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INVENTION
Russian Federation Patent RU2165110

CERAMIC SPONGE for concentration and solidification of liquid OSOBOOPASNYH WASTE AND PROCESS FOR ITS PREPARATION

CERAMIC SPONGE for concentration and solidification of liquid OSOBOOPASNYH WASTE AND PROCESS FOR ITS PREPARATION

Name of the inventor: Anshits AG .; Vereshchagin TA .; Pavlov VF .; Sharonov OM
The name of the patentee: Anshits Alexander G.
Address for correspondence: 660036, Krasnoyarsk, Akademgorodok, P / 26706, Vereshchagin TA
Starting date of the patent: 1999.04.28

The invention relates to the treatment of liquid osoboopasnyh waste containing heavy metals and / or radionuclides, in particular to waste cured by including them in artificial ceramic compounds, and can be used for reprocessing nuclear industry and weapons-nuclear complex, but also in the chemical and metallurgical industries. For concentrating and solidifying liquid wastes used osoboopasnyh ceramic sponge based hollow aluminosilicate microspheres with diameters greater than 20 microns, with a wall thickness greater than 2 microns, a softening point above 800 o C and a bulk density greater than 0.3 g / cm 3, characterized by thermal stability and mechanical strength greater than 2.6 MPa, and having an open porosity and with the magnitude of free volume available to 70 vol. %. To obtain hollow aluminosilicate microspheres recovered from fly ash from the combustion of coals is mixed with a wetting agent and a silicate binder in a weight ratio of 1: 0,012-0,29: 0.18 to give the molding composition, it is removed from the gas with the simultaneous formation of inclusion predetermined size of blocks and sintered at a temperature above 800 o C but below the softening temperature and at atmospheric pressure. The technical result - high mechanical strength during transport, handling and storage, and thermal stability and acid resistance and.

DESCRIPTION OF THE INVENTION

The claimed technical solution relates to the processing of liquid osoboopasnyh waste, including radioactive, in particular a curable waste through their inclusion in artificial ceramic compounds suitable for transportation and safe long-term disposal, and can be used for reprocessing nuclear industry and weapons-nuclear complex and in the chemical and metallurgical industries.

The porous ceramics is widely used mainly as thermal insulation and building materials. In recent years, due to the need to eliminate large amounts of liquid inorganic waste increased danger accumulated at the enterprises of the chemical and metallurgical, ore-dressing and weapons-nuclear complex, and converting them into stable solidified form of increased interest in the porous oxide materials as a matrix for concentration and curing salt solutions radionuclides and heavy metals [1-4]. It is expected that these materials impregnation with subsequent waste solutions and drying stages allow the high temperature treatment to achieve localization radionuclides and other salt components in the matrix volume and make the cured compound suitable for safe long-term disposal. To this end, it proposed to use microporous adsorbents such as silica gel [2] and zeolites [3], and a porous blocks based on granular silica ICSD marks, molded with an inorganic binder pseudoboehmite porous sodium silicate glass or porous iron [4]. The disadvantages of such materials is the limited field of application because they are specific to certain structures and the degree of activity of liquid radioactive waste. Furthermore, microporous materials can not operate continuously in real conditions of the waste liquid formulations containing non-radioactive salt slurry and macro components that clog the pores and thereby reduce the capacity of impregnating the solid adsorbents. It should be noted, and the complexity of the complete dehydration of microporous materials, which are required for the temperature to 500 o C, and the instability of most materials in acidic environments.

More promising direction of liquid waste to obtain stable cured ceramic compounds should be considered as including all the salt components in the porous ceramic matrix, which avoids the additional processing steps saline solutions. For this ceramic sponge must have the following properties:

homogeneous porous structure that provides a uniform distribution of liquid waste in its components and consistency desired properties of the cured ceramic compound;

high open porosity, ensuring accessibility of the internal volume of the sponge to the curable solution;

easily remove moisture at low temperatures, which allows to avoid the formation of aerosols radionuclides and other toxic components in the drying step;

thermal stability;

resistance to strong acids;

mechanical strength, dimensional stability ensures the unit during transportation, handling and storage;

water leaching low speed component of the ceramic matrix;

the ability to create multiple barriers of isolation of radionuclides within the scope of a ceramic compound that ensures the implementation of the principle of protection of the biosphere multibarernogo from exposure to toxic substances.

Analysis of the literature showed that as the ceramic matrix material for disposal of long-lived radionuclides can be viewed primarily ZrO 2 and TiO 2, characterized by high thermodynamic stability in the preferred range of geochemical indicators of natural groundwater (9> pH> 5 and +0,6 B> E h> -0,3 V) [5]. Oxides and hydroxides of Fe and Al, characterized by the partial overlap of the fields of stability to this region of the existence of natural underground waters are suitable material for encapsulation of heavy metals. However, the process of producing porous materials of these oxides by conventional methods (e.g., foaming melts using gas-forming components) sufficient energy intensive and expensive, and the inclusion of toxic elements in the ceramics based on them most effectively accomplished by co-crystallization of high surface oxides with the previously adsorbed or coprecipitated components of waste [6]. There remains the problem of disposal of related salts contaminated with traces of toxic elements.

Another known approach to the preparation of porous ceramic material with a predetermined pore structure and meet the requirements of thermal stability, chemical resistance and mechanical strength, which is used for forming a porous hollow glass ceramic matrix [7] or ceramic microspheres [8]. Thus, in the method [7] The high strength porous ceramics obtained by mixing the synthetic hollow glass spheres with a ceramic composition comprising a ceramic component (aluminosilicate lithium), a binder (calcium aluminate and / or colloidal solution of SiO 2) and water, followed by molding and, If necessary, annealing to provide the necessary strength properties. Moreover, the composition of glass hollow spheres is selected such that its softening temperature is below the melting temperature of the ceramic component, while heating the molded article is carried out below the melting temperature of the ceramic matrix, but higher than the softening temperature of the glass spheres. The resulting ceramic matrix body in closed pores are formed with a spherical shape vitrified wall. A characteristic feature and a major disadvantage is the closed type ceramics porosity, and the need to use synthetic and glass spheres, whose production is laborious separate process.

The closest in technical essence to the claimed technical solution is a method of [8], wherein the glass ceramic hollow microspheres derived from fly ash from coal-burning power (cenospheres) are used to form the porous structure of ceramic material. In this case, obtaining a porous ceramics comprising the following steps:

selection hollow ceramic microspheres, preferably with a low content of aluminosilicate Fe, Mg, Na, K and Ti, 20-200 microns in diameter, with a wall thickness of more than 2 m, a softening temperature above 800 o C, a bulk density exceeding 0.3 g / cm 3 ;

mixing the microspheres with the composition of the silicate binder in a weight ratio of 1: 2.1, and in the case of SiO 2 - a 1: 1.4;

removing gaseous inclusions from the mixture;

sintering the mixture at a temperature below the softening temperature but higher than 700 o C and pressure to increase the contact area of the microsphere and more effective sealing material.

With the introduction of the silicate binder wetting agent component ratio microspheres: wetting agent: a bunch of up to 1: 0,012-0,016: 1.2-1.6. As a result of this treatment, the final product is a close-packed array of microspheres, characterized by the following parameters:

Operating temperature - above 800 o C

Thermal conductivity - Less than 0.2 W / m / o C

Mechanical strength - more than 400 psi (2,6 MPa)

The main drawback of such a ceramic, which does not allow its use in the processes of absorption and subsequent curing brines is closed type and porosity. The method of [8] and ceramic sponge obtained by this method, taken as a prototype.

The purpose of the claimed technical solution is to simplify the process of concentration and solidification of liquid osoboopasnyh waste and improving accessibility for saline solutions of the internal volume of the porous ceramic material based on hollow glass-ceramic microspheres selected from fly ash from the combustion of fossil fuels.

This object is achieved by the fact that the concentration and solidification of liquid wastes used osoboopasnyh ceramic sponge-based glass-ceramic hollow microspheres, preferably aluminosilicate, a diameter greater than 20 mm, with wall thickness of 2 mm, a softening point of more than 800 o C and a bulk density of more than 0.3 g / cm 3, characterized by thermal stability and mechanical strength greater than 2.6 MPa, and a type of open porosity value of the free volume available to 70 vol.%.

For ceramic sponge is recovered from the fly ash from the combustion of coals hollow glass ceramic microspheres, preferably aluminosilicate, more than 20 microns in diameter, with a wall thickness of 2 mm, a softening point above 800 o C and a bulk density greater than 0.3 g / cm 3, blended microspheres with a wetting agent and a silicate binder to obtain a molding material is removed from its gas inclusions and sintered at a temperature above 700 o C, but below the liquidity temperature, while mixing the microspheres with a wetting agent and a silicate binder is carried out at a weight ratio of 1: 0.012 0.29: 0.18, the removal of gaseous inclusions are molding shrinkage by weight of 1.1-1.2 times at one-sided squeezing of the mold a predetermined diameter, whereupon the ceramic block was dried at 160 o C for 2 hours, and sintering is conducted at a temperature above 800 o C, but below the softening temperature and at atmospheric pressure. Another difference is that after the separation of fly ash microspheres are further subjected to sieve separation into fractions of different sizes. Furthermore, to obtain a ceramic sponge is used the perforated microspheres.

The essence of the claimed technical solution is as follows. Ceramic sponge based crystalline glass hollow microspheres in the form of preformed blocks of various configurations with an optimal volume to external surface area having a uniform porous structure, high fractional free volume available for salt solutions (70-75 vol.%), Significant macropore size in the range of 0,01-0,29 mm, provides the following functional flow processes, significantly simplifying liquid waste conditioning technology to produce a cured ceramic compounds:

  • absorption solutions in unit volume due to capillary forces and high wettability inner surface;
  • the evaporation of water and its intense removal of working gas developed working surface at low temperatures (about 25 o C);
  • re-saturation solution at low salt waste composition to achieve the desired degree of filling;
  • binding of radionuclides and / or heavy metals introduced into the volume unit stable high surface oxides;
  • reliable fixation of radionuclides and / or heavy metals and associated salts within the unit at the final stage of the process by calcination rich ceramic matrix.

Furthermore, a distinctive feature of ceramic sponge based on hollow glass ceramic microspheres is the possibility microencapsulation radionuclides and / or heavy metals in internal cavities microspheres bounded stable crystalline glass envelope containing different fractions depending on size and bulk density of the microspheres, wt%:. SiO 2 - up to 65; Al 2 O 3 - to 44; Fe 2 O 3 - 8; CaO - to 4; MgO - 3, Na 2 O - 11; K 2 O - 11; TiO 2 - and 1. Application of the microspheres on the inner surface of thin films of ZrO 2, TiO 2, Fe 2 O 3 or Al 2 O 3 prior to impregnation of radionuclides and / or heavy metal makes it possible for the directed synthesis of ceramics, encapsulated in these microspheres that makrokapsuliruyuschim with a protective coating provides protection multibarernogo realization principle within the volume of the ceramic compound and creates conditions for the immobilization particularly reliable components osobotoksichnyh liquid waste, primarily long-lived radionuclides.

The advantages of porous ceramic blocks on the basis of hollow aluminosilicate microspheres should include their high mechanical strength, providing dimensional stability unit during transportation, handling and storage, but also acid resistance and thermal stability which allows their use in a wide range of pH, temperature and the radionuclide composition of the liquid waste .

The implementation of such basic processes as the absorption of salt solutions and intensive evaporation of water from the interior of the ceramic sponge at low temperatures, but also multibarernoe encapsulation of components of waste becomes possible only in the case of achieving high values ​​of open porosity ceramic sponge that ensures the availability of the free volume between the microspheres and within . For this purpose, the sintering of the microspheres should be carried out with a minimum content of binder and under conditions preventing compaction microsphere array. These conditions are the pressure exerted on the ceramic composition with a binder on the block molding and calcination stages, and the temperature and the heat treatment conditions of the molded block, which is primarily determined by thermochemical properties of silicate binder. Thus optimal conditions microspheres are consolidating temperature 850-900 o C, which is well below the softening temperature of glass-ceramic shell microspheres. Sintering at these temperatures, it provides a porous blocks with suitable characteristics, including strength.

Sieve the separation of microspheres results in a more uniform size glass-ceramic products, which allows us to solve the optimization problem of the porous block structure in order to improve the kinetic parameters of its drying. The criterion was chosen as the removal of 80% of moisture (T 80) of Intersectoral free volume when the air flow rate through the unit of 0.1 m / s and a temperature of 25 o C. These conditions were compared blocks differing ratio V / S, and the resulting different types of microspheres. It is shown that at one and the same ratio V / S the lowest indicators of T 80 have blocks of narrow fractions of microspheres. Among each series of blocks obtained by varying the type of microspheres and the geometrical dimensions can be identified single module (or unit cell) with a specific ratio V / S, which corresponds to a predetermined time and the unit drying conditions and can be used in the design of a porous ceramic honeycomb block.

To ensure availability of the internal volume of the microspheres require additional perforation of the shell, which involves an additional treatment of the microspheres in the selection stage. It is possible to achieve open porosity to a value of 70 vol.%, Which actually represents the theoretical limit of the available pore volume.

SUMMARY confirmed by the following examples.

Example 1. Fly ash from burning coal recovered fraction Kuznetsk hollow aluminosilicate microspheres size of 50-400 microns and a bulk density of 0.42 g / cm 3, containing, by weight%:. SiO 2 - 65,5, AlO 3 - 20,3, Fe 2 O 3 - 3,9, CaO - 2,6, MgO - 2,2, which is mixed with water and silicate binder at a weight ratio of 1: 0,012-0,29: 0.18 to give the plastic molding composition. Formation of blocks is effected by the shrinkage of the molding composition to 1.1-1.2 times at one-sided squeezing of the mold of a given diameter, then the blocks are dried at a temperature of 160 o C for 2 hours and then calcined in a muffle furnace at 900 o C 0.25-0.5 hours and at atmospheric pressure. The characteristics of the blocks are given in Table 1.

Blocks with the ratio V / S 0,65 and 0,67 were tested for adhesion, Pu, Cr, Ni concentration in the solution and curing the first simulator raffinate extraction cycle standard uranium waste processing units (OSUB) of the following composition:

HNO 3 g / l - 30

Fe (3), g / L - 20

Cr (3), g / L - 15

Ni, g / L - 15

Pu, mg / L - 15

For this unit with the ratio V / S 0,65 by repeated impregnation with active ventilation and an intermediate drying at 50-150 o C for 2 hours, saturated with said solution. After the final drying stage saturated salts unit calcined in a muffle furnace at 800 o C for 2 hours. The encapsulation unit is not carried out. Pu fixation strength test, Cr and Ni in a ceramic shell encapsulating compound shall not performed as described [9].

We obtained the following results:

Filling unit waste oxides,% - 42.2

Pu content in block mg - 2.3

Cr content of the unit g - 2.3

The content of Ni in the block, g - 2.3

Average speed Pu leaching in water for 93 days, g / cm 2 · d - 5.9 × 10 -6

High Cr leaching rate in water for 93 days, g / cm 2 · d - 1.0 × 10 -4

The average rate of Ni leaching in water for 93 days, g / cm 2 · d - 1.5 × 10 -5

Block with the ratio V / S 0,67 saturated with a similar composition but in which the plutonium content reached 43 mg / l. After calcination stage saturated block is coated low-melting glass, which has the following characteristics:

Softening point, o C - 352

The coefficient of linear expansion, hail -1 - 1.03 × 10 -5

Chemical composition:

. B 2 O 3 wt% - 16.0

PbO, wt% -. 80.0

ZnO, wt% -. 4.0

Pu fixation strength test, Cr and Ni in a ceramic shell compounds with makrokapsuliruyuschey performed as described [9]. We obtained the following results:

Filling unit waste oxides,% - 44.7

Pu content in block mg - 6.5

Cr content of the unit g - 2.3

The content of Ni in the block, g - 2.3

Average speed Pu leaching in water for 93 days, g / cm 2 · d - 2.5 × 10 -7

High Cr leaching rate in water for 93 days, g / cm 2 · day - 4.65 x 10 -6

The average rate of Ni leaching in water for 93 days, g / cm 2 · d - 2.6 × 10 -6

Example 2. Preparation of ceramic sponge was carried out as in Example 1, but further subjected to a sieving separation of the microspheres, and a sponge used to produce microspheres fractions 400-800, 200-400 and 100-160 microns. Characteristics units given in Table 2.

Example 3. Preparation of ceramic sponge was carried out as in Example 1, but for this purpose, the perforated microspheres. Characteristics blocks shown in Table 3.

Thus, these results show that the cured ceramic compounds sufficiently firmly hold Pu and heavy metals, and further contributes to the strength makrokapsulirovanie toxic fixation elements to a level acceptable for long term burial osoboopasnyh solidified waste [10].

USED ​​BOOKS

1. A. Nikiforov, VV Kulichenko, Zhiharev MI Disposal of liquid radioactive waste. - M .: Energoatomizdat, 1985 - 164 p.

2. Pat. RF N 2095867, G 21 F 9/16, 9/12, 9/14. Bull. N 31, 1997. A method of curing solutions transuranic elements.

3. Pat. RF N 2038637, G 21 F 9/16, Bull. N 18, 1995. A method for fixing a solid phase radioactive isotopes of alkali and alkaline earth elements.

4. Pat. RF N 2091874, G 21 F 9/12, Bull. N 27, 1997. A method of processing radioactive waste.

5. Anshits AG, Revenko Yu, Vereshchagin TA et al. Physical and chemical criteria for long-term disposal of radioactive waste in the form of oxide / Chemistry for Sustainable Development, vol. 6, N 4, 1998, p. 293-302.

6. Melikhov AV, MS Merkulova Co-crystallization. - M .: Chemistry, 1975. - 280 p.

7. Pat. US N 3888691, C 03, C 011/00, 1975. Porous ceramic.

8. Pat. US N H0000200, C 30 B 029/16, B 29, C 071/02, 1987. High temperature structural insulating material - (prototype).

9. GOST 29114-91. The method of measuring chemical stability of solidified radioactive waste by a long leaching.

10. GOST P 50926-96 "Waste highly cured. Technical requirements."

CLAIM

1. Ceramic sponge for concentrating and solidifying liquid wastes osoboopasnyh based crystalline glass hollow microspheres, preferably aluminosilicate, more than 20 microns in diameter, with a wall thickness of 2 mm, a softening point above 800 o C and a bulk density greater than 0.3 g / cm 3, characterized by thermal stability and mechanical strength greater than 2.6 MPa, wherein the open porosity has a size of free volume available to 70 vol.%.

2. A method for producing a ceramic sponge according to claim 1, comprising isolating energy from coal fly ash microspheres, hollow glass ceramic, aluminosilicate preferably, more than 20 microns in diameter, with a wall thickness of 2 mm, a softening point above 800 o C and a bulk density of more than 0.3 g / cm 3, a mixture of microspheres with a wetting agent and a silicate binder to obtain a molding material, removing from it of gaseous inclusions and its sintering at a temperature above 700 o C, but below the liquidity temperature, characterized in that the mixture of microspheres with a wetting agent and silicate bonding is performed at a weight ratio of 1: 0.012 - 0.29: 0.18, the removal of gaseous inclusions are by weight of molding shrinkage of 1.1 - 1.2 times at one-sided squeezing of the mold of a given diameter, then dried ceramic blocks at 160 o C for 2 hours, and sintering is carried out at a temperature above 800 o C, but below the softening temperature and at atmospheric pressure.

3. A method according to claim 2, characterized in that after the separation of fly ash microspheres are subjected to separation into narrow sieve fractions of different sizes.

4. A method according to claim 2 or 3, wherein the ceramic sponge for use perforated microspheres.

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Publication date 20.02.2007gg