RU2523823C2 - Method of extracting caesium radionuclides from aqueous solutions - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to sorption extraction of caesium radionuclides from aqueous solutions. The method of extracting caesium radionuclides includes filtering an aqueous solution through a selective sorbent which is iron-potassium ferrocyanide on a support, desorption of caesium from the sorbent with an alkaline solution containing Trilon B and potassium oxalate. The eluate obtained from desorption is further filtered through a sorbent which is nickel-potassium ferrocyanide.

EFFECT: faster caesium extraction and minimal volume of obtained concentrate containing caesium radionuclides.

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Description

The invention relates to a technology for the sorption extraction of radionuclides from aqueous solutions and can be used for the purification of liquid radioactive waste and in radioanalytical chemistry, with environmental monitoring, in order to determine the content of cesium radionuclides in sea and fresh water and in various technological solutions.

A known method for the extraction of cesium-137 from aqueous solutions by coprecipitation with a precipitate of nickel ferrocyanide, requiring a significant amount of time for the complete extraction of cesium (Radiochemistry, 2008, vol. 50, No. 1, p. 57-59).

A known method of extracting cesium-137 from tap water using ferrocyanides of iron and copper deposited on a canvas of polyacrylonitrile (PAN) (Inorganic materials, 1999, v. 35, No. 8, p. 949-952). This method requires a large consumption of sorbent and considerable time for the complete extraction of cesium.

A known method of extracting radioactive cesium from technological solutions and liquid waste of nuclear power plants, including the use of iron ferrocyanide as a selective sorbent of cesium (AS USSR No. 1686960, Remez V.P. and others from 06.22.1991). The disadvantage of this method is the low speed of cleaning solutions.

Closest to the claimed method according to the technical nature, purpose and achieved result is a known method of processing low-saline liquid radioactive waste (RU 2437177 from 11.25.2010), selected as a prototype. This method consists in filtering a solution containing cesium radionuclides through a selective sorbent based on nickel-potassium ferrocyanide applied to sawdust, 1-4 mm in size. After use, the sorbent is burned at a temperature of 800-1000 ° C, which leads to a reduction in the generated solid radioactive waste by 40-60 times.

The main disadvantage of this method is the use of a large amount of expensive toxic nickel-potassium ferrocyanide, as well as the need for its thermal destruction at temperatures up to 1000 ° C under conditions of transition of cesium into an aerosol state, which requires the use of complex and expensive equipment. In addition, if we take into account that the ash content of sawdust cannot be less than 3-5%, and the decomposition at 1000 ° С of nickel-potassium ferrocyanide will lead to the formation of nickel, iron and potassium compounds in an amount of at least 5-8% by weight of the initial sorbent , it can be determined that the reduction in the generated solid radioactive waste from burning treated sorbents will not be 40-60 times (as stated in the prototype), but not more than 10 times, which was repeatedly established in practice by the author of the claimed invention (Remez V. P. "Environmental protection for the sake of active contaminants through the creation and use of pulp and inorganic sorbents ", 1999, thesis for the degree of Doctor of Technical Sciences, s.163-167).

The aim of the invention is the creation of an economical method for the extraction of cesium radionuclides from aqueous solutions, which allows you to quickly and efficiently concentrate cesium isotopes, obtaining the final concentrate of radionuclides of a minimum volume.

This goal is achieved in that an aqueous solution containing cesium radionuclides is first filtered through a cesium selective sorbent - iron-potassium ferrocyanide, deposited on durable granules or fibers (zeolite, silica gel, PAN, wood pulp, etc.). After the entire volume of the solution has passed through the sorbent column, the iron-potassium ferrocyanide layer is dissolved in three to four volumes of a solution containing 1-5 g / l Trilon B, 1-5 g / l potassium oxalate at pH = 10-12. The resulting eluate is filtered through a column of nickel-potassium ferrocyanide chemically stable in this medium, applied to strong granules or fibers of mineral or organic composition. Since nickel-potassium ferrocyanide is chemically stable in an alkaline trilonate-oxalate medium and is highly selective for cesium, cesium radionuclides completely transfer from the eluate to the solid phase of the sorbent.

The ratio of the volumes of the sorbent based on iron-potassium ferrocyanide to the volume of the nickel-containing sorbent is selected in the range from 10 to 100, depending on the problem being solved. A large amount of sorbent based on iron ferrocyanide used in the first stage of the implementation of the proposed method allows you to quickly extract cesium radionuclides from a large volume of the solution to be purified, and the minimum amount of nickel-containing sorbent used in the second stage provides a significant reduction in the volume of solid radioactive waste containing cesium radionuclide concentrate .

The granules or carrier fibers remaining after dissolving the iron-potassium ferrocyanide with an alkaline trilonate-oxalate solution do not contain radionuclides (since all cesium is converted to the eluate) and can be reused to produce new batches of sorbents or can be disposed of as inactive materials.

In the presence of equipment providing safe thermal decomposition of the obtained concentrates, in the second stage of the proposed method, nickel-potassium ferrocyanide deposited on a combustible substrate (sawdust, cellulose, etc.) can be used, which will allow, as in the prototype method, by burning spent sorbent, reduce the amount of solid radioactive waste received by 3-4 times.

Since the nickel salts used to prepare the ferrocyanide sorbent are about 30 times more expensive than iron salts, and the sanitary standards for the discharge of industrial wastes containing nickel are 50 times more stringent than iron-containing effluents, the cost of the sorbent based on iron-potassium ferrocyanide is several times cheaper than nickel based sorbent. Therefore, a decrease in the amount of nickel ferrocyanide used for the concentration of cesium by 10-100 times gives a significant economic effect.

In addition, the rate of extraction of cesium from aqueous solutions with iron-potassium ferrocyanide is higher than that of nickel-potassium ferrocyanide (Table 1), which can significantly reduce the total concentration time of cesium.

Table 1 Sorption of cesium-137 and seawater (Peter the Great Bay), volumetric activity of the source seawater for cesium-137 1.7 × 10 ³ Bq / l ³ Filtration rate of sea water, m / h The number of purified (before the breakthrough) thousands of column volumes of sea water Iron-Potassium Ferrocyanide Nickel Potassium Ferrocyanide twenty thirty thirty 40 thirty 25 60 thirty 22 80 28 21 one hundred 26 eighteen

Both sorbents contained 10% ferrocyanide-containing material deposited on granulated wood pulp with a grain size of 0.5-1 mm.

The following are examples of the implementation of the proposed method.

Example 1

Sorption of cesium-137 from 1000-liter seawater samples (Peter the Great Bay), volumetric activity 3.2 × 10 ⁵ Bq / m ³

Prototype The inventive method Sorbent 50 cm ³ nickel-potassium ferrocyanide, cleans up to breakthrough of 20 thousand column volumes of solution The first stage: 1 l of iron-potassium ferrocyanide Cesium recovery time 33 hours 2.5 hours The volume of the final concentrate (nickel-potassium ferrocyanide) with cesium-137 50 cm ³ Second stage: Dissolution of the concentrate obtained in the 1st stage with 3 liters of alkaline trilonate-oxalate solution and extraction of cesium-137 from the obtained eluate in 10 cm ^{3 of} nickel-potassium ferrocyanide in 30 minutes Total concentration time 33 hours 3 hours The volume of concentrate obtained 50 cm ³ 10 cm ³ The amount of ash residue obtained by burning cesium-137 concentrate 10 cm ³ 2 cm ³

From the presented results it is seen that the extraction time of cesium-137 by the claimed method is reduced by more than 10 times compared with the prototype, and the volume of the resulting radioactive concentrate is reduced by 5 times.

The data presented in example 1 were obtained during the development of rapid analysis of sea water for environmental monitoring of migration of cesium isotopes in the ocean environment. It was shown that the cost of sorbents and reagents in the inventive method is 3-5 times less than the cost of the sorbent used in the prototype, and taking into account the ship time required for the collection and processing of sea water samples, the inventive method is 12-17 times cheaper .

Example 2

Sorption of cesium-137 from the floor drain of a nuclear power plant at an initial volumetric activity of 1.4 × 10 ⁴ Bq / L. Before the "slip" missed 3000 liters. When using the prototype, the concentration time was 125 hours, the volume of the obtained concentrate was 150 cm. When implementing the inventive method, the total concentration time (both stages) was 11 hours, and the volume of the obtained cesium-137 concentrate was 40 cm ³ .

The composition of the trilonate-oxalate alkaline solution used to wash cesium radionuclides from the sorbent based on iron-potassium ferrocyanide, used in the first concentration stage, was selected experimentally. It was shown that lower concentrations of reagents do not completely transfer cesium radionuclides from the sorbent into the solution, and the use of large quantities of reagents is not economically feasible.

The ratio of the volumes of sorbents (iron-potassium ferrocyanide to nickel-potassium ferrocyanide), which is in the range from 10 to 100, is selected based on the requirements of the tasks to be solved related to the extraction of cesium radionuclides from aqueous solutions. So, to solve the radioanalytical problems associated with obtaining a radiocesium concentrate of a given volume (for gamma spectrometry of the drug in a specific detector volume), the volume of nickel-potassium ferrocyanide used in stage 2 is determined by the volume of the detector, and the volume of iron-potassium ferrocyanide ( Stage 1) is selected based on the time required to extract cesium isotopes from the original sample.

When cleaning liquid radioactive waste from cesium isotopes, when it is necessary to obtain a highly active concentrate of a minimum volume suitable for long-term storage, the ratio of sorbent volumes in the range of 80-100 is chosen, which allows for a slight increase in the concentration of radioactive cesium to obtain minimal amounts of radioactive waste.

Claims (1)

A method of extracting cesium radionuclides from aqueous solutions, comprising filtering the solution through a selective sorbent, which is iron-potassium ferrocyanide deposited on a carrier, eluting cesium with a solution of Trilon B and potassium oxalate, filtering the eluate through nickel-potassium ferrocyanide deposited on a carrier, characterized in that the ratio of sorbents based on iron-potassium ferrocyanide and nickel-potassium ferrocyanide is (10-100): 1, and the eluting solution contains 1-5 g / l Trilon B and 1-5 g / l potassium oxalate at pH = 10-12.