RU2172991C1 - Composite material for cleaning polluted water media containing radionuclides - Google Patents

Abstract

FIELD: decontamination of water media, for example, in servicing power units for transport. SUBSTANCE: composite material used for cleaning water media of radionuclides and oil products in pre-treatment of storage tanks for liquid radioactive wastes by sorbing them has in its composition natural filler (mordenite and, in addition, peat) and polymeric binder. Used as polymeric binder is superhigh-molecular polyethylene whose molecular mass is (1,5-4,0)×10⁶. Proportion of ingredients is as follows, mass percent: filler: mordenite 10-30; peat 87-67; binder: superhigh-molecular polyethylene of molecular mass (1,5-4,0)×10⁶ - 3-10. EFFECT: enhanced efficiency; reduced number of radiation hazard operations in extraction and recovery of spent sorbent. 2 tbl, 2 ex

Description

 The claimed technical solution relates to the field of treatment of aqueous media from radioactive contamination by sorption and can be used in the operation of transport power plants. The wastewater of these plants containing cesium radionuclides is characterized by an uncertain salt composition and is contaminated with various oil products. Preliminary treatment of water from liquid radioactive waste (LRW) storage tanks from cesium radionuclides and oil products should be carried out continuously in closed storage tanks for 2-3 months. Such preliminary cleaning can be carried out by a sorbent floating on the surface, selective for cesium radionuclides and absorbing oil products.

 In the prior art it is known that peat can be used to purify water from radionuclides [Kuznetsov Yu.A., Schebetkovsky AN, Trusov AG Basics of water purification from radioactive contamination. M .: Atomizdat, 1974.]. The disadvantage of this sorption material is leaching in slightly acidic and alkaline environments, which leads to additional water pollution. The use of granular peat does not give the desired result, since when used in an aqueous medium, peat granules lose their mechanical strength due to high swelling.

Known sorption-active material for water purification from oil products [Volkov F.V. Study of the processes for producing fiber-film and block products from ultra-high molecular weight polyethylene. Abstract. dis. for a job. student Art. Ph.D. St. Petersburg, 1994, reg. N 04.9.90 008 125.] with a peat content of up to 97 wt.%. The polymer binder in the specified material is ultrahigh molecular weight polyethylene (UHMWPE) with a molecular weight (MM) (1.5-4.0) • 10 ⁶ . This sorbent has a sorption capacity in relation to oil products of up to 6.5 kg per 1 kg of sorbent and positive buoyancy over 4 months. Sorbent is made in the form of blocks of various shapes or granules. The disadvantages of this sorption material include the impossibility of using it as an effective sorbent for the integrated extraction of radionuclides in the presence of oil products in an aqueous medium, since the rate of extraction of oil products exceeds the rate of sorption of radionuclides.

 The closest analogue to the claimed technical solution is a porous composite material [RF Patent N 2135278, MKI 6 B 01 J 20/18, G 21 F 9/12, C 02 F 1/28. Publ. 27.08.99. The method of sorption extraction of cesium radionuclide from aqueous media / Goncharov B.V., Bytsan N.V., Doilnitsyn V.A. ] for the purification of contaminated aqueous media from cesium radionuclides, including the natural sorbent mordenite fractions of 5-15 microns and polyvinyl formal binder, taken in the ratio (15-85) - (85-15) wt.%. The sorbent is made in the form of blocks that are placed in LRW storage tanks. The disadvantage of this material is the inability to use it for pre-treatment of water containing cesium radionuclides and petroleum products. Given the low speed of removal of cesium radionuclides and oil products dissolved in water, the sorbent should be introduced into the tank several months before the start of water treatment in regular treatment systems. Separate use of the sorbent for oil products and cesium selective sorbent in this case is impractical, since the amount of spent radioactively contaminated sorbents (solid radioactive waste) increases, which requires additional processing costs. In addition, the application of a sorbent to oil products and its removal after a quick extraction of surface oil products (films), followed by the introduction and removal of the sorbent on cesium radionuclides leads to two radiation hazardous operations instead of one. After removing the oil film from the surface, in the process of destruction of oil emulsions in water or changes in the physicochemical characteristics of water when any additional LRW is added to it, oil products can again be collected on the water surface and should be removed again. A technological disadvantage of the mordenite-containing material is that it sinks to the bottom of the LRW storage tank, making it difficult to recover it later.

 The technical result of the claimed invention is the integrated extraction of radionuclides and petroleum products from water during the preliminary processing of LRW storage tanks.

The technical result is achieved by the fact that the composite material for the purification of radioactively contaminated aqueous media includes a natural filler mordenite, additionally contains peat, and ultra high molecular weight polyethylene with a molecular weight of (1.5-4.0) • 10 ^{6 is} used as a polymer binder with the following content of components , wt.%:
Filler - mordenite - 10-30
Peat - 87-67
Binder - ultra high molecular weight polyethylene - 3-10
Composite material (KM) in the form of granules (for example, spherical in shape) with a mass of 10-15 g is placed in a LRW storage tank with radioactively contaminated water containing petroleum products at the rate of 1 kg KM per 1 m ^{3 of} water and removed from the tank after 2-3 months. During operation, KM floats on the surface of the water, absorbing an oil film from the surface and extracting radionuclides from the volume of purified water.

Example 1
Obtaining sorption-active material for water purification from oil products and 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 S.] preparing a solution of UHMWPE with a concentration of 1 wt.%. As a solvent, paraffin is used (TU 6-09-3637-87). At 140 ^o C and continuous stirring (150 rpm) 0.1 kg of UHMWPE (TU 6-05-1896-80) with MM 1.5 • 10 ^{6 are} loaded into the solvent and the suspension process takes place for 1 min. The dissolution is carried out with increasing temperature to 150 ^o C for 9 minutes with constant stirring. Filler - peat warms up at 130 ^o C for 60 minutes The heated filler (peat) is loaded into the polymer solution at a temperature of 140 ^o C in an amount of 0.9 kg. The composition is mixed at 25-30 rpm for 5 minutes The resulting composition is placed in a mold and cooled at room temperature. The cooled composite to remove paraffin from it is extracted with a C ₆ -C ₁₀ hydrocarbon at the boiling point of the hydrocarbon. Then the material is dried at 70 ^o C for 30 minutes The finished sorption-active material is a composite with a filler (peat) content of 90 wt.% And a binder content (UHMWPE) of 10 wt.%.

Example 2
Obtaining sorption-active material for water purification from oil products and 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 S.] preparing a solution of UHMWPE with a concentration of 1 wt.%. As a solvent, paraffin is used (TU 6-09-3637-87). At 140 ^o C and continuous stirring (150 rpm) 0.15 kg of UHMWPE (TU 6-05-1896-80) with MM 1.5 • 10 ^{6 is} loaded into the solvent and the suspension process takes place for 1 min. The dissolution is carried out with increasing temperature to 150 ^o C for 9 minutes with constant stirring. Fillers - peat and mordenite are heated at 130 ^o C for 60 minutes Heated fillers (peat and mordenite) are loaded into the polymer solution at a temperature of 140 ^o C in the amount of 4.35 kg of peat and 0.5 kg of mordenite. The composition is mixed at 25-30 rpm for 5 minutes The resulting composition is placed in a mold and cooled at room temperature. The cooled composite to remove paraffin from it is extracted with a C ₆ -C ₁₀ hydrocarbon at the boiling point of the hydrocarbon. Then the material is dried at 70 ^o C for 30 minutes Ready sorption-active material is a composite with a filler content of 97 wt. % (peat - 87 wt.%. and mordenite - 10 wt.%.), and the binder content (UHMWPE) of 3 wt.%.

 It is proposed to introduce the following designation for a floating composite material - PCM UHMWPE wt.% + Peat wt.% + Mordenite wt.% (For example, PCM 3% + 87% + 10% means that in the porous composite material the binder content is 3 wt.% , peat content - 87 wt.%, mordenite content - 10 wt.%).

The sorption activity of PCM was verified under model conditions. The chemical composition of the model aqueous medium: sodium chloride -3.0 g / l; hardness salts (Ca ⁺ + Mg ⁺ ) - 0.05 g / l; pH 9.6 (adjusted with ammonia). To study the sorption of cesium radionuclides, a radioactive label of cesium-137 (without carrier) was used. The specific volume activity of the solution was 3.6 • 10 ^6-5 Ku / l. In the case of an aqueous medium contaminated with oil products, TAd-17 oil was added to the model water in an amount of 0.05 g (based on a concentration of 1 g / l) and the solution was shaken for 10 minutes in order to obtain an oil emulsion. PCM samples having a mass of 0.05 g were placed in bottles with 50 ml of model aqueous medium. The solution in the bottle was not mixed. After 24 days, Tad-17 oil was added to the solution in an amount of 0.05 g in order to check the efficiency of the sorbent in relation to oil products during the entire operation period. After certain time intervals, samples of the solution were taken for radiometric measurements, and water absorption and sorption capacity with respect to oil products were determined for the sorbent. Water absorption and sorption capacity in relation to oil products were determined by the gravimetric method [Lurie Yu.Yu. Analytical chemistry of industrial wastewater. M .: Chemistry, 1984. - 448 p.]. The results are presented in table. 1.

The activity of the analyzed sample was measured using a Ge (Li) detector as part of a gamma spectrometer (sensitive volume is 100 cm ³ ). The resolution of the spectrometric path is 2.7 keV at E = 1.63 MeV. To suppress background radiation, the detector is surrounded by a lead shield. Under such conditions, the limit for determining the activity of a sample for cesium-137 with a 95% probability is 1 Bq for an exposure time of 1 hour. The spectra are recorded with a multi-channel analyzer, the exposure time is chosen 10 (30) min [RF Patent N 2135278, MKI 6 V 01 J 20/18, G 21 F 9/12, C 02 F 1/28. Publ. 08/27/99. The method of sorption extraction of cesium radionuclide from aqueous media / Goncharov B.V., Bytsan N.V., Doilnitsyn V.A. ].

где J_исх и J_кон - исходная и конечная (на время взятия пробы) активности водной среды, Бк/дм³; V - объем водной среды, см³; m - масса сорбента, г.According to the measurement results, the purification coefficient (K) and the distribution coefficient of radionuclides between the aqueous medium and the sorbent (K _p ) were calculated. The calculation was made according to the formulas:

where J _ref and J _con - initial and final (at the time of sampling) activity of the aquatic environment, Bq / dm ³ ; V is the volume of the aquatic environment, cm ³ ; m - sorbent mass, g.

. Было проведено три серии опытов. Результаты эффективности сорбции цезия-137 из водной среды (среднее значение) представлены в табл.2.In our experiment

. Three series of experiments were carried out. The results of the efficiency of sorption of cesium-137 from an aqueous medium (average value) are presented in Table 2.

As can be seen from the table. 2, the sorbent p / p-1 (analog) shows a low efficiency of cleaning from cesium radionuclides, K _p does not exceed 400 with a cleaning time of 58 days. The introduction of mordenite significantly increases K _p both in the presence and in the absence of oil products, it should be noted that an increase in the mordenite content in the composite over 30% has little effect on the cleaning efficiency. Duration of cleaning over 38 days practically does not increase the efficiency of PCM cleaning, this is especially noticeable on sorbents with a mordenite content of 30% and higher. There is no difference in the effectiveness of PCM purification of water contaminated with oil products and without them.

 Sorbent p / p-9 (prototype), located at the bottom of the box, shows the cleaning efficiency comparable to the cleaning efficiency using PCM with 30% mordenite content.

 During the preliminary treatment of LRW, the sorbent made in the form of granules is loaded into a storage tank. During the entire period of operation (2-3 months), the PCM is on the surface of the water. After placing the sorbent on a contaminated water surface, it actively absorbs oil products. Within 25-30 minutes, the maximum value of the sorption of the oil product with its excess or cleaning the surface of the water with an excess of sorbent is reached. The salt content in the water does not affect the process of its purification from oil products by this sorbent. Sorption of radionuclides occurs during the entire period of operation of the sorbent. In the event of the additional ingress of oil products into the water, they are absorbed by the sorbent in 25-30 minutes, if the maximum value of the sorption value is not reached. Repeated sorption of oil products does not affect the process of water purification from radionuclides. After 2-3 months, the PCM is collected from the water surface by a net and is disposed of.

 The conducted industrial tests confirmed the effectiveness of water purification from cesium radionuclides and oil products with a sorbent of the following composition, wt.%: UHMWPE - 3, peat - 67 and mordenite - 30.

(то есть 1 кг сорбента на 1 м³ обрабатываемых ЖРО) коэффициент очистки воды составляет 17-20, а коэффициент распределения К_р 16000-20000.Based on the foregoing, we can conclude:
the most effective for cleaning water containing petroleum products are porous composite materials with a content of 3% UHMWPE, 67-87% peat, 10-30% mordenite;
the duration of the sorbent during water treatment is at least one and a half months;
with the ratio

(that is, 1 kg of sorbent per 1 m ^{3 of} processed LRW), the water treatment coefficient is 17-20, and the distribution coefficient K _{p is} 16000-20000.

Claims (1)

Composite material for the purification of contaminated aqueous media, including radionuclides, including a natural mordenite filler, characterized in that the material additionally contains peat, and as a polymer binder - ultra-high molecular weight polyethylene with mol.m. (1.5 - 4.0) • 10 ⁶ with the following content of components, wt.%:
Mordenite filler - 10 - 30
Peat - 87 - 67
Binder - ultra high molecular weight polyethylene with a mol.m. (1.5 - 4.0) • 10 ⁶ - 3 - 10o

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