A method for sublimation purification of ultra-high purity rare earth compounds

Abstract

This invention discloses a sublimation purification method for ultra-high-purity rare earth compounds. This method transforms a standard rare earth metal salt raw material (99%-99.9%) through a two-step chemical reaction and a single sublimation operation to produce a rare earth product with a purity of 99.99-99.999% based on the rare earth element. This method meets the stringent purity requirements for rare earth elements in fields such as semiconductors and specialty surface treatments. Compared with traditional rare earth separation and purification processes, this method boasts rapid operation, high purification efficiency, and high product purity.

Description

Technical Field

[0001] The present invention relates to the technical field of rare earth compound purification, and in particular to a sublimation purification method for ultra-high purity rare earth compounds. Background Art

[0002] Ultra-high-purity rare earth elements (UHPREs) are rare earth elements with purities far exceeding those required for general industrial applications, typically reaching 99.999% (5N) or higher. These UHPREs are widely used in a variety of high-tech fields due to their exceptional performance. The following are the key advantages and applications of UHPREs: UHPRE materials can significantly improve product performance and stability in certain applications, reducing the impact of impurities. Their superior physical, chemical, and optical properties make them ideal materials for manufacturing high-end products. The use of UHPREs in semiconductor and electronic materials improves component consistency and reliability. Their low impurity content reduces defects and failures caused by impurities. UHPREs exhibit higher efficiency in catalytic, optical, and magnetic applications. For example, in magnetic materials, they provide stronger and more stable magnetic properties. Due to their exceptional physical, chemical, and optical properties, UHPREs play a key role in modern high-tech industries. They are widely used in a wide range of fields, including electronics, optics, magnetic materials, catalysts, aerospace, and new energy, driving technological advancement and industrial upgrading. Its advantages lie in improving product quality, performance and stability while reducing environmental pollution, and it has important application value.

[0003] Currently, established rare earth separation technologies, such as solvent extraction, precipitation, gravity separation, flotation, and electromagnetic separation, are ineffective in producing ultra-high-purity rare earth products. Newer methods, such as ion exchange and electrolysis, can yield relatively high-purity rare earth products, but they are slow, energy-intensive, unsuitable for large-scale industrial production, and pose significant environmental challenges. Ultimately, due to the similar chemical properties of trivalent rare earth ions, conventional separation methods cannot effectively produce ultra-high-purity rare earth products. Summary of the Invention

[0004] The purpose of the present invention is to overcome the defects in the prior art. The present invention provides a simple and efficient preparation method for obtaining ultra-high purity rare earth compounds based on the organic coordination chemistry of positive divalent rare earth metals.

[0005] To achieve the above-mentioned purpose, the technical solution of the present invention is to design a sublimation purification method for ultra-high-purity rare earth compounds, wherein a rare earth salt is reacted with a ligand in a non-coordinating solvent; then the rare earth salt is reduced to a positive divalent complex by a reducing agent; and then sublimation purification is performed to obtain an ultra-high-purity rare earth product.

[0006] In the above technical solution, the trivalent rare earth complex with a low reduction potential can be reduced to a divalent complex by an alkali metal. Here, the trivalent rare earth complex with a low reduction potential refers to Ce, Sm, Eu, and Yb.

[0007] Furthermore, the rare earth salt is an anhydrous rare earth salt, and the anhydrous rare earth salt includes at least one or more of anhydrous fluoride, chloride, iodide, and triflate;

[0008] The ligand is a cyclopentadienyl salt with large steric hindrance, wherein the cyclopentadienyl salt with large steric hindrance includes a cyclopentadienyl salt with any substituent on the cyclopentadienyl ring, specifically, at least one of pentamethylcyclopentadienyl salt, pentaisopropylcyclopentadienyl salt, and 1,2,4-triethylpropylcyclopentadienyl salt; wherein the ligand is a cyclopentadienyl ligand with large steric hindrance, and a divalent rare earth complex can be obtained stably;

[0009] The bulky hindered cyclopentadiene salt is a bulky hindered cyclopentadiene alkali metal salt, wherein the alkali metal is one of lithium, sodium, potassium or rubidium.

[0010] Furthermore, the chemical formula of the ultra-high purity rare earth product is Ln(Cp R )2, wherein Ln is a rare earth ion Ce, Sm, Eu or Yb; and R is a substituent on the cyclopentadiene ring.

[0011] Furthermore, the reducing agent is at least one or more of alkali metal graphite, alkali metal element and alkali metal naphthyl compound;

[0012] Among them, the alkali metal graphite is at least one or more of graphite potassium, graphite rubidium or graphite cesium; the alkali metal element is at least one or more of elemental lithium, elemental sodium, elemental potassium or elemental rubidium; the alkali metal naphthalene compound is at least one or more of lithium naphthalene reagent, sodium naphthalene reagent or potassium naphthalene reagent.

[0013] Furthermore, the non-coordinating solvent includes at least one or more of toluene, benzene, xylene, trimethylbenzene, n-hexane, n-pentane and alkane solvents.

[0014] Furthermore, the molar ratio of the rare earth salt to the ligand is 1:0.8-1:5.

[0015] Furthermore, the molar ratio of the rare earth salt to the ligand is 1:1-1:3; specifically, the molar ratio of the rare earth salt to the ligand can be 1:1, 1:1.5, 1:2, 1:2.5, 1:3, and any value within the range of any two of the above values.

[0016] Preferably, the molar ratio of the rare earth salt to the ligand is 1:2-1:3; specifically, the molar ratio of the rare earth salt to the ligand can be 1:2.1, 1:2.2, 1:2.3, 1:2.4, 1:2.5, 1:2.6, 1:2.7, 1:2.8, 1:2.9, 1:3, and any value within the range of any two of the above values.

[0017] Furthermore, the amount of the reducing agent is 0.9 to 1.5 times the molar amount of the initial rare earth salt. Specifically, the amount of the reducing agent is 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5 times the molar amount of the initial rare earth salt, or any value within the range of any two of the above values.

[0018] Preferably, the amount of the reducing agent is 1.0 to 1.2 times the molar amount of the initial rare earth salt.

[0019] Most preferably, the amount of the reducing agent is 1.1 times the molar amount of the initial rare earth salt.

[0020] Furthermore, the amount of the non-coordinating solvent added is 10-100 ml / g of rare earth salt. Specifically, the amount of the non-coordinating solvent added is 10 ml / g of rare earth salt, 20 ml / g of rare earth salt, 30 ml / g of rare earth salt, 40 ml / g of rare earth salt, 50 ml / g of rare earth salt, 60 ml / g of rare earth salt, 70 ml / g of rare earth salt, 80 ml / g of rare earth salt, 90 ml / g of rare earth salt, 100 ml / g of rare earth salt, or any value within a range consisting of any two of the above values.

[0021] It should be noted that the amount of non-coordinating solvent added in the present invention is calculated based on the mass of the initial rare earth salt; for example, the amount of non-coordinating solvent added is 20 ml / gram of rare earth salt, which means that 20 ml of non-coordinating solvent is added for every gram of initial rare earth salt.

[0022] A sublimation purification method for ultra-high purity rare earth compounds, characterized in that the purification steps are as follows:

[0023] (1) Mixing the rare earth salt and the ligand, adding the mixture to a dry non-coordinating solvent, stirring vigorously, and heating to above the boiling point of the solvent, and reflux;

[0024] (2) cooling the solution and filtering it, washing the filter cake with a non-coordinating solvent, and mixing the washing solution with the filtrate;

[0025] (3) Add a reducing agent to the mixed solution of the washing liquid and the filtrate obtained in the previous step, and stir vigorously at room temperature for 24 hours, or stop the reaction when it is observed that the reducing agent is completely consumed;

[0026] (4) filtering the above system, mixing the filtrate and the filter cake washing liquid, and evaporating the solvent under reduced pressure;

[0027] (5) The solid obtained in step (4) is sublimed using a high vacuum sublimation device. The solid obtained by desublimation is an ultra-high purity rare earth product. Specifically, the residue obtained in the previous step is placed in a cold finger sublimation device, the bottom of which is heated to 120-200°C, the vacuum degree is 0.001-0.015Pa, and the cold finger is cooled by circulating water at room temperature; after sublimation is completed, the product is desublimated on the cold finger and collected and weighed.

[0028] Preferably, in step (1), the rare earth salt and the ligand are mixed and added to a dry non-coordinating solvent, vigorously stirred and heated to above the boiling point of the solvent used, and refluxed for 5-36 hours; the amount of the non-coordinating solvent added is 10-100 ml / gram of rare earth salt. Specifically, the amount of the non-coordinating solvent added is 10 ml / gram of rare earth salt, 20 ml / gram of rare earth salt, 30 ml / gram of rare earth salt, 40 ml / gram of rare earth salt, 50 ml / gram of rare earth salt, 60 ml / gram of rare earth salt, 70 ml / gram of rare earth salt, 80 ml / gram of rare earth salt, 90 ml / gram of rare earth salt, 100 ml / gram of rare earth salt, and any value within the range of any two of the above values. Preferably, the amount of the non-coordinating solvent added is 10-30 ml / gram of rare earth salt; most preferably, the amount of the non-coordinating solvent added is 20 ml / gram of rare earth salt.

[0029] Preferably, in step (2), the solution in step (1) is cooled and then filtered, and the filter cake is washed 2-6 times with a non-coordinating solvent, and the washing liquid is mixed with the filtrate; wherein, the amount of the non-coordinating solvent added is 3-10 ml / gram of rare earth salt; specifically, the amount of the non-coordinating solvent added is 3 ml / gram of rare earth salt, 4 ml / gram of rare earth salt, 5 ml / gram of rare earth salt, 6 ml / gram of rare earth salt, 7 ml / gram of rare earth salt, 8 ml / gram of rare earth salt, 9 ml / gram of rare earth salt, 10 ml / gram of rare earth salt, and any value within the range consisting of any two of the above values.

[0030] It should be noted that the amount of non-coordinating solvent added in step (1) and step (2) is calculated based on the mass of the initial rare earth salt. For example, if the amount of non-coordinating solvent added in step (1) is 20 ml / g of rare earth salt, it means that 20 ml of non-coordinating solvent is added for every gram of initial rare earth salt. If the amount of non-coordinating solvent added in step (2) is 5 ml / g of rare earth salt, it means that 5 ml of non-coordinating solvent is used for washing every gram of initial rare earth salt.

[0031] Preferably, in step (2), the amount of the non-coordinating solvent added is 5 ml per gram of rare earth salt;

[0032] Preferably, in step (2), the filter cake is washed three times with a non-coordinating solvent;

[0033] Preferably, in step (3), a reducing agent in an amount of 0.9-1.5 times the molar number of the initial rare earth salt is added to the mixed solution of the washing liquid and the filtrate obtained in step (2), and the mixture is vigorously stirred at room temperature for 24 hours, or the reaction is stopped when it is observed that the reducing agent is completely consumed; wherein, preferably, in step (3), the amount of the reducing agent is 0.9-1.2 times the molar number of the initial rare earth salt.

[0034] Preferably, in step (3), a reducing agent in an amount 1.1 times the molar number of the initial rare earth salt is added to the mixed solution of the washing liquid and the filtrate obtained in the previous step, and the mixture is vigorously stirred at room temperature for 24 hours, or the reaction is stopped when it is observed that the reducing agent is completely consumed; specifically, for example, the reaction is stopped when it is observed that the golden graphite potassium has completely turned black; or the reaction is stopped when it is observed that the metallic potassium is completely consumed.

[0035] It should be noted that in step (3), the reaction is stopped after vigorous stirring at room temperature for 24 hours or when the reducing agent is observed to be completely consumed. For example, if the reducing agent is completely consumed within 24 hours, the reaction is stopped when the reducing agent is observed to be completely consumed; if the reducing agent is not completely consumed within 24 hours, the reaction is stopped after vigorous stirring at room temperature for 24 hours.

[0036] Preferably, in step (4), the system is filtered, the filtrate and the filter cake washing liquid are mixed, and the solvent is evaporated to dryness (recovered) under reduced pressure;

[0037] Preferably, in step (5), the residue obtained in step (4) is placed in a cold finger sublimation apparatus, the bottom of which is heated to 120-200°C, the vacuum degree is 0.005 Pa, and the cold finger is cooled by circulating water at room temperature; sublimation is completed within 2 hours, and the product condenses on the cold finger and is collected and weighed. Preferably, in step (5), the bottom is heated to 150°C.

[0038] The invention discloses a sublimation purification method for ultra-high purity rare earth compounds, which can be applied to the purification of cerium, europium, samarium and ytterbium.

[0039] An ultra-high-purity rare earth product prepared by a sublimation purification method of an ultra-high-purity rare earth compound can be converted into an ultra-high-purity industrial product through hydrolysis, high-temperature decomposition, and acidification according to specific industrial needs.

[0040] The advantages and beneficial effects of the present invention are:

[0041] (1) This invention converts a rare earth metal salt raw material of ordinary purity (99%-99.9%) into a rare earth product with a purity of 99.99-99.999% based on the rare earth element through a two-step chemical reaction and a single sublimation operation, thereby meeting the stringent requirements for rare earth element purity in the fields of semiconductors and special surface treatment. Compared with traditional rare earth separation and purification processes, this method has the characteristics of rapid operation, high purification efficiency, and high product purity.

[0042] (2) The rare earth compounds separated by the present invention are stable divalent rare earth complexes, which are suitable for the separation of Ce, Sm, Eu, and Yb. Other rare earth elements cannot form stable divalent compounds during the operation of the present invention and have different physical properties from the divalent compounds of Ce, Sm, Eu, and Yb, thereby achieving separation. DETAILED DESCRIPTION

[0043] The following examples are only used to illustrate the technical solution of the present invention more clearly, and are not intended to limit the scope of protection of the present invention.

[0044] Example 1:

[0045] An industrial-grade anhydrous cerium trichloride powder has a particle size of approximately 100 microns and a purity of 99.6% based on rare earth impurities (as shown in Table 1).

[0046] The following operations are all anhydrous and oxygen-free and can be performed in a vacuum chamber or glove box protected by an inert atmosphere. The non-coordinating solvents (such as toluene) used are pre-treated using standard solvent drying methods, such as solvent drying columns, to a final water content of less than 50 ppm.

[0047] (1) Cerium chloride powder and KCp iPr5 (1,2,3,4,5-pentaisopropylcyclopentadienyl potassium) in a molar ratio of 1:2.2, and add dry toluene (20 ml of toluene is added for every gram of initial rare earth salt), stir vigorously, heat to 130 degrees, and reflux for 24 hours.

[0048] (2) Cool the solution from the previous step and filter it. Wash the filter cake three times with toluene (5 ml of toluene per gram of initial rare earth salt). Combine the washing solution with the filtrate.

[0049] (3) Adding graphite potassium in an amount 1.1 times the molar number of the initial rare earth salt to the mixed solution of the washing liquid and the filtrate obtained in the previous step, stirring vigorously at room temperature for 24 hours, or stopping the reaction when the golden-yellow graphite potassium is observed to have completely turned black.

[0050] (4) Filter the above system, mix the filtrate and the filter cake washing liquid, and evaporate (recover) the solvent under reduced pressure.

[0051] (5) The residue obtained in the previous step was placed in a cold finger sublimation apparatus, the bottom of which was heated to 150°C and the vacuum was 0.005 Pa. The cold finger was cooled by circulating room temperature water. Sublimation was completed within 2 hours, and the product condensed on the cold finger and was collected and weighed. The yield was calculated as 75% based on cerium trichloride.

[0052] (6) The product was digested in electronic grade nitric acid and diluted for ICP-MS analysis. The results are shown in Table 1. The purity was 99.9918% based on rare earth impurities.

[0053] Example 2:

[0054] An industrial-grade anhydrous cerium trichloride powder has a particle size of approximately 100 microns and a purity of 99.6% based on rare earth impurities (as shown in Table 1).

[0055] The following operations are all anhydrous and oxygen-free and can be performed in a vacuum chamber or glove box protected by an inert atmosphere. The non-coordinating solvents (such as toluene) used are pre-treated using standard solvent drying methods, such as solvent drying columns, to a final water content of less than 50 ppm.

[0056] (1) Cerium chloride powder and NaCp iPr5 (1,2,3,4,5-pentaisopropylcyclopentadienyl sodium) in a molar ratio of 1:2.2, and add dry toluene (20 ml of toluene is added for every gram of initial rare earth salt), stir vigorously, heat to 130 degrees, and reflux for 24 hours.

[0057] (2) The above solution was cooled and filtered, and the filter cake was washed three times with toluene (5 ml toluene per gram of initial rare earth salt), and the washing liquid was mixed with the filtrate.

[0058] (3) Adding metallic potassium in an amount 1.1 times the molar number of the initial rare earth salt to the mixed solution of the washing liquid and the filtrate obtained in the previous step, stirring vigorously at room temperature for 24 hours, or stopping the reaction when it is observed that the metallic potassium is completely consumed.

[0059] (4) Filter the above system, mix the filtrate and the filter cake washing liquid, and evaporate (recover) the solvent under reduced pressure.

[0060] (5) The residue obtained in the previous step was placed in a cold finger sublimation apparatus, the bottom of which was heated to 150°C and the vacuum was 0.005 Pa. The cold finger was cooled by circulating room temperature water. Sublimation was completed within 2 hours, and the product condensed on the cold finger and was collected and weighed. The yield, calculated based on cerium trichloride, was 78%.

[0061] (6) The product was digested in electronic grade nitric acid and diluted for ICP-MS analysis. The results are shown in Table 1. The purity was 99.99947% based on rare earth impurities.

[0062] Table 1: Rare earth impurity measurement results of products obtained from two examples of raw materials (m 杂质 / m 铈 ), “-” means not detected

[0063] raw material Example 1 Example 2 La 9.9E-04 2.1E-07 - Pr 7.0E-04 7.2E-05 - Nd 2.3E-05 - - Sm 6.7E-04 1.1E-07 1.7E-07 Eu 1.1E-03 4.0E-07 7.0E-08 Gd 1.6E-04 - - Tb 4.2E-05 - - Dy 4.6E-05 - - Ho 4.3E-04 7.3E-06 1.1E-06 Er 1.2E-05 - - Tm 8.1E-05 1.0E-06 3.1E-07 Yb 1.6E-05 - - Lu 4.6E-05 5.5E-07 3.1E-06 Y 8.5E-05 - - Sc 4.5E-07 4.5E-08 -

[0064] The present invention obtains a rare earth product with a purity of 99.99-99.999% in terms of rare earth elements by converting a rare earth metal salt raw material of ordinary purity (purity 99%-99.9%) into a rare earth product with a purity of 99.99-99.999% in terms of rare earth elements, thereby meeting the stringent requirements for rare earth element purity in the fields of semiconductors, special surface treatment, etc.

[0065] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for sublimation purification of ultra-high purity rare earth compounds, characterized in that: The rare earth salt reacts with the ligand in a non-coordinating solvent; then the ligand is reduced to a divalent complex by a reducing agent; and then sublimated and purified to obtain an ultra-high purity rare earth product; The chemical formula of the ultra-high purity rare earth product is Ln(Cp R )2, wherein Ln is a rare earth ion; R is a substituent on the cyclopentadiene ring; said Ln is Ce, Sm, Eu, or Yb; The ligand is a sterically hindered cyclopentadiene salt, and the sterically hindered cyclopentadiene salt is at least one of pentamethylcyclopentadiene salt, pentaisopropylcyclopentadiene salt, and 1,2,4-triethylpropylcyclopentadiene salt; The non-coordinating solvent includes at least one or more of toluene, benzene, xylene, trimethylbenzene and alkane solvents.

2. The method for sublimation purification of an ultra-high purity rare earth compound according to claim 1, characterized in that: The rare earth salt is an anhydrous rare earth salt, and the anhydrous rare earth salt includes at least one or more of anhydrous fluoride, chloride, iodide, and triflate; The bulky hindered cyclopentadiene salt is a bulky hindered cyclopentadiene alkali metal salt, wherein the alkali metal is one of lithium, sodium, potassium or rubidium.

3. The method for sublimation purification of an ultra-high purity rare earth compound according to claim 1, characterized in that: The reducing agent is at least one of alkali metal graphite, alkali metal element and alkali metal naphthyl compound; Among them, the alkali metal graphite is at least one or more of graphite potassium, graphite rubidium or graphite cesium; the alkali metal element is at least one or more of elemental lithium, elemental sodium, elemental potassium or elemental rubidium; the alkali metal naphthalene compound is at least one or more of lithium naphthalene reagent, sodium naphthalene reagent or potassium naphthalene reagent.

4. The method for sublimation purification of an ultra-high purity rare earth compound according to claim 1, characterized in that: The alkane solvent includes at least one of n-hexane and n-pentane.

5. The method for sublimation purification of an ultra-high purity rare earth compound according to claim 4, characterized in that: The molar ratio of the rare earth salt to the ligand is 1:0.8-1:5; the amount of the reducing agent is 0.9 to 1.5 times the molar amount of the initial rare earth salt.

6. The method for sublimation purification of an ultra-high purity rare earth compound according to claim 5, characterized in that: The purification steps are as follows: (1) Mixing the rare earth salt and the ligand, adding the mixture to a dry non-coordinating solvent, stirring vigorously, and heating to above the boiling point of the solvent, and reflux; (2) cooling the solution prepared in step (1) and filtering it, washing the filter cake with a non-coordinating solvent, and mixing the washing solution with the filtrate; (3) Add a reducing agent to the mixed solution of the washing liquid and the filtrate obtained in the previous step, and stir vigorously at room temperature for 24 hours, or stop the reaction when it is observed that the reducing agent is completely consumed; (4) filtering the system obtained in step (3), mixing the filtrate and the filter cake washing liquid, and evaporating the solvent under reduced pressure; (5) The solid obtained in step (4) is sublimated using a high vacuum sublimation device, and the solid obtained by desublimation is an ultra-high purity rare earth product.

7. The method for sublimation purification of an ultra-high purity rare earth compound according to claim 6, characterized in that: In step (1), the amount of the non-coordinating solvent added is 10-100 ml / g of rare earth salt; in step (2), the amount of the non-coordinating solvent added is 3-10 ml / g of rare earth salt; in step (3), the amount of the reducing agent used is 0.9 to 1.5 times the molar amount of the initial rare earth salt.

8. The method for sublimation purification of an ultra-high purity rare earth compound according to any one of claims 1 to 7, characterized in that: The ultra-high purity rare earth product is converted into an industrial product of any one of ultra-high purity cerium, europium, samarium or ytterbium through hydrolysis, high temperature decomposition or acidification.