阅读说明：本技术 一种核纯氟化锂的提纯方法 (Purification method of nuclear pure lithium fluoride ) 是由 肖吉昌 宗国强 王荣荣 陆人杰 于 2021-03-30 设计创作，主要内容包括：本发明公开了一种核纯氟化锂的提纯方法,其包括如下步骤：(1)将氟化锂原料与有机溶剂-氟化氢络合物混合至完全溶解,得到液体A；混合的温度为40-100℃；(2)将步骤(1)中的液体A与水的混合物,进行固液分离,取固体,即可。本发明的提纯方法能够实现提纯后的氟化锂中金属杂质符合熔盐堆对初始原料氟化盐的质量允许指标要求,同时,提纯后氟化锂的产物收率较高(质量损失小于10％),纯度可达99.97％及以上,且该方法采用的设备简单,操作简单,成本低,无污染,安全性高,能耗小。(The invention discloses a purification method of nuclear pure lithium fluoride, which comprises the following steps: (1) mixing a lithium fluoride raw material and an organic solvent-hydrogen fluoride complex until the lithium fluoride raw material is completely dissolved to obtain a liquid A; the mixing temperature is 40-100 ℃; (2) and (2) carrying out solid-liquid separation on the mixture of the liquid A and the water in the step (1) to obtain a solid. The purification method can realize that the metal impurities in the purified lithium fluoride meet the requirement of the molten salt pile on the quality allowable index of the initial raw material fluoride salt, meanwhile, the yield of the purified lithium fluoride product is high (the mass loss is less than 10 percent), and the purity can reach 99.97 percent or more.)

1. A method for purifying nuclear-pure lithium fluoride is characterized by comprising the following steps:

(1) mixing a lithium fluoride raw material and an organic solvent-hydrogen fluoride complex until the lithium fluoride raw material is completely dissolved to obtain a liquid A; the mixing temperature is 40-100 ℃;

(2) and (2) carrying out solid-liquid separation on the mixture of the liquid A and the water in the step (1) to obtain a solid.

2. The method for purifying nuclear-pure lithium fluoride according to claim 1, wherein the lithium fluoride raw material is lithium fluoride containing impurities of a metal element existing in an ionic form;

and/or the purity of the lithium fluoride raw material is 99.9-99.95%;

and/or the lithium fluoride in the lithium fluoride raw material is lithium fluoride-7, for example, the lithium fluoride raw material is prepared by⁷And reacting LiOH with hydrofluoric acid to obtain lithium fluoride-7.

3. The method of purifying nuclear-pure lithium fluoride as claimed in claim 2, wherein said metal element includes one or more of Fe element, Cr element and Ni element.

4. The method of claim 3, wherein the Fe element is present in the lithium fluoride source in an amount of 0 to 1000ppm but not 0, such as 200, 550 or 800 ppm;

and/or the content of the Cr element in the lithium fluoride raw material is 0-100ppm but not 0, such as 20, 56 or 70 ppm;

and/or the Ni element is present in the lithium fluoride source in an amount of 0 to 100ppm but not 0, such as 35, 50 or 80 ppm.

5. The method for purifying nuclear-pure lithium fluoride according to claim 1, wherein the organic solvent-hydrogen fluoride complex is a nitrogen-containing organic solvent-hydrogen fluoride complex;

and/or in the step (1), the mass ratio of the lithium fluoride raw material to the organic solvent-hydrogen fluoride complex is 1 (3-10);

and/or, in the step (1), the temperature of the mixing is 60, 70, 80 or 90 ℃;

and/or, in the step (1), the operation of mixing comprises a step of stirring;

and/or, in the step (1), a filtering step is further included after the mixing;

wherein, the material of the filter membrane used for filtering is preferably PTFE, PP or spray Teflon; the pore size of the filter membrane used for the filtration can be 10-50 μm, preferably 20 μm.

6. The method for purifying nuclear-pure lithium fluoride according to claim 5, wherein the organic solvent-hydrogen fluoride complex is one or more of hydrogen fluoride-pyridine complex, N, N-dimethylformamide-hydrogen fluoride complex, and triethylamine-hydrogen trifluoride complex;

and/or in the step (1), the mass ratio of the lithium fluoride raw material to the organic solvent-hydrogen fluoride complex is 1:3, 1:3.5, 1:4, 1:5 or 1: 7;

and/or, in the step (1), when the operation of mixing includes a step of stirring, the stirring includes a step of first stirring and a step of second stirring; the temperature of the first stirring is 20 +/-5 ℃, and the temperature of the second stirring is 40-100 ℃.

7. The method for purifying nuclear-pure lithium fluoride according to claim 6, wherein the first stirring is performed for 1 to 5 hours;

and/or the time of the second stirring is 1-5 h;

and/or the temperature of the second stirring is 60, 70, 80 or 90 ℃.

8. The method for purifying nuclear-pure lithium fluoride according to claim 1, wherein in the step (2), the mass of the water is 3 to 10 times, preferably 4 to 6 times, the mass of the organic solvent-hydrogen fluoride complex;

and/or in the step (2), the mixture of the liquid A and the water is obtained by mixing the liquid A and the water under the conditions of heat preservation and stirring; wherein the content of the first and second substances,

the temperature of the incubation is preferably 40-100 ℃, e.g. 60, 70, 80 or 90 ℃;

the stirring time is preferably 1-5 h;

and/or, in the step (2), the solid-liquid separation comprises a step of filtration, preferably at a temperature of 40-100 ℃, for example at 60, 70, 80 or 90 ℃.

9. The method for purifying nuclear-pure lithium fluoride according to claim 1, further comprising, after the step (2), a step (3): washing and drying the solid obtained in the step (2).

10. The method for purifying nuclear-pure lithium fluoride according to claim 9, wherein in the step (3), the number of washing is 1 to 5, such as 3;

and/or, in the step (3), the washing reagent is water, such as deionized water;

and/or, in the step (3), the mass of the reagent used for washing is 0.5 to 5 times, for example, 1 time, the mass of the lithium fluoride raw material;

and/or, in the step (3), the drying is vacuum drying.

Technical Field

The invention relates to a purification method of nuclear pure lithium fluoride.

Background

Molten Salt Reactor (MSR) is one of 6 candidate nuclear energy systems chosen by the fourth generation international forum for nuclear energy (GIF). Compared with other reactor types, the reactor has incomparable advantages in neutron economy, radioactive waste treatment, inherent safety, nuclear diffusion prevention and the like. Because the fluoride fused salt has a series of characteristics of small neutron absorption cross section, good high-temperature stability, high thermal conductivity, high specific heat, high boiling point, low saturated vapor pressure, low viscosity and the like, the MSR is made of alkaline earth metalFluorides as carriers and coolants for nuclear fuels, binary mixtures thereof⁷LiF-BeF₂Is the most commonly used candidate molten salt system. Applied to MSR⁷LiF-BeF₂Molten salts have very high purity requirements and some corrosive metal impurities have very strict limits in molten salts.

Lithium fluoride-7 (⁷LiF) is prepared⁷LiF-BeF₂The control of the basic raw material and the impurity content of the molten salt is directly related to the purity of the molten salt prepared by the molten salt. And preparation of⁷The method of LiF comprises⁷LiOH is a raw material which is very expensive and therefore, in the production and purification of nuclear pure grades⁷In the process of LiF, the quality loss should be avoided as much as possible. In that⁷Preparation of nuclear pure by LiOH fluorination⁷In the LiF process, hydrofluoric acid with strong corrosiveness is used as a fluorinating agent, and accidents such as raw material introduction or equipment corrosion and the like in individual batches can occur⁷Metal impurities are introduced into LiF, the LiF is light brown, and purification treatment is needed when the metal impurities exceed the allowable content indexes (Fe is less than or equal to 100ppm, Cr is less than or equal to 25ppm, and Ni is less than or equal to 25ppm) of impurities in the initial raw material fluoride salt by the oak ridge molten salt reactor. Due to the fact that⁷LiF has a low solubility in a conventional solvent such as water, and these metal impurities (fluoride or oxide) are included therein and are hardly removed by washing.

No specific targeting of removal has been found so far⁷Although an ion exchange method or a solvent extraction method is a common method for removing impurities in LiF, the method has the disadvantages of slow speed, additional equipment, complex equipment, high energy consumption, high cost and the like, and more other impurities can be introduced due to complex processes or addition of a purification reagent.

Disclosure of Invention

The invention aims to overcome the defects that metal impurities in nuclear pure lithium fluoride-7 are difficult to remove or the operation is complex in the prior art, and provides a purification method of nuclear pure lithium fluoride. The purification method of nuclear pure lithium fluoride has good effect of removing metal ions in the nuclear pure lithium fluoride, and has the characteristics of simple and rapid operation.

The invention solves the technical problems through the following technical scheme:

a method for purifying nuclear-pure lithium fluoride, which comprises the following steps:

(1) mixing a lithium fluoride raw material and an organic solvent-hydrogen fluoride complex until the lithium fluoride raw material is completely dissolved to obtain a liquid A; the mixing temperature is 40-100 ℃;

(2) and (2) carrying out solid-liquid separation on the mixture of the liquid A and the water in the step (1) to obtain a solid.

In the present invention, the lithium fluoride starting material may be lithium fluoride containing impurities of the metal element in the form of ions, which is conventional in the art. The purity of the lithium fluoride starting material may be 99.9-99.95%.

In the present invention, the lithium fluoride in the lithium fluoride raw material may be lithium fluoride-7, for example, lithium fluoride-7⁷And (3) reacting LiOH with hydrofluoric acid (aqueous hydrogen fluoride) to obtain lithium fluoride-7.

Among them, the metal element may include metal elements conventional in the art, which are impurities introduced during the conventional lithium fluoride manufacturing process, such as one or more of Fe element, Cr element, and Ni element.

Wherein the content of the Fe element in the lithium fluoride raw material may be 0 to 1000ppm but not 0, for example 200, 550 or 800 ppm.

Wherein the content of the Cr element in the lithium fluoride raw material may be 0 to 100ppm but not 0, for example, 20, 56 or 70 ppm.

Wherein the Ni element may be contained in the lithium fluoride raw material in an amount of 0 to 100ppm but not 0, for example, 35, 50 or 80 ppm.

In the present invention, the organic solvent-hydrogen fluoride complex generally refers to a complex of an organic solvent and hydrogen fluoride. For example, the triethylamine trihydrofluoride complex is triethylamine trihydrofluoride complex obtained by complexing triethylamine with hydrogen fluoride. Organic solvent-hydrogen fluoride complexes are commonly used in the art as fluorinating agents in the synthesis of organofluoro compounds.

In the present invention, the organic solvent-hydrogen fluoride complex is preferably a nitrogen-containing organic solvent-hydrogen fluoride complex; more preferably one or more of hydrogen fluoride-pyridine complex (PPHF), N-dimethylformamide-hydrogen fluoride complex and triethylamine trihydrofluoride complex.

In the present invention, in the step (1), the mass ratio of the lithium fluoride raw material to the organic solvent-hydrogen fluoride complex is preferably 1 (3 to 10), for example, 1:3, 1:3.5, 1:4, 1:5, or 1: 7.

In the present invention, in the step (1), the temperature of the mixing is preferably 60, 70, 80 or 90 ℃.

In the present invention, in the step (1), the mixing operation preferably includes a stirring step.

Wherein, the stirring preferably comprises the steps of first stirring and second stirring; the temperature of the first stirring is 20 +/-5 ℃, and the temperature of the second stirring is 40-100 ℃.

The time for the first stirring is preferably 1 to 5 hours.

The time of the second stirring is preferably 1 to 5 hours.

The temperature of the second stirring is preferably 60, 70, 80 or 90 ℃.

In the present invention, in the step (1), preferably, a filtration step is further included after the mixing.

Wherein, the device used for filtering can be a filtering device which is conventional in the field and resists the corrosion of hydrofluoric acid. The material of the filter membrane used for filtering is preferably PTFE, PP or spray Teflon; the filter membrane used for the filtration may have a pore size as is conventional in the art, for example, 10 to 50 μm, preferably 20 μm.

In the present invention, in the step (2), the mass of the water is preferably 3 to 10 times, more preferably 4 to 6 times that of the organic solvent-hydrogen fluoride complex.

In the present invention, in the step (2), preferably, the mixture of the liquid a and water is obtained by mixing the liquid a and water under the conditions of heat preservation and stirring.

Wherein the temperature of the incubation is preferably 40-100 ℃, such as 60, 70, 80 or 90 ℃.

Wherein the stirring time is preferably 1-5 h.

In the present invention, in the step (2), the solid-liquid separation may be performed as a conventional solid-liquid separation in the art. Preferably, the solid-liquid separation comprises a step of filtration, preferably at a temperature of 40-100 ℃, for example at 60, 70, 80 or 90 ℃.

In the present invention, preferably, after the step (2), a step (3) is further included: washing and drying the solid obtained in the step (2).

Wherein, in the step (3), the number of washing is preferably 1 to 5, for example, 3.

In the step (3), the washing reagent may be a reagent conventionally used in the art, preferably water, such as deionized water. Used for removing acid and salt impurities adsorbed on the surface.

In the step (3), the mass of the reagent used for washing is preferably 0.5 to 5 times, for example, 1 time the mass of the lithium fluoride raw material.

Wherein, in the step (3), the drying may be a drying operation conventional in the art, and preferably is vacuum drying.

In the present invention, preferably, the content of the impurity components in the purified lithium fluoride prepared by the purification method meets the following standard: fe is 100ppm or less, Cr is 25ppm or less, Ni is 25ppm or less, for example, Fe is 95ppm, Cr is 16ppm, and Ni is 13 ppm.

In the present invention, the purity of the lithium fluoride obtained by the purification method is preferably 99.97% or more, for example, 99.981%, 99.974% or 99.978%.

In the invention, the nuclear purity generally means that the purity is nuclear purity grade.

In the present invention, lithium-7 and⁷in LiF⁷Li generally refers to the lithium element with a mass number of 7.

The above preferred conditions can be arbitrarily combined to obtain preferred embodiments of the present invention without departing from the common general knowledge in the art.

The reagents and starting materials used in the present invention are commercially available.

The positive progress effects of the invention are as follows:

1. the purification method provided by the invention realizes removal of impurity ions, and can realize that metal impurities in the purified lithium fluoride meet the requirement of a molten salt pile on the quality allowable index of the initial raw material fluoride; meanwhile, the yield of the purified lithium fluoride product is high (the mass loss is less than 10%), and the purity can reach 99.97% or more.

2. Compared with the method adopting an ion exchange method or a solvent extraction method, the purification method has the advantages of higher impurity ion removal speed, simple equipment, simple operation, low cost, no pollution, high safety and lower energy consumption, and the organic solvent-hydrogen fluoride complex can be recycled after being purified, so that under the original production condition of producing lithium fluoride, no additional equipment is required to be added, and the good purification effect and economic applicability are realized.

Detailed Description

The invention is further illustrated by the following examples, which are not intended to limit the scope of the invention.

In the following examples and comparative examples, hydrogen fluoride-pyridine complex, N-dimethylformamide hydrogen fluoride complex, triethylamine trihydrofluoride complex were purchased from Shanghai Tantake technology Ltd and had a purity of more than 99%.

In the following examples and comparative examples, the methods for analyzing and calculating the purity of the sample refer to the industrial standard HG/T4507-2013 for lithium fluoride, which is a high-purity industrial product, wherein the mass fractions of sodium, potassium, magnesium, calcium, iron, copper, silicon, chloride and sulfate are subtracted from 100%, so as to obtain the mass fraction of lithium fluoride on a dry basis. The simultaneous measurement of multiple elements was performed using inductively coupled plasma emission spectroscopy (ICP-OES), in which the chloride and sulfate contents were measured by ion chromatography.

Example 1

Checking the reaction kettle is intact, vacuumizing 50 kg of hydrogen fluoride-pyridine complex into the reaction kettle, adding the hydrogen fluoride-pyridine complex into the reaction kettle from a feed inlet under the condition of stirringTo be purified⁷10.0 kg of LiF raw material (purity 99.9%, Fe: 550ppm, Cr: 56ppm, Ni: 35ppm) is stirred for 1h at normal temperature to be completely dissolved, and then the temperature is raised to 80 ℃ and stirred for 1 h; will dissolve completely⁷And (3) putting the LiF mixed solution into a filter tank (made of PTFE material and with the aperture of the filter membrane being 20 mu m) for filtering, and obtaining filtrate for later use. Pumping the filtrate into a reaction kettle, and heating to 80 ℃. Under the condition of heat preservation and stirring, 200 kg of 4 times of deionized water is gradually added from the elevated tank to precipitate⁷LiF products; stirring for 1 hour under constant temperature, and filtering while it is hot. Collecting the filtrate into a ton barrel for subsequent purification treatment; after filtering, pumping deionized water, and washing for three times by 10 kilograms at a time to remove acid and salt impurities adsorbed on the surface; after washing, vacuum drying is carried out to obtain 9.1 kg of product. Sampling analysis, Fe:95ppm, Cr:16ppm, Ni:13ppm, found to be 99.981% pure.

Example 2

Checking the reaction kettle is intact, vacuum-pumping 35 kg of N, N-dimethylformamide hydrogen fluoride complex into the reaction kettle, adding the N, N-dimethylformamide hydrogen fluoride complex to be purified from a feed inlet under the condition of stirring⁷10.0 kg of LiF raw material (purity 99.9%, Fe: 550ppm, Cr: 56ppm, Ni: 35ppm) is stirred for 1h at normal temperature to be completely dissolved, and then the temperature is raised to 80 ℃ and stirred for 1 h; will dissolve completely⁷And (3) putting the LiF mixed solution into a filter tank (made of PTFE material and with the aperture of the filter membrane being 20 mu m) for filtering, and obtaining filtrate for later use. Pumping the filtrate into a reaction kettle, and heating to 80 ℃. Under the condition of heat preservation and stirring, 210 kilograms of 6 times of deionized water is gradually added from the elevated tank to be separated out⁷LiF products; stirring for 1 hour under constant temperature, and filtering while it is hot. Collecting the filtrate into a ton barrel for subsequent purification treatment; after filtering, pumping deionized water, and washing for three times by 10 kilograms at a time to remove acid and salt impurities adsorbed on the surface; after washing, vacuum drying is carried out to obtain 8.9 kg of product. Sampling analysis, Fe: 63ppm, Cr: 20ppm, Ni: 9 ppm. The purity was found to be 99.974%.

Example 3

Checking the reaction kettle is intact, vacuum-pumping 40 kg triethylamine hydrogen trifluoride complex into the reaction kettle, adding the triethylamine hydrogen trifluoride complex to be purified from a feed inlet under the stirring condition⁷LiF raw material10.0 kg (purity 99.9%, Fe 550ppm, Cr 56ppm, Ni 35ppm), stirring at room temperature for 1h to dissolve completely, heating to 80 deg.C, and stirring for 1 h; will dissolve completely⁷And (3) putting the LiF mixed solution into a filter tank (made of PTFE material and with the aperture of the filter membrane being 20 mu m) for filtering, and obtaining filtrate for later use. Pumping the filtrate into a reaction kettle, and heating to 80 ℃. Under the condition of heat preservation and stirring, 240 kilograms of 6 times of deionized water is gradually added from the elevated tank to be separated out⁷LiF products; stirring for 1 hour under constant temperature, and filtering while it is hot. Collecting the filtrate into a ton barrel for subsequent purification treatment; after filtering, pumping deionized water, and washing for three times by 10 kilograms at a time to remove acid and salt impurities adsorbed on the surface; after washing, vacuum drying is carried out to obtain 9.3 kg of product. Sampling analysis, Fe: 82ppm, Cr: 22ppm, Ni: 17ppm, found to be 99.978% pure.

Comparative example 1

Checking the reaction kettle is intact, vacuumizing 50 kg of hydrogen fluoride-pyridine complex into the reaction kettle, adding the hydrogen fluoride-pyridine complex to be purified from a feed inlet under the stirring condition⁷10.0 kg of LiF raw material (purity 99.9%, Fe: 550ppm, Cr: 56ppm, Ni: 35ppm) is stirred at normal temperature for 1h without complete dissolution, and then stirred at room temperature for 2 h; will not be completely dissolved⁷And (3) putting the LiF mixed solution into a filter tank (made of PTFE material and with the aperture of the filter membrane being 20 mu m) for filtering, and obtaining filtrate for later use. Pumping the filtrate into a reaction kettle, and heating to 80 ℃. Under the condition of heat preservation and stirring, 200 kg of 4 times of deionized water is gradually added from the elevated tank to precipitate⁷LiF products; stirring for 1 hour under constant temperature, and filtering while it is hot. Collecting the filtrate into a ton barrel for subsequent purification treatment; after filtering, pumping deionized water, and washing for three times by 10 kilograms at a time to remove acid and salt impurities adsorbed on the surface; after the washing, the product was dried in vacuo to give 7.8 kg (low yield). Sampling analysis, Fe: 105ppm, Cr: 20ppm, Ni: 18ppm, purity measured 99.971%.

Comparative example 2

Checking the reactor is intact, vacuum pumping 50 kg hydrofluoric acid (49%) into the reactor, adding the material to be purified from the feed inlet under stirring⁷LiF raw material 10.0 kg (purity 99.9%, Fe 550ppm, Cr 56ppm, N)i: 35ppm), stirring for 1 hour at normal temperature until the materials are not completely dissolved, and then heating to 80 ℃ and stirring for 1 hour; will not be completely dissolved⁷And (3) putting the LiF mixed solution into a filter tank (made of PTFE material and with the aperture of the filter membrane being 20 mu m) for filtering, and obtaining filtrate for later use. Pumping the filtrate into a reaction kettle, and heating to 80 ℃. Under the condition of heat preservation and stirring, 200 kg of 4 times of deionized water is gradually added from the elevated tank to precipitate⁷LiF products; stirring for 1 hour under constant temperature, and filtering while it is hot. Collecting the filtrate into a ton barrel for subsequent purification treatment; after filtering, pumping deionized water, and washing for three times by 10 kilograms at a time to remove acid and salt impurities adsorbed on the surface; after the washing, the product was dried in vacuo to give 6.2 kg (low yield). Sampling analysis, Fe: 158ppm, Cr: 46ppm, Ni: 17ppm, found to be 99.965% pure.

Comparative example 3

Checking the reaction kettle is intact, extracting 50 kg of triethylamine into the reaction kettle in vacuum, adding 10 kg of 49% hydrofluoric acid, and adding the material to be purified from a feed inlet under the condition of stirring⁷10.0 kg of LiF raw material (purity 99.9%, Fe: 550ppm, Cr: 56ppm, Ni: 35ppm) is stirred for 1 hour at normal temperature and is not completely dissolved, and then the temperature is raised to 80 ℃ and the mixture is stirred for 1 hour; will not be completely dissolved⁷And (3) putting the LiF mixed solution into a filter tank (made of PTFE material and with the aperture of the filter membrane being 20 mu m) for filtering, and obtaining filtrate for later use. Pumping the filtrate into a reaction kettle, and heating to 80 ℃. Under the condition of heat preservation and stirring, 200 kg of 4 times of deionized water is gradually added from the elevated tank to precipitate⁷LiF products; stirring for 1 hour under constant temperature, and filtering while it is hot. Collecting the filtrate into a ton barrel for subsequent purification treatment; after filtering, pumping deionized water, and washing for three times by 10 kilograms at a time to remove acid and salt impurities adsorbed on the surface; after the washing, the product was dried in vacuo to give 6.8 kg (low yield). Sampling analysis, Fe: 175ppm, Cr: 18ppm, Ni: 17ppm, found to be 99.958% pure.

While specific embodiments of the invention have been described above, it will be appreciated by those skilled in the art that this is by way of example only, and that the scope of the invention is defined by the appended claims. Various changes and modifications to these embodiments may be made by those skilled in the art without departing from the spirit and scope of the invention, and these changes and modifications are within the scope of the invention.