RU2397145C1 - Method of producing uranium tetrafluoride - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention can be used to produce nuclear fuel. Uranium metal is dissolved in a solvent containing hydrochloric acid with concentration of 50-200 g/dm³, and fluoride compounds of uranium (IV) with uranium concentration of 30-300 g/dm³ and molar ratio of uranium to fluorine equal to 1:(1.6-4.0). During the entire process of dissolving uranium metal, the said concentration of hydrochloric acid is kept on a constant level through its further addition. A hydrate of uranium tetrafluoride is precipitated from the obtained hydrofluoric acid solution. The pulp is washed with water, filtered, dried and the uranium tetrafluoride residue is roasted. The fluoride compounds of uranium can be obtained by heating uranium dioxide, uranium tetrafluoride or fluoride and chloride salts of uranium separately or together in the presence of hydrofluoric and hydrochloric acid.

EFFECT: method enables complete dissolution of metal, pike-like formation of hydrogen, reduces loss of material, chemical consumption and increases safety of the process.

2 cl, 1 tbl, 3 ex

Description

The invention relates to the production of uranium tetrafluoride (UF ₄ ) used as a material for the production of nuclear fuel, and relates to methods for its production from metallic uranium.

Known methods for producing uranium tetrafluoride from metal raw materials are based on the dissolution of uranium, for example, in hydrochloric acid (HCl) in the presence of fluorine-containing acid (J. Katz, E. Rabinovich. Uranium Chemistry. Foreign Literature Publishing House. M., 1954, p. 144) , it is better in the presence of hydrofluoric acid (HF) (N.P. Galkin et al. Chemistry and technology of uranium fluoride compounds. Gosatomizdat. M., 1961, p.66) with the formation of a fluoride-chloride complex salt of uranium and subsequent precipitation with the addition of hydrofluoric acids (B.V. Gromov. In ction in chemical technology of uranium. Atomizdat. M., 1978, s.250-252).

As a development of these methods, a method for producing uranium tetrafluoride is known, including dissolving uranium metal in a solvent - an aqueous solution of hydrochloric acid, heating, precipitating uranium tetrafluoride hydrate from a solution, drying and calcining (US Pat. No. 5,017,345 A, C01G 43/06, 1991).

However, this method, which is presented by examples of only laboratory experiments, when used on an industrial scale, produces finely dispersed uranium tetrafluoride, moreover, with significant losses of uranium due to the formation of by-products of hydrolysis, oxidation, complexation and polymerization, as well as due to the need for processing significant volumes of uterine solutions.

The preparation of finely dispersed tetrafluoride (weighted average size less than 20 μm) leads to a sharp deterioration in filtration, obtaining an irrigated product, which, during the subsequent drying – calcination process, pellets, forms aggregates and, as a result, is rejected by the granulometric composition and the sum of mass fractions of uranyl fluoride and uranium dioxide.

In addition, the use of this method leads to a significant consumption of hydrofluoric and hydrochloric acids.

A significant disadvantage of this method is the fact that when using HF to dissolve metallic uranium, there is a strong overheating of the reaction mass and a peak-like (volley) hydrogen evolution. This reduces the safety of the process.

Uranium tetrafluoride from aqueous media is released in the form of crystalline hydrates of variable composition depending on the conditions of the dissolution and precipitation processes.

The objective of the invention is to obtain high-quality uranium tetrafluoride while reducing raw material losses, reducing the consumption of chemicals and increasing the safety of processes due to the complete dissolution of the metal and elimination of peak formation of hydrogen.

The technical result is achieved in that in the proposed method, comprising dissolving uranium metal in a solvent containing hydrochloric acid, heating, precipitating uranium tetrafluoride hydrate from a solution, drying and calcining the filtered precipitate, the solvent contains hydrochloric acid with a concentration of 50-200 g / dm ³ and uranium fluoride compound (IV) with the concentration of uranium in the 30-300 g / dm ³ at a molar ratio of uranium to fluorine 1: (1,6 ÷ 4,0), wherein said hydrochloric acid concentration is maintained constant st throughout uranium metal dissolution process by its additional injection.

Uranium (IV) fluoride compounds are obtained by heating uranium dioxide, uranium tetrafluoride, a fluoride-chloride complex salt of uranium individually or in combination in the presence of hydrofluoric and hydrochloric acids.

Distinctive features in the proposed method are those associated with the composition of the solvent, which contains hydrochloric acid with a concentration of 50-200 g / dm ³ and fluoride compounds of uranium (IV) with a uranium concentration of 30-300 g / dm ³ with a molar ratio of uranium to fluorine 1 : (1.6 ÷ 4.0), and the indicated concentration of hydrochloric acid is maintained throughout the entire process of dissolution of metallic uranium by its additional introduction.

Distinctive features provide complete dissolution of the metal, stabilization (reduction in dispersion) of the particle size distribution with an increase in the proportion of coarse-grained hydrate of uranium tetrafluoride, a decrease in the proportion of by-products of uranium, thereby achieving high quality uranium tetrafluoride while reducing raw material losses, and reducing the consumption of chemicals.

In addition, a high concentration of uranium in the solvent during the dissolution of metallic uranium, the absence of free HF, since all fluorine is bound to uranium (IV), and a moderate background of hydrochloric acid provide a smooth course of hydrogen evolution with a tendency to its gradual termination, which makes the process more safe and manageable.

An additional source of reducing the consumption of expensive reagents is the use of dissolving circulating and substandard products, which reduces the cost of their processing and increases recovery.

Recycled and substandard products are used as additional sources for the formation of a solvent, in particular, for fluorine, uranium (IV), hydrochloric acid.

Working products include a fluoride-chloride complex salt in the form of a solution obtained after dissolving uranium metal in the claimed solvent and partially not used for the deposition of uranium tetrafluoride. This solution contains up to 200 g / dm ³ for uranium, up to 10 g / dm ³ for fluorine, up to 80 g / dm ³ for HCl. The mother liquor also remains circulating, which remains after precipitation and filtration and contains up to 12 g / dm ³ for uranium and up to 5 g / dm ³ for fluorine mainly in the form of uranium tetrafluoride and up to 160 g / dm ³ for HCl. The use of the mother liquor is allowed in such minimally possible quantities that exclude the accumulation of impurities.

Non-standard tetrafluoride, which does not meet the technical requirements according to criteria not related to the impurity composition, for example, by size, moisture, and density of the shake, also refers to negotiable.

The proposed method is as follows.

Example 1

A 2.7 m ³ solution of fluoride-chloride complex salt of uranium, hydrochloric and hydrofluoric acid is poured into the reactor, and 3.3 m ^{3 of} solvent is obtained with a concentration of 150 g / dm ³ for uranium, 50 g / dm ³ for HCl and a molar ratio U : F = 1: 1.6. The solvent is heated to 60 ° C, 500 kg of uranium metal in the form of an ingot are loaded into it and dissolved at a temperature of 60-90 ° C. During dissolution, hydrochloric acid is additionally poured to maintain a concentration of 50 g / dm ³ . The resulting product with a volume of 3.5 m ^{3 is} sent to the precipitation of hydrate of uranium tetrafluoride hydrofluoric acid. Next, the crystal pulp is washed with water, filtered, and the precipitate is dried and calcined in furnaces to obtain marketable uranium tetrafluoride.

Example 2

1.0 m ^{3 of} mother liquor, 1.0 m ^{3 of} pulp of uranium oxide, 150 kg of substandard uranium tetrafluoride, hydrofluoric and hydrochloric acid are poured into the reactor, and 3.2 m ^{3 of} solvent are obtained with a concentration of 170 g / dm ³ in uranium, according to HCl - 200 g / dm ³ and with a molar ratio of U: F = 1: 4.0. The solvent is heated to 60 ° C, after which 500 kg of uranium metal in the form of an ingot are loaded into it and further operations are carried out as described in example 1.

Example 3

The reactor was poured 1.1 ^m3 of mother liquor, 1.7 m ³ uranium oxide slurry, hydrochloric and hydrofluoric acid to obtain 3.5 ^m3 of the solvent with the concentration of uranium 100 g / dm ^3, of HCl - 50 g / dm ³ and with a molar ratio of U: F = 1: 1.6. Further actions, as described in example 1.

Other dissolution experiments were carried out at a different ratio in the solvent of the uranium compound and acids and at different initial concentrations and molar ratio U: F, which is shown in the table.

Other combinations of uranium compounds and acids in a solvent are possible.

For comparison, the dissolution of 500 kg of metallic uranium in the form of an ingot by the prototype method was carried out.

In the course of work, after precipitation and filtration, samples were taken to determine the size of uranium tetrafluoride, the same product was subjected to drying-calcination in laboratory conditions, and the amount of by-products and particle size distribution were determined in the obtained crystalline hydrate. All test and analysis results are presented in the table.

During the tests, the hydrogen content in the ventilation system was also controlled from the operation of dissolving uranium metal. From the test results presented in the table, it follows that the highest quality uranium tetrafluoride is obtained using the claimed solvent, which contains hydrochloric acid with a concentration of 50-200 g / dm ³ and uranium fluoride compounds with a concentration of 30-300 g / dm ³ at a molar ratio uranium to fluorine 1: (1.6 ÷ 4.0), and the indicated concentration of hydrochloric acid is kept constant throughout the entire process of dissolution of metallic uranium by its additional introduction. Such results are repeated using a solvent composed of a fluoride-chloride complex salt of uranium, or from substandard uranium tetrafluoride, or from uranium oxide, or from combinations thereof (experiments No. 4-6, 13-15, 22-24). The crystals of uranium tetrafluoride obtained under these conditions are large and have a uniform structure. When using a solvent with different parameters, crystalline hydrates of various variable composition are obtained, unstable, prone to oxidation, poorly filtered and clumped during drying-calcination.

The specific cost of hydrofluoric and hydrochloric acids to obtain 1 mole of uranium tetrafluoride by the present method is lower than by the prototype method. The yield of uranium in the claimed method is higher than for the prototype.

The hydrogen content in the ventilation system from the operation of dissolving the metal uranium was stably low, ensuring the safety of the process.

Thus, the task has been solved to create a method for producing uranium tetrafluoride with higher quality characteristics, lower consumption of chemicals and a higher yield of uranium while ensuring process safety.

Claims (2)

1. A method of producing uranium tetrafluoride, comprising dissolving uranium metal in a solvent containing hydrochloric acid, heating, precipitating uranium tetrafluoride hydrate from a solution, drying and calcining a filtered precipitate, characterized in that the solvent contains hydrochloric acid with a concentration of 50-200 g / dm ³ and uranium fluoride compound (IV) with a uranium concentration of 30-300 g / dm ³ at a molar ratio of uranium and fluorine 1: (1,6 ÷ 4,0), wherein said hydrochloric acid concentration was kept constant at n otyazhenii only uranium metal dissolution process by its additional administration. 2. The method according to claim 1, characterized in that the uranium (IV) fluoride compounds are obtained by heating uranium dioxide, uranium tetrafluoride, a fluoride-chloride complex salt of uranium individually or in combination in the presence of hydrofluoric and hydrochloric acids.