Preparation method of high-purity ammonium fluoberyllate

Abstract

The invention relates to a preparation method of high-purity ammonium fluoberyllate, which comprises the following steps: (S1) slowly adding hydrofluoric acid into turbid liquid of beryllium hydroxide under a stirring condition, continuously stirring when a system is in a transparent solution state, slowly adding ammonia water, and washing and drying precipitates to obtain a crude product; and (S2) preparing a mixed solvent of water, a water-miscible aprotic polar organic solvent and a hydrophilic ionic liquid, heating until the solution system is clear, adding the crude product into the mixed solvent, stirring to dissolve the crude product, quickly cooling to 2-6 DEG C, layering the ionic liquid and a water phase, discarding the ionic liquid phase, and filtering, washing and drying the precipitate of the water phase to obtain the water-soluble ionic liquid. A high-purity ammonium fluoberyllate product is obtained; the hydrophilic ionic liquid is imidazole metal halide with C4-6 alkyl groups. According to the method, the purity and the yield of the product ammonium fluoberyllate are improved at the same time, the purity is larger than or equal to 99.99%, and the yield can reach 80% or above.

Description

Technical Field

[0001] The invention belongs to the preparation of beryllium-containing compounds, and specifically relates to a method for preparing high-purity ammonium fluoroberyllate. Background Art

[0002] High-purity beryllium fluoride is an important strategic raw material. For example, in molten salt nuclear reactors, high-purity LiF-BeF2 is a molten salt nuclear reactor coolant with many advantages such as small neutron absorption cross section, good high-temperature stability, high thermal conductivity, and high boiling point. However, as a molten salt nuclear reactor coolant, its purity requirements are very high, especially for elements with strong neutron absorption, such as Na, Fe, B, Ni, etc. The raw material for preparing high-purity LiF-BeF2 is beryllium fluoride, and ammonium fluoroberyllate is generally used as an important raw material for preparing high-purity beryllium fluoride. Ammonium fluoroberyllate is generally prepared by leaching beryllium-containing ore with sulfuric acid to prepare beryllium hydroxide, which is then reacted with hydrofluoric acid and added with ammonia water. It inevitably contains a large amount of harmful impurities, which seriously affect the quality of ammonium fluoroberyllate.

[0003] CN105948082A discloses a method for preparing ammonium fluoroberyllate. The patent uses basic beryllium carbonate as a raw material, reacts with hydrofluoric acid, concentrates and then adds liquid ammonia, and obtains ammonium fluoroberyllate after cooling, crystallization and solid-liquid separation. Its basic beryllium carbonate has high purity and few impurities, and can be used as a raw material to prepare high-purity ammonium fluoroberyllate. The preparation method of basic beryllium carbonate is: a phosphoric acid extractant, an alcohol and a sulfonated kerosene are mixed as an extractant, a beryllium-containing solution and an extractant are subjected to multi-stage countercurrent extraction, an oxalic acid aqueous solution and an organic phase after extraction are subjected to multi-stage countercurrent washing, ammonium carbonate and the organic phase after washing are subjected to multi-stage countercurrent stripping, and a beryllium-containing stripping solution is hydrolyzed at 65-75°C, and an EDTA metal chelating agent is added, and the hydrolysis is continued at 80-105°C to obtain a precipitate, which is the product basic beryllium carbonate. The patent process is complicated, and the purity cannot actually meet the requirements.

[0004] CN103601222A discloses a method for preparing high-purity ammonium fluoroberyllate, which is to drip hydrofluoric acid in a suspension of beryllium hydroxide to form a transparent solution, then drip ammonia to produce a precipitate, and then recrystallize to obtain high-purity ammonium fluoroberyllate. The patent is recrystallized with a mixed solution of water and alcohol (methanol or ethanol), which can reduce the concentration of impurity metal ions and sulfate ions. However, in order to obtain highly purified ammonium fluoroberyllate, it is necessary to perform at least 2 recrystallizations, and the product yield is relatively low, less than 50%. In addition, the patent generates the product obtained in ammonium fluoroberyllate, and the impurity metal ion content is 5ppm, but the inventor, after repeated tests, finds that by the patented method, the metal impurity content can not be controlled to the 5ppm claimed in the patent. Summary of the invention

[0005] In order to overcome the defects of the prior art that it is difficult to balance the yield and purity of ammonium fluoroberyllate, as well as the complicated preparation process, the present invention proposes a method for preparing high-purity ammonium fluoroberyllate, by compounding water, aprotic polar organic solvents and specific ionic liquids as recrystallization solvents, and combining with rapid cooling of an ice salt bath, the purity and yield of the ammonium fluoroberyllate product are improved at the same time, the purity is ≥99.99%, and the yield can reach more than 80%. Specifically, the present invention provides the following technical solutions to solve the above technical problems:

[0006] A method for preparing high-purity ammonium fluoroberyllate comprises the step of recrystallizing a crude ammonium fluoroberyllate product by using a mixed solvent, wherein the mixed solvent consists of water, a non-protonic polar organic solvent miscible with water and a hydrophilic ionic liquid, and the hydrophilic ionic liquid is an imidazole metal halide with a C4-6 alkyl group.

[0007] Furthermore, the temperature of the cooling medium for the recrystallization is -20°C to -10°C.

[0008] Furthermore, the cooling medium temperature of the recrystallization is an ice-salt bath, preferably a mixture of metal halides (such as sodium chloride, potassium chloride, calcium chloride) and crushed ice; for example, a mixture of calcium chloride and crushed ice in a mass ratio of 50-80:100.

[0009] In a preferred technical solution of the present invention, the method for preparing high-purity ammonium fluoroberyllate comprises the following steps:

[0010] (S1) slowly adding hydrofluoric acid to the suspension of beryllium hydroxide under stirring conditions, and when the system is in a transparent solution state, continuing stirring, slowly adding ammonia water, precipitating with alcohol, washing the precipitate, and drying to obtain a crude product;

[0011] (S2) preparing a mixed solvent of water, a non-protonic polar organic solvent miscible with water and a hydrophilic ionic liquid, heating the mixture until the solution system is clear, adding the crude product to the mixed solvent, stirring to dissolve the crude product, then cooling and recrystallizing at -20°C to -10°C, separating the ionic liquid and the aqueous phase, discarding the ionic liquid phase, filtering the precipitate in the aqueous phase, washing, and drying to obtain a high-purity ammonium fluoroberyllate product.

[0012] Furthermore, in step (S1), the purity of beryllium hydroxide is ≥95%. The present invention does not need to use high-purity beryllium hydroxide raw materials, and can use industrial-grade beryllium hydroxide with a purity of more than 95%. It can be used directly without purification, making industrial-scale production possible and facilitating production.

[0013] Further, in step (S1), the molar ratio of beryllium hydroxide, hydrofluoric acid, and NH3 is 1:4-6:7-10; further, the concentration of the suspension of beryllium hydroxide is 15-20wt%, the concentration of hydrofluoric acid is 30-40wt%, the concentration of ammonia water is 20-30wt%, and electronic grade raw materials with a purity of ≥99.9% are used when preparing hydrofluoric acid and ammonia water. Ultrapure water is used for preparing hydrofluoric acid and ammonia water. The slow addition can be dropwise addition, and the addition can be completed within 0.5-1h. The alcohol used for alcohol precipitation is selected from at least one of methanol, ethanol, isopropanol, ethylene glycol, and propylene glycol.

[0014] There are no special requirements for washing and drying, for example, washing is done with anhydrous ethanol and drying is done with vacuum drying.

[0015] Furthermore, in step (S2), the volume ratio of water, the aprotic polar organic solvent miscible with water and the ionic liquid is 40-60:15-25:30-40, and the aprotic polar organic solvent is selected from at least one of DMSO and DMF.

[0016] Furthermore, in step (S2), the hydrophilic ionic liquid is selected from at least one of 1-methyl-3-butylimidazolium chloride, 1-methyl-3-butylimidazolium bromide, 1-methyl-3-hexylimidazolium chloride, and 1-methyl-3-hexylimidazolium bromide.

[0017] Furthermore, in step (S2), the mass volume ratio of the crude product to the mixed solvent is 1 kg: 3-3.5 L, preferably 1 kg: 3-3.2 L.

[0018] Further, in step (S2), the heating is to 60-80°C, and the recrystallization is cooled under an ice-salt bath condition of -20°C to -10°C. The phosphate ionic liquid used in the present invention is a hydrophilic ionic liquid, but it can be miscible with water at 40-50°C or above. The unexpected discovery of the present invention is that the use of an alkyl imidazole ionic liquid with a specific hydrophilic ability as a co-solvent for recrystallization can effectively remove the trace metal impurities and acid radical anions remaining in the system, and the yield is much higher than the alcohol-water system or water system reported in the prior art. When the recrystallization is cooled to below 40°C, the mutual solubility of the ionic liquid and water deteriorates, and it begins to automatically stratify, making the product purity higher. At the same time, aprotic polar organic solvents are also indispensable, otherwise the yield and purity are reduced. The inventor has found through a large number of experiments that the compounding of water, aprotic polar organic solvents and ionic liquids in a certain proportion range can simultaneously improve the purity and yield of the product. After recrystallization, the ionic liquid is stratified, which is convenient for recycling and has industrial advantages.

[0019] Further, in step (S2), the ice-salt bath is a cooling system of metal halides and crushed ice in a mass ratio of 50-80:100. Recrystallization generally selects conventional air cooling. The inventors also unexpectedly found that the rapid cooling and cooling under the conditions of the ice-salt bath not only did not reduce the purity of the product, but further improved the purity of the product. This may be due to the rapid cooling and recrystallization cooling step of the present invention. When cooling, the precipitation of solid products and the stratification of ionic liquids and aqueous phases occur simultaneously. Therefore, a faster cooling rate is more conducive to the rapid precipitation of products and the phase separation of the system. When the rates of the two are matched, high yield and high purity can be obtained at the same time. After experiments, the inventors found that faster cooling, such as cooling with dry ice or liquid nitrogen, cannot simultaneously achieve high yield and high purity.

[0020] The ammonium fluoroberyllate product obtained by the preparation method of the invention has low metal impurity content and purity of ≥99.99%; the product yield is high, and the primary recrystallization yield is above 80%.

[0021] Beneficial effects of the present invention:

[0022] 1. The present invention adopts a mixed solvent of water, aprotic polar organic solvent and hydrophilic ionic liquid as a recrystallization solvent, which can be recrystallized once, and the obtained product ammonium fluoroberyllate has low impurity content, high purity and high yield.

[0023] 2. In the preferred technical solution of the present invention, the temperature is lowered under the rapid cooling conditions of an ice-salt bath, which can further improve the yield and purity of the ammonium fluoroberyllate product.

[0024] 3. The preparation process of the present invention is simple, the raw materials are easily available, and industrial-grade beryllium hydroxide is used. There are no stringent requirements on the raw materials, and no pre-purification or continuous multiple extractions and extraction steps are required. It is suitable for industrial large-scale preparation of high-purity ammonium fluoroberyllate. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention.

[0026] Both hydrofluoric acid and ammonia water are prepared with electronic grade raw materials and ultrapure water and are made on-the-spot.

[0027] Beryllium hydroxide was obtained from Shanghai Taiyang Technology Co., Ltd. with a purity of 96.36 wt%.

[0028] Example 1

[0029] (S1) slowly adding hydrofluoric acid with a concentration of 36 wt % to a suspension of beryllium hydroxide with a concentration of 17.6 wt % under stirring for 1 h, and slowly adding ammonia water with a concentration of 22 wt % in an amount satisfying a molar ratio of beryllium hydroxide: hydrofluoric acid: NH 3 of 1:5:8, adding ethanol to precipitate, filtering the precipitate, washing with anhydrous ethanol, and vacuum drying to obtain a crude product;

[0030] (S2) A mixed solvent of water, DMSO and 1-methyl-3-butyl imidazole chloride was prepared in a volume ratio of 45:15:40, and the solution system was clarified by heating to 80°C under stirring. 1 kg of the crude product was added to 3 L of the mixed solvent under nitrogen atmosphere, and the crude product was dissolved by stirring. Then the system was transferred to an ice salt bath (CaCl2 and crushed ice in a mass ratio of 60:100), cooled to 5°C, the ionic liquid and the aqueous phase were separated, the ionic liquid phase was discarded, the precipitate obtained from the aqueous phase was filtered, washed with anhydrous ethanol 3 times, and vacuum dried to obtain a high-purity ammonium fluoroberyllate product. The product was tested by inductively coupled plasma atomic emission spectrometry, and the product purity was ≥99.99%, the yield was 82.2%, the impurity sulfate ion was 27 ppm, the Fe content was 7 ppm, the Al content was 10 ppm, the Mg content was 4 ppm, and the total content of other metal impurities was ≤5 ppm.

[0031] Example 2

[0032] The other conditions are the same as those in Example 1, except that in step (S2), the recrystallization solvent is water, DMSO and 1-methyl-3-hexyl imidazole chloride in a volume ratio of 50:20:30. The purity of the product ammonium fluoroberyllate obtained in Example 2 is ≥99.99%, the yield is 81.1%, the impurity sulfate ion is 29ppm, the Fe content is 9ppm, the Al content is 12ppm, the Mg content is 6ppm, and the total content of other metal impurities is ≤5ppm.

[0033] Example 3

[0034] The other conditions are the same as those in Example 1, except that in step (S2), the recrystallization solvent is water, DMSO and 1-methyl-3-butyl imidazole chloride in a volume ratio of 60:15:40. The purity of the obtained product ammonium fluoroberyllate in Example 3 is ≥99.99%, the yield is 80.8%, the impurity sulfate ion is 31ppm, the Fe content is 12ppm, the Al content is 11ppm, the Mg content is 7ppm, and the total content of other metal impurities is ≤5ppm.

[0035] Example 4

[0036] The other conditions are the same as those in Example 1, except that in step (S2), DMSO is replaced by DMF. The purity of the product ammonium fluoroberyllate obtained in Example 4 is ≥99.99%, the yield is 82.0%, the impurity sulfate ion is 33 ppm, the Fe content is 12 ppm, the Al content is 13 ppm, the Mg content is 7 ppm, and the total content of other metal impurities is ≤5 ppm.

[0037] Example 5

[0038] The other conditions are the same as those in Example 1, except that in step (S2), cooling in the air is replaced by cooling in the ice-salt bath. The product ammonium fluoroberyllate obtained in Comparative Example 5 has a yield of 80.6%, an impurity sulfate ion of 32 ppm, a Fe content of 14 ppm, an Al content of 13 ppm, a Mg content of 10 ppm, and a total content of other metal impurities of 6 ppm.

[0039] Example 6

[0040] The other conditions are the same as those in Example 1, except that in step (S2), the cooling under dry ice conditions is changed from ice-salt bath cooling. The yield of the product ammonium fluoroberyllate obtained in Comparative Example 6 is 82.0%, the impurity sulfate ion is 34 ppm, the Fe content is 19 ppm, the Al content is 14 ppm, the Mg content is 12 ppm, and the total content of other metal impurities is 9 ppm.

[0041] Comparative Example 1

[0042] The other conditions are the same as those in Example 1, except that in step (S2), the recrystallization solvent is water, the amount of the recrystallization solvent is 1.35 L, and the yield of the product ammonium fluoroberyllate obtained in Comparative Example 1 is 64.2%, the impurity sulfate ion content is 55 ppm, the Fe content is 58 ppm, the Al content is 35 ppm, the Mg content is 22 ppm, and the total content of other metal impurities is 14 ppm.

[0043] Comparative Example 2

[0044] The other conditions are the same as those in Example 1, except that in step (S2), the recrystallization solvent is water and 1-methyl-3-butyl imidazole chloride in a volume ratio of 45:40, i.e., DMSO is not added. The yield of the product ammonium fluoroberyllate in Comparative Example 2 is 79.8%, the impurity sulfate ion is 30 ppm, the Fe content is 22 ppm, the Al content is 19 ppm, the Mg content is 14 ppm, and the total content of other metal impurities is 11 ppm.

[0045] Comparative Example 3

[0046] The other conditions are the same as those in Example 1, except that in step (S2), the recrystallization solvent is water, DMSO and 1-methyl-3-octylimidazole chloride in a volume ratio of 45:15:40. The yield of the product ammonium fluoroberyllate obtained in Comparative Example 3 is 82.3%, the impurity sulfate ion is 32 ppm, the Fe content is 31 ppm, the Al content is 24 ppm, the Mg content is 15 ppm, and the total content of other metal impurities is 10 ppm.

[0047] Comparative Example 4

[0048] The other conditions are the same as those in Example 1, except that in step (S2), the recrystallization solvent is water, DMSO and 1-methyl-3-ethylimidazolium chloride in a volume ratio of 45:15:40. The yield of the product ammonium fluoroberyllate obtained in Comparative Example 4 is 78.4%, the impurity sulfate ion is 31 ppm, the Fe content is 17 ppm, the Al content is 16 ppm, the Mg content is 9 ppm, and the total content of other metal impurities is 7 ppm.

[0049] By comparing the above-mentioned embodiment and the comparative example, it can be seen that the preparation method of the present invention has a simple process, and adopts a mixed solvent of water, aprotic polar organic solvent and hydrophilic ionic liquid as a recrystallization solvent, and a single recrystallization can achieve high purity and yield of the product ammonium fluoroberyllate at the same time. The mixed solvent of water, aprotic polar organic solvent and hydrophilic ionic liquid, reducing one of the solvents, or changing the cooling medium of recrystallization, can not achieve the above-mentioned purpose of improving purity and yield at the same time. And the inventor has also found that the hydrophilicity of the hydrophilic ionic liquid should be appropriate, and the hydrophilicity is too good or too poor, and the purpose of the present invention can not be achieved. Comparative Examples 3 and 4 use 1-methyl-3-octyl imidazole chloride and 1-methyl-3-ethyl imidazole chloride as ionic liquids respectively, and the effect is obviously not as good as the embodiment. In addition, the product yield and purity can be further improved by cooling under the rapid cooling condition of ice salt bath.

Claims

1. A method for preparing high-purity ammonium fluoroberyllate, characterized in that: The invention discloses a step of recrystallizing the crude ammonium fluoroberyllate product by using a mixed solvent, wherein the mixed solvent is composed of water, a non-protonic polar organic solvent miscible with water and a hydrophilic ionic liquid, and the hydrophilic ionic liquid is an imidazole metal halide with a C4-6 alkyl group.

2. The preparation method according to claim 1, characterized in that: The temperature of the cooling medium for the recrystallization is -20°C to -10°C.

3. The preparation method according to claim 1, characterized in that: The cooling medium temperature of the recrystallization is an ice-salt bath, preferably a mixture of metal halides and crushed ice; for example, a mixture of calcium chloride and crushed ice in a mass ratio of 50-80:

100.

4. A method for preparing high-purity ammonium fluoroberyllate, characterized in that: The following steps are involved: (S1) slowly adding hydrofluoric acid to the suspension of beryllium hydroxide under stirring conditions, and when the system is in a transparent solution state, continuing stirring, slowly adding ammonia water, precipitating with alcohol, washing the precipitate, and drying to obtain a crude product; (S2) preparing a mixed solvent of water, a non-protonic polar organic solvent miscible with water and a hydrophilic ionic liquid, heating the mixture until the solution system is clear, adding the crude product to the mixed solvent, stirring to dissolve the crude product, then cooling and recrystallizing at -20°C to -10°C, separating the ionic liquid and the aqueous phase, discarding the ionic liquid phase, filtering the precipitate in the aqueous phase, washing, and drying to obtain a high-purity ammonium fluoroberyllate product.

5. The preparation method according to claim 4, characterized in that: In step (S1), the molar ratio of beryllium hydroxide, hydrofluoric acid and NH3 is 1:4-6:7-10.

6. The preparation method according to claim 4, characterized in that: In step (S1), the purity of beryllium hydroxide is ≥95%, the concentration of the beryllium hydroxide suspension is 15-20wt%, the concentration of hydrofluoric acid is 30-40wt%, the concentration of ammonia water is 20-30wt%, electronic grade raw materials with a purity of ≥99.9% are used when preparing hydrofluoric acid and ammonia water, and ultrapure water is used for preparing hydrofluoric acid and ammonia water; and the alcohol used for alcohol precipitation is selected from at least one of methanol, ethanol, isopropanol, ethylene glycol, and propylene glycol.

7. The preparation method according to claim 4, characterized in that: In step (S2), the volume ratio of water, aprotic polar organic solvent miscible with water and ionic liquid is 40-60:15-25:30-40, and the aprotic polar organic solvent is selected from at least one of DMSO and DMF.

8. The preparation method according to claim 4, characterized in that: In step (S2), the hydrophilic ionic liquid is selected from at least one of 1-methyl-3-butylimidazolium chloride, 1-methyl-3-butylimidazolium bromide, 1-methyl-3-hexylimidazolium chloride and 1-methyl-3-hexylimidazolium bromide.

9. The preparation method according to claim 4, characterized in that: In step (S2), the mass volume ratio of the crude product to the mixed solvent is 1kg:3-3.5L, preferably 1kg:3-3.2L.

10. The preparation method according to claim 4, characterized in that: In step (S2), the temperature is raised to 60-80°C, the cooling medium for recrystallization is an ice-salt bath, and the temperature of the ice-salt bath is -20°C to -10°C; preferably, the ice-salt bath is a cooling system of metal halide and crushed ice in a mass ratio of 50-80:100.