RU2286207C2 - Floating sorption-active polymeric sorbent for purification of the aqueous mediums from cerium radionuclides - Google Patents

Abstract

FIELD: chemical industry; purification of the aqueous medium from cesium radionuclides.

SUBSTANCE: the invention presents the floating sorption-active polymeric sorbent for purification of the polluted aqueous mediums including cesium radionuclides and containing as the filler nickel ferrocyanide of 1-100 nanometers fractions and the binder at the ratio of their components (in mass %): the filler - nickel ferrocyanide - 5-90; the binder - ultrahigh molecular polyethylene - 10-95 with their molecular mass of (1-4)10⁶. The invention allows to up-grade efficiency of the aqueous mediums polluted with cesium radionuclides.

EFFECT: the invention ensures improvement of efficiency of the aqueous mediums polluted with cesium radionuclides.

5 ex, 4 tbl

Description

The invention relates to a technology for the purification of aqueous media from radioactive contamination by sorption. The claimed technical solution can be used both for the treatment of aqueous media from radioactive contamination by sorption in storage tanks for liquid radioactive waste (LRW), and during the operation of power plants. The wastewater of these plants containing cesium radionuclides is characterized by an indefinite salt composition. Purification from radionuclides can be carried out by a sorbent floating on the surface, selective to cesium radionuclides.

The known method [RF patent No. 2135278, IPC B 01 J 20/18, G 21 F 9/12, publ. 27.08.99 The method of sorption extraction of cesium radionuclide from aqueous media. / Goncharov B.V., Bytsan N.V., Doilnitsyn V.A.] purification of aqueous media from cesium radionuclides using a porous composite material including a natural sorbent of mordenite fractions of 5-15 μm and binders of foamed polyvinyl formal taken in the ratio (15- 85) - (85-15) wt.%. Sorbent is made in the form of blocks that can be lowered to the bottom of LRW storage tanks for preliminary water purification from cesium radionuclides. The disadvantage of this material is the presence of two competing processes during operation: the sorption of oil products and the sorption of radionuclides, and the sorption of cesium radionuclides is small, since the main goal is the sorption of oil products. Also, due to two competing processes, the kinetics of sorption is small. The next disadvantage of this sorbent is the difficulty of its subsequent extraction, because it sinks to the bottom of the tank.

Known porous composite sorbent [RF Patent No. 2154526, IPC B 01 J 20/18, G 21 F 9/12 from 20,08,1999. Composite floating sorbent for the purification of aqueous media from cesium radionuclides and a method for sorption extraction of cesium radionuclides from aqueous media / Goncharov BV, Doilnitsyn VA, Ananyeva TA, Volkov FV] for cleaning aqueous media from of cesium radionuclides, including filler - aluminosilicates (vermiculite, mordenite) of fractions 5-250 microns and a binder - ultra-high molecular weight polyethylene (UHMWPE) with mol.m. (1-3) · 10 ⁶ taken in the ratio: filler 10-60%, a binder of 40-90%. The efficiency of purification from radionuclides, in particular cesium radionuclides, is low. (K _p = 300-25000 in 28 days) One of the drawbacks is that the use of mordenite having a layered structure, a highly developed specific surface, as well as an affinity for oil products, leads to selective sorption of oil products and a decrease in the degree of extraction of radionuclides in combined wastewater.

The closest analogue to the claimed technical solution is a floating composite material [patent No. 2231838 IPC G 21 F 9/12, B 01 J 20/22 from 06/27/2004. Floating composite material for the purification of aqueous media from cesium radionuclides and / or petroleum products. Goncharov BV, Doilnitsyn VA, Yankevich MI, Kvitko KV, Surzhko LF, Hadeeva VV, Utkin AV] - sorbents based on fiber-porous high molecular weight polyethylene containing fine (but not nanodisperse) powder of nickel ferrocyanide in an amount of 3 wt.% and microbiological culture of Kibdelosporandium aridum in an amount of up to 10 ⁷ cells per gram of polymer (WFP-FTs-3-Ka), and a sorbent based on fiber-porous high molecular weight polyethylene containing finely divided powder of nickel ferrocyanide in an amount of 3 wt.% (WFP-FTs-3). The disadvantage of these sorbents is the insufficiently high degree of extraction of cesium radionuclides, since the sorbent has a block shape, some of the filler may not be available, while the inventive sorbent has a film shape (thickness h = 0.046-1.22 mm), which allows access to to the entire filler.

The technical result of the claimed solution is: increasing the degree of extraction of cesium radionuclides from radioactively contaminated aqueous media. This object is achieved in that in a floating sorption-active polymer sorbent for the purification of contaminated aqueous media, including radionuclides, containing ultrahigh molecular weight polyethylene as a binder, nickel ferrocyanide of fractions 1-100 nm is used as a filler with the content of components, wt.%: Filler - nickel ferrocyanide 5-90, a binder - ultra-high molecular weight polyethylene 10-95 with mol.m. (1-4) · 10 ⁶ 10-95 with a polymer concentration of 1-7% in the initial solution.

It is known that ferrocyanides exhibit selectivity for cesium radionuclides [Krolko A.P. Chemistry of ferrocyanides. - M .: Nauka, 1971], therefore it is advisable to use them as sorbents for the extraction of cesium radionuclides, however, ferrocyanides are bulk solids, and therefore their use for sorption of cesium radionuclides (as precoop filters, etc.) is difficult (additional radiation hazardous technological operations). Significant differences of the proposed sorbent from the closest analogue is the joint use of nickel ferrocyanide with a binder - ultra-high molecular weight polyethylene - the following: the sorbent has the best sorption kinetics; upon receipt of the sorbent, one technological operation disappears (filler, solvent and polymer are loaded together).

The significance of the differences lies in the fact that the particle sizes of nickel ferrocyanide are in the nanoscale range. This range is characterized by the unique properties of substances and, in particular, significantly higher chemical activity of substances [Nanotechnology in the coming decade. Ed. Roko M.K., Williams R.S., Alivisatos P. - M .: Mir, 2002, - p. 3]. The increased chemical activity is manifested in a significantly better sorption kinetics (Table 1) of radionuclides and in achieving greater sorption completeness compared to a sorbent having a similar size of the matrix, having not nano- but macro-sizes of sorbent particles, i.e. sizes lying in the range of not 1-100 nm, but in the range of 10-30 microns. Moreover, the noted sorption effects are due not only to a simple increase in the total surface of the sorbent particles upon transition to smaller particles, but also to more subtle processes associated with the achievement of the nanoscale particle size by the sorbent particles. The use of nanosized particles of the sorbent makes it possible, in addition to purely sorption problems, to solve such a problem as the creation of very thin, floating sorbents with high sorption efficiency. The creation of composite sorption materials ensures reliable fixation of sorbent particles in the polymer matrix, the thickness of the polymer film in the created film composite material must exceed the sizes of the included particles by at least several times, and with a certain margin, by an order of magnitude. Therefore, for composite materials based on nanosized particles, it is possible to achieve thicknesses of the film composite at, for example, 10-30 μm, which is difficult to achieve for materials with particles in the micrometer range and, in some cases, impossible. The UHMWPE matrix differs from other polymer matrices in the possibility of producing meso- and macro-porous structures with a high specific surface. During the experiment, using adsorption methods (Fourier-IR spectroscopy, McBen), the specific surface of UHMWPE was determined (S ⁰ _beats = 34.6 m ² g ^-1 ). The porous structure of the CM is formed both during the introduction of the filler and in the process of curing the matrix. The amount of filler introduced is limited by the bulk density of the filler, which is determined by the size of the particles and their polydispersity. The used nickel ferrocyanide nanoparticles are polydisperse, in addition, they have a spherical shape. If you use spherical particles of nickel ferrocyanide with a size of 10-30 μm, then in this case the bulk density of the particles is minimal and high degrees of filling (as in example 3) lead to the appearance of particles on the surface of the material, which during operation are not retained and pass into the solution to be cleaned. In addition, when creating relatively thick films with a thickness of 10-30 μm and a significant degree of filling (50% or more by weight of the composite sorbent), with intensive stirring of the solution in contact with the sorbent, sintering of particles of the sorbent from the composite film sorption material is observed (table 2) .

In addition, particles of nickel ferrocyanide with a size of 10-30 μm during UHMWPE crystallization, by virtue of their size, have an orienting effect on the film, decreasing porosity (S ¹ _beats = 15.1 m ² g ^-1 ) and reducing the sorption efficiency of the material, since particles require a larger amount of binder and it goes into the discharge of thin films, which according to statistical theory reduces the defectiveness of the film, that is, makes it monolithic, non-porous. Due to its developed surface, nanoparticles of nickel ferrocyanide, when the laws of quantum mechanics begin to act, form agglomerates that loosen the structure of the material. This provokes the formation of closed pores that promote buoyancy and open channels that provide access of the sorbate to the active filler. The specific surface of the material increases (S ² _beats = 47.2 m ² g ^-1 ), ensuring the efficiency of sorption (table 1).

The use of nanodispersed particles with high sorption efficiency allows one to achieve the required completeness of water purification from radionuclides even in the case of not very high completeness of sorbent incorporation into the matrix. In this case, a sufficiently large free volume remains in the polymer matrix to create closed pores in it, which determine the buoyancy of the film sorption material. When the degree of inclusion is about 30-50% and the ratio of the volumes of closed and open pores in the sorbent is 1: 1 (open pores are necessary for the transport of radionuclides from the solution to the sorption centers in the polymer material), the sorbents are buoyant for a very long time - at least 1, 5-2 years, which can be considered an extremely high result for this class of sorbents.

During the experiment, it was found that films containing 90% nickel ferrocyanides are high strength, contain open and closed pores of meso- and macro-sizes, are able to work for a long time, covering the surfaces to be cleaned, thereby screening contaminated water bodies from the environment and effectively removing radionuclides.

Thus, the claimed combination of features provides both its properties and ensures both sorption efficiency and duration of operation, excluding the chipping of nickel ferrocyanide due to the high adhesion of the filler located on the surface (example 3) and the porosity of the matrix based on UHMWPE.

Table 1 Elimination time of 50% (τ _0.5 ) and 90% (τ _0.9 ) of cesium-137 radionuclides from 0.1 mol / L sodium chloride solution, days The particle size of the sorbent, nm τ _0.5 τ _0.9 10-90 four 9 10-10 ³ 7 fifteen (3-4) · 10 ⁴ 9 23

Film thickness 50-60 microns.

table 2 The intensity of chipping of a ferrocyanide sorbent from a film 50-60 μm thick at 50% filling of the polymer matrix with a sorbent The particle size of the sorbent, nm The intensity of the spalling particles of the sorbent 1 day 30 days 10-90 - - (3-4) · 10 ⁴ + ++ - lack of spalling;
+ weak chipping (single particles are chipping);
++ strong chipping (a significant number of sorbent particles are chipping).

Example 1

Obtaining sorption-active material for water purification of radionuclides is as follows. In a heated apparatus with a three-blade mixer [Vasiltsov EA, Ushakov V.G. Apparatus for mixing liquid media: a reference guide. L .: Chemistry, 1972. - 464 p.] Preparing a UHMWPE solution with a concentration of 2 wt.%. As a solvent, paraffin is used (TU 6-09-3637-87). At 140 ° C and continuous stirring (150 rpm), the solvent is loaded into the apparatus; 50 wt.% UHMWPE (TU 6-05-1896-80) with a mol.m. (1-4) · 10 ⁶ and the filler is nickel ferrocyanide in an amount of 50 wt.% And the suspension process takes place for 1 min. Dissolution is carried out with increasing temperature to 150 ° C for 9 minutes with constant stirring. The resulting composition is placed in a mold and cooled at room temperature. The cooled composite to remove paraffin from it is extracted with C ₆ -C ₁₀ hydrocarbon at the boiling point of the hydrocarbon. Then the material is dried at 70 ° C for 30 minutes. The finished sorption-active material is a composite with a filler content (nickel ferrocyanide) of 50 wt.%, And a binder content (UHMWPE) of 50 wt.%.

Example 2

Obtaining sorption-active material for water purification of radionuclides is as follows. In a heated apparatus with a three-blade mixer [Vasiltsov EA, Ushakov V.G. Apparatus for mixing liquid media: a reference guide. L .: Chemistry, 1972. - 464 p.] Preparing a UHMWPE solution with a concentration of 2 wt.%. As a solvent, paraffin is used (TU 6-09-3637-87). At 140 ° C and continuous stirring (150 rpm), the solvent is loaded into the apparatus; 95 wt.% UHMWPE (TU 6-05-1896-80) with a mol.m. (1-4) · 10 ⁶ and the filler is nickel ferrocyanide in the amount of 5 wt.% And the suspension process takes place for 1 min. Dissolution is carried out with increasing temperature to 150 ° C for 9 minutes with constant stirring. The resulting composition is placed in a mold and cooled at room temperature. The cooled composite to remove paraffin from it is extracted with C ₆ -C ₁₀ hydrocarbon at the boiling point of the hydrocarbon. Then the material is dried at 70 ° C for 30 minutes. The finished sorption-active material is a composite with a filler content (nickel ferrocyanide) of 5 wt% and a binder content (UHMWPE) of 95 wt%.

Example 3

Obtaining sorption-active material for water purification of radionuclides is as follows. In a heated apparatus with a three-blade mixer [Vasiltsov EA, Ushakov V.G. Apparatus for mixing liquid media: a reference guide. L .: Chemistry, 1972. - 464 p.] Preparing a UHMWPE solution with a concentration of 2 wt.%. As a solvent, paraffin is used (TU 6-09-3637-87). At 140 ° C and continuous stirring (150 rpm), the solvent is loaded into the apparatus; 10 wt.% UHMWPE (TU 6-05-1896-80) with a mol.m. (1-4) 10 and filler - nickel ferrocyanide - in the amount of 90 wt.% And, the suspension process takes place for 1 min. Dissolution is carried out with increasing temperature to 150 ° C for 9 minutes with constant stirring. The resulting composition is placed in a mold and cooled at room temperature. The cooled composite to remove paraffin from it is extracted with C ₆ -C ₁₀ hydrocarbon at the boiling point of the hydrocarbon. Then the material is dried at 70 ° C for 30 minutes. The finished sorption-active material is a composite with a filler content (nickel ferrocyanide) of 90 wt.%, And a binder content (UHMWPE) of 10 wt.%.

Example 4

The effectiveness of water purification from ¹³⁷ Cs radionuclides was determined using a working solution of sodium chloride with a NaCl concentration of 1 mol / L containing cesium radionuclides in an amount of (5-7) 10 ⁵ Bq / L.

50 ml of the indicated solution and 50 mg of sorbents were added to hermetically sealed glass jars. As sorbents we used ultra-high molecular weight polyethylene containing nanodispersed powder of nickel ferrocyanide (FCN) in an amount of 5.0 wt.% (UHMWPE-5% FCN), 10 wt.%, (UHMWPE-10% FCN), 30 wt.% (UHMWPE -30% FTsN), 50 wt.% (UHMWPE-50% FTsN), 90 wt.% (UHMWPE-90% FTsN).

The closest analogues were used as comparison sorbents: a sorbent based on fibrous-porous high molecular weight polyethylene containing finely dispersed (but not nanodispersed) nickel ferrocyanide powder in an amount of 3 wt.% (WFP-FC-3), as well as a sorbent based on fibrous-porous high molecular weight polyethylene containing finely divided powder of nickel ferrocyanide in an amount of 3 wt.% and microbiological culture of Kibdelosporandium aridum in an amount of up to 10 ⁷ cells per gram of polymer (WFP-FTs-3-Ka). In addition, KU-2-8 cation exchanger in sodium form, which is widely used in water treatment practice, was used as a comparison sorbent.

The contents of the boxes were mixed 1 time per day. After 1, 7, 14, 28, and 59 days, samples of the solution were taken for radiometric determination of the activity of the solution — the content of cesium radionuclides in the solution.

The activity was measured using a gamma spectrometer with a Ge (Li) detector with a volume of 100 cm ³ by measuring the intensity of the gamma line 661 keV, which is typical for the decay of ¹³⁷ Cs. Based on the found activity values of the initial (I _ref ) and equilibrium (I _equal ) solutions, the distribution coefficient of radionuclides (Cr, ml / g) was calculated by the formula

,

,

where I _ref is the specific volumetric activity for cesium-137 of the initial solution (Bq · l ^-1 ); I _equal - specific volumetric activity of cesium-137 equilibrium solution (Bq · l ^-1 ); V is the volume of the solution (ml); m is the mass of the sorbent in contact with the solution (g).

The results of experiments on the sorption of cesium radionuclides are presented in table 3.

Table 3 The efficiency of sorption of cesium radionuclides from 1 mol / l sodium chloride solution #example / Sorbent The value of the distribution coefficient ¹³⁷ Cs (K _p , ml / g) at the time of contact of the sorbent with the solution, days. one 6 fourteen 28 59 No. 2. UHMWPE-5% FCS 7.3 · 10 ² 2.9 · 10 ³ 6.910 ³ 1.7 · 10 ⁴ 1.9 · 10 ⁴ No. 4. SVMPE-10% FCS 7.910 ² 3.0 · 10 ³ 8.110 ³ 1.8 · 10 ⁴ 2.0 · 10 ⁴ No. 5. UHMWPE-30% FCS 8.7 · 10 ² 1.2 · 10 ⁴ 2.0 · 10 ⁴ 2,310 ⁴ 2.4 · 10 ⁴ No. 1. UHMWPE-50% FCS 9.4 · 10 ² 1.9 · 10 ⁴ 4.9 · 10 ⁴ 6.010 ⁴ 6.7 · 10 ⁴ Number 3. UHMWPE-90% FCS 1,2 · 10 ³ 2.210 ⁴ 5.210 ⁴ 6.310 ⁴ 6.910 ⁴ Runway-FTs-3 prototype 8.7 · 10 ² 3.2 · 10 ³ 4.210 ³ 5.510 ³ 5.7 · 10 ³ Runway-FTs-3-Ka prototype 8.3 · 10 ² 3.0 · 10 ³ 3.9 · 10 ³ 4,510 ³ 5.0 · 10 ³ KU-2-8 (Na) analogue 1.4 · 10 ² 7.910 ¹ 8.3 · 10 ¹ 9.0 · 10 ¹ 1,0 · 10 ¹

The experimental data presented indicate a high efficiency of sorption of cesium radionuclides by developed sorbents. It should also be noted that with an increase in the mass fraction of nanodispersed nickel ferrocyanide in the composite sorbent, the sorption efficiency increases.

Example 5

By the method described in Example 4, the sorption efficiency of cesium radionuclides by the developed sorbents and comparison sorbents from an aqueous solution of sodium chloride with a NaCl concentration of 200 g / L was determined.

The results are shown in table 4

Table 4 The efficiency of sorption of cesium radionuclides from a solution of sodium chloride with a concentration of 200 g / l Example No. / Sorbent The value of the distribution coefficient ¹³⁷ Cs (K _p , ml / g) at the time of contact of the sorbent with the solution, days. one 6 fourteen 28 59 No. 2. UHMWPE-5% FCS 2.310 ² 5.910 ² 7.2 · 10 ² 8.8 · 10 ² 9.0 · 10 ² No. 1. UHMWPE-50% FCS 6.810 ² 1.3 · 10 ³ 1,110 ⁴ 1,110 ⁴ 1,110 ⁴ Number 3. UHMWPE-90% FCS 1.3 · 10 ³ 2.8 · 10 ³ 1,110 ⁴ 1,110 ⁴ 1.2 · 10 ⁴ Runway-FTs-3 prototype 2.7 · 10 ² 5.8 · 10 ² 6.910 ² 8.7 · 10 ² 8.910 ² Runway-FTs-3-Ka prototype 2.5 · 10 ² 4.4 · 10 ² 5.7 · 10 ² 7.2 · 10 ² 7.3 · 10 ² KU-2-8 (Na) analogue <10 <10 <10 <10 <10

In accordance with the data presented, it can be argued that the developed sorbents retain high efficiency in the sorption of cesium radionuclides even from high-salt media and significantly exceed other sorbents in this indicator, including the closest analogues.

Claims (1)

Floating sorption-active polymer sorbent for the purification of contaminated aqueous media, including cesium radionuclides, containing ultrahigh molecular weight polyethylene as a binder, characterized in that nickel ferrocyanide fractions of 1-100 nm are used as a filler with the content of components, wt.%: Filler - Nickel Ferrocyanide 5-90 Binder - Ultra High Molecular Weight polyethylene with a molecular weight of (1 ÷ 4) 10 ⁶ 10-95