RU2499309C2 - Sorbent for removing radionuclides from water - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: radionuclides and toxic metal ions are removed from water using sorbents in form of gaize crumbs with diameter of 20-50 mm.

EFFECT: invention enables to avoid intermediate operations and use of deactivating substances.

Description

The invention relates to the removal of radionuclides of strontium, rubidium. cesium, uranium and some toxic metal ions from water streams using flasks. The invention can be used in all cases when it is necessary to purify any amount of water from radionuclides and heavy toxic metal ions.

There is a method of purifying water discharges from nuclear power plants by separating radionuclides from them using inorganic ion exchangers — cobalt cyanoferrates — potassium (cesium evolution), antimony crystalline acid (strontium emission) [1].

The disadvantage of this method is the necessity of using a large number of expensive and technologically inconvenient for further processing of ion-exchange materials in sorption technology.

Known sorption method, in which the sorbent used is calcium silicate hydrate of the composition CaSiO ₃ H ₂ O [2]. The sorbent exhibits ion exchange selectivity with respect to doubly charged cations Ni, Hg, Cu, Cd (k _d is 800-1000). A partial replacement of calcium in the sorbent by sodium gives it selectivity to cesium ions (K _d ~ 1000).

This method is characterized by a low distribution coefficient when extracting radionuclides from solutions containing a constant electrolyte.

A known method of neutralizing liquid radioactive waste, the essence of which is that in a solution of medium salt liquid radioactive waste (LRW) adjust the pH to a value of 8-12, create a salt content containing the amount of organic and inorganic substances not more than 25 g / l [3], enter in the prepared LRW solution, the selected fractions of the natural sorbent and sorption of radionuclides are carried out by mixing the LRW solution with the sorbent.

Flask and tripoli with a particle size of at least 0.1 μm (at the level of 80 μm) are used as a sorbent. The radioactive sorbent is isolated by pressure filtration through a membrane filter with a plasma-chemical coating, the sorbent is dumped into a storage ring and cemented into a geo-cement stone [RU 2189650 C2].

The disadvantages of the method include a large number of intermediate operations, as well as the use of deactivating substances, in particular, anionic surfactants, Trilon B, oxalic acid, industrial oils.

Known opal filler of toilets [4], including particles of porous natural mineral rocks of diatomaceous earth, or flasks, or tripoli and additives, characterized in that the particles of the filler are calibrated in diameter from 2 to 20 mm, and as additives, medium or acidic or double, or complex, or halogen-containing salts of barium, chromium, copper, iron.

The disadvantage of this solution is the introduction of barium, chromium, copper and iron salts into the toilets in any amount, which negates the sorption properties of natural aluminosilicates in relation to inorganic and organic compounds.

There is a method of decontamination from ¹³⁷ Cs in the mode of recirculation of neutral demineralized water from a fuel storage pool at a nuclear power plant in Bradwell [5, p. 3431. The purified water is first passed through a Decalsoi zeolite column, and then through an ion-exchange demineralizer.

In another technical solution [6 | 16 thousand column volumes of refrigerant were passed through granular synthetic mordenite from the pool to store spent fuel in recirculation mode; as a result, more than 95% of ¹³⁷ Cs, ¹¹⁰ Cs and Ag radionuclides were removed. The disadvantage of this method is the low selectivity of the sorbent, as indicated by a low cleaning coefficient but radiology (20) with a rather large filter cycle.

Known methods for decontamination using hexacyanofsrates of the aqueous coolant of the reactor from radiocaesium [7] and the pool water of spent fuel from nuclear plants from ¹³⁷ Cs and ⁹⁰ Sr. In the first method [8] through a glass column loaded with 1 cm ^{3 of} titanium hexacyanoferrate impregnated in a cation exchange resin in an amount of 23%, an imitate of the water coolant of the first circuit of the VVER-440 reactor (0.065 mol / l H ₃ VO ₃ , 0.025 mol was passed / l KOH, 0.002 mol / l NH ₄ OH) at a rate of 10 m / h (sorbent was obtained according to the Polish patent Np-2255191, 1985 [8]). At the end of the filtration cycle, in 25 thousand column volumes (co), the purification coefficient for ¹³⁷ Cs was 100, and the concentration of hexacyanoferrate ions was 2 mg / L. According to the second method [8], the water of the pools for spent fuel from radioactive impurities in the recirculation mode is treated using a mixed-action filter consisting of domestic KU-26 cation exchange resin in the H + form and AV-17 anion exchange resin in the OH form in the ratio 1: 1 , 10-20% of the amount of which of the total load of 300 l is preliminarily modified with nickel hexacyanoferrate by the method of impregnation. The purification coefficient of ¹³⁷ Cs and ⁹⁰ Sr, equal to 10, is achieved when passing 5000 and 10 k.o. water having a salinity of 400 mg / l and a total beta activity of 1107 Bq / dm ³ (0.27 Ci / l).

The main disadvantage of both methods [7,8] is the use of an inorganic sorbent based on a radiation-non-stable organic base. which, with a high specific activity of water (n107 Bq / l and higher), will significantly reduce the service life of the filter, and especially with the cyclic mode of its operation, when the activity absorbed by the sorbent has been in the columns for a long time (weeks and months). Another drawback, as can be seen from [9], is the low resource of the loading operation but the long-lived ⁹⁰ Sr, which is associated with the low selectivity of the sorbent modifier.

A known method, taken by us as a prototype, comprising clarifying low-mineralized slightly radioactive contaminated water in a settling tank into which a suspension of ground zeolite production wastes is introduced. Then, the residues of suspensions are cleaned by mechanical filters and ultrafilters with the return of the latter concentrate (50-90% of the water flow) to the settling tank and the post-treatment of water on filters with synthetic sodium zeolite. The purified water is fed into an intermediate tank, and the resulting precipitate containing secondary waste is enclosed in cement. This method of disposal allows you to achieve purification from beta-nuclides in 102-103 times, reduce the amount of secondary waste to 0.2% of the volume of source water and reduce the leachability of radionuclides from cured products to values not more than 1 · 10 ^-3 g / cm ² · day , which allows them to be buried in the simplest soil burial grounds [9]. In addition, this method allows for continuous purification of water from radionuclides and toxic elements in the stream.

The disadvantage of this method is the inability to remove radionuclides from saline waters.

The essence of the claimed invention lies in the fact that it is proposed to use flask [10] as an effective sorbent for purifying water from radionuclides and toxic heavy elements.

When studying the adsorption of a number of metal ions on them, it was found that in a wide pH range, many cations are strongly adsorbed, and in some cases irreversible sorption is observed. The ions of ammonium, potassium, rubidium, cesium, iron, cobalt, nickel, manganese (II), chromium (III), zinc, cadmium, lead, mercury, copper, and rare earths are strongly adsorbed. At the same time, ions of sodium, aluminum, gallium, zirconium are captured during adsorption from solutions. These ions can be desorbed not only by acidification of the eluting solution, but also by washing the sorbent with water.

An analysis of the results obtained in the study of cation adsorption made it possible to draw an initial conclusion: those ions that contain vacant d or f orbitals form strong adsorption complexes with flasks.

The flasks were used to extract from the water various degrees of salinity of potassium, rubidium, cesium, calcium, strontium and barium ions. For this, the adsorption of the listed ions from specially prepared solutions, as well as from the water of natural reservoirs and brines, which filled the tanks for storing gas condensate and liquid hydrocarbons, which were created by a special method according to the Vega project, was studied. The content of all considered ions was determined by flame photometry and atomic absorption spectroscopy.

Adsorption in dynamic mode. 2 kg of sorbent were loaded into the flow system — crushed flasks with a particle diameter of 20 to 50 mm. Water was passed through this sorbent at a speed of 1 cm ³ / s until the content of the studied ions in the outflowing water reached 10% of the content of these ions in the source water. The results of the experiments are given in table 1.

Table 1 The change in the content of metal ions in aqueous media as a function of time. Sorbent crumb flask with a diameter of 20-50mm. Water source or solution The initial content of ions, mg / DM ³ The content of ions, mg / DM³, depending on the flow time (min) one 10 60 600 6000 A solution prepared by dissolving salts in dist. water Ca ²⁺ one hundred 0.01 0.01 0.10 5.00 10.00 Sr ²⁺ fifty 0.01 0.01 0.10 0.25 5.00 Ba ²⁺ 10 0.01 0.01 0.10 0.25 5.00 K ⁺ one hundred 0.01 0.01 0.10 0.25 0.05 Rb ⁺ twenty 0.01 0.01 0.10 0.25 0.02 Cs ⁺ 10 0.01 0.01 0.10 0.01 0.02 Yer Bereket. 1000 m to the southeast from the Astrakhan Gas Processing Plant Ca ²⁺ twenty 0.005 0.005 0.01 1,0 2.0 Sr ²⁺ 5 0.001 0.001 0.005 0.01 0.5 Ba ²⁺ - - - - - - K ⁺ twenty 0.001 0.001 0.001 0.02 1,0 Rb ⁺ 0.5 <0.001 <0.001 <0.001 0.005 0.008 Cs ⁺ 0.1 not upd. not upd. not upd. 0.001 0.01 Brines from hydrocarbon storage tanks Ca ²⁺ fifty 0.01 0.01 0.05 0.5 5,0 Sr ²⁺ 10 0.01 0.01 0.02 0.05 1,0 Ba ²⁺ - - - - - - K ⁺ 250 0.01 0.01 0.01 0.05 0.10 Rb ⁺ 0.5 <0.001 <0.001 <0.001 0.005 0.008 Cs 0.5 <0.001 <0.001 <0.001 0.005 0.008 * Salt of the AXOL enterprise. Prepared 20% aqueous solution Ca ²⁺ twenty 0.005 0.005 0.01 0.01 5,0 Sr ²⁺ twenty 0.005 0.005 0.01 0.01 5,0 Ba ²⁺ - - - - - - K ⁺ 500 0.01 0.01 0.01 0.01 5,0 Rb ⁺ fifteen 0.001 0.001 0.001 0.1 2.0 Cs fifteen 0.001 0.001 0.001 0.1 2.0 * AXOL enterprise uses brines for the production of table salt from containers designed to store carbon

Adsorption in static mode. At the bottom of three steel containers (St-3) (1 × 1 × 0.5) m ^3, a crumb of flasks with a diameter of 20–50 mm, river sand, or a substrate were not specially created for a layer of 50 mm. 250 dm ^{3 of} test water was poured into each container and, at certain time intervals, the ion content in this water was determined. The results of the experiments are given in table.2.

table 2 Purification of water from metal ions in static mode with tiny flasks with a particle diameter of 20 to 50 mm. Water source or solution The initial content of ions, mg / DM ³ The content of ions. mg / dm ³ , depending on the transmission time (days) one 10 thirty 60 300 A solution prepared by dissolving salts in dist. water Ca ²⁺ one hundred 10.0 0.1 0.01 0.01 0.01 Sr ²⁺ fifty 10.0 0.1 0.01 0.01 0.01 Ba ²⁺ 10 5,0 1,0 0.10 0.05 0.01 K ⁺ one hundred 0.01 0.001 0.001 0.001 0.005 Rb ⁺ twenty 0.01 0.001 0.001 0.001 0.005 Cs ⁺ 10 0.01 0.001 0.001 0.001 0.005 er Bereket. 1000 m to the southeast from AGPZ Ca ²⁺ twenty 0.05 0.01 0.01 0.01 0.01 Sr ²⁺ 5 0.05 0.01 0.01 0.01 0.01 Ba ²⁺ - - - - - - K ⁺ twenty 0.01 0.001 0.001 0.001 0.002 Rb ⁺ 0.5 0.005 0.001 0.001 0.001 0.002 Cs ⁺ 0.1 <0.001 <0.001 <0.001 <0.001 <0.001 Brines from hydrocarbon storage tanks Ca ²⁺ fifty 0.01 0.01 0.01 0.01 0.01 Sr ²⁺ 10 0.01 0.01 0.01 0.01 0.01 Ba ²⁺ - - - - - - K ⁺ 250 0.01 0.001 0.001 0.001 0.005 Rb ⁺ 0.5 0.005 0.001 <0.001 <0.001 <0.001 Cs ⁺ 0.5 0.005 <0.001 <0.001 0.001 <0.001 * Salt of the AXOL enterprise. Prepared 20% aqueous solution Ca ²⁺ twenty 0.01 0.01 0.01 0.01 0.01 Sr ²⁺ twenty 0.01 0.01 0.01 0.01 0.01 Ba ²⁺ - - - - - - K ⁺ 500 0.01 0.005 0.001 0.001 0.005 Rb ⁺ fifteen 0.01 0.001 0.001 0.001 0.001 Cs ⁺ fifteen 0.005 0.001 0.001 0.001 0.002

As can be seen from the results given in Tables 1 and 2, flakes from flasks can be effectively used to purify water from calcium, strontium, barium, potassium, rubidium and cesium ions.

If the reservoir contains a significant amount of these elements, then the best option is to cover the bottom of this reservoir with a layer of fragmented flasks, and after some time the concentration in the water of these elements will decrease sharply. The elements themselves are not desorbed (Table 2) for a long time.

Sources:

1. Moskvin L.N. Methods of chemical and radiochemical control in nuclear energy. [Text] / L.N. Moskvin, M.F. Gumerov, A.A. Efimov // M., Energoatomizdat, 1989.

2. El-Korashy S.A. "Synthetic Crystalline Calcium Silicate Hydrate (I): Cation Exchange and Caesium Selectivity", Monatshefte fur Chemie, 2002, v.133, pp. 333-343.

3. RF patent No. 2189650, IPC G21F 09/12 from 09/20/06.

4. Patent 2153252 Russian Federation, IPC A01K 23/00, A01K 1/015. Opal litter of toilets [Text] / O.N. Khmyz, N.M., Eremochkina, L.F. Siromaha .: applicant and patent holder Oh.N. Khmyz, - No. 99101041/13; application 01/18/1999; publ. 07.27.2000, p. 2.

5. Kourim V. Vojtech O. Methods of fission product separation from liquid radioactive wastes // Atomic Energy Rev. - 1974. - Vol.12, N 2. P.215-273.

6. Berak L. Uher E. Marhol M. Sorbents for the purification of low- and medium level radioactive waters. Atomic Energy Rev. 1975. - Vol.13, N 2. - P.325-366.

7. Franta P. Vanura P. Tomic L. et al. Poloprovozni overeni technologie cisteni chladiva, bazenu skladovani vyhoreleho palivajaderne elektrarny VI sorpei na syntetickeni mordenitu // Jad. energ. - 1987. - T.33, N 12. - C.453-458 (Quoted from RZhKhim, 1988, 9I447).

8. A.c. USSR N 1679745 (bar "Particleboard"), cl. C02F 1/42, claimed 07/23/87.

9. Alykov N.N. Flasks of the Astrakhan region [Text] / N.N. Alykov, N.M. Alykov, T.V. Alykova, N.I. Voronin. Monograph. - Astrakhan; Ed. House "ASU", 2005. - 144 p.

10. Patent 2370312 Russian Federation, IPC B01J 20/16, B01F 1/29. A method of obtaining a natural sorbent for water purification in the drinking water supply system [Text] / N.M. Alykov, E.N. Alykov, N.I. Yavorsky, T.V. Alykova: application. 08/10/2007; publ. 10/10/2009, bull. No. 29.

Claims (1)

A sorbent for removing radionuclides from water to remove stable isotopes of potassium, cesium, calcium, strontium, barium, and also their radionuclides from water, a sorbent is proposed, characterized in that as a sorbent crumbs of flasks with a diameter of 20 to 50 mm are used.