RU2624920C1 - Method of extraction of molybdene from radioactive solutions - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method of extraction of molybdenum from radioactive solutions involves the extraction of molybdenum by solutions of hydroxamic acids dissolved in a mixture of not more than 30% alcohol with paraffinic hydrocarbons with a ratio of volumes of organic and aqueous phases of less than 0.1. The molybdenum and iodine extract is washed with a small volume of nitric acid solution with the addition of metal nitrates from the series: Hg (II), Cu (II), Ag (I), Pb (II), after which the extract is washed with a solution of nitric acid. The extrusion of molybdenum is carried out in a solution of nitric acid with heating upon the addition of a water-soluble complexing agent to be destroyed before or after such treatment, in the latter case with repeated re-extraction into the same solution. The destruction of hydroxamic acid in the extract can be accelerated by using an oxidation inducer. The final molybdenum re-extract is washed with an extractant.

EFFECT: invention allows to increase the concentration of molybdenum with its simultaneous purification from non-extractable impurities.

7 cl, 8 ex

Description

The invention relates to radiochemical technology and can be used in the separation of radionuclides from radioactive solutions of irradiated uranium targets used for biomedical purposes, as well as in the analysis of technological solutions in the processing of spent nuclear fuel.

When isolating medical molybdenum from irradiated low enriched uranium targets, both the speed of the process and the degree of purification from associated radionuclides are of great importance. The known method [Patent RU 2522544, publ. 12/20/2013, Bull. No. 35], which consists in the selective extraction of molybdenum with a solution of C ₆ -C ₁₂ hydroxamic acid in aliphatic alcohol, acid washing the extract from impurities and reextracting molybdenum together with iodine in a carbonate solution of a singly charged cation, for example methylamine carbonate, in the presence of a complexing agent, for example diethylenetriamine acid pentas (DTPA). In a second embodiment of this method, the initial radioactive solution is treated with a reducing agent. This method is the closest to the invention and adopted as a prototype. It provides selective extraction of molybdenum during extraction in the presence of ascorbic acid (AK) with hydrazine nitrate with 1000 times purification from metal impurities, including uranium, while 100 times from plutonium.

Its disadvantages are the relatively low degree of concentration of molybdenum (~ 25 times) and the coefficient of its purification from iodine (~ 3), as well as the presence of intractable reagents in the reextract, in particular DTPA.

The disadvantages of the operation of the extraction of molybdenum were partially overcome in another way [Patent RU 2575028, publ. 02/10/2016, Bull. No. 4], which provides for the selective re-extraction of molybdenum with a solution of destructible or removable oxidizing agent in nitric acid, in particular by heating the emulsion of the extract with nitric acid for hydrolysis and oxidation of hydroxamic acid, which ensures the transition of molybdenum into an aqueous solution of nitric acid. The solution of caprohydroxamic acid in n-octanol had the best combination of extraction properties according to the examples. The implementation of this method of stripping during extraction according to the prototype increases the concentration of molybdenum to 40-50 times, and the coefficient of its purification from iodine to 70 and to 10 ³ -10 ⁴ from other impurities.

The disadvantage of this method is the insufficient completeness of the re-extraction of molybdenum with a single re-extraction into a solution of hot nitric acid and a decrease in the yield of molybdenum in the re-extract with a decrease in its mass concentration, as well as technical difficulties with the use of other degradable oxidizing agents, except nitric acid itself, related both to their supply in the form of gaseous reagents (chlorine, nitrogen oxides, etc.), and because of the need for additional processing of the solution after their use. In addition, purification from radioactive and stable impurities seems insufficient for a one-stage process of concentration and purification of molybdenum.

The objective of the invention is to increase the concentration of molybdenum by more than 100 times with its simultaneous purification from non-extractable impurities in 10 ⁴ -10 ⁶ times, and from iodine - not less than 10 ³ times with the exception of special chemical operations to destroy or remove reagents in a molybdenum reextract .

To obtain the technical result indicated in the task, the radioactive nitric acid solution containing molybdenum is treated with a reducing agent, for example hydrazine nitrate, in the presence of an unextractable complexing agent, for example AK, molybdenum is extracted from this solution with an extractant containing organically soluble hydroxamic acids dissolved in a mixture of not more than 30 % alcohols C ₈ -C ₁₀ with paraffin hydrocarbons fractions in the range of C ₈ -C ₁₆ . The molybdenum extract obtained with a volume ratio of organic and aqueous phases of less than 0.1 is pre-washed with an equal volume of nitric acid solution with the addition of metal nitrates from the series: Hg (II), Cu (II), Ag (I), Pb (II), with the final washing of the molybdenum extract with an equal volume of nitric acid solution. Molybdenum is reextracted at a ratio of organic and aqueous phases of more than 10 by thermochemical treatment of the molybdenum extract with a solution of nitric acid with the addition of a water-soluble destructible complexing agent before or after such a thermochemical treatment, and in the latter case, molybdenum is re-extracted into the same solution after cooling. The destruction of adducts of molybdenum with hydroxamic acid in the extract can be accelerated by generating nitrogen oxides using an oxidation inducer introduced into an aqueous solution of nitric acid during the thermochemical treatment of the molybdenum extract, and the final reextraction of molybdenum is carried out with the introduction of a complexing agent. The final re-extract is washed with an extractant solution at 20-90 ° C. The extractant after re-extraction of molybdenum is regenerated by known methods.

Oxalic acid nitric acid solution is used as a water-soluble complexing agent introduced directly during thermochemical oxidation, and high purity solutions of hydrogen peroxide, acetohydroxamic or oxalic acid are used as water-soluble complexing agents of the solution introduced after thermochemical oxidation and cooling.

An aqueous formaldehyde nitrate solution can be used as an inducer to accelerate the oxidation of hydroxamic acids, and the complexing agent is introduced into the cooled re-extract before final re-extraction. The use of carbohydrates, such as glucose, as an oxidation inducer does not require the additional introduction of complexing agents, since the hydroxy acids formed during the oxidation of carbohydrates, such as sugar acid from glucose, are effective complexing agents for the re-extraction of molybdenum.

The performance of the proposed method is illustrated by examples.

Example 1

Verification of the example in the optimal embodiment of the process of concentration and purification of molybdenum by analogy [Patent RU 2575028]. Model nitric acid solution of irradiated uranium block containing 126 g / L HNO ₃ , 25 g / L Al, 1.2 g / L U, 100 mg / L Zr, 8 mg / L Mo, 10 ⁶ Bq / L ⁹⁹ Mo and 10 ⁶ Bq / L ¹²⁵ I, was treated with a phase volume ratio of O: B = 0.125 with an extractant representing 10 g / L caprynhydroxamic acid dissolved in n-octanol. 98.5% Mo, 98% I, 0.01% Zr and <0.01% U and Al went into the extract.

The molybdenum and iodine extract was heated to 90 ° C and held for 20 min, after which it was treated at a volume ratio of O: B = 5 with a solution of 2 mol / L nitric acid; while 40% of molybdenum and less than 1% of iodine are withdrawn into the re-extract. Molybdenum is concentrated 40 times when cleaning iodine more than 60 times. Loss of molybdenum with extractant was less than 60%. This method does not allow to efficiently reextract molybdenum in one stage.

The spent extractant was washed with a 1% NaOH solution to remove the formed sodium salts of fatty acids, and the purified solvent containing iodine was passed through a sorbent, which is silver nitrate, deposited on a porous carrier. The content of ¹²⁵ I in the treated solvent is 3⋅10 ⁴ Bq / l, which allows its reuse.

Example 2

Model nitric acid solution of the irradiated uranium block containing 126 g / l HNO ₃ , 25 g / l Al, 1.2 g / l U, 200 mg / l Hg, 100 mg / l Zr, 35 mg / l ²³⁹ Pu, 3, 1 mg / L Mo, as well as tags with activity of 10 ⁶ Bq / L ²³⁹ Np, 10 ⁶ Bq / L ⁹⁹ Mo and 10 ⁶ Bq / L ¹²⁵ I, to which 5 g / L AK and 8 g / L hydrazine nitrate were added. , treated with a phase volume ratio of O: B = 0.05 with an extractant representing 5 g / l caprynhydroxamic acid dissolved in a mixture of 20% n-decanol with 80% Isopar M, which is a mixture of isoparaffins C ₁₁ -C ₁₅ . 98.5% Mo, 11% I, 0.01% Zr, <0.1% U, ²³⁹ Pu, <0.01% Al, ²³⁹ Np, Hg passed into the extract.

The molybdenum and iodine extract was washed 2 times with 0.5 mol / L HNO ₃ , the first time at a content of 200 mg / L Hg in the form of nitrate, having obtained the total coefficient of Mo removal from metal impurities U, Al, Np> 10 ⁶ , Pu> 10 ⁵ , Hg, Fe> 2⋅10 ⁴ and ~ 500 from iodine. Losses of molybdenum with washing solutions did not exceed 1% in balance.

The obtained extract was heated to 90 ° C in a mixture with a solution of 5 mol / L HNO ₃ with a phase volume ratio of O: B = 12.5 and kept for 50 minutes. The system was cooled and an aqueous solution of 0.2 mol / L acetohydroxamic acid was added and contacted again for 10 minutes. Mo reextract was washed with 20% n-decanol in isopar M at O: B = 1 at a temperature of 40 ° C. As a result, 88% of molybdenum in the first stage and 98% in total were withdrawn into the re-extract; while molybdenum was concentrated a total of 196 times. The Mo reextract was washed with 20% n-decanol in isopar M at O: B = 1 at a temperature of 40 ° C, which makes it possible to increase the purification from iodine in relation to the initial solution by more than 2500 times. The coefficient of purification from other impurities was given above.

The molybdenum re-extract is transferred to the sublimation of molybdenum trioxide and the manufacture of a ^99m Tc generator. The extractant was subjected to regeneration for reuse, as in example 1.

Example 3

The molybdenum and iodine extract obtained under the conditions of Example 2 was washed 2 times with 0.5 mol / L HNO ₃ , the first time at a content of 50 mg / L Ag in the form of nitrate, having obtained the total coefficient of Mo removal from metal impurities U, Al, Np > 10 ⁶ , Pu> 10 ⁵ , Hg, Fe> 2⋅10 ⁴ and ~ 500 from iodine. Losses of molybdenum with washing solutions did not exceed 1% in balance.

The obtained extract was heated to 90 ° C in a mixture with a solution of 5 mol / L HNO ₃ with a phase volume ratio of O: B = 12.5 and kept for 50 minutes. The system was cooled and an aqueous solution of 0.2 mol / L H ₂ C ₂ O _{4 was} added and contacted again for 10 minutes. As a result, 87% of molybdenum in the first stage and 96% in total were withdrawn into the re-extract; while molybdenum was concentrated a total of 192 times. Mo reextract was washed with 20% n-decanol in isopar M at O: B = 1 at a temperature of 20 ° С with iodine purification more than 1600 times in relation to the initial solution.

Example 4

The molybdenum and iodine extract obtained under the conditions of Example 2 was washed 2 times with 0.5 mol / L HNO ₃ , the first time at a content of 450 mg / L Pb in the form of nitrate, having obtained a total Mo purification coefficient of metal impurities U, Al, Np > 10 ⁶ , Pu> 10 ⁵ , Hg, Fe> 2⋅10 ⁴ and ~ 500 from iodine. Losses of molybdenum with washing solutions did not exceed 1% in balance.

The obtained extract was heated to 90 ° C in a mixture with a solution of 5 mol / L HNO ₃ with a phase volume ratio of O: B = 12.5 and kept for 50 minutes. The system was cooled and an aqueous solution of 0.2 mol / L H ₂ O _{2 was} added and contacted again for 10 minutes. As a result, 88% of molybdenum in the first stage and 96% in total were withdrawn into the re-extract; while molybdenum was concentrated in total 191 times with purification from iodine in relation to the initial solution more than 800 times.

Example 5

The molybdenum and iodine extract obtained under the conditions of Example 2 was washed 2 times with 0.5 mol / L HNO ₃ , the first time at a content of 2 g / L Cu in the form of nitrate, having obtained the total coefficient of Mo removal from metal impurities U, Al, Np > 10 ⁶ , Pu> 10 ⁵ , Hg, Fe> 2⋅10 ⁴ and ~ 500 from iodine. Losses of molybdenum with washing solutions did not exceed 1% in balance.

The extract obtained was heated to 90 ° C in a mixture with a solution of 5 mol / L HNO ₃ and 0.2 mol / L H ₂ C ₂ O ₄ with a phase volume ratio of O: B = 12.5 and held for 50 minutes, followed by contacting within 10 minutes As a result, 96% of molybdenum was withdrawn into the re-extract; while molybdenum was concentrated a total of 220 times.

Example 6

The washed extract of molybdenum and iodine was obtained under the conditions of Example 2. Mo reextraction was carried out at 90 ° C in two stages, including the first with contacting for 50 min, introducing 5 mol / L HNO ₃ with 0.2 mol / l N ₂ C ₂ O ₄ before heating. The Mo reextract was cooled and 0.2 mol / L of acetohydroxamic acid was added at the O: B = 10 level in the second stage of reextraction. As a result, 98.5% Mo was withdrawn into the re-extract without changing other indicators.

Example 7

The molybdenum and iodine extract washed 2 times, obtained under the conditions of Example 2, was heated to 70 ° C in the presence of a solution of 7 mol / L HNO ₃ with 0.7 mol / L formaldehyde at O: B = 12.5 and held for 20 minutes . After cooling, an aqueous solution of 0.2 mol / L of acetohydroxamic acid was added at O: B = 10 and again contacted for 10 minutes. As a result, 86% Mo in the first stage and 98.1% of the total was removed into the re-extract; while molybdenum was concentrated a total of 194 times with respect to the initial solution.

Example 8

The 2 times washed extract of molybdenum and iodine obtained under the conditions of Example 2 was heated to 75 ° C in the presence of a solution of 8 mol / L HNO3 with 0.3 mol / L glucose at O: B = 12.5 and held for 30 min subsequent contact for 10 minutes Sugar acid resulting from the decomposition of glucose is an effective water-soluble complexing agent that effectively retains Mo. As a result, 99% Mo; while molybdenum was concentrated a total of 225 times with respect to the initial solution.

Claims (7)

1. A method for the extraction of molybdenum from radioactive solutions, including their reduction treatment, extraction of molybdenum with an extractant — alcohol insoluble in the aqueous phase, in the presence of hydroxamic acid as a complexing agent, washing the extract with a solution of nitric acid, subsequent re-extraction of molybdenum and regeneration of the extractant with alkaline treatment, characterized in that the extractant is a mixture of alcohol and paraffin hydrocarbons fraction c ₇ -C _16, resulting extract mo Ibdenum is washed with a solution of nitric acid with the addition of a metal nitrate selected from the series: Hg (II), Cu (II), Ag (I), Pb (II), the molybdenum is reextracted into the nitric acid solution by the destruction of hydroxamic acid when heated, including including the addition of an oxidation inducer, with the introduction of a water-soluble destructible complexing agent into the reextracting solution, introduced both after the indicated thermochemical treatment and in its process, after which the final molybdenum re-extract is washed with the extractant. 2. The method according to p. 1, characterized in that the extractant contains not more than 30% alcohol With ₈ -C ₁₀ . 3. The method according to p. 1, characterized in that the extraction is carried out at a volume ratio of organic and aqueous phases of less than 0.1. 4. The method according to p. 1, characterized in that as a water-soluble destructible complexing agent at the stage of re-extraction, hydrogen peroxide is used, as well as high-purity acetohydroxamic or oxalic acids or organic hydroxy acids, for example, sugar, and oxalic acid is introduced into the reextracting solution before thermochemical treatment, and hydrogen peroxide or acetohydroxamic acid is introduced into the cooled reextract before re-contacting the phases, while the molybdenum is reextracted with With a volume ratio of organic and aqueous phases of more than 10. 5. The method according to p. 1 or 4, characterized in that the nitric acid solution of formaldehyde is used as an oxidation inducer. 6. The method according to p. 1 or 4, characterized in that nitric acid solutions of carbohydrates, for example glucose, are used as an oxidation inducer, and carbohydrate oxidation products, for example, sugar acid, as a product of glucose oxidation, are used as a complexing agent. 7. The method according to p. 1, characterized in that the washing of the stripping extractant is carried out at 20-90 ° C.