KR102467909B1 - Method for seperating uranium from spent uranium catalyst - Google Patents

Abstract

The present invention relates to a method for separating uranium from a spent uranium catalyst, comprising the steps of: (a) separating the antimony contained in a spent uranium catalyst by heating the spent uranium catalyst at a temperature range of 850 to 1,315℃, separating the liquid phase of antimony into ingots, and separating the gas phase of antimony in a condenser; (b) performing phase separation of the spent uranium catalyst from which antimony is separated into a phase containing silica and a phase containing uranium and impurities; (c) treating the phase containing silica and the phase containing uranium and impurities, respectively, with acid; and (d) melting the phase containing silica at a temperature range of 1,600 to 1,700℃, crystallizing (directional solidification) at a temperature range of 1,450 to 1,550℃ to obtain purified silica, and evaporating the phase containing uranium and impurities to obtain purified uranium. According to the present invention, there is the effect of recycling liquid waste or maximally reducing disposal costs by realizing the theoretical maximum volume reduction.

Description

Method for separating uranium from spent uranium catalyst {METHOD FOR SEPERATING URANIUM FROM SPENT URANIUM CATALYST}

The present invention uses the property that metals are separated into ingots, vaporized bodies and slags when melted, and removes antimony by using the difference in melting points of metals contained in spent uranium catalysts, and then the remaining uranium and silica are separated using phase separation. and a method for separating pure uranium.

Waste uranium catalysts are difficult to process because they are not soluble in strong acids or bases and contain harmful antimony, so in most cases, a method of separating silica into a liquid phase or adding a vitrification additive to uranium has been used for disposal. Fundamentally, if it contains antimony, it is difficult to dispose of it in a radioactive waste repository, and if uranium is disposed of, not only does the amount of disposal increase, but there is a problem of excessive use of chemical solvents harmful to the environment.

Various studies are being conducted to solve these problems, and prior art 1 (Patent Publication No. 10-2004-0068901) makes sodium silicate soluble at a temperature of 1,000 ~ 1,600 ° C. to make it into a solution, or sodium hydroxide The solution method is used. Silica is the main component of the catalyst and the amount is considerable, so it is expensive to liquefy the silica, and there are problems with the high cost of wastewater treatment and the inflow of water-soluble uranium into the liquid. There is a problem of increasing the amount of disposal by adding.

Prior Art 2 (Public Patent Publication No. 10-2009-0046001) has a problem in that the amount of disposal increases by the amount of vitrified material because uranium and silica are added to vitrified material, and harmful antimony is vaporized together, so it is easier to process than ingots. and the potential for problems with the atmospheric environment.

Prior Art 3 (Patent Publication No. 10-2019-0008476) removes silica from uranium by a chemical method and discharges liquid radioactive waste below the regulatory level, but there is a problem in that a large amount of strong salt is consumed.

Patent Publication No. 10-2004-0068901 (2004.08.02. Publication) Patent Publication No. 10-2009-0046001 (published on May 11, 2009) Patent Publication No. 10-2019-0008476 (2019.01.24. Publication) Registered Patent No. 10-1200780 (registered on November 7, 2012)

In view of the above problems, an object of the present invention is to recycle liquid waste, unlike the existing prior art, to dry process it in an eco-friendly way so that there is little disposal amount, and to prevent excessive treatment costs from using uranium through an economical method. It is to provide a method for separating uranium from spent catalyst.

In order to achieve the above object, the present invention provides a method for separating uranium from a spent uranium catalyst, comprising: (a) separating antimony contained in the spent uranium catalyst, and the spent uranium catalyst is kept at a temperature range of 850 ° C to 1,315 ° C; separating the liquid phase of antimony into ingots and separating the gas phase of antimony in a condenser; (b) phase-separating the spent uranium catalyst from which antimony is separated into a phase containing silica and a phase containing uranium and impurities; (c) acid-treating the phase containing silica and the phase containing uranium and impurities, respectively; (d) melting the silica-containing phase at a temperature range of 1,600 ° C to 1,700 ° C and then crystallizing (directional solidification) at a temperature range of 1,450 ° C to 1,550 ° C to obtain purified silica, containing the uranium and impurities The phase may include evaporating to obtain purified uranium.

Preferably, the spent uranium catalyst is one selected from the group consisting of uranium antimony composite metal oxide, uranium composite metal oxide for producing acrylonitrile, or a mixture thereof, and contains antimony oxide, silicon oxide, iron, molybdenum and bismuth. can include

Preferably, the gas phase of step (a) may include antimony and bismuth.

Preferably, the ingot of step (a) may contain aluminum and antimony.

Preferably, in the step (b), the phase separation is carried out by heating at a temperature of 1,565 ° C to 1,600 ° C after adding the additive to separate iron-containing impurities into ingots, and cooling to a temperature of 600 ° C to 800 ° C. can do.

Preferably, the additive includes a boron oxide (B ₂ O ₃ ) or an alkali metal oxide, wherein the alkali metal oxide is any one selected from the group consisting of Li ₂ O, Na ₂ O and K ₂ O, and boron oxide 70 to 90% by weight or 10 to 30% by weight of an alkali metal oxide.

Preferably, in the step (b), the phase may be separated by heating to a temperature of 1,400 ° C. or higher to evaporate the phase containing silica.

Preferably, trichlorosilane (TCS, HSiCl ₃ ) is added as an intermediate to accelerate the evaporation, and evaporation of silica at a temperature range of 1,000 ° C to 1,200 ° C or evaporation using a copper catalyst may be further included.

Preferably, in the acid treatment step of step (c), the phase containing silica is solidified, the phase containing uranium and impurities is liquefied, the acid is mixed acid or nitric acid, and the mixed acid is HCl at a concentration of 3M to 5M. and HF at a concentration of 0.3M to 0.5M in a weight ratio of 1:1, and the acid is recyclable after the acid treatment process.

Preferably, it may include repeating step (b) without going through step (d) after step (c).

Preferably, in the step (d), residual uranium is removed in the process of removing particulate impurities existing in the silica by melting, and by crystallizing the silica that has undergone melting in the molten state by the crystallization, the remaining uranium is Removed.

Preferably, the crystallization may be omitted in step (d).

According to the method of separating uranium from the spent uranium catalyst of the present invention, it is possible to maximize the reduction in disposal cost by recycling or realizing the theoretical maximum volume reduction by extracting only uranium, and by using a dry method rather than a chemical method. There is no harmful liquid waste, and the used acid is recycled, and there is no need to use an excessive amount of strong acid and alkali as in the case of using the conventional wet method, so the problem of excessive liquid waste disposal cost can be improved.

In addition, radioactive waste disposal sites do not dispose of antimony, which is limited in disposal, but also limit the vaporization of antimony during the treatment process, so it has the advantage of protecting the environment. In terms of radioactivity management, recycling is not a problem.

In addition, the present invention can be applied not only to spent uranium catalysts but also to spent uranium catalysts containing diatomaceous earth.

1 is a flowchart illustrating a method of separating uranium from a spent uranium catalyst.
2 is a flowchart showing in detail a method for separating uranium from a spent uranium catalyst.
FIG. 3 is a diagram showing compositions of SiO ₂ , Na ₂ O, and B ₂ O ₃ at suitable temperatures for phase separation of slag containing uranium oxide and silica.
Figure 4 is an apparatus in which the separation of antimony of the present invention is carried out.
5 is a furnace in which melting and crystallization are performed.
6 is a conceptual diagram of phase separation.
7 is a solubility curve of amorphous silica and quartz according to pH.
8 is a solubility curve of amorphous silica and quartz as a function of temperature.

Hereinafter, the present invention will be described in detail.

1 is a flowchart of a method for separating uranium from a spent uranium catalyst. First, the spent uranium catalyst is heated to separate antimony. The spent uranium catalyst from which antimony is separated is phase-separated to separate a phase containing silica and a phase containing uranium and impurities. Thereafter, mixed acid (HCl:HF = 1:1 weight ratio) is treated in each phase to obtain purified silica and purified uranium.

Hereinafter, the present invention will be described in more detail through examples. These examples are only for illustrating the present invention, and it will be apparent to those skilled in the art that the scope of the present invention is not to be construed as being limited by these examples.

Example 1.

Referring to FIG. 2 , a flow chart illustrating a process of removing uranium from a uranium composite metal oxide can be seen. Referring to FIG. 2, uranium-antimony composite oxide in the form of a sintered body supported on a silica support is heated at a temperature of 850 ° C to 1,315 ° C to melt antimony and separate it into ingots, and partially evaporated antimony is recovered from a condenser and a melting furnace. Through the structure, most of them were separated into ingots.

Subsequently, as a phase separation step, an additive was added to the spent uranium catalyst from which antimony was separated. The additive was prepared by mixing 20% by weight of an alkali metal oxide (Na ₂ O) with 80% by weight of boron oxide (B ₂ O ₃ ). 25% by weight of additives were added to 100% by weight of the residue.

After adding additives, iron and molybdenum were separated in a liquid state by heating at a temperature of 1,565 ° C to 1,600 ° C, and the remaining silica and uranium oxide were stabilized at a temperature of 650 ° C to 700 ° C. It was separated into a phase containing uranium and impurities and a phase containing silica. By phase separation, uranium can be made chemically separable.

Subsequently, as an acid treatment process, a mixed acid obtained by mixing 4M HCl and 0.4M HF in a weight ratio of 1:1 was added to the phase containing silica and the phase containing uranium and impurities.

The phase containing silica and the phase containing uranium and impurities were treated with the mixed acid at a weight ratio of 1:1, respectively, to leach out uranium.

When treated with mixed acid, the silica contained in the silica-containing phase is separated in a solid state, and the uranium dissolved in the mixed acid is separated in a liquid state.

Thereafter, the silica was melted at a temperature of 1,600 to 1,700 ° C, and then crystallized at a temperature of 1,450 to 1,550 ° C to obtain purified silica.

In the acid treatment process, nitric acid at a concentration of 3M may be used in addition to the mixed acid of HCl and HF.

The uranium dissolved in the mixed acid was vaporized to obtain purified uranium, and the mixed acid was condensed and recycled.

As described above, in the present invention, after safely separating antimony into ingots, only uranium, a radioactive material, is separated from silica, thereby maximally reducing the amount of disposal, thereby achieving the theoretical maximum reduction effect.

About 25% of boron oxide and alkali metal oxide were added as additives to separate uranium, but since about 20% of boron oxide is removed in the acid treatment process, it is a process of adding additives in spent uranium catalysts, and eventually about 5% of boron oxide is removed. Although the treatment materials (additives) increase, all of them are not radioactive materials, and silica is not disposed of at the repository if the uranium is less than 1 Bq/g, so even if the additives are added, the amount of disposal does not increase.

Radioactive waste that can be effectively treated by the present invention includes various complex oxide catalysts containing uranium, especially waste uranium catalysts for producing acronitrile, and uranium, antimony oxide, and silicon oxide as main components, and containing iron, molybdenum, and bismuth. It is diatomaceous earth containing uranium waste and spent uranium catalyst.

The present invention effectively enables acid treatment through phase separation into a phase containing silica and a phase containing uranium and impurities by adding an additive after separation of antimony according to melting. The acid obtained by leaching uranium through acid treatment is recycled, and the acid treatment process is repeatedly performed when necessary, or only uranium can be extracted from the spent catalyst by performing a complex crystallization process in the acid treatment process.

Example 2.

Proceed in the same manner as in Example 1, but by separating silica and uranium without adding additives, the silica was evaporated at a temperature of 1,450 to 1,500 ° C, and the remaining uranium was recovered.

Silica is a chemical combination of silicon and oxygen and is represented by the chemical formula SiO ₂ , and the melting temperature of silicon (Si) is reported to be 1,414 ° C.

In order to accelerate evaporation, trichlorosilane (TCS, HSiCl ₃ ) is prepared and added as an intermediate, and may be evaporated at a temperature of 1,100 °C. Since the boiling point of uranium dioxide is 4,131℃ and the boiling point of silica is 2,230℃, it is possible to evaporate silica and separate it from uranium, but it takes a lot of time and energy to separate it. It has the advantage that impurities such as etc. are completely separated.

FIG. 3 is a diagram showing compositions of SiO ₂ , Na ₂ O, and B ₂ O ₃ at suitable temperatures for phase separation of slag containing uranium oxide and silica.

Figure 4 is an apparatus in which the separation of antimony of the present invention is carried out. When separating antimony, a furnace that primarily separates antimony reduces gas phase separation and separates it into ingots so as to be advantageous to the environment and the operator's environment. When separated into ingots, it becomes an easy form for self-disposal. For crystallization to be performed later, the temperature is finely adjusted and a separate furnace capable of crystallization is used, and the furnace may be a magnetic induction furnace, an electric induction furnace, or a cold crucible induction furnace.

According to the NUREG-1640 report of the US Nuclear Regulatory Commission, 75 to 99% of antimony melts at 1,600°C and is separated into ingots, and 1 to 20% is separated into exhaust gases.

If the furnace is heated to a temperature of 850 ° C to 1,315 ° C lower than the temperature of 1,600 ° C in order to separate antimony contained in the spent catalyst, the antimony separated into ingots will increase, and the amount separated into exhaust gas will decrease, increasing safety. do. Then, after adding additives to the furnace, when melted above the iron melting temperature (iron 1,538 ℃, iron oxide 1,377 ℃), silica and uranium oxide are separated into slag, and a small amount of iron is separated into ingots and exhaust gases. of uranium is trapped in the soft phase of silica. The exhaust gas is condensed back into the furnace through the furnace structure and recovered, or discharged through a filter through the exhaust port.

5 is a furnace in which melting and crystallization are performed. After the separation of antimony, trace amounts of uranium in the soft phase silica are liquefied by melting at 1,600 ° C and separated into impurities (partitioning) or crystallized at a silica stabilization temperature (1,550 ° C) to separate purified silica and uranium. Since the furnace of FIG. 5 performs crystallization, it is different in function from the furnace of FIG. 3, so it is preferable to use the furnace of FIG. 5.

If the residual radioactivity in the purified silica exceeds 1 Bq/g, the radioactivity is reduced by acid treatment again or the melting and crystallization process is performed again using the furnace of FIG. 5 .

6 is a conceptual diagram of phase separation. Phase separation is a phenomenon in which a material system forming one phase is split into two phases due to changes in variables such as temperature, pressure, and composition. In addition to phase separation such as gas phase-liquid phase and liquid phase-solid phase, there is separation into two phases with different structures in solution and mixed crystal.

7 is a solubility curve of amorphous silica and quartz according to pH. Silica present in the solution has three states: colloidal sol, silica gel, and filterable precipitate. As shown in the graph, the solubility of amorphous silica and quartz varies depending on the pH. Since amorphous silica and quartz are well soluble in sulfuric acid and relatively less soluble in hydrochloric acid than in sulfuric acid, the use of hydrochloric acid is advantageous in separating uranium because the elution of silica is reduced.

8 is a solubility curve of amorphous silica and quartz as a function of temperature. As shown in the graph, amorphous silica has higher solubility in aqueous solution than quartz, and the solubility increases as the temperature increases. However, referring to FIG. 7, the solubility is very low up to pH 9. Therefore, when hydrochloric acid and hydrofluoric acid (HF) are used, the solubility of silica is very low, and even if a small amount is mixed with uranium, there is no significant effect on uranium disposal.

In the above, specific parts of the present invention have been described in detail, and for those skilled in the art, it is clear that these specific descriptions are only preferred embodiments, and the scope of the present invention is not limited thereby. something to do. Accordingly, the substantial scope of the present invention will be defined by the appended claims and their equivalents.

Claims (12)

A method for separating uranium from a spent uranium catalyst,
(a) separating the antimony contained in the spent uranium catalyst by heating the spent uranium catalyst at a temperature range of 850° C. to 1,315° C. to separate the liquid phase of antimony into ingots and separating the gas phase of antimony in a condenser;
(b) phase-separating the spent uranium catalyst from which antimony is separated into a phase containing silica and a phase containing uranium and impurities;
(c) acid-treating the phase containing silica and the phase containing uranium and impurities, respectively;
(d) melting the silica-containing phase at a temperature range of 1,600 ° C to 1,700 ° C and then crystallizing (directional solidification) at a temperature range of 1,450 ° C to 1,550 ° C to obtain purified silica, containing the uranium and impurities A method for separating uranium from a spent uranium catalyst, comprising: evaporating the phase to obtain purified uranium. According to claim 1,
The spent uranium catalyst is one selected from the group consisting of uranium antimony composite metal oxide, uranium composite metal oxide for producing acrylonitrile, or a mixture thereof, and contains antimony oxide, silicon oxide, iron, molybdenum and bismuth. Method for separating uranium from spent uranium catalyst. According to claim 1,
The method of separating uranium from spent uranium catalyst, characterized in that the gas phase of step (a) contains antimony and bismuth. According to claim 1,
The method of separating uranium from spent uranium catalyst, characterized in that the ingot of step (a) contains aluminum and antimony. According to claim 1,
In the step (b), the phase separation is performed by heating at a temperature of 1,565 ° C to 1,600 ° C after adding an additive to separate iron-containing impurities into ingots, and cooling to a temperature of 600 ° C to 800 ° C to phase separate. Method for separating uranium from spent uranium catalyst. According to claim 5,
The additive includes boron oxide (B ₂ O ₃ ) or an alkali metal oxide, the alkali metal oxide is any one selected from the group consisting of Li ₂ O, Na ₂ O and K ₂ O, and 70 to 90 weight of boron oxide A method for separating uranium from a spent uranium catalyst, characterized in that it contains 10 to 30% by weight or 10 to 30% by weight of an alkali metal oxide. According to claim 1,
In the step (b), a method for separating uranium from a spent uranium catalyst, characterized in that the phase separation is performed by evaporating the phase containing silica by heating to a temperature of 1,400 ° C or higher. According to claim 7,
To accelerate the evaporation, trichlorosilane (TCS, HSiCl ₃ ) is added as an intermediate to evaporate silica at a temperature range of 1,000 ° C to 1,200 ° C or to separate uranium from a spent uranium catalyst further comprising evaporation using a copper catalyst. How to. According to claim 1,
In the acid treatment step of step (c),
The phase containing silica is solidified, and the phase containing uranium and impurities is liquefied, the acid is mixed acid or nitric acid, and the mixed acid is HCl at a concentration of 3M to 5M and HF at a concentration of 0.3M to 0.5M in a 1:1 weight ratio. A method for separating uranium from a spent uranium catalyst, characterized in that the acid is mixed with, and the acid is recyclable after the acid treatment process. According to claim 1,
A method for separating uranium from a spent uranium catalyst comprising the step of repeatedly performing step (b) without going through step (d) after step (c). According to claim 1,
Residual uranium is removed in the process of removing particulate impurities present in the silica by the melting in step (d),
A method for separating uranium from a spent uranium catalyst, characterized in that the remaining uranium is removed by crystallizing the silica that has undergone the fusion in a molten state by the crystallization. According to claim 1,
A method for separating uranium from a spent uranium catalyst, characterized in that the crystallization can be omitted in the step (d).

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