RU2230032C2 - Silver and cadmium radionuclide separation method - Google Patents

Abstract

FIELD: radiochemistry. SUBSTANCE: solution of silver and cadmium radionuclide nitrates containing nitric acid in concentration 0.1-2 mole/l and hydrazonium nitrate in molar concentration equal or superior to molar concentration of silver is first provided. Silver is precipitated by contacting above solution with carbonaceous sorbent. Solid phase is separated from mother liquor and washed with 0.1-2 M nitric acid solution containing at least 0.01 M hydrazonium nitrate. EFFECT: increased completeness of silver-cadmium separation. 2 cl, 2 tbl

Description

The invention relates to the field of radiochemistry and can be used in chemical technology and analytical chemistry.

A known method of extraction separation of radionuclides of silver and cadmium [Levin V.I. Getting radioactive isotopes. - M .: Atomizdat, 1972, p.182], including the steps of obtaining a solution of separable elements in a mixture of ammonium thiocyanate and sodium acetate, cadmium extraction with a mixture of pyridine with chloroform, cadmium reextraction with a solution of nitric acid. The disadvantages of this method are the incomplete separation of the components, as well as the complexity of its implementation in remote conditions (“hot” cameras and boxes).

The known method of ion-exchange separation of silver and cadmium radionuclides [Razbash AA, Sevastyanov Yu.G., Maklachkov AG, Alekseeva LG, Radiochemistry, 1981, v. 23, No. 3, p. 422], including the operations of obtaining a solution of separable elements in a mixture of nitric and hydrofluoric acids, their sorption on the strongly acidic cation exchange resin KRS-8p, elution of cadmium with a solution of hydrofluoric acid, desorption of silver with a solution of nitric acid. The disadvantages of this method are the incomplete separation of components, as well as the use of aggressive solutions that cause corrosion of protective equipment (“hot” chambers and boxes) made of stainless steel.

The above disadvantages are eliminated in the claimed method in that for the separation of silver and cadmium radionuclides, a solution of the nitrates of the elements to be separated in a mixture of nitric acid and hydrazonium nitrate (nitric acid salt of hydrazine, N ₂ H ₅ NO ₃ ) is obtained with a concentration of reagents in the solution: nitric acid from 0, 1 to 2 mol / l; hydrazonium nitrate with a molar concentration equal to or higher than the molar concentration of silver precipitates silver by contacting the resulting solution with a carbon sorbent SKN or with one of its modifications listed below: SKNK, SKN-1M, SKN-2M, SKN-3M, SKH-4M, SKN-1k, SKN-2k, SKNo-1, SKNo-4 (the name of the sorbent SKN and its modifications is given in accordance with TU 95.834-81), the mother liquor is separated from the solid phase (mixture of sorbent and metal), the solid phase is washed with a solution, containing nitric acid with a concentration of 0.1-2 mol / l and hydrate nitrate zoniya a concentration of at least 0.01 mol / l, and the washing solution was separated.

The distribution of silver and cadmium radionuclides by the claimed method is achieved due to the transition from a silver solution to a solid phase in the process of contacting the solution with the sorbent. When the silver concentration in the solution is about 0.005 mol / L or more, the metal formed is detected visually (light-colored granules that are easily separated from the sorbent).

After separation from the solid phase, the wash solution is combined with the mother liquor. The resulting solution contains at least 99% cadmium radionuclides and not more than 1% silver (relative to their initial amounts). Silver metal is transferred into the solution by methods known from the scientific and technical literature, for example, by treating the solid phase with a solution of nitric acid.

The presence of the operation of obtaining a solution of silver and cadmium nitrates containing nitric acid and hydrazonium nitrate in the indicated concentrations provides high yield values of the elements to be separated (and, therefore, the degree of their mutual purification) upon subsequent contact of the solution with the indicated sorbents.

The minimum concentration of nitric acid is determined by an increase in the absorption of cadmium by these sorbents, which leads to a decrease in its release into the mother liquor. The maximum concentration of nitric acid is determined by a decrease in the completeness of the release of silver into the solid phase, which leads to a decrease in its yield. The minimum concentration of hydrazonium nitrate is also determined by the decrease in the completeness of the release of silver into the solid phase. The maximum concentrations of cadmium, silver and hydrazonium nitrates are determined by the solubility of these compounds.

The presence of the operation of contacting the solution with the carbon sorbent of SKN or one of its above modifications makes it possible to separate silver radionuclides into the solid phase, which ensures their separation from the cadmium remaining in the solution.

The presence of a solid phase washing operation with a solution of a mixture of nitric acid and hydrazonium nitrate allows the mother liquor contained in the pores of the sorbent and metal precipitate to be extracted, which increases the cadmium yield. The minimum concentration of nitric acid is determined by an increase in the absorption of cadmium by these sorbents, which leads to a decrease in its yield in the washing solution. The maximum concentration of nitric acid is determined by a decrease in the completeness of the release of silver into the solid phase, which leads to a decrease in its yield. The minimum concentration of hydrazonium nitrate is determined by an increase in the silver content in the wash solution.

From the scientific and technical literature it is known to use hydrazine for the deposition of silver from its solutions in the form of a metal. It is also known that a high yield of silver in a metal is achieved only in an alkaline medium (in practice, deposition is carried out from ammonia solutions). In acidic environments, the effectiveness of hydrazine as a reducer of silver ions is much lower. So, if in a medium of 0.01 mol / L HNO ₃ , a metal yield of 98% is possible due to the use of a large excess of hydrazonium nitrate ([N ₂ H ₅ NO ₃ ] / [Ag ⁺ ] ≥20), then at a concentration of nitric acid 0.1 mol / L or more metal yield does not exceed 5% at any concentration of N ₂ H ₅ NO ₃ . Therefore, in the absence of these sorbents, the separation of silver and cadmium radionuclides is not achieved.

1) Crystalline silver and cadmium nitrates containing ^110m Ag and ^115m Cd radionuclides were dissolved in 0.30 mol / L nitric acid, hydrazonium nitrate (in the form of its 7 mol / L solution) was introduced into the solution. Reagent concentrations in the resulting solution were: nitric acid - 0.25 mol / l; silver nitrate - 0.05 mol / l; cadmium nitrate - 0.01 mol / l; hydrazonium nitrate - 0.1 mol / L.

Aliquots of this solution were contacted with air-dry sorbents SKN (particle size 0.3-0.4 mm) and SKNo-1 (particle size 0.25-0.30 mm) weighing 0.100 g. The temperature of the solutions was 23 ° C. The distribution of radionuclides in the process of separation according to the claimed method, as well as the conditions for the relevant operations are presented in table. 1.

From table 1 it is seen that the yield of the ^115m Cd radionuclide in the combined mother and washing solution was 99.5% (SKN sorbent) and 98.9% (SKN-1 sorbent). The activity of the ^110m Ag radionuclide in these solutions was 0.15% (SKN) and 0.80% (SKNo-1) of its activity in the initial solutions. The yield of ^110m Ag radionuclide in 12 mol / L HNO ₃ solutions was 99.8% (SKN) and 99.2% (SKNo-1). The activity of the ^115m Cd radionuclide in these solutions was 0.5% (SKN) and 1.1% (SKNo-1) of its activity in the initial solutions.

2) In this work, we used a sample of ¹⁰⁷ Ag (98 at%) enriched in ¹⁰⁷ Ag isotope metal silver weighing 0.100 g irradiated in the SM-3 nuclear reactor (SSC RF RIAR).

The exposed material was dissolved in hot nitric acid at a concentration of 10 mol / L. The resulting solution was evaporated to dryness, the dry residue was dissolved in a mixture of nitric acid and hydrazonium nitrate. Received 0,050 l of a solution with concentrations in it: [HNO ₃ ] ≈0.5 mol / l; [AgNO ₃ ] = 0.019 mol / L; [N ₂ H ₅ NO ₃ ] = 0.053 mol / L; [N ₂ H ₅ NO ₃ ] / [AgNO ₃ ] = 2.8.

The activity of radionuclides in the initial solution, Bq: ^108m Ag - 6.0 · 10 ⁸ ; ^110m Ag-4.2 · 10 ⁸ ; ¹⁰⁹ Cd-1,1 · 10 ^9.

The cottage solution was contacted with an SKNK sorbent weighing 0.350 g for 3 hours. The reaction mixture was stirred by sparging of compressed air, the temperature was ~ 25 ° C. The distribution of radionuclides in the process of their separation according to the claimed method, as well as the conditions for the relevant operations are presented in table.2.

From table 2 it is seen that the yield of radionuclide ¹⁰⁹ Cd in the combined uterine and wash solution was not less than 99.5%. The activity of ^{108m, 110m} Ag radionuclides in these solutions amounted to 0.2% of their activity in the initial solution. The yield of ^{108m, 110m} Ag radionuclides in a solution of 14 mol / L HNO ₃ was 99.8%. The activity of ¹⁰⁹ Cd radionuclide in this solution was not more than 0.5% of its activity in the initial solution.

Claims (2)

1. The method of separation of silver and cadmium radionuclides, which consists in obtaining a solution of their nitrates containing nitric acid with a concentration of 0.1-2 mol / l and hydrazonium nitrate with a molar concentration equal to or higher than the molar concentration of silver, silver deposition by contacting the resulting solution with carbon sorbent SNK, separation of the mother liquor from the solid phase, washing the solid phase with a solution of 0.1-2 mol / L nitric acid containing at least 0.01 mol / L hydrazonium nitrate, and separating the washing solution. 2. The method according to claim 1, characterized in that the deposition of silver from the solution is carried out on a modified carbon sorbent SNK.