RU2850221C1 - COMPOSITE SORPTION MATERIALS BASED ON MIXED FERROCYANIDES K-Co AND K-Cu FOR EXTRACTION OF CAESIUM FROM AQUEOUS MEDIA - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to the production of composite sorption materials. A method for producing composite sorption materials is disclosed, in which a metal salt solution and an aqueous solution of potassium ferrocyanide are combined, the resulting precipitate is washed with distilled water and dried, then granulated and the fraction of the resulting ferrocyanide Me-K with a particle size of 0.2-0.3 mm is separated, a homogeneous solution is prepared by combining high-pressure polyethylene and toluene, ferricyanide Me-K is added to the resulting homogeneous solution and mixed, then the resulting solution is cooled naturally, after which the resulting precipitate is separated by filtration and dried. In this case, cobalt chloride or copper (II) chloride are used as reacting metal salts in the presence of a siloxane-acrylate emulsion.

EFFECT: possibility of extracting caesium radionuclides from radiation-contaminated aquatic environments with 99% efficiency.

1 cl, 5 dwg, 1 tbl

Description

The invention relates to the field of chemical industry and can be used to produce composite sorption materials used to extract Cs ⁺ and ^Cs137 from radiation-contaminated aquatic environments.

A method for producing a sorbent is known, in which a solution of a metal salt and a solution of potassium ferricyanide are combined with stirring, the precipitate formed as a result of the interaction of the salts is washed with water, dried and granulated, obtaining a sorbent (RU Patent No. 2069094, IPC B01J 20/02, 1996).

A drawback of the known solution is that it is not suitable for water purification from cesium radionuclides (Cs ^-137) , as it is designed to extract them from animal bodies. Another drawback of the claimed method is the inability to reuse this sorbent, as the material is not regenerable, as the cesium it absorbs is not completely washed out.

The closest invention is a method for producing a sorbent (RU Patent No. 2787817, 12.01.2023) used to purify radiation-contaminated waters from the cesium radionuclide Cs ¹³⁷ , which results in a sorbent in the form of a polymer containing particles of Ni-K and Zn-K ferrocyanides.

The disadvantage of the claimed invention is the relatively low sorption capacity of the FC K-Ni-PE and FC K-Zn-PE materials; the efficiency of radiocesium extraction is 95%.

The objective of the claimed invention is to develop a technology for creating a composite sorption material designed to extract cesium radionuclide from radiation-contaminated aquatic environments.

The problem is solved in that the method for producing composite sorption materials involves combining, with vigorous stirring for 60 minutes, a metal salt solution, which is a 0.18 M aqueous solution of metal chloride, and a 0.08 M aqueous solution of potassium ferricyanide at a volume ratio of 1:1, the resulting precipitate is washed with distilled water and dried to a constant weight at a temperature of 100 ° C, then granulated and a fraction of the resulting K-Me ferrocyanide with a particle size of 0.2-0.3 mm is separated, a homogeneous solution is prepared by combining high-pressure polyethylene and toluene at a ratio of 1 g: 150 ml with vigorous stirring and heating to a temperature of 120 ° C, K-Me ferrocyanide is added to the resulting homogeneous solution and mixed, then the resulting solution is cooled naturally with stirring for 30 minutes, after which the resulting precipitate is separated filtered and dried for 24 hours at room temperature, differs in that Cobalt chloride or copper(II) chloride are used as reacting metal salts in the presence of a siloxane-acrylate emulsion. A comparative analysis of the claimed invention's features with those of the prototype and similar inventions demonstrates that the claimed solution meets the "novelty" criterion.

The technical result achieved by solving the assigned task is expressed in the high efficiency of radiocesium extraction from contaminated waters, which amounts to 99%.

The features of the invention formula provide a solution to the following functional problems.

The feature “…cobalt chloride or copper (II) chloride are used as reacting metal salts…” describes the K ferrocyanides used to obtain them.-Me metal salts.

The feature “…in the presence of a siloxane-acrylate emulsion” describes the use of a silacrylate emulsion to obtain an ordered porous structure sorption material based on K-Me ferrocyanide.

The independent features of the formula describe the technology for producing K-Me ferrocyanide with a given particle size, as well as the process of imparting hydrophobic properties to the sorption material by introducing polyethylene fibers into its structure.

Fig. 1 shows the X-ray diffraction patterns of the obtained samples:

a – obtained on the basis of FC K-Co-PE,

b – obtained on the basis of FC K-Cu-PE.

Fig. 2 shows model images of the crystal structures of mixed ferrationides.

Fig. 3 shows SEM images of the surface of mixed ferrationides:

a – FC K-Co-PE with the addition of polyethylene,

b – FC K-Cu-PE with the addition of polyethylene.

Fig. 4 shows the low-temperature sorption-desorption isotherms of nitrogen and histograms of the pore size distribution calculated by the DFT method for ferrationides:

a – FC K-Co-PE; b – FC K-Cu-PE.

Fig. 5 shows the isotherms of sorption of ¹³³ Cs from solutions of distilled water:

a – KCoFC-Pe,

b – KCuFC-Pe; approximation of experimental values (○) – 1, using 2 – the Freundlich equation.

The claimed method is carried out on standard equipment as follows.

The synthesis is carried out by slowly adding a mixture of 0.18 M MeCl ₂ solution and siloxane-acrylate emulsion in a ratio of 10:1 to a 0.08 M K ₄ [Fe(CN) ₆ ] solution equal in volume to MeCl ₂ with vigorous stirring for 60 minutes. Upon completion, the formed precipitate is washed with distilled water and dried at 100 °C in a drying oven in an air atmosphere, and the resulting irregularly shaped green granules of K-Me ferrocyanide are separated.

The next step involved producing a composite using a high-density polyethylene-based polymer matrix by integrating the resulting mixed ferrocyanide particles onto the surface of an organic template. Specifically, polyethylene fibers and toluene were mixed in a ratio of 1 g:150 ml with vigorous stirring and heating to 120 °C on a magnetic stirrer until the components were completely dissolved, forming a homogeneous mixture. K-Me ferrocyanide (0.2-0.3 mm particle size) was then added to the resulting solution, and the mixture was stirred on a magnetic stirrer for 60 minutes. As the heterogeneous solution gradually cooled, agglomeration occurred, whereby the polyethylene molecules, hardening through crystallization, bonded the solid K-Me ferrocyanide particles together. The resulting composite was filtered and dried for 24 hours at room temperature in an oven in an air atmosphere. The obtained sorption material is a porous polymer, in the volume of which there are integrated particles of ferration K-Me.

The study of the sorption properties of materials based on mixed Co-K and Cu-K ferrationides was carried out by sorption of the stable cesium isotope ( ¹³³ Cs) from solutions under static conditions.

Distilled and seawater served as the solutions in this experiment. The concentration of stable cesium introduced into each solution was approximately 150 mg/L. A 10 mg sample of the sorbent was placed in an Eppendorf tube, and 10 ml of stable cesium solution (s/l = 1000 ml/g) was added. The series of tubes was mounted on a vertical shaker and stirred at 20 rpm. Sorption was carried out for 48 hours. The sorbent was then separated from the solution on a blue ribbon filter, and the residual Cs ⁺ ion content was determined using AAS.

The calculation of the degree of purification (RE, %) was carried out according to the formula:

, (1)

where C ₀ is the initial concentration of Cs ⁺ in the solution, mg/l; C ₁ is the concentration of Cs ⁺ in the solution after sorption, mg/l.

For mathematical processing of experimental data on sorption isotherms, well-known models of sorption at the solid/liquid interface were used.

Freundlich equation:

G=K _f ⋅C ^m , (2)

where C is the equilibrium concentration of Cs ⁺ (mg/l); K _f is the Freundlich constant, which characterizes the relative adsorption capacity and represents the adsorption value at an equilibrium concentration equal to unity; m is the index of heterogeneity of exchange centers, which characterizes the change in the heat of adsorption depending on the degree of their filling,

Langmuir equation:

(3)

where Gmax is the maximum sorption value (mg/g); C is the equilibrium concentration of Cs ⁺ (mg/l); Kl are the adsorption equilibrium constants characterizing the adsorbent-adsorbate bond energy,

Combined Langmuir-Freundlich equation:

(4)

where G _max is the maximum sorption value (mg/g); C is the equilibrium concentration of Cs ⁺ (mg/l); Kl _f are the adsorption equilibrium constants characterizing the adsorbent-adsorbate bond energy; m is the index of heterogeneity of exchange centers characterizing the change in the heat of adsorption depending on the degree of their filling. The approximation of the experimental data by the specified equations in nonlinear form was performed using the SciDavis program.

The sorption characteristics of the samples were determined using the sorption of trace amounts of the ¹³⁷ Cs radionuclide as an example. Experiments were conducted under static conditions by continuously stirring a sample of air-dried sorbent weighing approximately 0.1 g, weighed to an accuracy of 0.0001 g, with 20 cm ³ of solution for 48 hours. The mixture was then filtered through a "white ribbon" paper filter, and the specific activity of ¹³⁷ Cs in the filtrate was determined by direct radiometry using an SKS-50M spectrometric complex (Green Star Technologies, Moscow). Based on the analysis results, the distribution coefficient (K _d ) of the corresponding radionuclide was calculated using the formula:

, (5)

where A _o , A _p are respectively the specific activity of the radionuclide in the initial solution and in the filtrate, Bq/dm ³ ; V _p is the volume of the liquid phase, cm ³ ; m _c is the mass of the sorbent, g.

A 1 mol/L _NaNO3 solution and seawater sampled in the Sevastopol Bay of the Black Sea (salinity 18.1, pH 7.75-8.25) were used as the liquid phase. Before the experiments, indicator amounts of ^137Cs radionuclide (approximately ¹⁰⁵ Bq/dm3 ⁾ were added to the solutions.

According to the X-ray diffraction data (see Fig. 1), the obtained materials have a highly organized crystalline structure, as evidenced by the high intensity of their diffraction maxima in the X-ray diffraction patterns of the analyzed materials.

To visualize the crystal structures of the obtained mixed ferrocyanides, their 3D structural models were constructed (see Fig. 2) using VESTA software. The unit cell parameters of the synthesized ferrocyanides match the calculated ones and correspond to the cubic form a=b=c=9.96000 Å.

Microscopic examination revealed that the surface of FC K-Co-PE (see Fig. 3) has a monolithic structure, with small particles formed during sample preparation present on the surface. The use of polyethylene results in the formation of a porous structure consisting of small, irregularly shaped crystallites that bind the polyethylene fibers together. SEM images of the surface of materials based on mixed FC K-Cu-PE are also shown. The sample has a structured surface and is characterized by a fine-grained porous structure. The introduction of polyethylene similarly leads to the formation of a looser structure in the form of a polymer with integrated FC K-Cu particles and an increase in porosity in the presence of polyethylene.

Fig. 4 shows that the low-temperature nitrogen adsorption-desorption isotherm for the (FC K-Co-PE) sample belongs to type I according to the IUPAC classification, characteristic of microporous bodies with a relatively small fraction of the external surface area of 57.1 ^m2 /g. Adsorption in micropores is described by an H1 type isotherm, which is characterized by the presence of a nearly horizontal plateau. The DFT method determined that complete filling of the pores occurs at very low relative pressures, which is confirmed by an identical range (5-20 nm) of the mesopore size. An obvious difference is observed for the (FC K-Cu-PE) sample, the SBET value increases to 124.9 m2/g, and the transition in the shape of the hysteresis loop of the nitrogen adsorption-desorption isotherm from type H1 to H2 indicates the formation of mesopores and macropores in the sample. This is confirmed by calculations using the DFT method, where the pore size distribution graph shows that mesopores in the range of 10–55 nm in size are formed in the sample volume.

The sorption properties of composite sorbents based on mixed polyethylene-based fluorocarbon sorbents were studied by sorption of a stable cesium isotope from solutions of distilled and seawater. The concentration of the introduced stable cesium in each solution was approximately 150 mg/L. Based on the residual cesium content in the analyzed samples, the sorption parameters of the studied materials were calculated using the AAS method. The cesium ion sorption isotherms (see Fig. 5) can be classified as H-type, which is characterized by a vertical initial section due to the high affinity of the sorption sites for cesium ions. The obtained isotherms are characterized by a clearly defined plateau, indicating the achievement of adsorption equilibrium and the filling of all sorption sites. The experimental data on the Cs ⁺ ion sorption isotherms were processed using the Freundlich model.

Table 1. Constants of the Langmuir and Freundlich equations calculated after approximating the experimental data

Equation Parameters FC K-Co-PE FC K-Cu-PE Langmuir G _max 401.81 ± 42.3 361.01 ± 30.6 K ₁ 0.010 ± 0.004 0.009 ± 0.003 R ² 0.96 0.96 Freundlich K _f 44.84 ± 16.54 35.47 ± 8.98 m 0.172 ± 0.054 0.231 ± 0.036 R ² 0.77 0.95

The degree of purification of the studied solutions from cesium using sorbents obtained on the basis of K-Co, K-Cu ferrocyanides in a composition with a siloxane-acrylate emulsion and polyethylene can reach 99%.

The average value of the distribution coefficient of cesium in seawater is 3.8×10 ⁴ ml/g with a solid/liquid ratio of 1000 ml/g, which indicates the potential for their use in purifying seawater from radioactive cesium.

Claims (1)

A method for producing composite sorption materials, in which a metal salt solution, which is a 0.18 M aqueous solution of metal chloride, and a 0.08 M aqueous solution of potassium ferricyanide are combined with intensive stirring for 60 minutes at a volume ratio of 1:1, the resulting precipitate is washed with distilled water and dried to a constant weight at a temperature of 100 ° C, then granulated and a fraction of the resulting Me-K ferrocyanide with a particle size of 0.2-0.3 mm is separated, a homogeneous solution is prepared by combining high-pressure polyethylene and toluene at a ratio of 1 g: 150 ml with intensive stirring and heating to a temperature of 120 ° C, Me-K ferrocyanide is added to the resulting homogeneous solution and mixed, then the resulting solution is cooled naturally with stirring for 30 minutes, after which the resulting precipitate is separated by filtration and dried for 24 hours at room temperature, characterized in that cobalt chloride or copper (II) chloride are used as reacting metal salts in the presence of a siloxane-acrylate emulsion.