fractions of the cascade, or in the selection of the heavy fractions of the cascade of all the heaviest components of the mixture with concentrations arbitrarily close to 100%. In the first case, enriched light isotopes of lanthanides and thorium will be obtained, in the second, the heaviest isotopes of these metals. When enriching isotopes of these elements with intermediate masses, it is necessary to carry out at least two cycles of processing the working gas in the separation unit, in the first of which the operating mode of the cascade is adjusted so that the enriched intermediate isotope becomes either the lightest (in the selection of heavy fractions cascade), or the heaviest (in the selection of light fractions) of the isotopes. In the second cycle, the working gas obtained in the selection of separated fractions of the cascade in which this target isotope is extremely heavy or extremely light is enriched in the target isotope.

Gaseous compounds of lanthanides and thorium used in the process according to the claimed solution are obtained similarly to the prototype according to the general scheme described by equations 4 and 5. The recycle of expensive reagents - lithium borohydride LiBH ₄ and lithium methyl borohydride Li [(CH ₃ ) BH ₂ ] is carried out according to the scheme, described by the equations of reactions 6, 7 and 8, 9, in contrast to the more complex and multistage scheme according to the prototype: the equations of reactions 1, 2 and 3. Chemical processing according to the claimed solution with the recycle of expensive reagents (equations of reactions 6, 7 and 8, 9) is carried out in accordance with the methods described in the literature, providing a high yield and safety of the process (AF Zhigach, DS Stasinevich. Chemistry of hydrides, M., Chemistry, 1969, 676 S.). The disadvantages of the prototype solution in terms of recycling expensive reagents is the need to obtain diborane or methylborane by the reaction described by equation 2, boron trichloride with hydrogen at high pressure. This process is technically extremely difficult to implement (AF Zhigach, DS Stasinevich. Chemistry of hydrides, Moscow, Chemistry, 1969, 676 p.).

The essence of the proposed method for producing isotopes of lanthanides and thorium is illustrated by the following examples.

Example 1. Obtaining the isotope ytterbium-168.

_{Ytterbium tris-methylborohydride Yb [B (CH 3} ) H ₃ ] _{3 was} used as a working gas for the separation of ytterbium isotopes; MD Taylor, CP Carter. Preparation of anhydrous lanthanide halides, especially iodides. J. Inorg. Nycl. Chem. 1962, 24, pp. 387-391). The starting lithium methyl borohydride was obtained by the reaction of trimethylboroxin (50% solution in THF) with LiAlH ₄ in diethyl ether (B. Singaram et al., Addition compounds of alkali-metal hydrides. Organometallics, 1984, 3 (5), p. 774 -777):

The reaction was carried out as follows. In a 2 L reaction vessel filled with argon, 500 ml of diethyl ether was mixed with 35 g (0.9 mol) of lithium aluminum hydride LiAlH ₄ and refluxed under argon for 3 hours until complete dissolution of lithium aluminum hydride. To the resulting solution was added with stirring and cooling to 0 ° C 41 ml (0.293 mol) of trimethyl boroxin in the form of a 50% solution in tetrahydrofuran. The resulting mixture was stirred at room temperature for 2 hours, the solution was separated by centrifugation, the precipitate was washed with 200 ml of ether, the solutions were combined. The resulting solution of lithium methylborohydride Li [CH ₃ BH ₃ ] was used to prepare the ytterbium complex:

To anhydrous ytterbium (III) chloride (80 g, 0.29 mol) was added a solution of lithium methyl borohydride prepared as described above. The reaction mixture was stirred for 6 hours at room temperature under argon atmosphere. The solvent was removed under reduced pressure and the residue was sublimated at 50-60 ° C in vacuum (0.05 mm Hg) into a receiving metal ampoule cooled to 0 ° C. The resulting product - 73 g (0.28 mol) was obtained in the form of colorless prismatic crystals with a vapor pressure of 0.4 mm Hg. at 80 ° C, 1.9 mm Hg at 100 ° C and 8 mm Hg at 120 ° C.

The working gas - tris-methyl borohydride of ytterbium Yb [CH ₃ BH ₃ ] ₃ , containing isotopes of ytterbium with a natural content (ytterbium-176-12.3%), is fed to the separation stage and the operating mode of the cascade is adjusted, which, when the feed stream is divided into two fractions provides in the selection of the heavy fraction of the cascade the selection of the maximum amount of working gas components with molecular weights of more than 261 with a minimum content of components with molecular weights of 260 or less. Based on the concentration of molecular masses in the initial working gas, the proportion of selection into the heavy fraction of the cascade should be about 7% of the feed flow. With the selection of only heavy components of the working gas with masses of 262 and more, the concentration of the Yb-176 isotope in the target selection of the heavy fraction of the cascade will be more than 99.5%. From 73 g of working gas with the initial natural content of isotopes, 5 g of ytterbium tris-methylborohydride with a ytterbium-176 content of 99.5% can be obtained. As a waste product - a light fraction - 68 g of ytterbium tris-methylborohydride with a reduced, relative to natural, ytterbium-176 content will be obtained.

For the recycling of lithium methyl borohydride, the light and heavy fractions of the working gas obtained during separation in a cascade of gas centrifuges are treated with an equimolar amount of anhydrous hydrogen chloride in a quartz glass apparatus:

Ytterbium trichloride-176 obtained by treating the heavy fraction according to reaction (13) is the final product of enrichment and, if necessary, can be converted into the chemical form of oxide Yb ₂ O ₃ by treating ytterbium chloride with water, followed by calcination at a high temperature. Ytterbium trichloride formed during the treatment with hydrogen chloride of the light fraction is a waste product. Methyl borohydride [CH ₃ BH ₃ ] ₂ , obtained by processing the heavy and light fractions of the working gas, is purified from impurities of excess hydrogen chloride by passing through an adsorption column with metallic calcium and sent to the synthesis of lithium methyl borohydride according to equation (9) in accordance with the described procedure ( AF Zhigach, DS Stasinevich. Chemistry of hydrides, M., Chemistry, 1969, 676 p.). Lithium methyl borohydride Li [CH ₃ BH ₃ ], obtained as a result of recycle, is used in the synthesis of a new batch of working gas - tris-methyl borohydride of yttrium according to equation (5). Example 2. Obtaining the isotope thorium-229.

The isotope thorium-229 is the parent nuclide for the generation of actinium-225, an extremely expensive medical radionuclide (A. Morgenstern et al., An Overview of Targeted Alpha Therapy with 225-Actinium and 213-Bismuth. Current Radiopharmaceuticals, 2018, 11, 200-208 ). Thorium-229 is absent in nature, and it is obtained artificially, for example, by irradiation in a radium-226 reactor (S. Hogle et al., Reactor production of Thorium-229. Applied Radiation and Isotopes, 114, 2016, p. 19-27). In this case, thorium-228 is formed as an impurity, which limits the possibilities of using the obtained thorium-229 for the generation of medical grade actinium-225. Therefore, the task is to purify thorium-229 from impurities of thorium-228, and this task can only be solved by isotope separation methods.

The starting material, thorium-229 with an admixture of thorium-228, was obtained by radiochemical processing of radium-226 irradiated with neutrons. Irradiated 80 g of radium-226 for 80 days with a thermal neutron flux of 1⋅10 ¹⁵ n / (s⋅cm ² ). After radiochemical processing of the irradiated material and subsequent "cooling" for the decay of the short-lived isotope thorium-227 (thorium-227, half-life 18.7 days) within 6 months, the material containing the following amount of radionuclides was obtained:

Thorium-228 - 8 g, or ~ 6000 Ci;

Thorium-229 - 2.7 g, or ~ 0.6 Ci;

Thorium-230 - 1 g, or ~ 0.01.

The task set - to obtain thorium-229 with a minimum of impurities of highly radioactive isotopes by purifying the material from highly active thorium-228 - is solved as follows.

For the separation of thorium isotopes, thorium tetra-methylborohydride Th [CH ₃ BH ₃ ] ₄ is used as a working gas. It is obtained through the sequential operations described below.

To exclude the radiolysis of chemical products in the process of isotopic separation, 55 g of natural, weakly radioactive thorium-232 was added to the material containing the radioactive isotopes thorium-228, thorium-229 and thorium-230. The material containing as a result: thorium-228 - 8 g, thorium-229 - 2.7 g, thorium-230 - 1 g and thorium-232 - 55 g, total - 66.7 g in the form of thorium dioxide is chlorinated to obtain tetrachloride thorium ThCl ₄ according to the procedure described in the literature (Klyuchnikov N.G. Guide to inorganic synthesis - M .: Chemistry, 1965. - 392 p.):

To obtain lithium methylborohydride by reaction (11), trimethylboroxin is used, enriched in the boron-11 isotope to a level of 99.9%:

The synthesis of lithium methyl borohydride Li [ ¹¹ BH ₃ CH ₃ ] is carried out according to the literature method (B. Singaram et al., Addition compounds of alkali-metal hydrides. Organometallics, 1984, 3 (5), p. 774-777): described above in example 1.

Thorium tetrachloride obtained by reaction (14) in an amount of 107 g (0.288 mol) is treated with lithium methyl borohydride Li [ ¹¹ BH ₃ CH ₃ ] in chlorobenzene as a solvent in accordance with the described procedure (R. Shinomoto et al., Syntheses and crystal structures of the tetrakis (methyltrihydroborato) compounds of zirconium (IV), thorium (IV), uranium (IV), and neptunium (IV). Inorg. Chem. 1983, 22, 17, 2351-2355):

The resulting solution of thorium tetrakis-methylborohydride Th [CH ₃ ¹¹ BH ₃ ] _{4 is} separated from the precipitate of lithium chloride LiCl, evaporated in vacuum at room temperature and the resulting product in the form of yellow-green crystals is sublimated into a receiving container cooled to -70 ° C with dry ice ... It turns out 99.5 g of a product with a vapor pressure of ~ 0.35 mm Hg at 40 ° C; ~ 7 mm Hg at 80 ° C.

The working gas - thorium tetrakis-methylborohydride Th [CH ₃ ¹¹ BH ₃ ] ₄ , containing the isotopes of thorium thorium-228, thorium-229, thorium-230 and thorium-232, is fed to the separation cascade. In this case, the operating mode of the cascade is adjusted in such a way that when the feed stream is divided into two fractions in the selection of the light fraction, the maximum number of components of the working gas with molecular weights of 344 ( ²²⁸ Th (CH ₃ ¹¹ BH ₃ ) _{4 is the} molecular weight of 344) is directed, and in the selection of the heavy fraction is directed to the components of the working gas with molecular weights 345 ( ²²⁹ Th (CH ₃ ¹¹ BH ₃ ) ₄ - molecular weight 345) and more: 346 ( ²³⁰ Th (CH ₃ ¹¹ BH ₃ ) _{4 -} molecular weight 346), 348 ( ²³² Th (CH ₃ ¹¹ BH ₃ ) _{4 -} molecular weight 348) with a minimum content of components with molecular weights 344 ( ²²⁸ Th (CH ₃ ¹¹ BH ₃ ) _{4 -} molecular weight 344). Based on the concentration of molecular weights in the starting working gas, the proportion of selection into the light fraction of the cascade should be about 12 g, or 12% of the feed flow. From 99.5 g of working gas containing thorium isotopes: thorium-228 -8 g; thorium-229 - 2.7 g; thorium-230 - 1 g; thorium-232 - 55 g, 87.5 g of thorium tetrakismethylborohydride can be obtained with a residual thorium-228 content of less than 0.001 g, or 0.75 Ci. When converting a heavy fraction of a gas, thorium-229 of the following radionuclide composition can be obtained:

Thorium-228 - less than 0.01 g or 0.7 Ci;

Thorium-229 - 2.6 g or 0.57 Ci;

Thorium-230 - 1 g or 0.01 Ci;

Thorium-232 - 55 g or less 0.000001 Ci.

Thus, according to the claimed solution, the production of thorium-229, purified from the harmful impurity of thorium-228, by a factor of 8500 can be achieved. The activity of thorium-228 in the resulting preparation of thorium-229 is relatively insignificant, which makes it possible to use thorium-229 for the generation of actinium-225.

The recycle of an expensive reagent - lithium methyl borohydride Li [CH ₃ ¹¹ BH ₃ ] is carried out in accordance with the procedures described in example 1 according to the following reactions:

Lithium methyl borohydride containing enriched B-11 is recycled to synthesize a new batch of working gas.

The obtained isotopically purified thorium-229 during chemical conversion was converted into the chemical form of chloride - equation 17, and after dissolution in water can be used to generate actinium-225 according to known methods (LI Guseva. Production of High-Purity a-Emitting 225-Ac and 213-Bi Radionuclides for Use in Nuclear Medicine. Radiochemistry, 2013, Vol. 55, No. 3, pp. 317-323).

The technical result of the application of the proposed technology is the production of isotopes of lanthanides and thorium using a highly efficient method of gas centrifugation. The proposed technology ensures the recycling of expensive reagents according to technically easy to implement methods.

Claims (3)

1. A method of separating isotopes of lanthanides and thorium by separating molecules of a gaseous metal compound according to their molecular weight in the field of centrifugal forces in a cascade of separating elements, including the synthesis of a volatile metal compound - metal tetrabohydride or metal tetramethylborohydride, feeding said metal compound into a cascade of separating elements and isolating a fraction gas enriched in the target isotope in accordance with the molecular weight of the gas molecules with the target isotope, at the outlet of a cascade of separating elements, characterized in that a cascade of gas centrifuges is used as a cascade of separating elements that separate molecules in the field of centrifugal forces by their molecular weight, and the processing of gas fractions obtained during separation in a cascade of separating elements is carried out with a chlorinating reagent. 2. A method according to claim 1, characterized in that hydrogen chloride is used as a chlorinating agent for the recycling of lithium borohydride or lithium methylborohydride used in the synthesis of a volatile metal compound. 3. The method according to claim 2, characterized in that when recycling lithium borohydride or lithium methyl borohydride using hydrogen chloride as a chlorinating reagent, diborane or, respectively, methylborane is obtained when processing gas fractions with hydrogen chloride, which is used to synthesize lithium borohydride or lithium methyl borohydride its interaction with lithium hydride.