Preparation method of 5N-grade ultra-pure lutetium oxide
A multi-step process involving lutetium chloride solution extraction and oxalic acid-ammonia precipitation was successfully used to prepare 5N-grade ultra-high purity lutetium oxide. This process solved the problem of excessive impurity content in lutetium oxide during preparation in existing technologies, and enabled the preparation of high-performance LYSO scintillation crystals, which are suitable for industrial production.
Patent Information
- Application Number
- CN202511274760.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-08
- Publication Date
- 2025-11-18
AI Technical Summary
Existing technologies make it difficult to prepare 5N-grade ultra-high purity lutetium oxide that meets the requirements for higher performance LYSO scintillation crystals. Excessive impurity content affects crystal defect density and luminescence efficiency.
Thorium and uranium were removed by lutetium chloride solution extraction, combined with oxalic acid and ammonia precipitation. Through multi-step impurity removal, including the extraction agent P350 and oxalic acid-ammonia double precipitation process, 5N grade ultra-high purity lutetium oxide was prepared.
The preparation of high-purity lutetium oxide was achieved, meeting the quality requirements of LYSO scintillation crystals, improving crystal performance, and making it suitable for industrial production.
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Abstract
Description
TECHNICAL FIELD
[0001] The application belongs to the technical field of rare earth material preparation, and particularly relates to a preparation method of 5N-grade ultra-high-purity lutetium oxide. BACKGROUND
[0002] Cerium-doped yttrium lutetium silicate ((Lu x Y 1-x )2SiO5:Ce, referred to as LYSO:Ce) as a new generation of inorganic scintillation crystal, has become the core material of positron emission tomography (PET / CT) equipment and high-energy physics detectors due to its high light output, fast decay time and high density. Lutetium oxide (Lu2O3) as the main matrix material of LYSO crystal accounts for about 80% of the weight of the crystal, and the impurity content will affect the crystal defect density and luminous efficiency. Among them, even if the radioactive impurities (Th / U) are slightly enriched, they will increase the background noise through spontaneous radiation, and deteriorate the signal-to-noise ratio of the PET image; non-rare earth element impurities may cause lattice distortion, destroy the structural stability, form non-radiation recombination centers, prolong the decay time, and reduce the light output. In order to obtain LYSO scintillation crystals with higher performance, the quality index requirements of lutetium oxide for manufacturing enterprises are also becoming more and more strict.
[0003] Current industrial production of lutetium oxide mainly relies on rare earth ore separation and purification. Lutetium ions are extracted from monazite or mixed rare earth ore, and then lutetium oxalate is generated by oxalate precipitation, and finally lutetium oxide is obtained by high-temperature calcination. Due to process limitations, the current market specifications of lutetium oxide are usually 4N, and the non-rare earth element impurity indexes are: 232 Th<1ppm, 38 U<1ppm, Cl<100ppm, CaO<20ppm, Si<20ppm, Fe<5ppm, C<200ppm, which cannot meet the quality index requirements of lutetium oxide for higher performance LYSO scintillation crystals. Therefore, developing a lutetium oxide purification process with multi-impurity coordinated removal, low background and economic process has become a key path to break through the performance bottleneck of LYSO. SUMMARY
[0004] The application provides a preparation method of 5N-grade ultra-high-purity lutetium oxide to solve the problems in the prior art.
[0005] In order to achieve the above purposes, the technical scheme of the application is as follows:
[0006] A preparation method of 5N-grade ultra-high-purity lutetium oxide, comprising the following steps:
[0007] 1) Removal of thorium and uranium by lutetium chloride solution: After mixing and stirring the lutetium chloride solution with the extractant, the mixture is allowed to stand and clarify to separate the solution from the extractant. The separated solution is a low-thorium and low-uranium lutetium solution. The extractant is a mixture including dimethyl heptyl methyl phosphate (P350) and kerosene.
[0008] 2) Primary precipitation and calcination: The low-thorium and low-uranium lutetium feed solution is mixed and stirred with oxalic acid solution to obtain lutetium oxalate. The lutetium oxalate is washed with high-purity water until no white precipitate is produced when silver nitrate is added to the mother liquor. Then, the lutetium oxalate is calcined once to obtain primary lutetium oxide product.
[0009] 3) Lutene oxide redissolution: The primary lutetene oxide product is redissolved with nitric acid to obtain lutetene nitrate solution;
[0010] 4) Secondary precipitation and calcination: The lutetium nitrate solution and the ammonia solution are mixed and stirred to obtain lutetium hydroxide. The solution is washed with high-purity water until the conductivity of the mother liquor is <100μs / cm. The lutetium hydroxide is then subjected to secondary calcination and sieving to obtain the 5N grade ultra-high purity lutetium oxide product.
[0011] Optionally, the lutetium chloride solution contains lutetium chloride at a concentration of 0.5–1.5 mol / L, ThO2 at a content of 5–25 mg / L, and UO3 at a content of 5–25 mg / L.
[0012] Optionally, the lutetium chloride solution undergoes the following pretreatment: adding 0.05%–0.15% (by weight) of hydrogen peroxide aqueous solution to the lutetium chloride solution, stirring for 0.5–2 hours, to remove Th from the lutetium chloride solution. 3+ Oxidation to Th 4+ U 3+ Oxidized U6 +. The weight ratio here refers to the weight ratio of hydrogen peroxide and lutetium chloride solution.
[0013] Optionally, the volume content of dimethylheptyl methylphosphate in the extractant is 30% to 50%.
[0014] Optionally, the volume ratio of the lutetium chloride solution to the extractant is 1:1.5 to 5, and the mixing time is 0.5 to 2 hours.
[0015] Optionally, the oxalic acid solution is prepared by purifying solid oxalic acid. The purification process is as follows: oxalic acid is dissolved in high-purity water at a mass-to-volume ratio of 0.3-0.8 kg:1 L, heated and evaporated to concentrate, cooled to 50-60°C, and filtered to obtain purified solid oxalic acid.
[0016] Optionally, in step 2), the first precipitation is mixing and reacting the low-thorium and low-uranium lutetium solution and the oxalic acid solution with a concentration of 100-150 g / L according to a stoichiometric ratio of 1:1-1.5 at 40-60℃; the temperature of the first burning is 900-1100℃, and the time is 4-6h.
[0017] Optionally, the nitric acid is electronic grade, and the concentration of the lutetium nitrate solution is 0.5-1.2 mol / L.
[0018] Optionally, the second precipitation is mixing and reacting the lutetium nitrate solution and the electronic grade ammonia water solution with a concentration of 1-2 mol / L according to a stoichiometric ratio of 1:1-1.5 at 50-60℃; the temperature of the second burning is 900-1100℃, and the time is 4-6h.
[0019] Optionally, the non- rare earth impurity indexes of the 5N grade ultra-high purity lutetium oxide meet 232 Th<0.05ppm, 38 U<0.05ppm, chloride <30ppm, CaO <5ppm, Si <10ppm, Fe <1ppm, C <50ppm.
[0020] The beneficial effects of the present application are:
[0021] The preparation of the ultra-high purity lutetium oxide and the deep removal of key impurities can be realized by the impurity grading removal of the extraction separation combined with the oxalic acid-ammonia water double precipitation, so as to meet the quality index requirements of the lutetium oxide for the LYSO scintillation crystal with higher performance; the preparation method has strong stability, high yield, and is suitable for industrialized production and application.
[0022] Other features and beneficial effects of the present application will be described in the subsequent description, and some of them will become apparent from the description, or be understood by implementing the present application. BRIEF DESCRIPTION OF DRAWINGS
[0023] Figure 1 The process flow chart of the preparation method of the 5N grade ultra-high purity lutetium oxide is shown. DETAILED DESCRIPTION
[0024] The present application will be further explained in combination with the drawings and specific embodiments.
[0025] In the present application, the high-purity water is water in which the dielectric medium (such as ions) is almost completely removed, and the impurities (such as colloids, gases, and organic matters) other than the dielectric medium are removed, and the resistivity of the water is ≥18.2 MΩ·cm at 25℃.
[0026] The electronic grade nitric acid needs to meet the following key indexes: single metal impurity content ≤50ppb, and particles (≥0.5um) ≤50EA / ml.
[0027] The electronic grade ammonia water needs to meet the following key indicators:
[0028] 1. Purity requirement: ammonia water (NH4OH) content ≥ 25%-30%, non-volatile residue ≤ 0.5 ppm (parts per million).
[0029] 2. Metal impurity limit: such as sodium (Na) ≤ 0.1 ppb (parts per billion), iron (Fe) ≤ 0.1 ppb, reference SEMIC36 standard.
[0030] 3. Particulate matter control: the number of particles ≥ 0.5 μm ≤ 5 pieces / mL, which needs to be detected by a laser particle counter.
[0031] Reference Figure 1 , the preparation method of 5N grade ultra-high purity lutetium oxide of the embodiment, which specifically comprises the following steps:
[0032] Step 1: Removing thorium and uranium from lutetium chloride solution
[0033] The initial raw material of lutetium oxide is often a southern ion adsorption type rare earth ore. In addition to the radioisotopes of rare earth itself, the southern ion type rare earth solution also contains trace amounts of uranium and thorium radioisotopes. The lutetium chloride solution is provided and pretreated, and 0.05%-0.15% by weight of hydrogen peroxide solution is added to the lutetium chloride solution, stirred for 0.5-2 h, and Th 3+ is oxidized to Th 4+ , U 3+ is oxidized to U 6+ . The concentration of lutetium chloride in the lutetium chloride solution is 0.5-1.5 mol / L, the content of ThO2 is 5-25 mg / L, and the content of UO3 is 5-25 mg / L.
[0034] The extraction agent is configured, which is mixed by neutral phosphorus extraction agent dimethyl heptyl methyl phosphate (P350) and kerosene, wherein the volume content of dimethyl heptyl methyl phosphate is 30%-50%.
[0035] After the lutetium chloride solution is mixed and stirred with the extraction agent according to the volume ratio of 1:1.5-5 for 0.5-2 hours, it is clarified to separate the solution from the extraction agent, and the separated solution is a low-thorium and low-uranium lutetium solution.
[0036] Through the oxidation pretreatment of hydrogen peroxide, Th 3+ is oxidized to Th 4+ , U 3+ is oxidized to U 6+ , Th 4+ / U 6+The charge density is higher, and the complexing ability with P350 extractant is stronger. Compared with traditional extractants such as TBP, the extraction separation coefficient of P350 is more, which will realize higher Th / U removal rate; and the high selectivity complexing of P350 avoids the loss of Lutetium. 4+ / U 6+ The high selectivity complexing of P350 avoids the loss of Lutetium.
[0037] Step 2 one-time precipitation and calcination
[0038] The low-thorium and low-uranium Lutetium solution is mixed with an oxalic acid solution with a concentration of 100-150 g / L at 40-60°C according to the stoichiometric ratio of 1:1-1.5 to obtain Lutetium oxalate, and the Lutetium oxalate is washed with high-purity water until the mother liquor does not produce white precipitate after silver nitrate is added dropwise. Then, the Lutetium oxalate is calcined once to obtain the first Lutetium oxide product. The temperature of the first calcination is 900-1100°C, and the time is 4-6h.
[0039] The oxalic acid solution used is prepared from purified oxalic acid solid. The purification process is as follows: according to the mass-volume ratio of 0.3-0.8 kg: 1 L, the commercially available oxalic acid is dissolved in high-purity water, heated to 100°C, concentrated by evaporation, and then cooled to 50-60°C. The purified oxalic acid solid is obtained by filtration. In the above purification process, through the selective evaporation crystallization, by the solubility difference between oxalic acid (H2C2O4) and impurity salts, the impurities are retained in the mother liquor after concentration; and the volatile organic compounds such as formic acid (HCOOH↑) in oxalic acid can be decomposed by evaporation at 100°C, so as to achieve the purpose of removing impurities in commercially available oxalic acid, and obtain refined oxalic acid, avoiding the influence of impurities in oxalic acid on the subsequent process.
[0040] The reaction formula of oxalic acid precipitation is as follows:
[0041] 2Lu 3+ +3H2C2O4→Lu2(C2O4)3↓+6H +
[0042] The reaction formula for detecting the end point of silver nitrate is as follows:
[0043] Ag + +Cl - →AgCl↓
[0044] The target impurities such as Cl- and SO42- are removed by oxalic acid precipitation. The temperature of high-temperature calcination is 900-1100°C, and at this temperature, Lu2(C2O4)3 is decomposed to generate Lu2O3 and carbon dioxide gas.
[0045] Then, screening is performed, which means that the oxide is passed through a screen with a certain mesh size to remove non-rare earth oxide impurities that may be brought in during the calcination process.
[0046] Step 3 Lutetium oxide redissolution
[0047] The primary lutetium oxide product is redissolved with electronic grade nitric acid to obtain a lutetium nitrate solution, and the concentration of the lutetium nitrate solution is 0.5-1.2 mol / L.
[0048] Step 4: secondary precipitation and calcination
[0049] The lutetium nitrate solution and electronic grade ammonia water solution with a concentration of 1-2 mol / L are mixed and stirred at 50-60°C according to a stoichiometric ratio of 1:1-1.5 to obtain lutetium hydroxide, which is washed with high-purity water until the conductivity of the mother liquor is less than 100 μs / cm, and then the lutetium hydroxide is subjected to secondary calcination and screening to obtain 5N ultra-high-purity lutetium oxide product. The temperature of the secondary calcination is 900-1100°C, and the time is 4-6 h.
[0050] The reaction formula of the ammonia water precipitation is as follows:
[0051] Lu 3+ + 3NH3·H2O→ Lu(OH)3↓ + 3NH4 +
[0052] The target impurities such as Ca 2+ , Fe 3+ , etc. are removed by ammonia water precipitation.
[0053] Screening refers to the removal of non-rare earth oxide impurities possibly brought in during the calcination process through a screen with a certain mesh size.
[0054] In actual application, subsequent processes such as a mixing process and a packaging process are also included, which are not described herein.
[0055] Through the synergistic effect of hydrogen peroxide oxidation-P350 extraction and the impurity grading removal by oxalic acid-ammonia water double precipitation, the non-rare earth impurity indexes of the 5N ultra-high-purity lutetium oxide product meet 232 Th <0.05 ppm, 38 U <0.05 ppm, chloride <30 ppm, CaO <5 ppm, Si <10 ppm, Fe <1 ppm, and C <50 ppm. Among them, the double precipitation technology reduces the entrainment of organic matter and reduces the carbon residue. Silicon is dissolved in the mother liquor during the precipitation and washing process, and the silicon residue can be effectively reduced by secondary precipitation.
[0056] Example 1
[0057] 1) oxalic acid purification. 5 kg of commercially available oxalic acid is dissolved in 10 L of high-purity water to obtain an oxalic acid solution, and then the oxalic acid solution is heated to 100°C, and the oxalic acid solution is evaporated and concentrated, and kept for 4 h, and then cooled to 55°C, and filtered to obtain purified oxalic acid solid. The purified oxalic acid solid is dissolved in high-purity water to prepare an oxalic acid solution as a precipitant for the first precipitation.
[0058] 2) Lutetium chloride solution removes radioactive elements thorium, uranium.
[0059] 2.1 Preparation of feed solution: LuCl3 solution with concentration of 1.1 mol / L, ThO2 content of 15.2 mg / L, UO3 content of 18.6 mg / L, volume of LuCl3 solution of 5 L; pretreatment of lutetium chloride solution: adding 0.05% to 0.15% by weight of hydrogen peroxide solution to the lutetium chloride solution, stirring for 1 h, and oxidizing Th 3+ in the lutetium chloride solution to Th 4+ , and oxidizing U 3+ in the lutetium chloride solution to U 6+ .
[0060] 2.2 Preparation of extractant: the extractant is prepared by mixing neutral phosphorus extractant dimethylheptyl phosphonate (P350) and kerosene at a volume ratio of 2:3, the volume of the extractant is 10 L, and the content of P350 (neutral phosphorus extractant dimethylheptyl phosphonate) is 40%;
[0061] 2.3 Extraction of thorium and uranium: the above-mentioned feed solution of 5 L and extractant of 10 L are added to a 30 L glass reactor, mixed and stirred for 1 h, and then allowed to stand to separate the feed solution from the extractant, and the feed solution is discharged from the bottom of the glass reactor to obtain lutetium feed solution with low thorium and low uranium.
[0062] 3) Primary precipitation and calcination to obtain lutetium oxide product. 1 L of high-purity water is added in advance in a 5 L beaker, the reaction temperature is controlled at 50℃, and stirring is performed, and then LuCl3 with a concentration of 1.1 mol / L and precipitant oxalic acid with a concentration of 120 g / L are simultaneously added into the beaker at a stoichiometric ratio of 1:1.15, and lutetium oxalate precursor is obtained after 50 min of reaction, and the lutetium oxalate is washed with high-purity water until no white precipitate is generated when silver nitrate is added dropwise, and then the lutetium oxalate is calcined at a high temperature of 1000℃ for 5 h to obtain primary lutetium oxide product.
[0063] 4) Reslurry of lutetium oxide. 200 g of primary lutetium oxide product is reslurried with electronic-grade nitric acid to obtain lutetium nitrate, and the feed solution is configured to have a concentration of 1.0 mol / L.
[0064] 5) Secondary precipitation and calcination to obtain lutetium oxide product. 1 L of high-purity water is added in advance in a 5 L beaker, the reaction temperature is controlled at 55℃, and stirring is performed, and then LuCl3 with a concentration of 1.0 mol / L and precipitant ammonia water with a concentration of 1.5 mol / L are simultaneously added into the beaker at a stoichiometric ratio of 1:1.2, and lutetium hydroxide precursor is obtained after 50 min of reaction, and the lutetium hydroxide is washed with high-purity water until the conductivity of the mother liquor is less than 100 μs / cm, and then the lutetium hydroxide is calcined at a high temperature of 1000℃ for 5 h to obtain secondary product 5N grade ultra-high-purity lutetium oxide.
[0065] 6) The 5N grade ultra-high purity lutetium oxide was detected. The product detection results are as follows:
[0066]
[0067] Example 2
[0068] 1) Oxalic acid purification. 500 kg of commercially available oxalic acid was dissolved in 1 m 3 of high-purity water to obtain an oxalic acid solution, and then the oxalic acid solution was heated to 100°C, the oxalic acid solution was concentrated by evaporation, and was kept for 4 h, and then was cooled to 55°C, and was filtered to obtain purified oxalic acid solid. The purified oxalic acid solid was dissolved in high-purity water to prepare an oxalic acid solution as a precipitant for the first precipitation.
[0069] 2) Removal of radioactive elements thorium and uranium from the lutetium chloride solution.
[0070] 2.1 Preparation of the feed solution: the LuCl3 solution with a concentration of 1.1 mol / L, wherein the ThO2 content is 19.2 mg / L, and the UO3 content is 20.6 mg / L, and the volume of the LuCl3 solution is 0.2 m 3 ; pretreatment of the lutetium chloride solution: 0.05% to 0.15% of hydrogen peroxide solution by weight was added to the lutetium chloride solution, and was stirred for 1 h, and Th 3+ in the lutetium chloride solution was oxidized to Th 4+ , and U 3+ was oxidized to U 6+ .
[0071] 2.2 Preparation of the extractant: the extractant was prepared by mixing the neutral phosphorus extractant dimethylheptyl phosphonate (P350) and kerosene at a volume ratio of 2:3, and the volume of the extractant was 1 m 3 , wherein the content of P350 (neutral phosphorus extractant dimethylheptyl phosphonate) is 40%;
[0072] 2.3 Extraction to remove thorium and uranium: the above-mentioned feed solution 0.2 m 3 , the extractant 1 m 3 was added to a 3.5 m 3 porcelain reaction kettle, and was mixed and stirred for 1 h, and was allowed to stand to separate the feed solution and the extractant, and the feed solution was discharged from the bottom of the porcelain reaction kettle to obtain a qualified low-thorium and low-uranium lutetium feed solution.
[0073] 3) First precipitation and calcination to obtain the lutetium oxide product. 1 m 3 of high-purity water was pre-added to a 5 m 3 PP reaction kettle., control reaction temperature is 50 DEG C, stirring, the concentration of 1.1mol / L LuCl3 and the concentration of 120g / L precipitant oxalic acid is simultaneously added to the beaker according to stoichiometric ratio 1:1.15, reaction 50min, the lanthanum oxalate precursor is obtained, using high-purity water to wash lanthanum oxalate until the mother liquor drops silver nitrate does not produce white precipitate, then the lanthanum oxalate is calcined at 1000 DEG C for 5h to obtain the primary lanthanum oxide product.
[0074] 4) lanthanum oxide redissolution. The primary lanthanum oxide product 200Kg is redissolved using electronic grade nitric acid to obtain lanthanum nitrate, and is configured to the liquid concentration of 1.0mol / L.
[0075] 5) secondary precipitation, calcination to obtain lanthananum oxide product. In 5m 3 PP reaction pot is pre-added high-purity water 1m 3 , control reaction temperature is 55 DEG C, stirring, the concentration of 1.0mol / L LuCl3 and the concentration of 1.5mol / L precipitant ammonia is simultaneously added to the beaker according to stoichiometric ratio 1:1.2, reaction 50min, the lanthanum hydroxide precursor is obtained, using high-purity water to wash lanthanum hydroxide until the mother liquor conductivity <100 μs / cm, for stop, then the lanthanum hydroxide is calcined at 1000 DEG C for 5h to obtain the secondary product 5N grade ultra-high purity lanthanum oxide.
[0076] 6) 5N grade ultra-high purity lanthanum oxide is detected. The product detection results are as follows:
[0077]
[0078] The application can realize the stable preparation of 5N grade ultra-high purity lanthanum oxide, break through the bottleneck of radioactivity background and lattice defects of LYSO scintillation crystal, provide core material guarantee for the performance improvement of PET / CT equipment and high-energy detector, and have significant technical advancement and industrialization value.
[0079] The above examples are only used to further illustrate the preparation method of the 5N grade ultra-high purity lanthanum oxide of the application, but the application is not limited to the examples, and any simple modification, equivalent change and modification according to the technical essence of the application to the above examples all fall within the protection scope of the technical scheme of the application.
Claims
1. A method for preparing 5N-grade ultra-high purity lutetium oxide, characterized in that, Includes the following steps: 1) Removal of thorium and uranium by lutetium chloride solution: After mixing and stirring the lutetium chloride solution with the extractant, the mixture is allowed to stand and clarify to separate the solution from the extractant. The separated solution is a low-thorium and low-uranium lutetium solution. The extractant is a mixture including dimethyl heptyl methyl phosphate (P350) and kerosene. 2) Primary precipitation and calcination: The low-thorium and low-uranium lutetium feed solution is mixed and stirred with oxalic acid solution to obtain lutetium oxalate. The lutetium oxalate is washed with high-purity water until no white precipitate is produced when silver nitrate is added to the mother liquor. Then, the lutetium oxalate is calcined once to obtain primary lutetium oxide product. 3) Lutene oxide redissolution: The primary lutetene oxide product is redissolved with nitric acid to obtain lutetene nitrate solution; 4) Secondary precipitation and calcination: The lutetium nitrate solution and the ammonia solution are mixed and stirred to obtain lutetium hydroxide. The solution is washed with high-purity water until the conductivity of the mother liquor is <100μs / cm. The lutetium hydroxide is then subjected to secondary calcination and sieving to obtain the 5N grade ultra-high purity lutetium oxide product.
2. The method for preparing 5N-grade ultra-high purity lutetium oxide according to claim 1, characterized in that: The lutetium chloride solution contains lutetium chloride at a concentration of 0.5–1.5 mol / L, ThO2 at a concentration of 5–25 mg / L, and UO3 at a concentration of 5–25 mg / L.
3. The method for preparing 5N-grade ultra-high purity lutetium oxide according to claim 1, characterized in that, The lutetium chloride solution underwent the following pretreatment: 0.05%–0.15% (by weight) of hydrogen peroxide solution was added to the lutetium chloride solution, and the mixture was stirred for 0.5–2 hours to remove Th from the lutetium chloride solution. 3+ Oxidation to Th 4+ U 3+ It is oxidized to U6+.
4. The method for preparing 5N-grade ultra-high purity lutetium oxide according to claim 1, characterized in that: The volume content of dimethylheptyl methyl phosphate in the extractant is 30% to 50%.
5. The method for preparing 5N-grade ultra-high purity lutetium oxide according to claim 1, characterized in that: The volume ratio of the lutetium chloride solution to the extractant is 1:1.5 to 5, and the mixing time is 0.5 to 2 hours.
6. The method for preparing 5N-grade ultra-high purity lutetium oxide according to claim 1, characterized in that: The oxalic acid solution is prepared by purifying solid oxalic acid. The purification process is as follows: oxalic acid is dissolved in high-purity water at a mass-to-volume ratio of 0.3-0.8 kg:1 L, heated and evaporated to concentrate, then cooled to 50-60°C and filtered to obtain purified solid oxalic acid.
7. The method for preparing 5N-grade ultra-high purity lutetium oxide according to claim 1, characterized in that: In step 2), the first precipitation is carried out by mixing the low-thorium and low-uranium lutetium feed solution and the oxalic acid solution with a concentration of 100-150 g / L at a stoichiometric ratio of 1:1-1.5 at 40-60°C; the first calcination temperature is 900-1100°C and the time is 4-6 h.
8. The method for preparing 5N-grade ultra-high purity lutetium oxide according to claim 1, characterized in that: In step 3), the nitric acid is electronic grade, and the concentration of the lutetium nitrate solution is 0.5–1.2 mol / L.
9. The method for preparing 5N-grade ultra-high purity lutetium oxide according to claim 1, characterized in that: The secondary precipitation is achieved by mixing the lutetium nitrate solution and an electronic-grade ammonia solution with a concentration of 1-2 mol / L at a stoichiometric ratio of 1:1-1.5 at 50-60°C; the secondary calcination is carried out at 900-1100°C for 4-6 hours.
10. The method for preparing 5N-grade ultra-high purity lutetium oxide according to claim 1, characterized in that: The non-rare earth impurity index of the 5N-grade ultra-high purity lutetium oxide meets the requirements. 232 Th < 0.05ppm, 38 U<0.05ppm, chloride<30ppm, CaO<5ppm, Si<10ppm, Fe<1ppm, C<50ppm.