WO2021137721A1

WO2021137721A1 - Method for recovering ni-63 from an irradiated target and purifying it of impurities

Info

Publication number: WO2021137721A1
Application number: PCT/RU2020/000553
Authority: WO
Inventors: Павел Сергеевич БУТКАЛЮК; Ирина Львовна БУТКАЛЮК; Александр Степанович КОРНИЛОВ; Евгения Валерьевна ЧЕРНООКАЯ; Валерий Алексеевич ДИТЯТКИН
Original assignee: Акционерное Общество "Государственный Научный Центр - Научно-Исследовательский Институт Атомных Реакторов"
Priority date: 2019-12-30
Filing date: 2020-10-19
Publication date: 2021-07-08
Also published as: RU2720703C1

Abstract

The invention relates to the field of radiation chemistry and can be used in analytical chemistry and in technology for recovering and purifying a preparation of the radionuclide Ni-63 and for recovering and purifying nickel from industrial waste. The aim of the present technical solution is that of recovering large amounts of Ni-63 (tens of grams) from targets and purifying it of the following impurities: Fe-59, Со-60, Cr-51, Mn-54, Sb-124, Sc-46, Sn-117, Zn-65. The desired radionuclide is purified of Fe-59, Со-60, Cr-51, Mn-54, Sb-124, Sc-46 and Sn-117 by the precipitation of said impurities at a pH=5-6 after isotope dilution with inactive cobalt and oxidation of the latter with potassium persulfate or sodium persulfate. The given pH value is maintained by the addition of insoluble carbonates of calcium or barium to the solution.

Description

Method for separating Ni-63 from an irradiated target and purifying it from impurities

The invention relates to the field of radiochemistry and can be used in analytical chemistry, technology for the isolation and purification of the preparation of the radionuclide Ni-63 and the isolation and purification of nickel from industrial waste.

A known method of purification of the preparation of the radionuclide Ni-63 [Egorov EV, Makarov SB. Ion exchange in radiochemistry. - M.: Atomizdat, 1971, p. 368], which consists in dissolving the irradiated material in 12 mol / l hydrochloric acid and passing the resulting solution through a column with a strongly basic anion exchanger Dowex-1. The disadvantage of this method is the impossibility of cleaning Ni-63 from the radioactive isotopes of chromium and manganese present in the irradiated material. This disadvantage is due to the low distribution coefficients of these elements on the anion exchanger. Another disadvantage of this method is the use of large amounts of concentrated hydrochloric acid. The solubility of nickel chloride in 12 mol / L HC1 is 3.7 g / L, and 2.7 liters of HC1 solution are needed to dissolve a reactor target containing 10 g of nickel. Accordingly, in order to process large quantities of nickel, it is necessary to proportionally increase the volume of hydrochloric acid. The use of hydrochloric acid leads to corrosion of expensive equipment for handling radioactive substances.

Another method of purification of Ni-63 is the coprecipitation of impurities with iron (III) hydroxide and the subsequent precipitation of hexammininickel perchlorate [Andreev OI, Kornilov AS, Filimonov V.T. Method of purification of the preparation of radionuclide nickel-63, RF patent N ° 2219133 dated 20.12.2003.]. Iron (III) nitrate is introduced into a solution of nickel (II) nitrate containing ammonia with a concentration of at least 4 mol / l in an amount corresponding to the mass ratio of Fe: Ni = 0.01-0.03 and hydrogen peroxide with a concentration of 0.01-0.1 mol / l. The solution is separated from the Fe (OH) precipitate. Ni-63 is precipitated from the filtrate in the form of hexammininickel perchlorate.

For this, sodium or ammonium perchlorate is introduced at a ratio of molar concentrations of perchlorate ions and nickel in the range of 10-20. Separate the mother liquor from the sediment. The precipitate is washed with a solution containing ammonia (at least 4 mol / l), perchlorate ions (0.5-2 mol / l) and hydrogen peroxide 0.01-0.1 mol / l. The precipitate is dissolved in nitric acid with a concentration of 0.5-2 mol / l at a molar ratio of the amounts of acid and nickel of 8-10. From the resulting solution, the Ni-63 radionuclide is sorbed on a strongly acidic cation exchanger Dowex-50. The sorbent is sequentially washed with water and a solution of hydrochloric acid with a concentration of 0.3-0.5 mol / l. Desorbate Ni-63 with a solution of hydrochloric acid with a concentration of 4-6 mol / l. The method allows to purify Ni-63 from radioactive isotopes of cobalt, cesium, barium, europium, cerium, ruthenium, iodine, silver, niobium, chromium, manganese. This method has its drawbacks. According to the chemical formula of hexamminenickel perchlorate, there are 6 mol of ammonia per 1 mol of nickel, and when the precipitate is dissolved in an acid, 6 mol of ammonium ions are formed, respectively. When the obtained nitric acid solution is passed through a column with a Dowex-50 cation-exchange resin, nickel and ammonium ions are sorbed, while the perchlorate ions remain in the solution. The presence of a sixfold excess of ammonium ions leads to an increase in the required amount of sorbent and the volume of the column. Accordingly, the volume of solutions required for the separate elution of ammonium and nickel cations increases, which is technologically inconvenient. The use of hydrochloric acid in the process leads to corrosion of expensive equipment for handling radioactive substances. Hexamminickel perchlorate is unstable, dry salt explodes from a spark and when heated, this precipitate also has large volumes. All this limits the amount of recyclable nickel.

The task of the proposed technical solution is to separate and purify large amounts of Ni (tens of grams) from impurities: Fe-59, Co-60, Cr-51, Mn-54, Sb-124, Sc-46, Sn-117, Zn-65 from targets.

To solve this problem, in a method for separating Ni-63 from an irradiated target and purifying it from impurities, including dissolving the irradiated target, precipitating impurity radionuclides, separating the precipitate from the mother liquor, at the first stage, radioactive isotopes of iron, cobalt, chromium, manganese, antimony, scandium are precipitated and tin by introducing water-soluble salts of cobalt (II) and potassium or sodium persulfate at pH = 5 6, separating the precipitate, at the second stage precipitating the zinc isotope by introducing potassium fluoride and ethyl alcohol into the mother liquor with acidity adjustment with a dilute solution of nitric acid, separating the precipitate , the precipitates are washed, respectively, with bidistilled water and alcohol, the mother and washing solutions are combined, and the purified nickel is concentrated by precipitation in the form of a poorly soluble nickel compound.

If necessary, at the second stage, additional zinc salts are introduced into the mother liquor as an isotopic carrier for the reprecipitation of zinc fluoride.

With the introduction of water-soluble salts of cobalt and sodium or potassium persulfate, cobalt (II) is oxidized to cobalt (III) hydroxide.

When oxidizing cobalt (II) salts, the molar ratio of persulfate ions to cobalt is at least 15.

During the deposition of radioactive isotopes of iron, cobalt, chromium, manganese, antimony, scandium and tin, the pH of the solution is maintained in the 5-He range by introducing calcium carbonate. The molar ratio of calcium carbonate to sodium or potassium persulfate must be at least 2.

Zinc fluoride is precipitated from an aqueous-alcoholic solution under conditions of partial precipitation of nickel fluoride, which is a non-isotopic carrier for zinc fluoride.

The introduction of cobalt in the target solution in the form of Co (NO ₃ ) ₂ and potassium or sodium persulfate, followed by its precipitation, makes it possible to co-precipitate the microcomponents-impurities Fe-59, Co-60, Cr-51, Mn-54, Sb-124, Sc- 46, Sn-117. The deposition of not a macrocomponent - nickel, but microcomponents - impurities in all operations allows working with sufficiently concentrated, 50-100 g / l, nickel solutions.

The use of calcium carbonate regulates the pH of the solution at a level of 5-6, it practically does not dissolve under these conditions and does not introduce additional contaminants.

Experiments have shown that at pH = 5-6, CO (N0 ₃ ) ₂ is oxidized with potassium persulfate (PCS) and precipitated as Co (OH) ₃

It has been experimentally proven that the degree of precipitation of cobalt depends on the molar ratio of PSA / Co (Figure 1). As can be seen from the figure, the maximum degree of precipitation of cobalt, equal to 99.96%, is achieved at a molar ratio of PSA / Co more than 13.

The use of calcium carbonate regulates the pH of the solution at a level of 5-6, it practically does not dissolve under these conditions and does not introduce additional contaminants. The dependence of the pH of the solution on the molar ratio of potassium persulfate (PAC) to calcium carbonate has been experimentally proved.

As can be seen from Figure 2, to maintain pH = 5-6, the molar ratio of PSA / CaCO ₃ should be no more than 0.5.

The introduction of potassium fluoride and ethyl alcohol into the solution at the second stage makes it possible to precipitate Zn. Zinc forms sparingly soluble fluoride (solubility is 4.47-10 ⁴ ), which makes this compound convenient for removing zinc from solution.

The use of ethyl alcohol (as a salting-out agent) leads to a decrease in the solubility of most inorganic compounds.

It was experimentally obtained that for the most complete precipitation of zinc fluoride and a decrease in the coprecipitation of nickel, the alcohol content in the solution should be at least 40% (Figure 3).

Experiments show that a decrease in the solubility of NiF ₂ in aqueous-alcoholic solutions can lead to significant losses of nickel.

With a large excess of nickel, competition between zinc and nickel for the fluoride ion is possible, which will result in a decrease in the degree of zinc deposition and, accordingly, in a decrease in the factor of nickel purification from zinc.

With a relatively small difference in solubility, partial precipitation of nickel fluoride can be used to remove zinc from solution, which will be a non-isotopic carrier for zinc fluoride. With a large difference in solubility, the deposition of zinc fluoride is best carried out using an isotopic carrier - non-radioactive zinc.

Tables 1-2 show the data on the distribution of zinc between the fluoride precipitate and the solution during the deposition of Z11F2 with a support and without a support, depending on the concentration of alcohol and the initial concentration of nickel. The distribution of zinc was estimated by the factor of purification of nickel from zinc - the ratio of the initial content of zinc in nickel to the final one.

From the data in Tables 1-2, it can be seen that at initial nickel concentrations of 30 - 75 g / l, it is more advantageous to carry out the deposition without a carrier, in this case the role of a non-isotopic carrier will be played by nickel fluoride. However, in this case, the loss of nickel can reach 15-20%. At initial nickel concentrations of less than 30 g / l, precipitation with a carrier — non-radioactive zinc — is expedient (Table 2). The most effective will be the consistent application of the described methods. After non-relative precipitation, a fluoride precipitate is formed, containing 15-20% of nickel and all of Zn-65, and a mother liquor containing 80-85% of purified nickel. The precipitate is dissolved in nitric acid, evaporated to salts, and dissolved in water to obtain a solution with a nickel concentration of 10 g / l. Inactive zinc is added to this solution and zinc fluoride is precipitated from a 30-50% alcohol solution. Nickel losses in this case will not exceed 12% (table 1). The purified nickel mother liquor is added to the first mother liquor. The total nickel losses are 2-3%.

The method is illustrated by figures, where: Figure 1 - the dependence of the degree of precipitation of cobalt on the molar ratio of PSA / Co; Figure 2 - the dependence of the pH value on the molar ratio of PSA / CaCO3; Figure 3 - Dependence of the solubility of NiF ₂ and ZnF ₂ on the concentration of alcohol at pH = 5.

To 200 ml of a diluted nitric acid solution obtained by dissolving an irradiated Ni-62 target, nickel and cobalt nitrates were added to a nickel concentration of 75 g / L and a cobalt concentration of 0.2 g / L, respectively. The solution was evaporated to wet salts, the evaporation residue was dissolved in 200 ml of bidistilled water. To the solution were added 5 g of calcium carbonate and 2.74 g of potassium persulfate. The solution was kept in a boiling water bath for 30 minutes and cooled to room temperature over 3 hours. The precipitate was separated from the mother liquor by centrifugation and washed 2 times with 50 ml of bidistilled water. Washes attached to the mother liquor solution. To the combined mother liquor was added 95 ml of 1.27 mol / L KF solution with pH = 5 (a dilute solution of nitric acid was used to adjust the acidity) and 490 ml of alcohol. The solution was kept for 20 hours. The precipitate was separated from the mother liquor by filtration, washed 2 times with 100 ml of 50% alcohol. The washings were added to the mother liquor. The precipitate was dissolved in 100 ml of 1 mol / L HNO ₃ , added 200 mg of zinc in the form of nitrate and evaporated to wet salts. The salt residue was dissolved in 200 ml of a 0.3 mol / L KF solution with pH = 5. Added 225 ml of alcohol, mixed and incubated for 20 hours. The precipitate was separated from the mother liquor by filtration, washed twice with 70 ml of 50% alcohol. The washings were added to the mother liquor and mixed with the first precipitation mother liquor. The combined mother liquor was evaporated to 300 ml, the nickel content and the activity of impurity radionuclides were determined.

From the resulting solution, nickel was precipitated with nickel hydrazine hydrate. The precipitate of nickel metal powder was dried and weighed. The results are shown in Table 3.

The nickel content in the combined mother liquor was 14.7 g, the weight of the metallic nickel powder was 14.4 g, and the nickel yield was 96%.

As can be seen from the data in Table 3, the factor of purification from the most significant radionuclides Co-60, Fe-59, Zn-65, Sb-124 is at least 1500, which makes it possible to obtain a preparation of the radionuclide Ni-63 with the total activity of gamma impurities to the preparation no more than 1-10% of the activity of Ni-63. Table 1. Deposition of ZnF ₂ without support. Dependence of the degree of deposition of NiF ₂ and the degree of purification of nickel from zinc on the concentration of alcohol and the initial concentration of nickel.

Table 2. Deposition of ZnF2 with a support. Dependence of the factor of purification of nickel from zinc on the concentration of alcohol. [Zn] = l g / l, [Ni] = T0 g / l.

Table 3

Claims

Claim

1. A method of separating Ni-63 from an irradiated target and purifying it from impurities, including dissolving the irradiated target, precipitating impurity radionuclides, separating the precipitate from the mother liquor, at the first stage, radioactive isotopes of iron, cobalt, chromium, manganese, antimony, scandium and tin are precipitated by introducing into a solution of salts of cobalt (II) and potassium or sodium persulfate at pH = 5 6, the precipitate is separated, at the second stage the zinc isotope is precipitated by introducing potassium fluoride and ethyl alcohol into the mother liquor with acidity adjustment with a dilute solution of nitric acid, the precipitate is separated, the precipitates are washed accordingly with bidistilled water and alcohol, combine the mother liquor and washing solutions and concentrate the purified nickel by precipitation in the form of a poorly soluble nickel compound.

2. The method according to claim 1, characterized in that water-soluble cobalt (II) salts are added.

3. The method according to claim 1, characterized in that the impurities are precipitated at a molar ratio of persulfate ions to cobalt of at least 15.

4. The method according to claim 1, characterized in that calcium carbonate is added to maintain the pH of the solution in the range of 5-H5.

5. The method according to claim 4, characterized in that the impurities are precipitated at a molar ratio of calcium carbonate to sodium or potassium persulfate of at least 2.

6. The method according to claim 1, characterized in that at the second stage, impurities are precipitated with potassium fluoride from an aqueous-alcoholic solution with an alcohol content in the solution of at least 40.

7. The method according to 1, characterized in that the reprecipitation of zinc fluoride is carried out with the addition of zinc salts as an isotopic carrier.