Method for separating boron isotopes by chemical exchange method and co-producing high-activity potassium fluoride

Abstract

The application provides a method for separating boron isotopes and co-producing high-activity potassium fluoride by chemical exchange, wherein potassium hydroxide absorption liquid is used to absorb boron trifluoride gas, and potassium tetraborate solid obtained is added with acid to recover boric acid again; on one hand, first mother liquor containing potassium fluoride obtained by separating the potassium tetraborate solid is recycled, so that waste discharge is greatly reduced; on the other hand, when the potassium fluoride is enriched to a certain degree, cooling crystallization is carried out, and potassium fluoride solid obtained can be used to produce high-activity potassium fluoride. Therefore, the method can meet the requirement of environmental protection and improve economic benefits.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of separating boron isotopes by chemical exchange method, and particularly relates to a method for separating boron isotopes by chemical exchange method and co-producing high-activity potassium fluoride. BACKGROUND

[0002] There are two isotopes of natural boron, boron-10 and boron-11, wherein boron-10 has good neutron absorption characteristics and can be used for controlling the chain reaction speed of nuclear reactors, preparing nuclear radiation protection equipment, and serving as a neutron radiation targeting drug in nuclear medicine. Since the content of boron-10 in natural boron is only about 19%, chemical exchange method is usually used for separation and purification to improve the boron-10 abundance. The main raw material used is boron trifluoride gas, and anisole is used as a complexing agent. The final product is enriched high-abundance boron trifluoride-10 (BF3), which can be converted into borate solid product by hydrolysis reaction, facilitating storage and transportation. 10 In the prior art, the industrial conversion method mainly includes three main contents of absorption hydrolysis, borate crystallization and purification, and HF byproduct treatment. On the one hand, since the hydrolysis reaction generates HF byproduct, a corrosion-resistant reaction kettle needs to be used to reduce corrosion, resulting in increased equipment cost. On the other hand, the HF byproduct treatment often uses lime milk to treat fluorine-containing wastewater, and the fluorine ion concentration in the wastewater needs to be reduced to <10 mg / L (national standard) before being discharged, increasing environmental protection investment.

[0003] In the prior art, after the separation and purification of boron trifluoride gas, borate is obtained by water absorption. The absorption liquid usually contains boron-10 with high value and fluorine with high toxicity. The fluorine in the absorption liquid is usually removed by precipitation method, which not only pollutes the environment but also reduces the yield and purity of borate. Therefore, purification treatment is also needed. The purification treatment process generates a large amount of low-concentration fluorine-containing waste liquid, which contains not only fluorine but also boron-10 with high value, greatly reducing the production yield.

[0004] In summary, for the boron trifluoride gas obtained by chemical exchange method for separating boron isotopes, a new type of absorption treatment method needs to be developed, which can not only meet the environmental protection requirements but also improve the economic benefits. SUMMARY

[0005] In view of the problems existing in the prior art, the present invention provides a method for separating boron isotopes and co-producing highly active potassium fluoride by chemical exchange. The method uses potassium hydroxide absorbent to absorb boron trifluoride gas, and the resulting potassium tetraborate solid is then acidified to recover boric acid. On the one hand, the first mother liquor containing potassium fluoride obtained from separating the potassium tetraborate solid is recycled, greatly reducing waste emissions. On the other hand, after the potassium fluoride is enriched to a certain extent, it is cooled and crystallized, and the resulting potassium fluoride solid can be used to produce highly active potassium fluoride. Therefore, the method of the present invention can both meet environmental protection requirements and improve economic benefits.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] The purpose of this invention is to provide a method for separating boron isotopes and co-producing highly active potassium fluoride by chemical exchange, the method comprising the following:

[0008] For boron trifluoride gas obtained by separating boron isotopes by chemical exchange, it is absorbed by potassium hydroxide absorbent, and after the first solid-liquid separation, potassium tetraborate solid and a first mother liquor containing potassium fluoride are obtained.

[0009] Potassium hydroxide is added to the first mother liquor to form a new potassium hydroxide absorbent liquid, which is then used to absorb a new batch of boron trifluoride gas, thus achieving recycling. This process continues until the potassium fluoride content in the first mother liquor obtained from the last recycling reaches the target content. The mother liquor is then cooled and crystallized, followed by a second solid-liquid separation to obtain potassium fluoride solid and a second mother liquor. The potassium fluoride solid is used to prepare highly active potassium fluoride.

[0010] It should be noted that the boron trifluoride gas obtained by separating boron isotopes using the chemical exchange method described in this invention is preferably high-abundance boron trifluoride-10 (BJT-10). 10 BF3) gas, or it can be the byproduct boron trifluoride-11 (BF3) gas. 11 The present invention focuses on providing a novel absorption and treatment method for BF3 gas, which is different from hydrolysis absorption.

[0011] In existing technologies, the absorbent for separating boron-10 isotopes via chemical exchange is obtained by absorbing high-abundance boron-10 trifluoride gas into water via a hydrolysis reaction. The main components of the absorbent include borates and fluoroborates (MBF). x (OH) 4-x), fluoride, etc., and according to the difference of the hydrolysis system, it can also contain chlorine, sodium, potassium, calcium ions, etc. If the boron trifluoride is directly prepared by hydrolysis, the absorption liquid needs to be defluorinated, that is, the fluorine needs to be treated as waste, and the defluorination process needs to add additional chemicals, which will inevitably introduce new impurity ions. The potassium hydroxide absorption liquid is used for absorption in the present application, and the obtained potassium tetraborate is acidified to prepare boric acid, which belongs to the existing technology with mature process, and very pure boric acid can be obtained, which can greatly reduce the influence of impurity ions.

[0012] The method for separating boron isotopes by chemical exchange method and co-producing high-activity potassium fluoride, for absorbing and treating the boron trifluoride gas obtained by the chemical exchange method for separating boron isotopes, focuses on using potassium hydroxide absorption liquid to absorb the boron trifluoride gas, and the corresponding chemical equation of the absorption process is as follows:

[0013] 4BF3 + 14KOH = K2B4O7‧5H2O + 12KF +2H2O

[0014] After the first solid-liquid separation, potassium tetraborate solid and a first mother liquor containing potassium fluoride are obtained. The potassium tetraborate solid contains a small amount of potassium fluoride, which can be recrystallized and purified, and then acid is added to recover boric acid. Based on the solubility difference between potassium fluoride and potassium tetraborate, potassium hydroxide can be added to the first mother liquor containing potassium fluoride to form a new potassium hydroxide absorption liquid to absorb a new batch of boron trifluoride gas, thereby reducing the discharge amount of waste liquid through recycling. When the potassium fluoride is enriched to a certain extent, cooling crystallization is performed, and the obtained potassium fluoride solid is used to prepare high-activity potassium fluoride. Compared with the high waste liquid discharge amount in the prior art, the method can effectively recover the high-value boron-10 component, avoid direct solidification and waste, greatly improve the income of the chemical exchange method, and convert the byproduct fluorine into a high-value fluoride product.

[0015] It should be noted that the present application uses potassium hydroxide absorption liquid to absorb boron trifluoride gas, which can be carried out at room temperature without additional temperature limitation.

[0016] It should be noted that the potassium tetraborate solid in the present application is first dissolved in water after recrystallization and purification, and a saturated solution is prepared. Then, hydrochloric acid (or sulfuric acid) is slowly added under stirring until the solution is acidic. Cooling crystallization, filtration and washing, and drying are sequentially performed to obtain pure boric acid. The related content is the prior art, and will not be described here.

[0017] It should be noted that the second mother liquor in the present application can participate in the absorption and recycling of boron trifluoride gas, that is, it can be purified according to the actual situation, and then potassium hydroxide is added to prepare potassium hydroxide absorption liquid.

[0018] As a preferred technical scheme of the present application, the absorption liquid system with precipitates is heated and stirred before the first solid-liquid separation, and the first solid-liquid separation is performed while the system is hot.

[0019] As a preferred technical scheme of the present application, the temperature of the heating and stirring is 60-70℃, such as 60℃, 61℃, 62℃, 63℃, 64℃, 65℃, 66℃, 67℃, 68℃, 69℃ or 70℃, but is not limited to the listed values, and other values not listed in the above value range are also applicable.

[0020] As a preferred technical scheme of the present application, the time of the heating and stirring is 30-40min, such as 30min, 31min, 32min, 33min, 34min, 35min, 36min, 37min, 38min, 39min or 40min, but is not limited to the listed values, and other values not listed in the above value range are also applicable.

[0021] It should be noted that in the absorption process using potassium hydroxide absorption liquid, the solubility of potassium tetraborate in water is small, and the solubility changes little with temperature, while the solubility of potassium fluoride in water is large, and the solubility changes greatly with temperature. After absorbing boron trifluoride gas, the generated potassium tetraborate is supersaturated and precipitates. The heating and stirring before the first solid-liquid separation increases the solubility of potassium fluoride greatly, and avoids the precipitation of potassium fluoride during the first solid-liquid separation while hot, thereby improving the purity of potassium tetraborate.

[0022] As a preferred technical scheme of the present application, after the absorption is completed, an inert gas is used to purge the upper part of the absorption liquid system, and the purged gas is absorbed together with the next batch of boron trifluoride gas.

[0023] It should be noted that the purpose of purging is to avoid the leakage of unabsorbed BF3 in the gas path pipeline, so nitrogen is used to clean the BF3 in the gas path, and the subsequent heating and stirring is to promote the complete hydrolysis of BF3 and prevent the formation of tetrafluoroborate.

[0024] As a preferred technical scheme of the present application, the content of potassium hydroxide in the potassium hydroxide absorption liquid is 15-25wt%, such as 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, 20wt%, 21wt%, 22wt%, 23wt%, 24wt% or 25wt%, but is not limited to the listed values, and other values not listed in the above value range are also applicable.

[0025] It should be noted that the content of potassium hydroxide in the new potassium hydroxide absorption liquid formed by adding potassium hydroxide to the recycled first mother liquor is also 15-25wt%.

[0026] As a preferred technical solution of the present application, the absorption is carried out under stirring until the pH value of the absorption liquid system is reduced to 9-10, for example, the pH value is reduced to 9, 9.1, 9.2, 9.3, 9.4, 9.5, 9.6, 9.7, 9.8, 9.9 or 10, etc., but not limited to the listed values, and other values not listed in the above value range are also applicable.

[0027] It should be noted that the present application controls the pH value of the absorption liquid system to be reduced to 9-10 before stopping absorption, which is mainly for safety consideration, so that there is still part of the excess potassium hydroxide in the absorption liquid, avoiding the generation of HF gas due to excessive absorption of boron trifluoride.

[0028] As a preferred technical solution of the present application, the target content of potassium fluoride in the first mother liquor obtained by the last cycle is 50-60%, for example, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59% or 60%, etc., but not limited to the listed values, and other values not listed in the above value range are also applicable, and the alkalinity of the absorption liquid is reduced to 8-10.

[0029] As a preferred technical solution of the present application, the cooling crystallization is cooled to 15-25℃, for example, 15℃, 16℃, 17℃, 18℃, 19℃, 20℃, 21℃, 22℃, 23℃, 24℃ or 25℃, etc., but not limited to the listed values, and other values not listed in the above value range are also applicable.

[0030] As a preferred technical solution of the present application, the preparation method of the high-activity potassium fluoride includes: sequentially performing ethanol washing, water resuspension and spray drying on the potassium fluoride solid to obtain high-activity potassium fluoride.

[0031] It should be noted that the potassium fluoride solid of the present application contains a small amount of potassium tetraborate, and the solubility of potassium fluoride in ethanol is much smaller than that of potassium tetraborate, so a small amount of ethanol can be used to wash the potassium fluoride solid, and the potassium tetraborate as an impurity is dissolved and recovered, and the ethanol can be recovered by simple distillation. The related content is prior art, which will not be described here.

[0032] Compared with the prior art, the present application has at least the following beneficial effects:

[0033] The application provides a method for separating boron isotopes by chemical exchange method and co-producing high-activity potassium fluoride, which absorbs boron trifluoride gas by using a potassium hydroxide absorption liquid, and recycles boric acid by adding acid to obtained potassium tetraborate solid. On one hand, the first mother liquor containing potassium fluoride obtained by separating potassium tetraborate solid is recycled, so that waste discharge is greatly reduced. On the other hand, when the potassium fluoride is enriched to a certain degree, cooling crystallization is carried out, and the obtained potassium fluoride solid can be used to produce high-activity potassium fluoride. Therefore, the method can meet the requirements of environmental protection and improve economic benefits. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 is a flowchart of the method for separating boron isotopes by chemical exchange method and co-producing high-activity potassium fluoride. DETAILED DESCRIPTION

[0035] The technical solutions of the application are further described below in combination with the drawings and specific embodiments.

[0036] The application provides a method for separating boron isotopes by chemical exchange method and co-producing high-activity potassium fluoride, as shown in Figure 1 The method comprises the following contents:

[0037] For boron trifluoride gas obtained by separating boron isotopes by chemical exchange method, a potassium hydroxide absorption liquid with a potassium hydroxide content of 15-25wt% is used for absorption, the absorption is carried out under stirring until the pH value of the absorption liquid system is reduced to 9-10, and then the absorption is stopped; after the absorption is completed, inert gas is used to purge the upper part of the absorption liquid system, and the purged gas is used for absorption together with the next batch of boron trifluoride gas; under stirring, the absorption liquid system with precipitate is heated to 60-70℃ and continuously stirred for 30-40min, heating and stirring are carried out, and first solid-liquid separation is carried out while hot, to obtain potassium tetraborate solid and first mother liquor containing potassium fluoride; the potassium tetraborate solid is used for preparing boric acid;

[0038] Potassium hydroxide is added to the first mother liquor containing potassium fluoride to form a new potassium hydroxide absorption liquid, and a new batch of boron trifluoride gas is absorbed, so that recycling is realized, until the potassium fluoride content in the first mother liquor obtained by the last recycling reaches a target content (the target content is 50-60%), the first mother liquor obtained by the last recycling is cooled to 15-25℃ under stirring, cooling crystallization is carried out, and through second solid-liquid separation, potassium fluoride solid and second mother liquor are obtained, and the potassium fluoride solid is sequentially subjected to ethanol rinsing, water redissolution and spray drying, to obtain high-activity potassium fluoride.

[0039] In the method, the first mother liquor containing potassium fluoride is used to directly dissolve potassium hydroxide as a new potassium hydroxide absorption liquid, and the absorption of boron trifluoride gas is carried out in the absorption liquid system with a pH value of 9-10. White solids are precipitated during the absorption process, and the main component of the white solids is potassium tetraborate. Since the solubility of potassium fluoride is relatively large, almost all of the potassium fluoride remains in the solution, i.e. the first mother liquor after separation of potassium tetraborate. The first mother liquor can be recycled for multiple times to realize enrichment of potassium fluoride. When the potassium fluoride is enriched to a certain extent, cooling crystallization is carried out to precipitate potassium fluoride solids containing a small amount of potassium tetraborate, and then high-activity potassium fluoride is co-produced. On the one hand, the first mother liquor after separation of potassium tetraborate can be added with potassium hydroxide again to prepare a potassium hydroxide solution for absorbing boron trifluoride gas, thereby realizing recycling and reducing waste liquid discharge. On the other hand, the obtained potassium fluoride solids are washed with a small amount of ethanol and used for preparation of high-activity potassium fluoride. Therefore, the method can meet the environmental protection requirements and improve economic benefits.

[0040] In order to better illustrate the present application and facilitate the understanding of the technical solutions of the present application, the typical but non-limiting embodiments of the present application are as follows:

[0041] Embodiment 1

[0042] The embodiment provides a method for separating boron isotopes by chemical exchange and co-producing high-activity potassium fluoride, and the method comprises the following contents:

[0043] In order to reduce the corrosion of fluorine ions to the reactor, a 20wt% potassium hydroxide solution of 10L is prepared by using a stainless steel equipment, boron trifluoride gas is absorbed under stirring, and the pH value of the absorption system is detected. When the pH value of the absorption liquid system is reduced to 9, the absorption is stopped. After the absorption is completed, the absorption bottle is purged with nitrogen for 30min, and the purge gas can be absorbed by the next group of absorption devices. It can be known from the weight difference of the solution before and after absorption that about 0.56kg of boron trifluoride gas is absorbed, and some white precipitate is precipitated in the absorption liquid. The absorption liquid system with the precipitate is heated to 60℃ under stirring for 30min, and then the first solid-liquid separation is carried out while hot to obtain potassium tetraborate solids and a first mother liquor containing potassium fluoride. The potassium tetraborate solids are about 0.63kg, and after simple purification, they are main products borate;

[0044] The first mother liquor containing potassium fluoride obtained is detected, and the potassium fluoride content is 24%, which does not reach the target content, and can be recycled; 2 kg of potassium hydroxide is added to about 10 L of the first mother liquor containing potassium fluoride, and a new potassium hydroxide absorption liquid is formed after complete dissolution, a new batch of boron trifluoride gas is absorbed, and the pH value of the absorption system is detected at the same time; when the pH value of the absorption liquid system is reduced to 10, the absorption is stopped; after the absorption is completed, the absorption bottle is purged with nitrogen for 30 min, and the purge gas can be absorbed by the next group of absorption devices; it is known from the weight difference of the solution before and after absorption that about 0.55 kg of boron trifluoride gas is absorbed, and some white precipitate is precipitated in the absorption liquid; the absorption liquid system with the precipitate is heated to 60 DEG C under stirring condition and continues to stir for 30 min, heating and stirring are carried out, and first solid-liquid separation is carried out while hot, to obtain potassium tetraborate solid and the first mother liquor containing potassium fluoride; the potassium tetraborate solid is about 0.62 kg, and after simple purification, it is the main product boronic acid;

[0045] The first mother liquor containing potassium fluoride obtained is detected, and the potassium fluoride content is 52%, which reaches the target content; the first mother liquor containing potassium fluoride obtained is cooled to 20 DEG C under stirring condition, cooling crystallization is carried out, and potassium fluoride solid and second mother liquor are obtained through second solid-liquid separation; the potassium fluoride solid is about 1.4 kg, and the main component is potassium fluoride; the potassium fluoride solid obtained is fully washed with 1 L of ethanol for three times, is dissolved with 3 L of pure water, and the potassium fluoride solution obtained is spray dried, so that small-particle high-activity potassium fluoride is obtained.

[0046] In summary, the method for separating boron isotopes and co-producing high-activity potassium fluoride by chemical exchange method provided by the application absorbs boron trifluoride gas by using a potassium hydroxide absorption liquid, and the potassium tetraborate solid obtained is added with acid to recover boronic acid again, on the one hand, the first mother liquor containing potassium fluoride obtained by separating the potassium tetraborate solid is recycled, so that waste discharge is greatly reduced, and on the other hand, when the potassium fluoride is enriched to a certain degree, cooling crystallization is carried out, and the potassium fluoride solid obtained can be used to produce high-activity potassium fluoride. Therefore, the method provided by the application can not only meet the requirements of environmental protection, but also improve economic benefits.

[0047] The above embodiments are used to illustrate the detailed structural features of the application, but the application is not limited to the above detailed structural features, that is, the application does not mean that the application must rely on the above detailed structural features to be implemented. It should be understood by those skilled in the art that any improvement of the application, equivalent replacement of the components selected by the application, increase of auxiliary components, selection of specific modes, etc. fall within the protection scope and disclosure scope of the application.

[0048] The preferred embodiments of the present application are described in detail above, but the present application is not limited to the specific details of the above-described embodiments, and various simple modifications can be made to the technical solutions of the present application within the technical concept of the present application, and these simple modifications all belong to the protection scope of the present application.

[0049] In addition, it should be noted that each specific technical feature described in the above specific embodiments can be combined in any appropriate manner without contradiction, and in order to avoid unnecessary repetition, the present application will not further describe various possible combinations.

[0050] In addition, various different embodiments of the present application can also be combined in any manner, as long as it does not deviate from the idea of the present application, and it should also be considered as disclosed by the present application.

Claims

1. A method for the co-production of high activity potassium fluoride by chemical exchange process for the separation of boron isotopes, characterized in that, The method comprises the following contents: For the boron trifluoride gas obtained by separating boron isotopes by chemical exchange method, a potassium hydroxide absorption liquid is used for absorption, and through first solid-liquid separation, potassium tetraborate solid and a first mother liquor containing potassium fluoride are obtained; Potassium hydroxide is added to the first mother liquor to form a new potassium hydroxide absorption liquid, absorption of a new batch of boron trifluoride gas is carried out, recycling is realized, and until the potassium fluoride content in the first mother liquor obtained by the last recycling reaches a target content, cooling crystallization is carried out, through second solid-liquid separation, potassium fluoride solid and a second mother liquor are obtained, and the potassium fluoride solid is used for preparing high-activity potassium fluoride.

2. The method of claim 1, wherein, Before the first solid-liquid separation, the absorption liquid system with precipitates is heated and stirred, and the first solid-liquid separation is carried out while hot.

3. The method of claim 2, wherein, The temperature of the heating and stirring is 60-70°C.

4. The method according to claim 2 or 3, characterized in that, The time of the heating and stirring is 30-40 min.

5. The method of claim 1, wherein, After the absorption is completed, an inert gas is used to blow the upper part of the absorption liquid system, and the gas after blowing is used for absorption together with the next batch of boron trifluoride gas.

6. The method of claim 1, wherein, The potassium hydroxide content in the potassium hydroxide absorption liquid is 15-25 wt%.

7. The method of claim 1, wherein, The absorption is carried out under stirring until the pH value of the absorption liquid system is reduced to 9-10, and then the absorption is stopped.

8. The method of claim 1, wherein, In the first mother liquor obtained by the last recycling, the target content corresponding to the potassium fluoride content is 50-60%.

9. The method of claim 1, wherein, In the cooling crystallization, cooling is carried out to 15-25°C.

10. The method of claim 1, wherein, The preparation method of the high-activity potassium fluoride comprises the following steps: the potassium fluoride solid is sequentially subjected to ethanol rinsing, water redissolution, and spray drying, and high-activity potassium fluoride is obtained.

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