KR101137436B1 - The equipment of removal rare earth in the eutectic and the method thereof - Google Patents

Abstract

The present invention relates to an apparatus for removing rare earths in eutectic salts and a method for removing the same, and more particularly, K ₃ PO ₄ and Li capable of igniting / precipitating rare earths in the same manner as eutectic compositions in LiCl-KCl eutectic salts containing rare earths. After adding ₃ PO ₄ , argon gas is dispersed by using a vertical dispersion tube and reacted. After the reaction, the temperature of the eutectic salt is raised again and oxygen gas is dispersed, and the remaining rare earth is oxidized / precipitated by reaction with oxygen. . When the reaction is completed and stagnated in the vessel, all particles produced in the eutectic salt sink to the bottom of the metal reaction vessel. After cooling naturally, the layer is solidified in the separated state, and the solidified eutectic salt is separated from the metal reaction vessel using a solid salt separation device, and then separated into a pure salt layer on the upper side and a precipitate layer on the lower side through a mechanical method. Done. The separated pure salt layer can be directly recycled to the electrolytic refining process, and the solid eutectic salt of the phosphide deposit layer can be recycled to the electrolytic refining process after treatment through distillation / condensation.

Description

Rare earth removal device in eutectic salt and rare earth removal method using same {The equipment of removal rare earth in the eutectic and the method

The present invention relates to a rare earth removal device in the eutectic salt and a rare earth removal method using the same.

Despite the many advantages of nuclear power plants, such as no carbon emissions and long-term and stable energy sources, the spent fuel problem remains a challenge to be solved. Spent fuel contains about 94% of useful resources, and recycling it to high-speed fuel reduces the disposal volume by 1/20, and the disposal toxicity by 1/1000, reducing the site management period from 300,000 to 300 years. Can be reduced to years. Recycling valuable resources can also increase uranium resource utilization by a factor of 100. In order to take advantage of many of these advantages, countries around the world are speeding up their technology development with the goal of establishing a high-speed cyclic fuel system linked with recycled spent fuel.

Technology to reduce the generation of high level wastes by removing fission products (FPs) nuclides contained in electrolytic reduction and electrolytic smelting processes and recycling the recycled salts in the pyroprocessing process and residual wastes for disposal The research aims to develop technology and process equipment for manufacturing high solidified solids suitable for temporary storage or disposal.

One of the processes using hot molten salt in the liquid phase is the eutectic salt (LiCl-KCl) waste treatment process generated in the pyroprocessing process of spent nuclear fuel. The pyroprocessing process is a technique for recovering U and TRU nuclides contained in spent nuclear fuel, which is carried out in hot molten salt and using electrical methods. The pyroprocessing process produces eutectic salt wastes containing rare earth nuclides, all of which have to be solidified in a stable form and finally disposed of. Therefore, if only the nuclides contained in the eutectic salt waste generated in pyroprocessing are separated / recovered and recycled, the purified salt can be greatly improved in operability of the entire pyroprocessing process.

Rare earth nuclides contained in the eutectic salt waste from pyroprocessing of spent nuclear fuel are dissolved in eutectic salts in the form of chlorides.These rare earth nuclei are separated into various compounds that are insoluble in the eutectic salts. Research into the technique of converting to sedimentation / separation is underway. In order to precipitate / separate rare earth nuclides, a precipitant addition method is generally used. A method of converting rare earth carbonates by adding carbonate (Li (or K) ₂ CO ₃ ) and converting Li ₃ PO ₄ or K ₃ PO ₄ to And ion exchange technology using zeolite.

However, the above methods have a problem in reusing purified eutectic salts after separating rare earths. In other words, in order to reuse the rare earth separated eutectic salt in the pyroprocessing process, it must be satisfied that there are no impurities in the eutectic salt and maintain a constant eutectic composition. Precipitant, which is added in the equivalent amount and remains in the unreacted state, remains in the eutectic salt, and LiCl and KCl are formed due to side reactions during the conversion reaction, and thus the eutectic composition changes, so an additional secondary process is required for reuse of the eutectic salt. Done. In addition, when using a zeolite, there is a problem of the initial disposal of the zeolite substituted (ie, ion exchanged) with a rare earth element and difficulty in expanding the process using the zeolite. In order to solve this problem, oxidizing / precipitating nuclides (rare earth and superuranium (TRU)) in eutectic salt waste using oxygen dispersing method without using precipitant, and then separated and recovered into eutectic salt layer and sediment layer. The eutectic salt layer was directly recycled and the eutectic salt in the sediment layer was separated / recovered using a distillation / condensation process (Korea Patent Registration 10-0861262). The above technique using oxygen dispersion does not cause side reactions due to the absence of added chemicals, so the removal of rare earth elements and the reusability of the refined eutectic salts are very high. 800 ℃) has to be operated and the long operation time (more than 10 hours) has a disadvantage that can cause problems for the volatilization of eutectic salts.

In order to improve the method and apparatus more efficiently, the present inventors have removed the eutectic salt containing rare earth by precipitating rare earth using phosphide at a relatively low temperature of 400-600 ° C., and removing residual rare earth by oxygen dispersion method. The present invention was completed by confirming that the method of removing oxides or oxychlorides was used to reduce the operation time and lower the temperature of the process.

An object of the present invention is to provide a rare earth removal device in the eutectic salt.

Another object of the present invention is to provide a rare earth removal method using the rare earth removal device in the eutectic salt.

In order to achieve the above object, the present invention comprises a metal reactor having an upper diameter and a lower diameter than the lower diameter; Located in the bottom of the metal reactor, the upper diameter of the cone-shaped metal reaction vessel than the lower; A vertical dispersion tube arranged in the metal reaction vessel to supply gas to the metal reaction vessel; And a eutectic salt layer separation device including a heating unit surrounding a side of the metal reactor, and a solid salt separation device for separating solid eutectic salts separated by inverting the metal reaction vessel and heating the outside of the metal reaction vessel. It provides a salt rare earth removal apparatus.

The present invention also provides a rare earth removal method using the rare earth removal device in the eutectic salt.

The rare earth removal device in the eutectic salt has the effect of shortening the process time and lowering the process temperature by removing the rare earth by sequentially applying the phosphide method and oxygen dispersion method to the process. In addition, it is possible to prevent the clogging phenomenon by modifying the shape of the dispersion tube, which was a problem of the existing invention, and to simplify the process apparatus by allowing rare earth precipitation and layer separation in one reactor so that no salt transfer process is required. In addition, by modifying the shape of the existing metal reactor of the present invention it has the effect of preventing the external leakage of eutectic salts and rare earth precipitate during the process. Furthermore, the present invention can greatly reduce the final disposal cost by minimizing the amount of eutectic salt waste generated in the spent electrolytic refining process of spent nuclear fuel, and can reuse the separated eutectic salt to increase the economics of the electrolytic refining process. It works.

1 is a schematic view of a rare earth removal device in the eutectic salt according to the present invention,
2 is a schematic diagram of a layer separation apparatus according to the present invention,
3 is a schematic view of a vertical dispersion tube according to the present invention,
Figure 4 is a schematic diagram of a solid salt separator according to the present invention,
5 is an XRD analysis result of rare earth precipitates generated after phosphide addition and oxygen dispersion.

Hereinafter, the present invention will be described in detail.

The present invention comprises a metal reactor consisting of a top and bottom but the upper diameter is larger than the lower diameter; Located in the bottom of the metal reactor, the upper diameter of the cone-shaped metal reaction vessel than the lower; A vertical dispersion tube arranged in the metal reaction vessel to supply gas to the metal reaction vessel; And a eutectic salt layer separation device including a heating unit surrounding a side of the metal reactor, and a solid salt separation device for separating solid eutectic salts separated by inverting the metal reaction vessel and heating the outside of the metal reaction vessel. A salt rare earth removal device is provided.

In the eutectic salt separation apparatus, a phosphide addition method and an oxygen dispersion method are used to remove the rare earth nuclides present. First, more than 80% of the rare earth elements present in the entire eutectic salt are separated by precipitation using a phosphide method. The remaining rare earth is removed by forming an oxide or oxychloride by precipitation using oxygen dispersion. The rare earth removal device in the eutectic salt can be processed at a low temperature by using a phosphide addition and oxygen dispersion method at the same time, the process time can be shortened. On the other hand, in order to remove the rare earth precipitated by binding with the phosphide, the layer separation apparatus is cooled to separate the eutectic salt in the solid state into the eutectic salt layer and the pure eutectic salt layer in which the rare earth is precipitated. Pure eutectic salts can be used directly in the electrolytic refining process, and the eutectic salts remaining in the precipitate can be reused in the electrolytic refining process by distillation / condensation separation using the distillation process, which increases the economic efficiency of the electrolytic refining process. The cost of final disposal can be greatly reduced by minimizing the amount of waste generated in the wastewater.

An apparatus for separating a layer of the eutectic salt according to the present invention is shown in FIG. 2, specifically as follows. The heating part 4 surrounding the metal reactor 1 is provided, and the upper part of the metal reactor consists of two stages, the lower part of the metal reaction vessel 6 is located, and the upper part has a diameter of about 2-3 times the lower part. It is preferable to have. Through this, the eutectic salt volatilized during the phosphide addition process and the oxygen dispersion process and the generated phosphide, oxide, and oxychloride are prevented from clogging due to accumulation in the outlet pipe 3. Chlorine gas generated by the reaction of the oxygen gas and the eutectic salt injected for the oxygen dispersion process and the remaining amount of oxygen gas after the reaction go out to the outlet pipe. In the existing invention, the upper and lower parts have the same diameter, Precipitation of oxides and oxychlorides produced by the generated oxygen was swept away by the flow of the gas and accumulated at the outlet. By making the diameter of the upper part wider than the lower part like the metal reactor according to the present invention, the phosphide, oxychloride and oxide precipitates that have been swept with the gas can be recovered to the metal reaction vessel along the wall, and during the process Sedimentation of eutectic salts and rare earths has the effect of preventing the outflow of the metal reaction vessel.

The metal reaction vessel 6 uses a metal material and has a cone shape with a lower diameter than the upper portion, so that the dispersion characteristics of oxygen in the eutectic salt can be stabilized to disperse a higher oxygen flow rate, thereby converting rare earth nuclides into precipitates. It is possible to shorten the time required for the process, and the precipitate formed by the oxygen dispersion process and the eutectic salts are stagnant and then cooled to make the eutectic salts in the solid phase to facilitate separation between the pure eutectic salt layer of the upper portion and the rare earth precipitate layer of the lower portion. There is an advantage. In addition, the upper diameter of the metal reaction vessel is preferably about the same or slightly smaller than the diameter of the bottom of the upper metal reactor. This can prevent external runoff as rare earth precipitates and liquid eutectic salts are swept away from the gas stream and recovered.

The vertical dispersion pipe (2) for supplying argon and oxygen gas in the eutectic salt layer is provided with a baffle (5) in the middle portion, so that the precipitate which rises along the flow of the gas adheres to the baffle and is easily recovered. The tube is a vertical dispersion tube, arranged in a triangular pitch of about 5 to 7 cm depending on the diameter of the reaction vessel, and a hole of 0.5 to 3 mm is formed along the side of the vertical dispersion tube at the bottom. . If the diameter of the gas supply pipe is less than 0.5 mm, the holes of the supply pipe are blocked by rare earth precipitates generated during the reaction, and thus the gas dispersion is not performed smoothly in the argon-phosphide addition process and the oxygen-oxygen dispersion process (reaction time and reaction efficiency). ) Will fall. If it exceeds 3 mm, the size of the initial bubbles is increased, the diameter of the bubbles is large and rapidly rises, so that the mixing phenomenon in the process is lowered and the reactivity is decreased, and the outflow shape of the salts and the rare earth precipitates flowing out from the surface of the eutectic salt layer. This deepening has a problem that difficulty occurs in the operation of the premise process.

Meanwhile, in the case of the existing invention, the pure eutectic salt and the precipitate layer were transferred by siphon in the molten state of the eutectic salt, and a recovery tank was used separately, but according to the rare earth removal apparatus in the eutectic salt according to the present invention, the pure eutectic salt and By separating the precipitates, the separated eutectic salts can be used directly in the process, so that the process equipment has a simple advantage.

Solid salt separation apparatus according to the present invention is shown in Figure 4, specifically as follows. When heat is applied by the heating units 21 and 23 surrounding the metal reaction vessel 22 containing the eutectic salt converted into a solid state, the surface of the solid eutectic salt melts and is easily detached. At this time, the heating part is a cylindrical top block is blocked, the temperature of the top and side surfaces can be controlled respectively. The solid eutectic salt separated from the metal reaction vessel 22 is a rare earth precipitate 24 at the upper portion and a pure eutectic salt 25 at the lower portion.

In addition,

Removing rare earths by reaction by adding phosphide in the eutectic salt (step 1);

Injecting oxygen into the eutectic salt to completely remove residual rare earth (step 2);

Cooling to form a solid eutectic salt (step 3);

Separating the solid eutectic salt from the metal reaction vessel (step 4); And

It provides a rare earth removal method in the eutectic salt comprising the step (step 5) of separating the solid eutectic salt into a pure salt layer and a precipitate layer.

Hereinafter, the present invention will be described in detail for each step.

Apparatuses for performing each of these steps are outlined in FIG. That is, steps 1, 2 and 3 are performed in a layer separation apparatus, step 4 is a solid salt separation apparatus, and step 5 is performed in an apparatus for separation of a pure eutectic salt layer and a rare earth precipitate layer.

Step 1 according to the present invention is a step of removing rare earths by adding and reacting phosphide in the eutectic salt. The added phosphide preferably contains Li ₃ PO ₄ and K ₃ PO ₄ , and the amount added is equal to the molar number of the weight corresponding to 70 to 90% of the weight of the rare earth chloride initially present. It is preferable to make it equal to the molar ratio of the eutectic salt used for a refining process. When the amount of phosphide added is equal to the molar ratio of eutectic salt used in the electrorefining process, the amount of LiCl and KCl formed by reaction with rare earth elements present in the form of chloride in the eutectic salt is determined by the amount of LiCl-KCl of the initial eutectic salt. The same composition (LiCl = 0.58, KCl = 0.42) does not change the eutectic composition, so the separated pure salt can be directly used for electrolytic refining without further treatment. That is, for example, the input ratio of phosphide input to the process to convert a total of 10 mol of rare earths into phosphide is Li ₃ PO ₄ = 5.8 mol, K ₃ PO ₄ = 4.2 mol.

If the exact amount of rare earths contained in the initial eutectic salt waste is known correctly, it is preferable to remove 100% of the rare earths by phosphide addition. However, if a larger amount of phosphide is added due to the measurement error of the measured rare earth amount, it is difficult to recover the recovered eutectic salt due to K ₃ PO ₄ and Li ₃ PO ₄ dissolved in the unreacted eutectic salt. Therefore, less rare earth than the measured value is separated using a phosphide, wherein the added phosphide is all reacted and do not remain in the eutectic salt phase. By treating the remaining 10% of rare earths using oxygen dispersing method which does not cause any problem for regeneration, it is possible to regenerate the rare earths recovered through this process.

It is preferable that the process reaction temperature of the said step 1 is 400-600 degreeC, and it is more preferable that it is 450 degreeC. If the reaction temperature is less than 400 ℃ it is difficult to proceed with the reaction because the complete melting of the eutectic salt does not occur, if the above 600 ℃ there is a problem in that the eutectic salt is vaporized to cause a loss. Moreover, it is preferable that reaction time is 30 minutes-1 hour. If the reaction time is less than 30 minutes, there is a problem that a sufficient reaction does not occur, and there is no advantageous effect even if it exceeds 1 hour or more.

The amount of rare earth removed by precipitation using phosphide in step 1 is 70 to 90% of the initial rare earth amount. In addition, in order to promote the reaction rate between the phosphide and the rare earth chloride during the reaction of step 1, it is preferable to inject argon gas into the eutectic salt using a vertical dispersion tube. This increases the mixing phenomenon in the eutectic salt, and when the raw materials are introduced into the reactor as in the continuous flow reactor (CSTR), the mixing occurs instantaneously and achieves a spatially uniform state. The use of the argon gas is an inert gas, because it can give the effect of dispersion without reacting with other materials, because the value of the inert gas is the cheapest.

Step 2 according to the present invention is the step of injecting oxygen into the eutectic salt to completely remove residual rare earths. When the step 1 is completed, the temperature of the salt is raised to 600 ~ 700 ℃, the reaction time is preferably 3 to 6 hours. Oxides or oxyoxides are not active at less than 600 ℃, so the oxidation time is too long to oxidize. Above 700 ℃, volatilization of eutectic salts can occur and corrosion of the device may be accelerated by relatively high temperature. There is a problem that can be. In addition, when the reaction time is less than 3 hours, the reaction may not be sufficiently achieved, even if the reaction time exceeds 6 hours is not advantageous because there is no advantageous effect. At this time, the gas of the vertical dispersion tube is converted from argon to oxygen gas to perform oxidation and precipitation reaction of the residual rare earth material by oxygen dispersion. After the reaction time at the reaction temperature, more than 99% of the rare earth nuclides are converted into precipitates or oxides or oxychlorides in the form of particles which are insoluble in eutectic salts.

Step 3 according to the invention is the step of cooling to form a solid eutectic salt. After completion of phosphorylation and oxidation, the vertical dispersion tube is lifted to the upper part of eutectic salt layer, and after stabilizing at 450 ℃ for about 3 hours, and naturally cooled, the rare earth solid particles, phosphide, oxide and oxychloride, are precipitated. The silver is divided into a pure eutectic salt layer at the top and a rare earth precipitate layer at the bottom.

Step 4 according to the present invention is the step of separating the solid eutectic salt from the metal reaction vessel. In step 3, the solid salt cooled in the state divided into the pure salt layer and the precipitate layer is separated from the solid salt existing in the separated state in the metal reaction vessel by using the solid salt separator as shown in FIG. In the solid salt separator, the metal reaction vessel (6) of FIG. 2 is inverted, placed in the solid salt separator, and heated at a temperature of 400 ° C. to melt the surface of the eutectic salt in the metal reaction vessel to separate the metal reaction vessel and the solid eutectic salt. do.

Step 5 according to the present invention is a step of separating the solid eutectic salt into a pure salt layer and a precipitate layer. The separated common salt is separated into an upper pure eutectic salt layer and a lower rare earth precipitated layer using a mechanical method such as a saw blade. At this time, the pure pure eutectic salt layer can be reused immediately in the electrolytic refining process, and the remaining eutectic salt residue in the precipitate layer is distilled / condensed through the distillation process and reused in the electrolytic refining process.

Hereinafter, the present invention will be described in detail with reference to examples. However, the following examples are merely to illustrate the invention, the content is not limited by the following examples.

< Example  1> Eutectic salt  Rare earth removal

Step 1. In eutectic salt  Removing rare earths by adding phosphide

The rare earth removal apparatus in the eutectic salt according to the present invention as shown in FIG. 1 was used. 2.5 kg of eutectic salt containing rare earth (rare-earth, RE = Y, Ce, Nd, Pr, Gd, Sm, Eu, La) was put into a metal reaction vessel and heated to 450 ° C. for melting. The same moles of Li ₃ PO ₄ and K ₃ PO ₄ as moles of weight corresponding to 80% of the total weight of rare earth chloride present initially were used. The molar ratio used was Li ₃ PO ₄ : K ₃ PO ₄ = 0.58: 0.42, 40.76 g of Li ₃ PO ₄ and 53.49 g of K ₃ PO ₄ were added and argon gas was injected through the vertical dispersion tube for 1 hour. . The injected argon gas was injected to disperse the eutectic salt and convert it into a phosphate (rare-earth phosphate, REPO ₄ ) which is insoluble in the eutectic salt formed by reaction with Li ₃ PO ₄ and K ₃ PO ₄ and rare earth elements.

Step 2. Eutectic salt  Removing residual rare earth by injecting oxygen gas

By raising the eutectic salt from which most rare earths were removed from the eutectic salt to 700 ℃ and performing oxygen dispersion process for 4 hours to remove residual eutectic salts, more than 99% of the rare earth elements (chloride based) that were initially present were insoluble in the eutectic salt. Converted to particles and removed.

Step 3. Cool to form a solid eutectic salt

After solid molten salt (phosphorus, oxide or oxychloride) formed by stabilizing the molten salt converted to rare earth at precipitation for 3 hours at 450 ° C, it was separated into the pure salt layer of the upper eutectic salt and the sediment layer of the lower eutectic salt. Natural cooling was performed to convert the liquid eutectic salt to a solid.

Step 4. Solid Eutectic salt  Separation from metal reaction vessel

The metal reaction vessel containing the eutectic salt converted to the solid was inverted, placed in a solid salt separator, and heated at a temperature of 400 ° C. to separate the solid eutectic salt from the metal reaction vessel.

Step 5. Solid Eutectic salt Pure salt layer With sediment layer  Separation and Recovery

In step 4, the solid eutectic salt separated from the metal reaction vessel was separated from the pure eutectic salt layer and the rare earth precipitate layer by a mechanical method such as a saw blade. At this time, the pure salt layer of the upper portion was directly put into the electrolytic refining process and recycled, and the precipitate layer of the lower layer was separated by distillation under reduced pressure through a distillation process and used for the electrolytic refining process.

Experimental Example 1 Characteristics of Rare Earth Particles Produced by Phosphorus Addition and Oxygen Dispersion

XRD analysis was performed on the rare earth precipitate after the process by phosphide addition and oxygen dispersion according to Example 1 was terminated, and the results are shown in FIG. 5. As shown in FIG. 5, the produced rare earth precipitate is a mixture of rare earth phosphide (REPO ₄ ), rare earth oxides (REO ₂ and RE ₂ O ₃ ), and rare earth oxychloride (REOCl). Could know.

<Experiment 2> Change of eutectic salt composition according to reaction time of phosphide addition and oxygen dispersion

Samples of eutectic salts were collected according to the operation time in the course of carrying out Example 1, dissolved in distilled water, filtered and analyzed for the composition ratio of LiCl and KCl using ICP-MS, and the results are shown in Table 1 below. If only Li ₃ PO ₄ is injected to convert rare earth to phosphide, rare earth 3 moles of LiCl are generated per mole to change the composition of the initial eutectic salt

RECl + Li ₃ PO ₄ → REPO ₄ + 3LiCl

In addition, when only K ₃ PO ₄ is added, KCl is formed to change the composition of the eutectic salt.

RECl ₃ + K ₃ PO ₄ → REPO ₄ + 3KCl

According to the present invention, since Li ₃ PO ₄ and K ₃ PO ₄ are used simultaneously, and the amount added is the same as the composition ratio of the initial eutectic salt, the amount of LiCl and KCl produced is the same so that the composition of the eutectic salt does not change. Table 1 shows the eutectic composition results of the phosphide addition method and the oxygen dispersion method. As shown in Table 1, the eutectic composition of the pure salts in all processes was the same as the composition of the initial eutectic salts, and thus it was found that the recovered eutectic salts were suitable for immediate use.

Driving time
(time) KCl mole fraction LiCl mole fraction Before reaction 0.42 0.58 Phosphorus addition method One 0.42 0.58 Oxygen dispersion 2 0.42 0.58 3 0.42 0.58 4 0.42 0.58 5 0.42 0.58

As described above, the present invention has been described in the rare earth removal apparatus and the rare earth removal method using the same in the eutectic salts, the present invention is not limited by the embodiments and drawings disclosed herein, it can be applied within the scope of the technical spirit is protected. .

1: metal reactor 2: vertical dispersion tube
3: vent 4: heating
5: baffle 6: metal reaction vessel
21: heating part (temperature control-1) 22: metal reaction vessel
23: heating part (temperature control-2) 24: rare earth precipitate
25: pure eutectic salt

Claims (9)

A metal reactor composed of an upper portion and a lower portion whose upper diameter is larger than the lower diameter; Located in the bottom of the metal reactor, the metal reaction vessel of the cone type larger than the upper diameter; A vertical dispersion tube arranged in the metal reaction vessel to supply gas to the metal reaction vessel; And a solid salt separator for separating the eutectic salts separated by inverting the metal reaction vessel by heating the outside of the metal reaction vessel by inverting the metal reaction vessel and heating the outside of the metal reaction vessel. Rare earth removal device in eutectic salt.
2. The rare earth removal apparatus according to claim 1, wherein the upper diameter of the metal reactor is two to three times the lower diameter.
The apparatus of claim 1, wherein the vertical dispersion tube has a circular tube shape and has two rows of holes having a diameter of 0.5 to 3 mm along a circumference of the side surface of the dispersion tube.
Removing rare earths by reaction by adding phosphide in the eutectic salt (step 1);
Injecting oxygen into the eutectic salt to completely remove residual rare earth (step 2);
Cooling to form a solid eutectic salt (step 3);
Separating the solid eutectic salt from the metal reaction vessel (step 4) and
Separating the solid eutectic salt into a pure salt layer and a precipitate layer (step 5) removing the rare earth in the eutectic salt.
5. The method of claim 4 wherein the phosphide added in step 1 comprises Li ₃ PO ₄ and K ₃ PO ₄ .
6. The method of claim 5, wherein the amount of phosphide added in step 1 is equal to the number of moles of weight corresponding to 70 to 90% of the initial weight of rare earth chloride, and the molar ratio of eutectic salts used (LiCl = 0.58, KCl = 0.42). Removing the rare earth in the eutectic salt, characterized in that the same as.
The method of claim 5, wherein the reaction temperature of step 1 is 400 to 600 ℃, the reaction time is 30 minutes to 1 hour, characterized in that the removal of rare earth in the eutectic salt.
6. The method of claim 5 wherein argon is injected to promote the reaction between the eutectic salt and the phosphide in step 1.
The method of claim 5, wherein in step 2, the reaction temperature is 500 to 700 ° C and the reaction time is 3 to 6 hours.

Images