Method for matrix immobilization of industrial wastes of radiochemical and chemical-metallurgical works

FIELD: recovery of radioactive wastes.

SUBSTANCE: proposed method for matrix immobilization of industrial wastes includes preparation of source solution of industrial wastes and impregnation of ceramic matrix with this solution followed by roasting this matrix; source liquid radioactive wastes used for the purpose are first treated with promoter crystallization solution doped with oxide-forming admixtures whereupon radioactive wastes are introduced in ceramic matrix and roasted using microwave energy at temperature of 900 - 1 000 °C. Such procedure provides for recovering great amount of radioactive wastes included and chemically bonded in ceramic matrix which makes it possible to reduce leaching and to enhance matrix strength and life.

EFFECT: facilitated procedure, reduced cost, enhanced quality of radioactive waste immobilization and environmental friendliness.

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The invention relates to the field of processing liquid active (including radioactive) industrial waste, in particular to their immobilization matrix, and can be used at the enterprises of nuclear energy and the chemical and metallurgical industries.

The most promising from the point of view of chemical, thermal and radiation resistance as a form of disposal of radioactive waste (RW) are ceramic matrix.

The inclusion of radioactive waste in ceramic matrix can be implemented in two ways:

1) mixing raw with components, of which at their joint firing is formed of a ceramic matrix with "included" in it so RAO;

2) when the impregnation solution RAO received in advance of the porous ceramic matrix, with subsequent firing.

In the first embodiment there is a method of incorporating radioactive waste in ceramic matrix (U.S. Pat. Of the Russian Federation No. 2086019, CL G 21 F 9/16, 1997) (1). The method includes pre-processing liquid RW - mixing with bentonite, a clay loam, with a mixture of Tripoli and Al hydroxide, a reducing agent (urea) and mineralizer (crematoria ammonium). Then the mixture is heated at t=100-190°C for 10-12 h and at t=900°C for 1 hour. The disadvantage of this method is the need for contact mixing RAO with the specified components of the ri heated and the duration of the process, what makes it-low-tech; in addition, the properties of the obtained matrices are low and do not meet the requirements.

The closest technical solution proposed is representative of the second variant solve - method of curing liquid radioactive waste and ceramic material for its implementation (Patent RF №2197763, CL G 21 F 9/16, 2001) (2). This method involves the impregnation of ceramic material with a solution of RAO with intermediate venting and drying, and subsequent high-temperature processing - roasting in an electric furnace at t=1350-1500°C. as a ceramic material use pre-heat-treated material from a mixture of oxides of BA, CA, Al and Si with a particle size of ≤20 µm, taken in the ratio of 2-10:3-7:50-70:23-35.

The main disadvantage of this method is its low manufacturability, since the production and firing of ceramics, its treatment, aeration and drying, treatment with a solution of precipitators, re-drying and firing in the furnace, all operations are carried out in different places, using different hardware and each time the operations of loading and unloading and transportation, which requires special measures for ensuring industrial safety. In addition, the firing with the use of electric heating is not possible by solid state sintering Khimich the ski to "bind" a large number of raw mineral matrix, that reduces the effectiveness of its application.

Major General disadvantages of these known methods are:

low speed of reaction of formation of minerals in solid-phase sintering even when t>1500°C; higher temperatures up to 2000° - it is difficult, and requires additional complexity of the technology (the use of hot pressing under high pressure, etc.);

- obtain matrices with low porosity reduces the number of UES that can be included in the matrix;

- requires an additional operation (dosage and mixing of the dry components, the elimination of dust-aerogravimetry etc.);

- the need to place the main equipment in the hot cells and remote service;

- the presence in the liquid phase industrial RAO dissolved chemical elements and crystalline, firing which leads to the formation of complex compounds of complex structure, complicating the formation of insoluble metal oxides for forming minerals of the matrix a given composition.

These drawbacks make the use of known methods ineffective.

Eliminate these drawbacks is possible with the solution of two main problems - the problems of rational preliminary preparation of liquid waste prior to their immobilization in a ceramic matrix, and the sample is neither low-temperature synthesis of durable ceramic matrix, can include chemically "bind" a large amount of liquid waste with minerals of the matrix into a single unit, having thus, the final product for subsequent disposal.

The purpose of the proposed technical solution is the creation of a method of matrix immobilization of active industrial waste in ceramic matrices, which allows to improve the quality of immobilization, to increase the amount included in the ceramic matrix RAO, increase its strength and durability and to reduce leaching and make the way to cheaper, workable and safe for its practical use.

This goal is achieved by way of the matrix immobilization of industrial waste radiochemical and chemical and metallurgical industries, including preparation of the starting solution of industrial waste and impregnating them with a ceramic matrix, with subsequent annealing, characterized in that the applied source of liquid waste, which at the stage of preliminary preparation is treated with a solution of the crystallization promoter with Oktiabrski additives, after which the radioactive waste is introduced into the ceramic matrix and fired with the use of microwave energy at a temperature of 900-1000°C. the Method can be implemented when combined processes of synthesis, impregnation and firing ceramic matrix enabled the RAO and microwave firing is subjected to directly pulp RAO immediately after preliminary preparation, or when the microwave firing is subjected to specially manufactured ultrapolite quartz ceramic matrix, pre-multiply saturated liquid waste.

Preliminary preparation of liquid waste is carried out taking into account their specificity and the possibility of directed synthesis after microwave roasting only those minerals with the "included" in the RW, which are necessary to achieve the objectives of the properties.

So, in a solution of Mn-containing RAO is most expedient to additionally introduce Al3+-containing components in the calculation of the formation in the matrix after microwave annealing the first oxide of Al, and then on its basis the spinel composition of MnO·Al2About3(Al2O4one of the most thermally and chemically resistant minerals.

Processing of Am-containing liquid waste is appropriate at the stage of preliminary preparation introduction of a mixture of concentrated solutions of nitric and phosphoric acid in an amount necessary to ensure the precipitation of phosphate Am directly in the ceramic matrix after the completion of the process of impregnation; in addition, it is sensible to introduce Si4+, Al3+and Ti4+-containing components in the calculation of the formation in the matrix after microwave roasting the mineral monazite composition (Am, Ce, La, Th)·[PO4]·[SiO2, TiO2, Al2About3] - chemically and thermally stable compounds.

In addition, the problem is solved in that the thus prepared liquid Mn-, Am-containing RAO used for multiple (2-5 times) impregnation of the ceramic matrix. At this stage, it is advisable to take into account the specifics of the RAO. Thus, the Mn-containing RAO can be used in two ways : either for multiple impregnation specially made ceramic matrix (for example, on the basis of ultrapolite quartz ceramics), followed each time the microwave calcination at t=800-1000°or in the case of the introduction of the additive Al3+-containing components, when the operation of impregnation and calcination can be combined, so as ceramic matrix based on the spinel formed in the firing process may be fully saturated Mn-containing RAO at the stage of preparation of the solution RAO to immobilization.

Am-containing liquid waste is usually in the form of a solution Am(NO)3)3can also be used for the two-stage variant impregnation or for multiple impregnation them ultrapolite quartz ceramics, specially previously obtained by compacting and sintering of optical fibers made of quartz glass (SiO2the production of the research Institute for High temperatures RAS, with subsequent microwave roasting at 900-1000°for education is the volume of the voids of the matrix oxides etc. Am metals, final impregnation of the matrix orthophosphoric acid, H3PO4for deposition AmPO4(2nd stage) and the final firing (sintering), ceramic matrix with "included" in it RAO; or for one-step impregnation of a matrix of ultrapolite quartz ceramic with a mixture of concentrated solutions of nitric and phosphoric acids, the concentration and amount of which are selected so that the precipitation of phosphate Am (RAO with any cations forming insoluble phosphates of metals) occurred in the ceramic matrix after each impregnation during microwave baking.

The distinguishing feature of the claimed invention is used as an energy source of microwave radiation, which has, compared to traditional electric and induction methods of heating, the disadvantages listed above in the known methods of immobilization, the benefits of energy transmission through the waveguide is lossless conversion into heat directly in the whole volume of the material, carrying out all stages of immobilization, including the disposal, directly in the same crucible container, no secondary waste electrodes, inductors and others, the possibility of processing a wide range of compositions RAO, including those that cannot be melting in existing melters; at the same time "hot" camera are only a crucible is a container with radioactive waste, stationary container cover and hoisting-and-transport mechanism to move it.

The advantages of microwave heating in conjunction with a relatively low firing temperature ceramic (1000°C)a high degree of inclusion of radioactive waste into the matrix and its high thermal and chemical resistance, no treatment of dust and particulate materials (extrusion) and the possibility of industrial safety of technical staff and process automation immobilization existing robotics, make the proposed method is techno-economically efficient and promising for practical applications.

Summary of the invention the following examples.

Example 1.

Mn-containing aqueous suspension of radioactive waste with concentrations of MnO2=135-200 g/l=(a 5.0 to 7.4 parts by weight or of 13.5 to 20.0%); other: UO2- up to 5 parts by weight of (13,5%); Fe2O3- to 15.0 parts by weight (40,5%); NiO - to 6 parts by weight of (16,2%); Cr2O3- to 1.0 parts by weight of (2.7 percent); SiO2- to 2.0 parts by weight of (5,4%); Al2About3- to 3.0 parts by weight of (8,2%) at the stage of pre-processing were processed with the use of the crystallization promoter N3PO484.7% of concentration for deposition of insoluble phosphates of metals with the addition of Al3+Si4+, Ti4+-containing components in the calculation of the formation of the spinel MnO·Al2About3(O4) is its analogs were placed in the reactor container and subjected to microwave firing with the use of microwave generators with a capacity of 5-10 kW at a frequency of 2450± 2% MHz and a power of 25 to 50 kW at a frequency of 915±1,4% at a temperature of 900-1000°C.

When the microwave heating MnO2(pyrolusite) enters MnO (manganese); formed in the firing process of the ceramic matrix based spinels and other minerals due to the parallel process of dehydration-calcined has a high initial porosity and permeability for the Mn-containing aqueous suspension RAO, therefore, the operation of impregnation its matrix and the firing of the matrix are combined and occur at the same time, ending at 1000°after firing at this temperature for 10-15 minutes

The main minerals of the thus obtained matrix (except spinel): Brunet 3Mn2About3·SiO3hausmannite MnMn2O4hollandite (manganate Mn, Ba, Fe3+), senait MnTiO2, pyrophanite MnTiO3, bixbyite (Fe, Mn)2O3, retzian (phosphate Mn, Ca, Y), bradenburger 3Mn3O4·2F2O3Galaxie (Mn, Fe)O·(Al, Fe)2O3.

Testing the strength of fixation carried out according to GOST 29114-91 "measurement Method for chemical resistance of solidified radioactive waste through long-term leaching showed the following results:

1. The content of the oxide of manganese
(without radionuclide, % by weight of sample) of 17.0
2. The density of SPECA, g/cm32,0
3. The limit of compressive strength, MPa58,5
in bending, MPa4,5
4. The rate of leaching for 93 days, g/cm2/d1,7·10-6

Example 2.

Liquid Am-containing RAO (research were used imitators of americium - 241 is its conventional non-toxic crystal analogues neodymium Nd, Nd(NO3)3, NdPO4Nd2O3and minerals based on them) in combination with HNO3(4-5 mol/l), Al3+(0.5 to 0.8 mol/l) and F-(0,2-0,3 mol/l) was used for the two-stage variant of impregnation. In the first stage units industrial ultrapolite quartz ceramics with open porosity 90-95% of the original volume of 1 liter, obtained at the research Institute for High temperatures RAS during sintering of pressed blocks of optical fibers made of quartz glass (SiO2), five times soaked up one stripped off with a solution of neodymium nitrate Nd(NO3)3density 1.5 g/cm3(impregnation was carried out by immersing samples of ceramic blocks in one stripped off solution for 24 hours).

After each impregnation of the ceramic matrix was subjected to microwave firing mode, shown in Example 1 at t-re 900-1000°With; in the volume of the matrix formed oxides of neodymium and hydroxy what s other metals, which gradually increase the degree of impregnation, filled pores and the capillary channels of the ceramic matrix. After five impregnation and five microwave roastings capacity ceramic matrix solution of Nd(NO3)3was 4.6 l on 1 sample of the ceramic block with a volume of 1 L. the Degree of inclusion of neodymium oxide in ultrapolite quartz ceramics after 5 impregnations and roastings was about 80%. However, despite the high porosity of the original quartz ceramics, the rate of leaching of neodymium is small and is in accordance with the methodology MSS-1, of order 10-7-10-8g/cm2/day (after 1 hour of contact with water).

Soaked and annealed thus the ceramic matrix in the second stage of work was additionally impregnated (1) phosphoric acid, H3PO484.7% of concentration, and then subjected to microwave firing at the above mode. This operation was conducted in order to chemically link the oxides of neodymium and other metals that do not form heat - and chemical-resistant strength of a structure with a 100% continuity and low water-permeability, "devimahatmya" from the matrix high-density, strong and durable minerals-type phosphate neodymium and other metals, and other minerals with similar type properties of monazite (Am-Nd, Ce, La, Th)·[PO4]·[SiO2, TiOsub> 2, Al2About3].

Testing the strength of fixation carried out according to GOST 29114-91 "measurement Method for chemical resistance of solidified radioactive waste through long-term leaching", showed the following results:

1. The content of the oxide of neodymium (after 5 cycles "impregnation-calcination without radionuclide, % by weight of sample) approximately 80

2. The density of SPECA, g/cm32,1
3. The open porosity SPECA %10-20
4. The limit of compressive strength, MPa50,0
in bending, MPa4,0
5. The rate of leaching for 93 days, g/cm3/d2,3·10-7

Thus, the above test results show that microwave immobilization of active industrial waste on the proposed method allows to obtain a strong and durable ceramic matrix, highly saturated active industrial waste, in particular, Mn-, Am-containing RAO, chemically "bound" with the mineral matrix in a single unit. The matrix can be disposed of in geological formations or the storage of waste that will ensure the ecological safety of the environment for periods measured in hundreds of years.

The way the matrix Immobili the emission of industrial waste radiochemical and chemical and metallurgical industries, including the preliminary preparation of the starting solution of industrial waste and impregnating them with a ceramic matrix, with subsequent annealing, characterized in that the applied source of liquid radioactive waste, which at the stage of preliminary preparation is treated with a solution of the crystallization promoter with Oktiabrski additives, after which radioactive waste is introduced into the ceramic matrix and fired with the use of microwave energy at a temperature of 900-1000°C.



 

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