Method of extracting americium from wastes

FIELD: chemistry.

SUBSTANCE: method involves dissolving wastes in concentrated nitric acid, oxalate precipitation from the solution, drying and calcining the americium oxalate to americium dioxide. The solution obtained by dissolving wastes with high concentration of impurity cations, one of which is ferric iron, is mixed with a reducing agent for reducing ferric iron to ferrous iron. After reduction, the solution with acidity by nitric acid of 1-2.5 mol/l is taken for extraction of americium with a solid extractant based on different-radical phosphine oxide, followed by washing and re-extraction of americium. Oxalate precipitation is carried out from the re-extract with americium concentration of not less than 3 g/l and nitric acid concentration of not less than 3 mol/l, said precipitation being carried out in two steps: adding an oxalate ion to the americium-containing solution in weight ratio to americium of (2-7):1 and then adding water to the separated precipitate in volume ratio to the precipitate of (3-8):1 and the oxalate ion in weight ratio to americium of (1-4):1. The obtained reaction mixture is boiled and taken for separation of americium oxalate from the solution.

EFFECT: high output of the product and degree of purity thereof.

4 cl

 

The invention relates to a method of extraction of americium in the form of americium dioxide from radioactive waste chemical and metallurgical production. Americium is used, for example, as a source of gamma radiation in devices for measuring the thickness of metal plates, soil compaction, testing and radiographic exploration (logging) research.

There is a method of extraction of americium in the form of americium dioxide [RF Patent №2335554, IPC SW 60/02, SU 3/20 (2006.01), publ. 10.10.2008]. The method involves coprecipitation from a nitric acid solution containing americium and impurities, americium oxalate and calcium oxalate, calcining the resulting sludge to oxides, dissolution in nitric acid to obtain a nitric acid solution, from which the extraction of americium using solid extractant based on diisooctyl-phosphonate, reextraction americium, deposition of one stripped off of reextract americium oxalate and its annealing to americium dioxide.

The solution obtained by dissolution of solid radioactive waste, which precipitated americium on the media, contains traces of iron, aluminum, magnesium, etc. in gram quantities. The method is not applicable for separation of americium from waste with a high content of cations when dissolved which will have concentrated solverstone, containing americium in which impurities reach a concentration of 12 M by cations (up to hundreds of grams per litre).

There is a method of extraction of americium in the form of americium dioxide from solid radioactive waste [U.S. Patent No. 3781404, IPC C01G 65/00, publ. 25.12.1973]. According to this method dissolved solid waste containing americium, as well as fluoride, chloride and iodide of calcium and magnesium oxide and others, in concentrated 10-15 M nitric acid, the final concentration of nitric acid is 6 mol/l After filtration the solution add ammonium hydroxide to reduce the acidity of 0.1-0.3 M, and the solution is performed oxalate deposition of americium by the addition of oxalic acid in excess, while the final concentration of oxalic acid is 0.1 M. the Precipitate is filtered, dried and calcined at a temperature of 600°C for 4-6 hours. Get americium dioxide, slightly contaminated rare earth elements.

The method chosen for the prototype. The method is also not applicable to wastes with a high content of cations.

In conditions of high concentration impurity cations when using the described methods oxalate deposition or no formation of precipitate (formed poorly soluble dissociatively oxalate complexes, for example, iron, aluminum and others), or americium is redistributed between Sadko and solution. For separation of americium from such solutions require additional excess oxalate-ion battery, with full recovery of americium in the sediment still not happening (up to 70% of the initial concentration), due to the presence of deposited impurities the amount of sludge increases 3-4 times, further complicating the extraction of americium.

The objective of the invention is to expand the Arsenal of methods of extraction of americium from waste, increase the yield and purification of americium from impurities.

Task is the fact that the method of extraction of americium in the form of americium dioxide from radioactive waste, including the waste dissolution in concentrated nitric acid, oxalate precipitation from a solution containing americium, drying and calcination selected from a solution of oxalate to americium americium dioxide, a solution obtained by dissolving waste in concentrated nitric acid with high concentration of cation impurities, one of which is trivalent iron, add the reducing agent to restore the ferric to the ferrous state, after recovery solution with the acidity of nitric acid 1-2,5 mol/l is directed to the extraction of americium solid extractant based phosphine oxide raznorabochego (tax HUF) with subsequent washing and reextracting americia-6 M solution of nitric acid, and reextract, or received from reextract solution, with the concentration of americium at least 3 g/l and the concentration of nitric acid is not less than 3 mol/l, perform oxalate deposition, which is carried out in two stages: by adding to a solution containing americium oxalate ion in a mass ratio to the americium (2-7):1 and then adding to the selected draught of water in a volume ratio to the precipitate (3-8):1 and oxalate ion in a mass ratio to the americium (1-4):1, the reaction mixture is boiled and directed to the selection of from a solution of oxalate of americium.

When dissolved waste get a solution with a concentration of impurity cations 5-12 mol/L.

In use as a reducing agent rongalit or ascorbic acid or hydrazine.

From reextract get a solution with a concentration of americium at least 3 g/l by deposition of americium hydroxide hydroxides of alkali metals or ammonium at pH of 6.0-7.0 and subsequent dissolution of the precipitate in nitric acid of a smaller amount.

The method is as follows.

Recycle radioactive waste (solids, slurry)obtained during the purification of water and tailings solutions for chemical and metallurgical production, sent to landfill, with the purpose of extraction of americium. The content of americium in the waste from 0.1 to 10 g per 1 kg of waste (activestate.com from 1.3·10 10Bq to 1.3·1011Bq). Waste contain micropremie: iron, magnesium and, as a rule, aluminum, calcium, chromium, Nickel, vanadium, sodium, fluorine, chlorine, etc. and may contain some trace amounts of a number of: barium, manganese, copper, titanium, tungsten, silicon and other Metals in the waste are mostly in the form of hydroxide, fluoride and chlorine in the form of fluoride and chloride ions.

Waste is dissolved in conc. of 12.5 to 15.4 mol/l nitric acid to a residual acidity of 1-2 .5 mol/L. Get nitric acid solutions having concentrations of americium 0,5÷8.0 g/l and micro-dopes: iron 5 to 20.0 g/l of aluminum from 5 to 25.0 g/l, calcium from 5 to 20 g/l, magnesium from 50 to 170 g/l of chromium from 2 to 15.0 g/l, Nickel from 2 to 5.0 g/l of vanadium from 2 to 10 g/l, sodium from 20 to 100 g/l of fluoride from 2 to 20.0 g/l, chlorine from 7 to 50.0 g/l, other elements (barium, manganese, copper, titanium, tungsten, silicon and others) from 0.5 to 3 g/l for each item, total metals, as a rule, from 100 to 500 g/L.

The resulting solution has a concentration of americium suitable for deposition without the media, but the concentration of cation impurities in the solution reaches 5-12 mol/l of these solutions along with the deposition of americium happens precipitation of impurities, and in large quantities, i.e. visible purification of americium will not happen. As the operation of extraction of americium from the waste solution is proposed extraction is the use of solid extractant of tax HUF (solid-phase extractant, obtained by copolymerization of a mixture of monomers and solvent. As monomers are styrene and divinylbenzene as the extractant - phosphine oxide rasoredeleniy).

To improve the efficiency of extraction of americium extractant of tax HUF carry out the reduction of iron (III) to ferrous (iron (III) reduces the efficiency of extraction of americium) adding to the solution obtained by dissolving waste nitric acid, a given quantity of reducing agent selected from the range: rongalite (sodium formaldehyde sulfoxylate - HOCH2SO2Na·2H2O), ascorbic acid, hydrazine in the form of hydrazine hydrate or hydrazine-nitrate. Then, if necessary, conduct the adjustment of the solution pH (nitric acid 1-2,5 mol/l) by adding acid or water or alkali. After surgery recovery solution with the acidity of nitric acid 1-2,5 mol/l is directed to the extraction. When the specified pH of the solution during the extraction occurs precipitation of impurities (iron, titanium, tungsten, aluminum), complicating the extraction, the use of solid extractant is possible to eliminate the formation of interfering third phase (jellyfish).

The extraction is carried out in a static mode by contacting the solution containing americium, with extra Tom tax HUF, placed in a container taken in a predetermined ratio within a specified time. After extraction, the extractant is washed with nitric acid 1-2,5 M solution and extravert americium in the form of americium nitrate concentrated 4-6 mol/l nitric acid.

As a result of Stripping receive the nitric acid solution-reextract containing 4-6 mol/l nitric acid and americium. When the concentration of americium in at least 3.0 g/l spend the concentration of americium by deposition of americium in the form of americium hydroxide hydroxides of alkali metals or ammonium at pH of 6.0-7.0 and dissolving the obtained precipitate in a solution of nitric acid at a smaller volume, which can be and reextract. If necessary, increase the acidity of the solution to a value of not less than 3 mol/l by the addition of nitric acid.

Then in the solution add the oxalate ion in a mass ratio to the americium (2-7):1 in the form of oxalic acid or ammonium oxalate or diethyloxalate. After stirring and aging the reaction mixture for a specified time get the precipitate of oxalate containing americium.

Share the mother solution and the precipitate containing americium, add water to the precipitate (3-8 volumes of water per 1 volume of sediment) and the oxalate ion in a mass ratio to the americium (1-4):1, then bring mixture to a boil and boil for a specified time. While the use of the and, settled with americium, moving from the precipitate in the solution, forming, apparently, soluble compounds. The precipitate of oxalate of americium are separated from the solution, for example by filtration, dried and calcined to americium dioxide.

1. The method of extraction of americium in the form of americium dioxide from radioactive waste, including the waste dissolution in concentrated nitric acid, oxalate precipitation from a solution containing americium, drying and calcination selected from a solution of oxalate to americium americium dioxide, characterized in that the solution obtained by dissolving waste in concentrated nitric acid with high concentration of cation impurities, one of which is trivalent iron, add the reducing agent to restore the ferric to the ferrous state, after recovery solution with the acidity of nitric acid 1-2,5 mol/l is directed to the extraction of americium solid extractant based on the phosphine oxide raznorabochego (tax HUF) with subsequent washing and reextracting americium 4-6 M solution of nitric acid, and reextract, or received from reextract solution with a concentration of americium at least 3 g/l and the concentration of nitric acid is not less than 3 mol/l exercise oxalate deposition, which is carried out in two stages, one of which is dobavlaut to the solution, containing americium oxalate-ion mass ratio to americium (2-7):1 and then adding to the selected draught of water in a volume ratio to the precipitate (3-8):1, and the second type of the oxalate ion in a mass ratio to the americium (1-4):1, the reaction mixture is boiled and is directed to the selection of americium oxalate from the solution.

2. The method according to claim 1, characterized in that, when dissolved waste get a solution with a concentration of impurity cations 5-12 mol/L.

3. The method according to claim 1, characterized in that as the reducing ferric use rongalit or ascorbic acid or hydrazine.

4. The method according to claim 1, characterized in that reextract get a solution with a concentration of americium at least 3 g/l by deposition of americium hydroxide hydroxides of alkali metals or ammonium at pH of 6.0-7.0 and subsequent dissolution of the precipitate in nitric acid of less volume.



 

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1 ex

FIELD: chemistry.

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FIELD: chemistry.

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1 tbl, 1 ex

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1 ex

FIELD: chemistry.

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FIELD: metallurgy.

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45 cl, 18 dwg, 4 ex

FIELD: metallurgy.

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EFFECT: higher efficiency, lower costs.

1 ex

FIELD: process engineering.

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EFFECT: solution suitable for further extraction.

3 cl, 2 tbl

FIELD: chemistry.

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EFFECT: obtaining high-quality products.

5 cl, 2 tbl, 2 ex

FIELD: rare, dispersed and radioactive metal metallurgy, in particular hydrometallurgy.

SUBSTANCE: invention relates to method for reprocessing of polymetal, multicomponent, thorium-containing radwastes, formed when reprocessing of various mineral, containing rare-earth elements, Nb, Ta, To, V, Zr, Hf, W, U, etc. Method includes treatment of solution and/or slurry with alkaline agent; introducing of sulfate-containing inorganic compound solution and barium chloride; treatment of obtained hydrate-sulfate slurry with iron chloride-containing solution, and separation of radioactive precipitate from solution by filtration. As alkali agent magnesia milk containing 50-200 g/dm2 of MgO is used; treatment is carried out up to pH 8-10; sodium sulfate in amount of 6-9 g Na2SO4/dm2 is introduced as solution of sulfate-containing inorganic compound; barium chloride solution is introduced in slurry in amount of 1.5-3 g BaCl2/dm2. Hydrate-sulfate slurry is treated with solution and/or slurry containing 0.8-16 Fe3+/dm2 (as referred to startingsolution) of iron chloride, followed by treatment with high molecular flocculating agent and holding without agitation for 0.5-2 h. Radioactive precipitate is separated from mother liquor, washed with water in volume ratio of 0.5-2:1; then washed with sodium chloride-containing solution and/or slurry in volume ratio of 0.5-2:1; radioactive precipitate is removed from filter and mixed with mineral oxides in amount of 0.5-0.8 kg MgO to 1 kg of precipitate. Formed pasty composition is fed in forms and/or lingots and presses with simultaneous heating up to 80-1200C.

EFFECT: filtrate with reduced radioactivity due to increased codeposition coefficient of natural Th-232-group radioactive nuclide, in particular Ra-224 and Ra-228, with radioactive precipitates.

10 cl, 1 ex

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