Sublimation purification method of ultra-pure rare earth compound

Abstract

The invention discloses a sublimation purification method of an ultra-pure rare earth compound, which comprises the following steps: carrying out two-step chemical reaction and one sublimation operation on a rare earth metal salt raw material with common purity (99-99.9%) to obtain a rare earth product with the purity of 99.99-99.999% in terms of rare earth elements. Therefore, strict requirements on rare earth element purity in the fields of semiconductors, special surface treatment and the like are met. Compared with the traditional rare earth separation and purification process, the method has the characteristics of high operation speed, high purification efficiency and high product purity.

Description

Technical Field

[0001] The 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 refers to rare earth elements with purity far higher than that required for general industrial applications, and its purity usually reaches 99.999% (5N) or even higher. This type of ultra-high purity rare earth is widely used in many high-tech fields due to its excellent performance. The following are the main advantages and application areas of ultra-high purity rare earth: Ultra-high purity rare earth materials can significantly improve the performance and stability of products in certain applications and reduce the interference of impurities. Its superior physical, chemical and optical properties make it an ideal material for manufacturing high-end products. The use of ultra-high purity rare earth in semiconductor and electronic materials can improve the consistency and reliability of components. The low impurity content reduces defects and failures caused by impurities. Ultra-high purity rare earth materials show higher efficiency in catalytic, optical and magnetic applications. For example, in magnetic materials, it can provide stronger and more stable magnetism. Ultra-high purity rare earth materials play a key role in modern high-tech industries due to their excellent physical, chemical and optical properties. They are widely used in many fields such as electronics, optics, magnetic materials, catalysts, aerospace and new energy, promoting technological progress and industrial upgrading. Its advantage lies in improving product quality, performance and stability while reducing environmental pollution, and it has important application value.

[0003] At present, the relatively mature rare earth separation technologies such as solvent extraction, precipitation, gravity separation, flotation, electromagnetic separation and other methods cannot effectively obtain ultra-high purity rare earth products. New methods such as ion exchange and electrolysis can obtain relatively high purity rare earth products, but the processing speed is slow, the energy consumption is high, it is not suitable for large-scale industrial production, and the environmental protection problem is prominent. In the final analysis, due to the similarity of the chemical properties between trivalent rare earth ions, conventional separation methods cannot effectively obtain 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, and the trivalent rare earth complex with a low reduction potential here 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; 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; The sterically hindered cyclopentadiene salt is an alkali metal salt of sterically hindered cyclopentadiene, wherein the alkali metal is one of lithium, sodium, potassium or rubidium.

[0008] 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.

[0009] Furthermore, the reducing agent is at least one or more of alkali metal graphite, alkali metal element and alkali metal naphthoxide; Among them, the alkali metal graphite is at least one or more of potassium graphite, rubidium graphite or cesium graphite; the alkali metal element is at least one or more of lithium element, sodium element, potassium element or rubidium element; the alkali metal naphthyl compound is at least one or more of lithium naphthalene reagent, sodium naphthalene reagent or potassium naphthalene reagent.

[0010] Furthermore, the non-coordinating solvent includes at least one or more of toluene, benzene, xylene, trimethylolbenzene, n-hexane, n-pentane and alkane solvents.

[0011] Furthermore, the molar ratio of the rare earth salt to the ligand is 1:0.8-1:5.

[0012] 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.

[0013] 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.

[0014] Further, the amount of the reducing agent is 0.9 to 1.5 times the mole 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 mole of the initial rare earth salt, and any value within the range of any two of the above values.

[0015] Preferably, the amount of the reducing agent is 1.0 to 1.2 times the molar amount of the initial rare earth salt.

[0016] Most preferably, the amount of the reducing agent is 1.1 times the molar amount of the initial rare earth salt.

[0017] Further, 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, and any value within the range of any two of the above values.

[0018] 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.

[0019] A sublimation purification method for ultra-high purity rare earth compounds, characterized in that the purification steps are as follows: (1) mixing a rare earth salt and a ligand, adding the mixture to a dry non-coordinating solvent, vigorously stirring the mixture, heating the mixture to a temperature above the boiling point of the solvent, and reflux; (2) cooling the solution and filtering it, washing the filter cake with a non-coordinating solvent, and mixing the washing liquid with the filtrate; (3) Adding a reducing agent 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 reducing agent is completely consumed; (4) filtering the system, 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 condensation 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 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 condensed on the cold finger and collected and weighed.

[0020] Preferably, in step (1), the rare earth salt and the ligand are mixed and added to a dry non-coordinating solvent, stirred vigorously 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.

[0021] 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 composed of any two of the above values.

[0022] It should be noted that the amount of the non-coordinating solvent added in step (1) and step (2) is calculated based on the mass of the initial rare earth salt. For example, the amount of the non-coordinating solvent added in step (1) 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. The amount of the non-coordinating solvent added in step (2) is 5 ml / gram of rare earth salt, which means that 5 ml of non-coordinating solvent is used for washing for every gram of initial rare earth salt.

[0023] Preferably, in step (2), the amount of the non-coordinating solvent added is 5 ml / g of rare earth salt; Preferably, in step (2), the filter cake is washed three times with a non-coordinating solvent; 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 reducing agent is in an amount of 0.9-1.2 times the molar number of the initial rare earth salt.

[0024] 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; for example, the reaction is stopped when it is observed that the golden yellow graphite potassium is completely turned into black; or the reaction is stopped when it is observed that the metallic potassium is completely consumed.

[0025] 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 after vigorous stirring at room temperature for 24 hours; if the reducing agent is not completely consumed within 24 hours, the reaction is stopped after vigorous stirring at room temperature for 24 hours.

[0026] Preferably, in step (4), the system is filtered, the filtrate and the filter cake washing liquid are mixed, and the solvent is evaporated (recovered) under reduced pressure; Preferably, in step (5), the residue obtained in step (4) is placed in a cold finger sublimation device, the bottom 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, the product condenses on the cold finger, and is collected and weighed. Preferably, in step (5), the bottom is heated to 150°C.

[0027] 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.

[0028] 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.

[0029] The advantages and beneficial effects of the present invention are: (1) The present invention obtains a rare earth product with a purity of 99.99-99.999% in terms of rare earth elements by subjecting a rare earth metal salt raw material of ordinary purity (purity 99%-99.9%) to a two-step chemical reaction and a sublimation operation, thereby meeting the stringent requirements for the purity of rare earth elements in the fields of semiconductors, special surface treatment, etc. Compared with the traditional rare earth separation and purification process, this method has the characteristics of fast operation, high purification efficiency and high product purity.

[0030] (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

[0031] The specific implementation of the present invention is further described below in conjunction with the examples. The following examples are only used to more clearly illustrate the technical solutions of the present invention, and cannot be used to limit the protection scope of the present invention.

[0032] Embodiment 1: The particle size of an industrial grade anhydrous cerium trichloride powder is about 100 microns. Its purity is 99.6% based on rare earth impurities. (As shown in Table 1)

[0033] The following operations are all water-free and oxygen-free operations and can be carried out in a vacuum box or glove box protected by an inert atmosphere. The non-coordinating solvents (toluene, etc.) used are pre-treated using standard solvent drying methods, such as using a solvent drying column, and the final water content is less than 50ppm.

[0034] (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.

[0035] (2) The solution from the previous step is cooled and filtered, and the filter cake is washed three times with toluene (5 ml toluene per gram of initial rare earth salt), and the washing liquid is mixed with the filtrate.

[0036] (3) Adding graphite potassium in an amount 1.1 times the molar number of the initial rare earth salt into 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 into black.

[0037] (4) Filter the above system, mix the filtrate and the filter cake washing liquid, and evaporate (recover) the solvent under reduced pressure.

[0038] (5) The residue obtained in the previous step is placed in a cold finger sublimation device, the bottom is heated to 150 degrees Celsius, the vacuum degree is 0.005Pa, 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, is collected and weighed, and the yield is 75% calculated based on cerium trichloride.

[0039] (6) The product was digested in electronic grade nitric acid and diluted for ICP-MS detection. The results obtained are shown in Table 1. The purity was 99.9918% based on rare earth impurities.

[0040] Embodiment 2: The particle size of an industrial grade anhydrous cerium trichloride powder is about 100 microns. Its purity is 99.6% based on rare earth impurities. (As shown in Table 1)

[0041] The following operations are all water-free and oxygen-free operations and can be carried out in a vacuum box or glove box protected by an inert atmosphere. The non-coordinating solvents (toluene, etc.) used are pre-treated using standard solvent drying methods, such as using a solvent drying column, and the final water content is less than 50ppm.

[0042] (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 toluene is added for every gram of initial rare earth salt), stir vigorously, heat to 130 degrees, and reflux for 24 hours.

[0043] (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.

[0044] (3) Adding metallic potassium in an amount 1.1 times the molar number of the initial rare earth salt into 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.

[0045] (4) Filter the above system, mix the filtrate and the filter cake washing liquid, and evaporate (recover) the solvent under reduced pressure.

[0046] (5) The residue obtained in the previous step was placed in a cold finger sublimation device, the bottom was heated to 150 degrees Celsius, the vacuum degree was 0.005Pa, and the cold finger was cooled by circulating water at room temperature. Sublimation was completed within 2 hours, and the product condensed on the cold finger, collected and weighed. The yield was 78% calculated based on cerium trichloride.

[0047] (6) The product was digested in electronic grade nitric acid and diluted for ICP-MS detection. The results obtained are shown in Table 1. The purity was 99.99947% based on rare earth impurities.

[0048] Table 1: Rare earth impurity measurement results of products obtained from two examples of raw materials (m 杂质 / m 铈 ), “-” means not detected 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 G 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 - The present invention obtains a rare earth product with a purity of 99.99-99.999% in terms of rare earth elements by subjecting a rare earth metal salt raw material of ordinary purity (purity 99%-99.9%) to a two-step chemical reaction and a sublimation operation, thereby meeting the stringent requirements for the purity of rare earth elements in the fields of semiconductors, special surface treatment, etc.

[0049] 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 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 is reacted with the ligand in a non-coordinating solvent; then reduced to a positive divalent complex by a reducing agent; and then sublimated and purified to obtain an ultra-high purity rare earth product.

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 ligand is a bulky hindered cyclopentadienyl salt, wherein the bulky hindered cyclopentadienyl salt includes a bulky hindered cyclopentadienyl salt having any substituent on the cyclopentadienyl ring; specifically, it can be at least one of pentamethylcyclopentadienyl salt, pentaisopropylcyclopentadienyl salt, and 1,2,4-triethylpropylcyclopentadienyl salt; The sterically hindered cyclopentadiene salt is an alkali metal salt of sterically hindered cyclopentadiene, 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 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.

4. 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 potassium graphite, rubidium graphite or cesium graphite; the alkali metal element is at least one or more of lithium element, sodium element, potassium element or rubidium element; the alkali metal naphthyl compound is at least one or more of lithium naphthalene reagent, sodium naphthalene reagent or potassium naphthalene reagent.

5. The method for sublimation purification of ultra-high purity rare earth compounds according to claim 1, characterized in that: The non-coordinating solvent includes at least one or more of toluene, benzene, xylene, trimethylbenzene, n-hexane, n-pentane and alkane solvents.

6. The method for sublimation purification of ultra-high purity rare earth compounds according to claim 5, 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 number of the initial rare earth salt.

7. The method for sublimation purification of ultra-high purity rare earth compounds according to claim 6, characterized in that: The purification steps are as follows: (1) mixing a rare earth salt and a ligand, adding the mixture to a dry non-coordinating solvent, vigorously stirring the mixture, heating the mixture to a temperature above the boiling point of the solvent, and reflux; (2) cooling the solution in step (1) and filtering it, washing the filter cake with a non-coordinating solvent, and mixing the washing liquid with the filtrate; (3) Adding a reducing agent 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 reducing agent is completely consumed; (4) filtering the system, 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 condensation is an ultra-high purity rare earth product.

8. The method for sublimation purification of ultra-high purity rare earth compounds according to claim 7, 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.

9. A sublimation purification method for an ultra-high purity rare earth compound as described in any one of claims 1 to 8 can be applied to the purification of cerium, europium, samarium and ytterbium.

10. An ultra-high purity rare earth product prepared by the sublimation purification method of an ultra-high purity rare earth compound as described in any one of claims 1 to 8, which can be converted into an ultra-high purity industrial product through hydrolysis, high temperature decomposition, and acidification according to specific industrial needs.