RU2321909C1 - Method for recovering liquid radioactive waste (alternatives) - Google Patents

Abstract

FIELD: recovering liquid radioactive waste by immobilizing radionuclides in crystalline material.

SUBSTANCE: proposed method involves synthesis of insoluble compounds immobilizing long-living radionuclides. Insoluble compounds in the form of salts or oxides are synthesized under hydrothermal conditions in flow by passing liquid waste being recovered and reagents required for synthesis through layer of insoluble particles at rate affording crystallization of radionuclide-containing compounds being synthesized on surface of particle layer. Insoluble particles are essentially oxides of metals, such as ferric, manganous, and cobaltous oxides, zirconium, or salts, for instance hydroxyapatite. Hydrothermal synthesis is conducted at temperature of 180-250 °C and pressure of 20-150 at.

EFFECT: enhanced degree of solution decontamination, segregation coefficient, ability of forming high-strength long-living ceramic matrix, minimized radionuclide leaching.

3 cl, 3 dwg, 5 tbl

Description

The invention relates to environmental protection, and in particular to methods of processing liquid radioactive waste (LRW), providing for their immobilization in crystalline material, acceptable from an environmental point of view, and can be used in nuclear power plants and chemical and metallurgical industries.

The processing of liquid radioactive waste is associated with the need to achieve safe long-term storage of radioactive waste (RW), for which solid radioactive waste (SRW) must be converted to a state that minimizes the leaching of radionuclides by natural waters. This problem is solved using such well-known methods as bitumen, cementing and vitrification of radioactive waste (RF patent No. 2088986, 08/27/1997; RF patent No. 2271586, 03/10/2006; RF patent No. 2111152, 05/27/1999; Donald IW, Metcalfe BL, Taylor RNJ The immobilization of high level radioactive wastes using ceramics and glasses. Review. Journal of Materials Science, 32, 1997. p.5856-5862). The smallest degree of leaching is provided by vitrification of radioactive waste and has a value of the order of 10 ^-6 g / cm ² · day.

At present, interest in oxide materials as matrices for the concentration and curing of solutions of salts of radionuclides and heavy metals used in the processing of liquid radioactive waste has noticeably increased. This form of waste disposal seems to be the most promising, because provides higher radiation, chemical and thermal resistance in comparison with the above methods.

A representative of such forms of RW immobilization is a ceramic material widely known under the trade name Synroc, the matrix of which, as a rule, is a combination of hollandite (BaAl ₂ Ti ₂ O ₆ or BaAl ₂ Ti ₆ O ₁₆ ), perovskite (CaTiO ₃ ) and zirconolite ( CaZrTi ₂ O ₇ ).

A large number of works have been devoted to the synthesis and use of Synroc ceramics for RW immobilization (RF patent No. 2153717, 07.27.2000, EP No. 0007236, 01/23/1980; US No. 4274976, 06/23/1981; Ringwood AE, Kesson SE, Reeve KD, Levins DM, Ramm EJ Synroc. In: Radioactive Waste Forms for the Future. Eds. Lutze W. and Ewing RC Amsterdam: Elsevier Science Publishers BV, 1988. P.233-334; Donald IW, Metcalfe BL, Taylor RNJ The immobilization of high level radioactive wastes using ceramics and glasses. Review. Journal of Materials Science, 32, 1997. p. 5862-5865 and others). Materials of this type can reduce the degree of leaching of radioactive waste from the ceramic matrix to 10 ^-9 g / cm ² · day.

The indicated methods for RW processing, in which the radioactive waste is immobilized into a ceramic matrix, along with the above advantages have a number of disadvantages due to the high energy intensity of the high-temperature processes (1000 ° C and above), multi-operation and the need to use special equipment.

In addition, it should be noted that the use of Synroc ceramics is effective in the case of immobilization of small volumes of radioactive waste, mainly high-level waste (HLW).

In recent years, work has been developing on the hydrothermal synthesis of ceramic materials and minerals suitable for the immobilization of radionuclides in RW processing processes.

Hydrothermal synthesis, during which the crystal growth rate increases manyfold compared with synthesis at ordinary temperatures, presents new opportunities for the selective extraction of radionuclides. However, the amount of ceramic materials synthesized hydrothermally and capable of immobilizing radionuclides is very limited (Johnson CD, Skakle JMS, Johnson MG Feldmann J. Macphee DE Hydrothermal synthesis, crystal structure and water stability of two cadmium arsenate phases, CdNH ₄ (HAsO ₄ ) OH and Cd ₅ H ₂ (AsO ₄ ) ₄ · 4H ₂ O. J. Mater. Chem., 2003, 13, 1429-1432).

Hydrothermal methods for processing radioactive waste show that the main problems of hydrothermal treatment of LRW from radionuclides are:

- the choice of the type of ceramic matrix formed as a result of hydrothermal synthesis, which should be selective for the corresponding radionuclides;

- the ceramic matrix should be formed in the environment of the purified LRW (pH, salt composition, and other indicators) when appropriate reagents are introduced into the solution at given temperatures and pressures in the system;

- separation coefficient of ceramics - the solution should be large enough to provide the necessary coefficient of purification of the solution from radionuclides.

New, promising for the extraction of radionuclides are sorption-reagent materials (SRM).

The principle of operation of sorption-reagent materials is the continuous formation of an insoluble compound that sorb radionuclides in a porous matrix of an inert material. In this case, a continuous growth of crystals of the insoluble compound occurs with the simultaneous sorption of radionuclides. As a result, crystalline materials are formed with a very small phase interface and sorbed radionuclides distributed throughout the volume of the crystalline material; therefore, the leaching of radionuclides from sorption-reagent materials is orders of magnitude lower than from selective ion-exchange sorbents with a large exchange capacity and, therefore, a large surface phase separation.

So, in the patent of the Russian Federation No. 2185671 07/20/2002 describes the extraction of strontium radionuclides from solutions with a high content of hardness salts and liquid radioactive waste of complex chemical composition. CPMs are formed directly during the cleaning process as a result of the interaction of the initial sorption-reagent material containing exchange barium cations with the solution to be purified containing sulfate ions, with the formation of insoluble barium sulfate crystallizing in the matrix of the sorption-reagent material.

This method is the closest to the proposed method.

The objective of the invention is to develop a method for processing liquid radioactive waste containing long-lived radionuclides, mainly cobalt, manganese and strontium, in hydrothermal conditions, providing a high degree of purification of solutions from the corresponding radionuclides, a high separation coefficient (ratio of volumes of purified LRW to SRW), the formation of durable durable ceramic matrix with minimal leaching of radionuclides.

The problem is solved by the method of processing liquid radioactive waste containing long-lived radionuclides, by synthesizing insoluble compounds immobilizing long-lived radionuclides, in hydrothermal conditions in a stream, by passing processed LRW and reagents necessary for synthesis through a layer of insoluble particles with a speed that ensures crystallization of the synthesized compounds containing radionuclides on the surface of the particles of the layer.

The optimal conditions for hydrothermal synthesis are a temperature of 180-250 ° C and a pressure of 20-150 atm.

Mostly, metal oxides or salts are used as insoluble particles.

Iron oxides and / or manganese oxide and / or cobalt oxide are used as metal oxides, and hydroxylapatite is used as a salt.

The task in the second embodiment is solved by the method of processing liquid radioactive waste containing long-lived radionuclides by synthesizing insoluble compounds that immobilize long-lived radionuclides into a crystal lattice when synthesizing the crystalline phase in the form of oxides in hydrothermal conditions in a stream, bypassing the processed LRW and the reagents necessary for the synthesis through a layer of metal oxides at a rate that crystallizes the synthesized oxides containing radionuclides on the surface of astits oxide layer.

Preferably, iron oxide and / or manganese oxide and / or cobalt oxide and / or zirconium oxide are used as transition metal oxides.

It is optimal to carry out hydrothermal synthesis at a temperature of 180-250 ° C and a pressure of 20-150 atm.

The task in the third embodiment is solved by a method of processing liquid radioactive waste containing long-lived radionuclides by synthesizing insoluble compounds immobilizing long-lived radionuclides into a crystal lattice, in hydrothermal conditions in a stream, passing processed LRW and reagents necessary for synthesis through a layer of transition metal oxides with speed, providing crystallization of the synthesized compounds containing radionuclides on the surface of the particles of the oxide layer.

Preferably, iron oxide and / or manganese oxide and / or cobalt oxide and / or zirconium oxide are used as transition metal oxides.

Optimally hydrothermal synthesis is carried out at a temperature of 180-250 ° C and a pressure of 20-150 atm.

The essence of the method in accordance with the first embodiment is as follows.

When a LRW solution and the reagents necessary for the synthesis of compounds are passed through a layer of insoluble particles under hydrothermal conditions on the particles making up the layer, a new crystalline phase grows, which is a compound that immobilizes radionuclides.

One of the differences of the method is that under hydrothermal conditions, the synthesis of oxides occurs by crystallization of a new phase on the surface of the particles of the layer, and not in the volume of the layer, as in the method known from patent RF 2185671.

It should also be noted that the composition of the synthesized compounds formed on the surface of the particles can be different from the composition of the particles of the layer and depends on the composition of the initial solution.

The essence of the method in accordance with the second option is as follows.

When a solution of LRW and reagents is passed through an oxide layer of insoluble particles under hydrothermal conditions on the oxide particles that make up the layer, a new crystalline phase, which is an oxide immobilizing radionuclides, grows.

One of the differences of the method is that under hydrothermal conditions, the synthesis of oxides occurs by crystallization of a new phase on the surface of the particles of the layer, and not in the volume of the layer, as in the known method (RF 2185671).

It should be noted that the oxides formed on the surface of the oxides, which are a layer of particles, can differ in composition from the oxides of the layer and depend on the composition of the initial solution.

The essence of the method in accordance with the third option is as follows.

When a solution of LRW and reagents is passed through a layer of insoluble oxides under hydrothermal conditions on the particles making up the oxide layer, a new crystalline phase grows, which is a compound that immobilizes radionuclides.

One of the differences of the method is that under hydrothermal conditions the synthesis of insoluble particles occurs by crystallization of a new phase on the surface of the oxide of the layer, and not in the volume of the layer, as in the known method (RF 2185671).

In this case, the term “crystallization” should be understood as the transition of a substance from a liquid state to a solid crystalline state, and by the term “crystallization on the surface of particles” - a heterogeneous formation of a crystalline phase on a solid surface.

The term "phase" in the context of the present invention should be understood to be generally accepted in the prior art "homogeneous in composition and properties of the part of the thermodynamic system, separated from other phases by interface surfaces on which some properties of the system are abruptly changed."

The term immobilization in the present invention should be understood to include radionuclides in the crystal lattice of insoluble compounds that crystallize on the surface of the particles of the layer.

During the process, a LRW solution is passed through a layer of particles. Moreover, on the surface of the layer under hydrothermal conditions, i.e. at elevated temperatures and pressures, new compounds are synthesized in the form of crystals that immobilize radionuclides. The rate of transmission of LRW solutions through a layer of particles should be such that the formation of crystals on the surface of a layer of particles immobilizing radionuclides provides the necessary degree of purification from radionuclides. At a flow rate greater than a certain value determined experimentally in each case, crystallization occurs in the volume of the solution, and not on the surface of the particles of the layer. At the same time, part of the crystals containing radionuclides is carried out beyond the layer and practically no purification takes place.

To carry out the cleaning process, it is necessary that the solution to be purified contains ions that form crystals of compounds immobilizing radionuclides under hydrothermal conditions. For the synthesis of the crystalline phase, reagents are added to the LRW solution, ensuring the presence of ions in the solution necessary for the synthesis. As such reagents can be used, for example, oxidizing agents, such as hydrogen peroxide or potassium permanganate, oxidizing ions that are part of LRW, to the degree of oxidation at which insoluble compounds and / or metal salts are formed.

As a result of the studies, it was found that the synthesis of crystals depends on the specific conditions of the hydrothermal process. So, at the same flow rate of the initial solution, not exceeding the crystallization rate in the temperature range from 180 to 250 ° C and pressure from 20 to 150 atm, crystallization occurs on the surface of the particles of the layer.

In the case of the process at a pressure of less than 20 atm and a temperature of less than 180 ° C, crystallization partially occurs in volume. Carrying out the process at a pressure above 150 atm and a temperature above 250 ° C is not economically justified.

In more detail, the process can be explained using the schemes shown in figures 1-3.

Figure 1 shows the AFM image of the particles of the layer before the hydrothermal synthesis (source particle), figure 2 - during the synthesis, and figure 3 - after the completion of hydrothermal synthesis.

The method for any of the options is as follows.

The necessary reagents corresponding to the type of processed LRW are introduced into the processed LRW, after which the LRW is fed into a flow reactor for hydrothermal synthesis, in which a layer of particles of insoluble compounds is placed.

The synthesis is carried out in the temperature range 180-250 ° C at a pressure of 20-150 atm, which corresponds to a sufficient crystal growth rate and the required degree of purification from radionuclides.

Compounds formed as a result of hydrothermal synthesis precipitate on insoluble particles forming a layer.

After completion of the process, when all particles of the layer are coated with crystals of synthesized compounds containing radionuclides, they are sent for storage or for further processing. The solution purified from radionuclides is an industrial non-radioactive waste.

Figure 1 shows the cleaning process at the initial time t. The LRW solution flow rate is sufficient for the formation of crystals on the surface of the particles of the fixed layer.

Figure 2 shows the process at an intermediate time t '. A new crystalline phase in the form of layered polycrystals was formed on the surface of particles forming a layer of insoluble particles. This corresponds to the implementation of the cleaning process under optimal conditions.

Scheme 3 shows the process at a finite time t когда when layered polycrystals immobilizing radionuclides formed on all insoluble particles of the layer.

The layered structure of the synthesized compound growing on the initial globular structure is visible in the images.

It was found that the degree of purification of solutions from the corresponding radionuclides in the process of hydrothermal synthesis of oxides ranged from 10 ² to 10 ⁴ . The ratio of volumes of purified LRW to the volume of the reactor, partially filled with the initial particles, amounted to 500-2000 or more, which corresponds to separation coefficients of more than 10 ⁶ .

The possibility of carrying out the invention is demonstrated by the following examples.

EXAMPLE 1 (option 1). LRW containing 2 g / l Trilon B and 0.5 g / l trisodium phosphate, having a calcium ion concentration of 0.1 g / l and containing strontium-90 radionuclides (1.5 · 10 ^-6 Ci / l) are passed through the layer hydroxylapatite Ca ₃ PO ₄ · Ca (OH) ₂ with a particle size of 0.1-0.3 mm, loaded into a heated cylindrical reactor with dimensions of 100 × 10 mm The process is carried out at a flow rate of 1 ml / min, at a temperature of 200 ° C and a pressure of 100 atm. The flow of the solution is provided by a high pressure chromatographic pump. At the same time, a 6% hydrogen peroxide solution is introduced into the reactor with a high pressure pump at a rate of 0.6 ml / min. The activity of the effluent solution is shown in Table 1. The values of the leaching coefficients of strontium radionuclide from the hydroxylapatite layer with synthesized polycrystals of calcium phosphates immobilizing the radionuclides (charge) determined after completion of the experiment are also given there.

Table 1 The volume of the past solution, ml The activity of strontium-90, Ki / l one hundred 1 · 10 ^-10 500 6.710 ^-10 1000 1.9 · 10 ^-9 2500 4.1 · 10 ^-8 The leaching coefficient for the mixture, g / cm ² · day 1 · 10 ^-5

EXAMPLE 2 (option 2). The bottom residue of the evaporation devices for special water treatment of nuclear power plants, purified from cesium radionuclides by filtration through ferrocyanide sorbents and containing cobalt-60 (1 · 10 ^-5 Ci / l) and manganese-54 (1 · 10 ^-8 Ci / l) radionuclides, is passed through a layer of iron-cobalt ferrite (iron-cobalt oxides) with a molar ratio of iron: cobalt of 1:01 and a particle size of 0.2-0.5 mm, loaded into a heated cylindrical reactor with dimensions of 100 × 10 mm. The process is carried out at a flow rate of 2 ml / min, at a temperature of 220 ° C and a pressure of 100 atm. The flow of the solution is provided by a high pressure chromatographic pump. At the same time, a 6% hydrogen peroxide solution is introduced into the reactor with a second high-pressure pump at a rate of 0.6 ml / min. The activity of the effluent solution is shown in table 2. The values of the cobalt radionuclide leach coefficient from the mixture of the formed oxides determined after the completion of the experiment are also given there.

table 2 The volume of the past solution, ml The activity of cobalt-60, Ki / l The activity of manganese-54, Ki / l one hundred 1.4 · 10 ^-9 <1 · 10 ^-11 500 1.1 · 10 ^-9 <1 · 10 ^-11 1000 1.7 · 10 ^-9 <1 · 10 ^-11 2500 1.5 · 10 ^-9 <1 · 10 ^-11 5000 2.110 ^-9 <1 · 10 ^-11 The leaching coefficient for the mixture, g / cm ² · day 2 · 10 ^-8 <1 · 10 ^-7

EXAMPLE 3 (option 3). LRW containing 2 g / l Trilon B and 0.5 g / l trisodium phosphate, having a calcium ion concentration of 0.1 g / l and containing strontium-90 radionuclides (1.5 · 10 ^-6 Ci / l) LRW containing 2 g / l Trilon B and 0.5 g / l trisodium phosphate, having a concentration of calcium ions of 0.1 g / l and containing strontium-90 radionuclides (1.5 · 10 ^-6 Ci / l), is passed through a layer of zirconium oxide with a particle size of 0 , 1-0.3 mm, loaded into a heated cylindrical reactor with dimensions of 100 × 10 mm The process is carried out at a flow rate of 1 ml / min, at a temperature of 200 ° C and a pressure of 100 atm. The flow of the solution is provided by a high pressure chromatographic pump. At the same time, a 6% hydrogen peroxide solution is introduced into the first reactor with a high pressure pump at a rate of 0.6 ml / min. The activity of the effluent solution is shown in table 3. The values of the leaching coefficients of the strontium radionuclide from the mixture of calcium and zirconium phosphates determined after the completion of the experiment are also given there.

Table 3 The volume of the past solution, ml The activity of strontium-90, Ki / l one hundred 1 · 10 ^-10 500 1.8 · 10 ^-9 1000 2.1 · 10 ^-8 The leaching coefficient for the mixture, g / cm ² · day 6 · 10 ^-5

EXAMPLE 4. Sea water contaminated with strontium-90 radionuclide (activity 2 · 10 ^-6 Ci / l) is passed through a layer of manganese dioxide with a particle size of 0.05-0.1 mm, loaded into a heated cylindrical reactor with a size of 100 × 10 mm. The process is carried out at a flow rate of 1 ml / min, at a temperature of 220 ° C and a pressure of 100 atm. The flow of the solution is provided by a high pressure chromatographic pump. At the same time, 0.1 n high pressure pumps are introduced into the reactor. a solution of manganese (II) chloride and 0.1 N. potassium permanganate solution at a rate of 0.6 ml / min. The activity of the effluent solution is shown in table 4. The values of the leaching coefficients of the strontium radionuclide from the mixture of the formed oxides determined after the completion of the experiment are also given there.

Table 4 The volume of the past solution, ml The activity of strontium-90, Ki / l one hundred 5.610 ^-9 500 4.0 · 10 ^-9 1000 4.310 ^-9 1500 4,5 · 10 ^-9 2000 5.910 ^-9 The leaching coefficient for the mixture, g / cm ² · day 1.4 · 10 ^-7

EXAMPLE 5. Decontamination LRW containing 2 g / l sodium oxalate and 0.5 g / l Trilon B, purified from cesium radionuclides by filtration through ferrocyanide sorbents and containing cobalt-60 radionuclides (1 · 10 ^-7 Ci / l) and strontium-90 (4 · 10 ^-7 Ci / l), sequentially passed through a layer of iron-cobalt ferrite with a molar ratio of iron: cobalt 1: 0.1 and a particle size of 0.2-0.5 mm, loaded into a heated cylindrical reactor 100 × 10 mm in size and through a layer of manganese dioxide with a particle size of 0.05-0.1 mm, loaded into a heated cylindrical a reactor with dimensions of 100 × 10 mm. The process is carried out at a flow rate of 1 ml / min, at a temperature of 200 ° C and a pressure of 100 bar. The flow of the solution is provided by a high pressure chromatographic pump. At the same time, a 6% hydrogen peroxide solution is introduced into the first reactor with a high-pressure pump at a rate of 0.6 ml / min, and 0.1 n into the second reactor. manganese (II) chloride solution. The activity of the effluent solution is shown in Table 5. The values of the cobalt radionuclide leaching coefficients from the resulting oxides determined after the completion of the experiment are also given there.

Table 5 The volume of the past solution, ml The activity of cobalt-60, Ki / l The activity of strontium-90, Ki / l one hundred <1 · 10 ^-11 1 · 10 ^-10 500 <1 · 10 ^-11 1.4 · 10 ^-10 1000 <1 · 10 ^-11 2.7 · 10 ^-10 2500 <1 · 10 ^-11 1 · 10 ^-10 5000 <1 · 10 ^-11 4.310 ^-9 The coefficient for batch leaching g / cm ² · day 2 · 10 ^-8 3 · 10 ^-7

EXAMPLE 6

Alkaline LRW containing 0.3 g / l sodium hydroxide and cobalt-60 radionuclides (1 · 10 ^-7 Ci / l) and cesium-137 (6 · 10 ^-7 Ci / l) are passed through a filter-perlite layer with the content iron 3.4%, loaded into a heated cylindrical reactor with dimensions of 100 × 10 mm The process is carried out at a flow rate of 0.3 ml / min at a temperature of 170 ° C and a pressure of 100 atm. The flow of the solution is provided by a high pressure chromatographic pump. The activity of the effluent solution is shown in Table 6. The values of the leaching coefficients of the cobalt and cesium radionuclide from the mixture of mixed iron oxides and aluminosilicates (mainly faujasite) determined after the completion of the experiment are also given there.

Table 6 The volume of the past solution, ml The activity of cobalt-60, Ki / l The activity of cesium-137, Ki / l one hundred 7.410 ^-10 2.110 ^-9 200 2.110 ^-10 7.810 ^-10 500 4.210 ^-10 1.1 · 10 ^-9 800 7.910 ^-10 1 · 10 ^-9 1000 1.1 · 10 ^-8 5.4 · 10 ^-8 The leaching coefficient for the mixture, g / cm ² · day 1 · 10 ^-6 1 · 10 ^-5 Leaching coefficient for cement stone, g / cm ² · day 5 × 10 ^-4 5 × 10 ^-4

The experimental data presented show that during the processing of LRW by the proposed methods, a charge is formed, which is either metal salts or metal oxides immobilizing radionuclides suitable for burial. The degree of leaching of radionuclides from them is at the level of 10 ^-5 -10 ^-7 g / cm ² · day. The solutions obtained after purification with a degree of purification of 10 ² -10 ⁴ are non-radioactive industrial waste.

Claims (10)

1. A method of processing liquid radioactive waste (LRW) containing long-lived radionuclides by synthesizing insoluble compounds immobilizing long-lived radionuclides, characterized in that the synthesis of insoluble compounds is carried out in hydrothermal conditions in a stream, passing processed LRW and reagents necessary for synthesis through a layer insoluble particles at a rate that crystallizes the synthesized compounds containing radionuclides on the surface of the particles of the layer. 2. The method according to claim 1, characterized in that the particles are metal oxides or salts. 3. The method according to claim 2, characterized in that iron oxide and / or manganese oxide and / or cobalt oxide are used as metal oxides, and hydroxylapatite is used as a salt. 4. The method according to claim 1, characterized in that the hydrothermal synthesis is carried out at a temperature of 180-250 ° C and a pressure of 20-150 atm. 5. A method of processing liquid radioactive waste (LRW) containing long-lived radionuclides by synthesizing insoluble compounds immobilizing long-lived radionuclides into a crystal lattice, characterized in that the crystalline phase is synthesized in the form of oxides under hydrothermal conditions in a stream, bypassing the processed LRW and the reagents necessary for synthesis, through a layer of metal oxides at a rate that crystallizes the synthesized oxides containing radionuclides on the surface of the particles of the oxide layer. 6. The method according to claim 5, characterized in that the iron oxides and / or manganese oxide and / or cobalt oxide and / or zirconium oxide are used as metal oxides. 7. The method according to claim 6, characterized in that the hydrothermal synthesis is carried out at a temperature of 180-250 ° C and a pressure of 20-150 atm. 8. A method of processing liquid radioactive waste (LRW) containing long-lived radionuclides by synthesizing insoluble compounds immobilizing long-lived radionuclides into a crystal lattice, characterized in that the synthesis of the crystalline phase is carried out in hydrothermal conditions in a stream, passing processed LRW and reagents necessary for synthesis through a layer of metal oxides at a rate that crystallizes the synthesized compounds containing radionuclides on the surface of the particles of the oxide layer. 9. The method according to claim 8, characterized in that the iron oxides and / or manganese oxide and / or cobalt oxide and / or zirconium oxide are used as metal oxides. 10. The method according to claim 9, characterized in that the hydrothermal synthesis is carried out at a temperature of 180-250 ° C and a pressure of 20-150 atm.

Images