RU2248324C1 - Method for plutonium recovery from fiberglass aerosol boron- containing filter - Google Patents

Abstract

FIELD: reprocessing and utilization of solid radioactive waste from atomic industry.

SUBSTANCE: plutonium is recovered from fiberglass aerosol boron-containing filter by alkaline opening of spent filtering material in presence of magnesium-containing reagent (e.g., magnesium carbonate) in mass ratio not less than 0.85 as calculated to magnesium and boron oxides. Then insoluble precipitate is treated with mixture of aqueous nitric and hydrofluoric acids. Obtained solution is purified from impurities by sorption method. Plutonium oxalate is deposited from purified solution and burned to obtain plutonium dioxide.

EFFECT: plutonium product with small boron content.

2 cl, 1 tbl, 5 ex

Description

The invention relates to the field of processing and disposal of solid radioactive waste from the nuclear industry, and in particular to a method for extracting plutonium from spent filters, which is used to produce a plutonium product.

The technological processes of radiochemical and chemical metallurgical industries are inextricably linked with the purification of gas-aerosol wastes containing valuable components, for example plutonium. To clean the air of radioactive aerosols, filters based on artificial inorganic ultrathin glass staple fibers with a diameter of less than 0.5 microns (microfine - MTB), from 0.51 to 1.0 microns (ultrathin - UTV) and from 1.01 to 3 have been developed , 0 μm (superthin - STV). For their production, glass No. 20 (brand ШШЩ-20, ТУ 21-23-92-76), which includes 3% boron oxide, is used [1].

In a filter worked out under chemical and metallurgical production conditions, with a filter material weighing from 2 to 3 kg, up to 500 g of plutonium is contained.

There is a method of extracting plutonium from spent fiberglass filters for fine purification of air [2]. Plutonium recovery technology includes:

- alkaline opening of the spent filter material with an aqueous solution with a concentration of sodium hydroxide of 100 g / l with a volumetric phase ratio (W) of 75-150 l / kg of feedstock, t = (105 ± 5) ° С and a processing time of 3 hours. In this case, boron leaching into the solution is 30-33% (С _в = 28-31 mg / l), and the plutonium content is from 0.5 to 0.6 mg / l (solutions discharged by its content). Suspension filtration rate ~ 800 l / m ² h;

- filtration after cooling the suspension and washing the precipitate on the filter with water;

- processing of insoluble precipitate with a mixture of aqueous solutions of 7 mol / L nitric and 0.3 mol / L hydrofluoric acid with a ratio of liquid and solid phases of 100-175 l / kg and t = (105 ± 5) ° С for 3 hours. At the same time, boron leachability into the solution is 67-70% of the initial amount (С _в = 60-65 mg / l), 99.9% plutonium recovery, plutonium content in solid waste less than 0.01% (discharge according to the technological regulations) . Filtration rate - 2200 l / m ² h;

- sorption purification of nitrogen-fluoride plutonium solution from impurities;

- precipitation of plutonium oxalate with subsequent calcination of the precipitate at a temperature of (525 ± 25) ° C to obtain plutonium dioxide. Moreover, the content of boron in plutonium dioxide is more than 1 · 10 ⁴ %, that is, the TU condition is not satisfied.

The disadvantages of the method are:

1. The presence of a large amount of boron in a nitrogen-fluoride plutonium solution, which, upon further processing, leads to the production of a substandard boron plutonium product (plutonium dioxide). According to TU, the mass fraction of boron in relation to PuO ₂ should not exceed 0.8 · 10 ^-4 %.

2. The presence of boron with a high content (60-65 mg / l) in the nitrogen-fluoride plutonium solution increases the neutron background in the α, n reaction by about 20%. This increases the radiation hazard for staff due to neutron irradiation.

In the analysis of the generally available literature, no other known analogues that are closest to the claimed method were found.

When creating the invention, the task was to reduce the content of boron in a nitrogen-fluoride plutonium solution in order to obtain plutonium dioxide, which is conditionally boron, by transferring it more fully to an alkaline solution, which is discharged by plutonium (<1.5 mg / l).

The problem is solved in that at the stage of alkaline opening of the raw material (waste filter material), a magnesium-containing reagent is introduced preferably in the form of MgCO ₃ with a quantitative mass ratio in terms of magnesium and boron oxides of at least 0.85 with the formation of magnesium boride.

The method is as follows:

1. alkaline opening of the spent filter material with an aqueous solution with a concentration of sodium hydroxide of 100 g / l with a volumetric phase ratio (W) of 75-150 l / kg of raw material, t = 105 ± 5 ° C and a processing time of 3 hours. Previously, a magnesium-containing reagent, for example MgCO ₃ , is introduced into the alkaline solution, with a mass ratio in terms of magnesium and boron oxides of at least 0.85;

2. filtering after cooling the suspension and washing the precipitate on the filter with water;

3. treatment of insoluble precipitate with a mixture of aqueous solutions of 7 mol / l nitric and 0.3 mol / l hydrofluoric acid with a ratio of liquid and solid phases of 100-175 l / kg and t = 105 ± 5 ° C for 3 hours;

4. sorption purification of nitrogen-fluoride plutonium solution from impurities (on resin VP-1AP);

5. precipitation of plutonium oxalate and its calcination at a temperature of 525 ± 25 ° C;

6. analysis of the obtained powders for boron content.

As a result of the introduction of magnesium into the alkaline solution, 88-90% of boron is leached, which ensures the production of plutonium dioxide in accordance with the requirements of technical conditions (less than 0.8-10 ^-4 % wt.) And reduces the neutron background by 20% compared to prototype, which significantly improves the radiation situation in the served working area.

Example 1

Mass ratio MgO: B ₂ O ₃ = 0.6. To 1 kg of the feedstock (fiberglass), which contains 3% B ₂ O ₃ (30 g), magnesium carbonate in terms of 18 g of MgO was added. Alkaline opening of raw materials with subsequent processing of the residue in a mixture of nitric and hydrofluoric acids was carried out according to the regime specified in the proposed processing technology. Thus in an alkaline solution at W = 100 L / kg passed 50-55% boron _(C = 46-52 mg / l) in nitric acid - 45-50% _(C = 42-46 mg / l). The concentration of plutonium in an alkaline solution was ≤0.5 mg / L, which is a waste value.

Example 2

Mass ratio MgO: B ₂ 0 ₃ = 0.7. Magnesium carbonate in terms of 21 g MgO was added to the feedstock. The processing of raw materials was carried out analogously to example 1. In this case, 65-70% of boron (С _в = 60-65 mg / l) passed into an alkaline solution at W = 100 l / kg, and 30-35% (С _в = 28-) passed into nitric acid solution 32 mg / l). The concentration of plutonium in the alkaline solution was 0.55 mg / L.

Example 3

The mass ratio of MgO: B ₂ O ₃ = 0.8. Magnesium carbonate in terms of 24 g MgO was added to the feedstock. The alkaline feedstock processing carried out analogously to Example 1. Thus in an alkaline solution at W = 100 L / kg passed 80-85% boron _(C = 75-79 mg / l) in nitric acid - 15-20% _(C = 14 -18 mg / l).

Example 4

Mass ratio MgO: B ₂ O ₃ = 0.85. Magnesium carbonate in terms of 25.5 g MgO was added to the feedstock. The alkaline treatment was carried out analogously to Example 1. Thus in an alkaline solution at W = 100 L / kg passed 88-92% boron _(C = 82-86 mg / l). The remaining 8-12% of boron entered the nitric acid solution (C _in = 8-8.6 mg / l).

Example 5

Mass ratio MgO: B ₂ O ₃ = 0.9. Magnesium carbonate in terms of 27 g MgO was added to the feedstock. The alkaline treatment was carried out analogously to Example 1. Thus in an alkaline solution at W = 100 L / kg passed 90-92% boron _(C = 84-86 mg / l). In a nitric acid solution, the boron concentration is 8–9 mg / L.

Table 1 presents the data from examples 1-5 on the boron content in the nitric acid solution and the final product (PuO ₂ ) obtained after sorption purification of the nitrogen-fluoride solution from impurities on VP-1AP resin, deposition of oxalate and calcination at a temperature of 525 ± 25 ° FROM.

Table 1
Boron content in acidic solutions and the final product Mass ratio MgO: B ₂ O ₃ The concentration of boron in nitric acid plutonium solution, mg / l The boron content in PuO ₂ ,% wt. 0.6 42-46 2 · 10 ^-3 0.7 28-32 4 · 10 ^-4 0.8 14-18 2 · 10 ^-4 0.85 8-8.6 0.7 · 10 ^-4 0.90 8-9 0.4 · 10 ^-4

The results shown in the table show that PuO ₂ in terms of boron content corresponds to TU only in cases where alkaline treatment was carried out with a mass ratio of MgO: B ₂ O _{3 of} not less than 0.85, that is, when the concentration of boron in the nitric acid solution did not exceed 10 mg / l.

LIST OF USED SOURCES

1. Karakhanidi N.G., Kibardin R.N., Tupitsin I.N., Polik B.M. Products from ultra-thin glass staple fiber. Overview, no. 2. - M., NIITEKHIM, 1993, p.1-2, 9-10.

2. Smooth S. I., Guzhavin V. I., Pyatin N. P., Evlanov D. S. Plutonium regeneration from spent glass filters for fine air purification. - Atomic energy, 2002, vol. 92, issue 3, pp. 201-204.

Claims (2)

1. The method of extraction of plutonium from fiberglass aerosol filters containing boron, including alkaline opening of the used filter material, processing of insoluble sediment with a mixture of aqueous solutions of nitric and hydrofluoric acids, sorption purification from impurities, characterized in that the alkaline opening is carried out in the presence of a magnesium-containing reagent in a quantitative ratio mass in terms of magnesium and boron oxides of not less than 0.85, followed by precipitation of plutonium oxalate from sorption solutions and calcination to producing plutonium dioxide. 2. The method according to claim 1, characterized in that magnesium carbonate is used as the magnesium-containing reagent.