RU2351388C2 - Method of producing highly enriched iridium isotopes - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention aims at nuclear engineering. Highly enriched iridium isotopes are produced by centrifugation process with using separating stages of gas centrifuges on dividing cascades of gas centrifuges with iridium tetra(trifluorophosphine)hydride as a working medium.

EFFECT: ¹⁹¹Ir isotopes of concentration exceeding 99,9% are produced.

1 tbl, 1 dwg

Description

The invention relates to the separation of isotopes of elements and can be used to obtain highly enriched iridium isotopes.

Iridium, an element of the eighth group of D. I. Mendeleev’s table, has two stable isotopes with molecular weights of 191 amu and 193 amu, the concentrations in natural iridium of these isotopes are 37.3% and 62.7%, respectively. The iridium-191 isotope is of interest for physical research.

It is known to use for the enrichment of isotopes of two-phase physicochemical separation methods in column type apparatuses - isotope exchange, cryogenic distillation.

This class of isotope separation methods is based on the difference for different isotopes of a shared element of the characteristics of physicochemical processes for compounds containing shared elements [1]. These methods require the search not only for appropriate chemical compounds, but primarily for suitable chemical reactions or physical processes. As a rule, this is possible only for the case of separation of light elements — hydrogen, nitrogen, oxygen, carbon, boron, etc., and the separation effect of the process is rather weakly associated with the molecular masses of the element isotopes. In addition, the use of column-type devices is associated with the requirement to participate in the process of a large amount of substance and is effective only with a large installation capacity.

Also known [2] and the method of electromagnetic separation is widely used to obtain stable isotopes of various elements. In this method, the atoms of an element separated into isotopes are ionized by an electron beam and in an electrostatic field, then the ionized beam enters the separation unit. In the installation, in a plane perpendicular to the plane of motion of the ion beam, a transverse electromagnetic field is created. When a charged particle moves in such a field, perpendicular to the direction of its flight, a force proportional to μ / e is applied to it, where μ is the molecular mass of the ion with charge e. Therefore, the physical effect of the spatial separation of ions of an element with different molecular masses and, accordingly, splitting in the electromagnetic field of the initial beam to 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 output of the installation, these beams are selectively deposited or captured. This method is the most universal and fundamentally unsuitable only for the separation of inert gas isotopes in connection with the problem of the selective capture of the separated fractions. However, due to the relatively small amounts of the element with which the electromagnetic separation units can work, the permissible density of the ion beam in vacuum is limited, the resulting quantities of milligram isotopes, hundreds of milligrams.

An object of the invention is to obtain highly enriched, more than 99%, isotopes of iridium-191, 193.

The technical solution to the problem is to use the centrifugation method to separate iridium isotopes, and the fluorine-containing compound of iridium - tetra (trifluorophosphine) iridium hydride, (PF ₃ ) ₄ IrH is used as a working substance.

The centrifugal isotope separation method compared with the isotope separation method considered above in column type apparatus has significant advantages in enrichment coefficient, which depends only on the difference in molecular weights of isotopes, in the amount of the starting substance, which should participate in the separation process and is more universal, since it requires only the presence of a suitable gaseous compound to be shared element. Compared to the electromagnetic separation method, the advantages of the centrifugal method in energy intensity are significantly greater than the capacity of the plants and in the possibility of multiplying the separation effect in a single gas centrifuge. The main problem for the possibility of using the centrifugal method is the presence of a gaseous compound of the element that satisfies a number of conditions for the molecular weight of the compound, for the elasticity of saturated steam at room temperature, the level of thermal stability, the level of permissible chemical activity with respect to the materials of the centrifugal separation unit, the possibility of developing a separation technology process, etc.

Obtaining high concentrations of the iridium isotope in the problem is solved by enriching the gaseous compound of iridium in a gas centrifuge. As a compound of iridium, satisfying the conditions of thermal and chemical stability, having a gas pressure of more than 5-10 mm Hg at room temperature, (PF ₃ ) ₄ IrH - tetra (trifluorophosphine) iridium hydride synthesized from elements Ir, P, F, H with a natural isotopic composition can be used. The elements P and F included in the compound have one isotope, hydrogen has two isotopes, iridium has two isotopes, therefore tetra (trifluorophosphine) iridium hydride has 4 components with molecular weights from 544 to 547. In addition, each of the iridium isotopes is distributed in several components of the compound with different masses, but only the iridium-191 isotope is included in the component with a molecular mass of 544, so when this component is isolated, it is possible to obtain its concentration up to 100%.

The principle of operation of a gas centrifuge is to separate the gas mixture in a centrifugal field of a rapidly rotating rotor and to multiply this effect by the height of the rotor. In this case, the separation effect, as in the case of electromagnetic separation, is determined by the difference in molecular masses µ of the components of the mixture being separated. Specially designed gas centrifuges are used to separate stable isotopes.

Multiplication of the separation effect is achieved by cascading - the serial connection of gas centrifuges (drawing). The length of the cascade - the number of steps is determined by the required degree of concentration of isotopes. The width of the cascade - the number of centrifuges in the steps determines the amount of isotope produced.

A method of obtaining enriched isotopes of iridium is as follows.

The working gas synthesized from iridium of the natural isotope composition — tetra (trifluorophosphine) iridium hydride, (PF ₃ ) ₄ IrH, is fed into the gas centrifuge cascade to step S. The fraction enriched in light components (PF ₃ ) ₄ IrH is taken from step K, the magnitude of the flow of selection - Wl. The selection of the fraction enriched in heavy components (PF ₃ ) ₄ IrH is carried out from step 1, the magnitude of the selection flow is Wt.

By choosing the cascade length, the ratio of the selection flow fractions Wn / Wr and the cascade supply flux F = Wl + Wt, it is possible to obtain the lightest component (PF ₃ ) ₄ IrH with a molecular weight of 544 with a concentration of up to 100%. This component of the gas mixture contains only isotopes: iridium-191, fluorine-19, phosphorus-31 and hydrogen-1. Therefore, the concentration of the iridium-191 isotope after chemical processing of the obtained selection of the light fraction of the (PF ₃ ) ₄ IrH cascade into the commodity form for storage and delivery of the iridium-191 isotope will be equal to the concentration of the component with a molecular weight of 544 in the selection of the W cascade.

The table shows the mass distribution of molecules of tetra (trifluorophosphine) iridium hydride molecules of natural composition and the distribution of iridium isotopes ¹⁹¹ Ir, ¹⁹³ Ir by mass components.

Table The distribution of tetra (trifluorophosphine) iridium hydride molecules of the natural composition of isotopes by mass components and the distribution of ¹⁹¹ Ir, ¹⁹³ Ir isotopes by mass components. Molecular mass The distribution of molecules of tetra (trifluorophosphine) iridium hydride of natural composition by mass components The distribution of the ¹⁹¹ Ir isotope in the corresponding component The distribution of the ¹⁹³ Ir isotope in the corresponding component but. eat. % 544 37.29 100.00 0.00 545 5.59 · 10 ^-3 100.00 0.00 546 62.69 0.00 100.00 547 9.4110 ^-3 0.00 100.00

A method of obtaining a highly enriched isotope of iridium-191 is as follows.

Of the compounds of iridium, hydrogen, fluorine and phosphorus with a natural concentration of isotopes, a working substance is synthesized - tetra (trifluorophosphine) iridium hydride.

Iridium tetra (trifluorophosphine) hydride, (PF ₃ ) ₄ IrH, is synthesized by heating an iridium halide salt (iridium trichloride or tribromide) with trifluorophosphine in the presence of a reducing agent (copper or silver) and hydrogen [3]. The substance is thermally stable, does not decompose in air, is explosion-proof and does not have a corrosive effect on structural materials.

The gas is fed into the cascade of gas centrifuges, the cascade operation mode is adjusted, and the source gas (PF ₃ ) ₄ IrH is divided into two fractions - the “light” fraction, which contains mainly the component with molecular weight 544 and traces of the component with molecular weight 545, and “heavy” fraction in which the component with a molecular weight of 544 is practically absent.

The technical result of the application of the proposed technology was the production of ¹⁹¹ Ir isotopes with a concentration of more than 99.9%.

Literature

1. Isotopes: properties, production, application. Ed. V.Yu. Baranova M .: Publisher, 2000, p. 167.

2. Isotopes: properties, production, application. Ed. V.Yu. Baranova M .: Publishing house, 2000, p. 220.

3. T. Kruck, Angewandte Chemie Int.Ed.Engl., 6, 53, 1967.

Claims (1)

A method of producing highly enriched iridium isotopes, in which the separation effect is determined by the molecular weight difference of the iridium isotopes, characterized in that the centrifugation method is used to separate the iridium isotopes, and iridium tetra (trifluorophosphine) iridium is used as the iridium-containing gaseous compound.