RU2069868C1 - Method for determination of radionuclides of strontium in natural objects - Google Patents

Abstract

FIELD: analytic chemistry. SUBSTANCE: method is carried out by solid extraction with the help of sorbent. This process takes place in nitrate solution (its concentration being 0.1-0.5 M as calculated for nitric acid) for isolation the element to be determined from the sample. Mentioned above nitrate solution contains aqueous solution of sodium dodecyl sulfonate and alcohol solution of dicyclohexyl-18-crawn. Sorbent of 40-160 μm fraction on the base of silica gel being modified with nitrile groups (content of carbon and nitrogen in them being 4.55 and 1.35 %, respectively) is used for said extraction. EFFECT: improves efficiency of the method. 1 dwg

Description

 The invention relates to the analysis of environmental objects for the general and technogenic content of radiotoxic radionuclides, in particular for radioanalytical methods of extraction isolation and concentration. The relevance of this task is explained by the fact that at present environmental problems, especially in connection with the Chelyabinsk and Chernobyl accidents, have acquired a vital character. At the same time, reliable methods for the determination of radionuclides that do not have γ radiation are very laborious and require considerable time.

A known extraction method for isolating the sum of strontium radionuclides in milk, including pre-processing milk to obtain a dry residue, dissolving the latter in water, removing impurities (REE) and Ba by coprecipitation with iron hydroxide and ammonium dichromate, extraction extraction of the sum of strontium isotopes with a solution of dicyclohexyl-18-crown -6 (DCG18K6) in chloroform. The degree of strontium recovery is 75% when strontium is separated from Mg, Ca, ¹⁰⁶ Ru, ¹³¹ J, ¹³⁷ Cs, Ba ¹⁴⁰ , La ¹⁴⁰ contained in the samples.

Chromatographic methods for strontium separation are known. The use of ion exchange is based on the different ability of the elements to be complexed with a number of ligands. The initial solution was evaporated to dryness, the residue was dissolved in several drops of diluted nitric acid, strontium, and yttrium was sorbed on a column filled with Dowex 50 × 8 cation exchange resin, ⁹⁰ Sr was washed with 20 ml of a 1.4 M nitric acid solution at a rate of 1 ml / min, and then washed ⁹⁰ Y with 3 M nitric acid solution (10 ml). When multiple allocation Y ⁹⁰ from one and the same preparation ⁹⁰ Sr ⁹⁰ Y selective elution is carried out ⁹⁰ Y 0.5 M solution of ammonium lactate with pH 2,9-3,45 ⁽⁹⁰ Sr remains on the column). The content of ⁹⁰ Sr is determined by ⁹⁰ Y.

 The listed methods have a number of disadvantages, the most common of which are: insufficient selectivity of strontium (without additional operations), low concentration coefficients, multi-stage, and the need to determine strontium by an independent method. The disadvantages of the above methods should also include the lack of the possibility of isotope analysis of strontium-90.

 Closest to the proposed invention is a method based on the use for the concentration of strontium from solutions obtained after decomposition of the sample, the liquid-phase extraction method followed by radiometric determination of strontium-90 in concentrate [1] The method includes preliminary sample preparation, extraction extraction of the sum of radionuclides, re-extraction of elements , sample exposure and radiometric determination of strontium radionuclides, while sample preparation is carried out by adjusting the content of a acid of 3.8-4.2 mol / l, administration to a concentration of 1-10 mg / ml of stable strontium as a carrier, the sample is treated twice with chloroform at a ratio of organic to aqueous phase (O B) 1.8 2.2: 1 . Subsequent extraction extraction of the sum of strontium radionuclides is carried out with a solution of dicyclohexyl-18-crown-6 (DTSG18K6) for 20-30 s and a ratio of OB 1 (0.8 1.2), the extract is washed twice with 2 mol / L nitric acid at a ratio of OB 1 (0.8 1.2). In the extract, the amount of strontium radionuclides is determined, then strontium is re-extracted with a 1-2% solution of nitrile trimethylene phosphonic acid in sodium hydroxide at a ratio of O: B 1: (0.8 1.2), and re-extraction of DCG18K6 in chloroform from 2-4 mol / l nitric acid. Then, yttrium-90 is determined radiometrically in the aqueous phase and the content of strontium-90 in natural objects is calculated from it. The disadvantage of this method is its complexity and duration of the analysis, as well as low values of the degree of extraction of strontium from acidic solutions, which significantly limits the use of these systems.

 The aim of the invention is to provide a reliable method for the determination of strontium radionuclides, characterized by the simplicity and completeness of extraction of the analyte, and the selectivity of extraction from acidic solutions. The relevance of this task is explained by the problems encountered in connection with the operation of nuclear power plants.

This goal is achieved by the fact that in the method for determining strontium radionuclides, including preliminary preparation of the sample by treating it with nitric acid and adjusting its content to a fixed value, isolating strontium radionuclides from the solution by treating it with DTsG18K6 solution, preparing the target and radiometric measurement, adjusting the nitric acid content to pH 0.1-0.5 m, before treatment with a solution DCH18C6 last added an aqueous solution of sodium dodecylbenzenesulfonate having a concentration of 10 ^-1 -10 ^-4 m, TSG18K6 used in the form of alcohol solution with a concentration of 10 ^-2 -10 ^-4 M, and the resulting cationic complex of the element is isolated using solid phase extraction by bubbling at a rate of 1-10 ml / min through a modified nitrile sorbent silicagel fraction 40-160 .mu.m and the carbon and nitrogen contents of 4.55 and 1.3%, respectively, 3 M nitric acid are desorbed. Targets are prepared by filtering strontium carbonate separated from the eluate through polymer membranes with a pore size of less than 0.5 microns or a blue ribbon filter. A radiometric determination of strontium is then carried out on a flow b-radiometer.

) и силохромы (с диаметром пор в диапазоне от 200-350 и 1000-1500

). Перед химическим модифицированием силикагели и силохромы гидроксилируют и обрабатывают кислотой для удаления ионов металлов с поверхности. Размер частиц сорбентов: 50-100, 100-300 и 300-500 мкм. Сорбенты используют в упаковках по 25, 50, 100, 250, 500 и 1000 см³ и в виде патронов. Патроны представляют собой капсулы из химически устойчивого полимера, заполненные сорбентами. Объем сорбента в патроне 1 мл.In the proposed method for the isolation of strontium using the method of solid phase extraction (TFE). TFE is a relatively new method of concentration, effectively used to isolate trace amounts of elements in solving problems of analysis of environmental objects. The essence of the method is that the isolated metal complex, namely the ionic associate of the cationic complex Sr (ДЦГ18К6) ²⁺ with a hydrophobic anion of an ion-pair reagent grafted onto the surface of a solid support. The sorbent used in the inventive method is obtained by covalent grafting of organic compounds containing a nitrile group to the surface of inorganic carriers, which are silica gels (with pore diameters ranging from 5-70 to 300-500

) and silochromes (with pore diameters ranging from 200-350 and 1000-1500

) Before chemical modification, silica gels and silochromes are hydroxylated and treated with acid to remove metal ions from the surface. The particle size of the sorbents: 50-100, 100-300 and 300-500 microns. Sorbents are used in packages of 25, 50, 100, 250, 500 and 1000 cm ³ and in the form of cartridges. Cartridges are chemically stable polymer capsules filled with sorbents. The volume of sorbent in the cartridge is 1 ml.

The high-density grafting of the alkyl and nitrile groups (at least 3.3 μmol / m ² ) and the use of monofunctional modifiers provide effective screening of the surface of the original carrier.

Characterization of the sorbent used in the work: fraction 40-160 microns, carbon content 4.55% nitrogen 1.3 specific surface area 250 m ² / g. The sorbent is characterized by the general formula SiO ₂ —OSi (CH ₃ ) CH ₂ CH ₂ CN and has a higher polarity than the Diasorb C16 sorbent, which in turn allows it to be more effective for the extraction of ion-associative metal complexes in acidic media, in particular, the Sr complex DTSG18K6 ²⁺ L ₂ .

 The previously mentioned sorbents were used in the chromatography of organic compounds. The main factors determining the degree of strontium extraction in the selected system are: the acidity of the solution, the ratio of the concentrations of DCG18K6 and DCNa, the rate of transmission of the solution through the sorbent. In the table. 1-3 and the drawing shows experimental data on the justification of the selected parameters to achieve the maximum value of the degree of extraction of strontium and the minimum for radiochemical impurities and macrocomponents.

The degree of metal recovery was determined radiometrically using ⁸⁵ Sr, ¹³⁷ CS, ⁴² K, ⁵⁹ Fe, ⁶⁴ Cu, ⁴⁵ Ca, ¹³¹ Ba radionuclides from the residual activity on the filter on a TESLA NRG-603 spectrometer. The activity was chosen so as to ensure a measurement error of not more than 10%. The degree of strontium extraction (Table 1) in the range of pH 6-1, at С _ДЦГ18К6 C _DCNa 1 • 10 ^-3 mol / L, as in the case of С16 sorbent, is an average of 95% and in 0.5 M HNO ₃ 62, 1 M HNO ₃ 59% Under these conditions, the sorbent C16 41 and 13%, respectively.

Changing the concentration ratio between DTSG18K6 and DCNa from 1 • 10 ^-3 to 1 • 10 ^-2 mol / L allows to increase the degree of strontium extraction from a solution of 0.5 M by HNO ₃ to 96% and from 1 M by HNO ₃ to 80% V in the case of sorbent C16, the degree of extraction under these conditions is 77 and 48%, respectively.

Based on the data given in the drawing, this ratio of the concentration of DCG18K6 and DCNa is optimal when strontium is extracted from a 0.5 M solution of HNO ₃ .

 The degree of strontium recovery with a change in the rate of transmission of the solution through the cartridge from 1 to 10 ml / min remains practically unchanged (table. 2).

Under conditions optimal for the extraction of strontium (0.5 M HNO ₃ , C _ДЦГ18К6 C _DCNa 1 • 10 ^-3 mol / l), the sorption of radionuclides of cesium and potassium, elements that interfere with the determination of strontium, as well as copper and iron, which are macrocomponents in most of the analyzed objects.

Subsequent washing of the cartridge with 20-30 ml of 0.5 M HNO ₃ (acidity of the mother liquor), which is used simultaneously for the quantitative transfer of the analyzed sample to the cartridge, makes it possible to obtain an eluate that is practically pure by concomitant radionuclides, especially cesium and potassium, which is especially important in the analysis of heavily contaminated samples, as well as for copper and iron.

In the table. 4 shows the degree of strontium recovery in the presence of a number of certain metals. As can be seen from the table. 4, the presence of iron, copper up to 1 mg / ml, Ba up to 0.1 mg / ml, Ca up to 0.01 mg / ml does not change the degree of extraction of strontium. For complete desorption of strontium from the sorbent, 3 M HNO _{3 was used} . In the table. 5 shows the degree of elution of sorbed strontium in the sorbent. The degree of elution was determined radiometrically from the activity of ⁸⁵ Sr in the eluate on a TESLA NRG-603 γ-spectrometer. With an eluent volume of 5 ml, the elution degree is 97%. After elution, the column is brought into operation. Double distillate (pH 5-6) is passed through until acid is washed, then 5 ml of alcohol, and the column is ready for operation. The speakers are reusable.

 The following are examples of specific applications of the proposed method for determining strontium radionuclides in water, soil and food products.

 Example 1

Analysis of rye grain. 1 kg of rye grain is calcined at 500 ^o C for 6 hours. The resulting ash is treated several times with a mixture of concentrated HNO ₃ and hydrogen peroxide in a ratio of 5: 1, wetting the precipitate when heated (until the grains of coal disappear, the precipitate becomes white). The precipitate was dissolved in 50 ml and 4 M HNO ₃ . An aliquot of 20 ml is taken, diluted with water so that the acidity of the solution is 0.5 M, 20 ml of an aqueous solution of 0.1 M DCNa and 20 ml of an alcohol solution of DCG18K6 are added to the solution, based on the total volume of 200 ml, so that With _DCG18K6 C _DCNa 1 • 10 ^-2 mol / L. Then the solution (V 200 ml) using a peristaltic pump brand PP-2-15 company "Zalimp" (Poland) with a speed of 10 ml / min is passed through a column with a nitrile sorbent (fraction 40-160 microns, 4.55% C, 1 , 3% N). The cartridge is then washed with 20 ml of 0.5 M HNO ₃ at a rate of 1 ml / min. Elution is carried out using 5 ml of 3 M HNO ₃ , passing the solution through the column at a rate of 0.4 ml / min. 5 mg of support (strontium nitrate) was added to the strontium eluate, the pH of the solution was adjusted to 8-9 by adding a saturated solution of Na ₂ CO ₃ or (NH ₄ ) ₂ CO ₃ until the precipitate of strontium carbonate was completely precipitated.

The precipitate formed is filtered through a nuclear filter, dried under an infrared lamp, and activity is measured on a flow b-radiometer. The time spent on the operations of strontium extraction and preparation of radiometric targets (excluding the stage of sample preparation) is 2 hours. The chemical yield for strontium
95%
Example 2

Analysis of rye processed products. 1 kg of rye processed products is calcined at 500 ^o C for 6 hours. The resulting ash is treated several times with a mixture of concentrated HNO ₃ and hydrogen peroxide in a ratio of 5: 1, wetting the precipitate when heated (until the grains of coal disappear, and the precipitate turns white). The precipitate was dissolved in 50 ml of 4 M HNO ₃ . An aliquot of 20 ml is taken, diluted with water, so that the acidity of the solution is 0.5 M. To the solution add 20 ml of an aqueous solution of 0.1 M DCNa and 20 ml of an alcohol solution of DCG18K6, based on a final volume of 200 ml, so that With _DCG18K6 C _DCNa 1 • 10 ^-2 mol / l. Then the solution (V 200 ml) using a peristaltic pump brand PP-2-15 company "Zalimp" (Poland) with a speed of 10 ml / min is passed through a column with a nitrile sorbent (fractions 40-160 microns, 4.55% C, 1 , 3% N). The cartridge is then washed with 20 ml of 0.5 M HNO ₃ at a rate of 1 ml / min. Elution is carried out using 5 ml of 3 M HNO ₃ , passing the solution through the column at a rate of 0.4 ml / min. 5 mg of support (strontium nitrate) is added to the strontium eluate, the pH of the solution is adjusted to 8-9 by adding a saturated solution of Na ₂ CO ₃ or (NH ₄ ) ₂ CO ₃ until the strontium carbonate is completely precipitated.

The precipitate formed is filtered through a nuclear filter, dried under an infrared lamp, and activity is measured on a flow b-radiometer. The time spent on the operations of strontium extraction and preparation of radiometric targets (without taking into account the sample preparation stage) was 2 hours. The chemical yield for strontium is 95%
Soil analysis. The selected soil sample 2.5 g is calcined for 3-4 hours in an electric muffle furnace with a temperature controller at 650 ^o C. The calcined soil sample is leached twice with 50 ml of 4 M HNO ₃ , heating for 30 minutes, each time filtered through a white ribbon filter. The combined filtrate was evaporated to dryness (without over-heating). The precipitate was dissolved in 2 ml of 4 M HNO ₃ by heating under a watch glass. The walls of the glass are washed with hot water, the volume of the solution is adjusted to 16 ml with hot distilled water and then to 50 ml of 0.5 M HNO ₃ . To the solution, add 5 ml of an aqueous solution of 0.1 M DCNa and 5 ml of a 0.1 M alcohol solution of DTsG18K6 calculated on the final volume of 50 ml, then the solution (V 50 ml) using a Zalimp brand peristaltic pump "(Poland) with a speed of 1 ml / min, a nitrile sorbent column (fraction 4-160 μm, 4.55% C, 1.3% N) is passed through the cartridge. The cartridge is then washed with 20 ml of 0.5 M HNO ₃ at a rate of 0.4 ml / min. By adding 5 mg of support to the strontium eluate, the pH of the solution was adjusted to 8-9, adding a saturated solution of Na ₂ CO ₃ or (NH ₄ ) ₂ CO ₃ until the strontium carbonate was completely precipitated. The precipitate formed is filtered through a nuclear filter, dried under an infrared lamp, and activity is measured on a flow b-radiometer. The time spent on the operations of strontium extraction and preparation of radiometric targets (without taking into account the sample preparation stage) was 2 hours. The chemical yield was not less than 95%
The results of determination of strontium radionuclides in rye, products of its processing and soil are summarized in table. 6.

Claims (1)

A method for determining strontium radionuclides in natural objects, including preliminary sample preparation by treating it with nitric acid and adjusting its content to a fixed value, isolating strontium radionuclides from the solution by treating it with dicyclohexyl-18-crown-6 (DTSG18K6) solution, preparing the target and radiometric measurement, according to which radionuclides of strontium are determined, characterized in that the adjustment of the nitric acid content is carried out up to 0.1 0.5 M; before treatment with DCG18K6, aqueous p target of sodium dodecylbenzenesulfonate having a concentration from 10 ^-1 to 10 ^-4 M, DCH18C6 used in the form of alcohol solution with a concentration of 10 ^-2 -10 ^-4 M, and the resulting cationic complex of the element is isolated using solid phase extraction by passing a speed of 1 10 ml / min through a sorbent modified with nitrile groups based on silica gel of a fraction of 40 160 μm and a carbon and nitrogen content of 4.55 and 1.3%, respectively, while the desorption is carried out with 3M nitric acid.

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