Preparation method of battery-grade sodium fluoride

Abstract

The invention relates to a preparation method of battery-grade sodium fluoride. The preparation method specifically comprises the following steps: (1) dissolving, filtering and removing impurities; (2) synthesis reaction; and (3) filtering, washing and drying. According to the method provided by the invention, the requirement on the purity of the raw material is relatively low, the low-price light sodium carbonate is used as the raw material, the content of the prepared sodium fluoride reaches 99.9% or above, the yield can reach 94% or above, the total content of metal impurities is less than 20 ppm, the water content is less than 100 ppm, and impurity ions such as calcium, iron, magnesium and potassium all meet the quality requirement of battery-grade sodium fluoride.

Description

Technical Field

[0001] The invention relates to the field of material technology, and in particular to a method for preparing battery-grade sodium fluoride. Background Art

[0002] With the continuous growth of global energy demand and the development of clean energy technology, the demand for secondary batteries such as lithium-ion batteries has increased dramatically. However, the over-exploitation of lithium ore resources, the raw material of lithium-ion batteries, has led to increasing costs. Sodium hexafluorophosphate is similar to lithium hexafluorophosphate in structure and properties, and its cost is much lower than that of lithium-ion batteries. It has a higher cost-effectiveness and has gradually become the focus of the market. Therefore, sodium-ion batteries with sodium hexafluorophosphate as the electrolyte are considered to be a potential alternative to lithium-ion batteries, which can achieve partial or even complete replacement.

[0003] Sodium hexafluorophosphate can be obtained by reacting sodium fluoride (NaF) and phosphorus pentafluoride (PF5) in anhydrous hydrogen fluoride. Therefore, in order to prepare battery-grade sodium hexafluorophosphate, battery-grade sodium fluoride is necessary. Battery-grade sodium fluoride has very high requirements for content, usually requiring its content to be no less than 99.5%, and the requirements for trace impurities are all measured in ppm.

[0004] There are two traditional sodium fluoride production process flows recorded in "Fine Chemicals Technology", and the chemical reaction equations are as follows: Na2CO3+2HF=2NaF↓+H2O+CO2↑ (1) 2Na2CO3+Na2SiF6+xH2O=6NaF↓+SiO2·xH2O+2CO2↑ (2) The sodium fluoride produced by the general method contains a large amount of impurity ions such as calcium, magnesium, potassium, and iron, and cannot be used as a raw material for battery-grade sodium hexafluorophosphate. Patent CN115744934B discloses a preparation method for purifying industrial-grade soda ash to produce electronic-grade sodium fluoride, that is, using equation (1) as the reaction mechanism, the specific steps are as follows: 1) preparing a saturated sodium carbonate solution, removing impurities through a screen and a filter membrane; 2) treating with a strong acid cationic resin absorption column, and then treating with an activated carbon absorption column after an acid-washing column; 3) carbonizing the sodium carbonate solution, and then separating the solid, filtering and drying to obtain a purified sodium carbonate solid; 4) adding purified sodium carbonate to the mother liquor, filtering through a filter membrane and entering a neutralization tank; 5) introducing the purified soda ash solution into a salt pool for heating and concentration; 6) cooling the salt pool to produce sodium fluoride crystals, and drying under reduced pressure to obtain a high-purity sodium fluoride product. Although this method can obtain high-purity sodium fluoride, the raw sodium carbonate must first be treated with a screen and a filter membrane to remove impurities, and then purified by a strong acid cationic resin absorption column and an activated carbon absorption column after acid washing. Although high-purity sodium fluoride was eventually produced, the yield of sodium fluoride was low (about 76%), the operation process was complicated, and the cost was high. Summary of the invention

[0005] The invention provides a method for preparing battery-grade sodium fluoride, so as to overcome the problems of low sodium fluoride yield, complicated operation process and high cost in the prior art.

[0006] The present invention uses light sodium carbonate as a raw material to prepare battery-grade sodium fluoride. Light sodium carbonate is low in price and widely available, but contains impurities such as calcium ions, iron ions, and magnesium ions. How to remove these impurities becomes the key point of the technical solution. Before synthesis, the present invention utilizes the different solubility characteristics of sodium fluoride, calcium fluoride, iron fluoride, and magnesium fluoride, and controls the amount of hydrofluoric acid added so that the sodium fluoride generated by the reaction with sodium carbonate is just completely dissolved, and reacts with calcium, iron, and magnesium impurity ions to generate calcium fluoride, iron fluoride, and magnesium fluoride precipitation, thereby cleverly removing calcium, iron, and magnesium impurities in light sodium carbonate, and the sodium carbonate solution is then reacted with hydrofluoric acid to prepare battery-grade sodium fluoride.

[0007] The specific technical solutions are as follows: A method for preparing battery-grade sodium fluoride, specifically comprising the following steps: (1) Dissolving, filtering and removing impurities Add a certain amount of desalted water (the second batch and the mother liquor of the previous batch of sodium fluoride) to the dissolving kettle, and then add a small amount of hydrofluoric acid to mix, and control the fluoride ion content in the water after mixing to be 0.1%~1.8% (when the fluoride ion content of the water is greater than 1.8%, it will react with sodium carbonate to generate too much sodium fluoride that cannot be completely dissolved in the aqueous solution, resulting in losses during filtration; when the fluoride ion content of the water is less than 0.1%, it cannot be completely precipitated to remove calcium and magnesium ions). Under full stirring, slowly add light sodium carbonate, the amount of light sodium carbonate added is 5%~11.5% of the weight of the desalted water (mother liquor) taken (when the amount added is greater than 11.5%, sodium carbonate cannot be completely dissolved and will be filtered out together with impurities, resulting in losses, and when the amount added is less than 5%, it will reduce production efficiency); after adding light sodium carbonate, stir and dissolve for 20 minutes, filter, and collect the sodium carbonate solution.

[0008] (2) Synthesis reaction Add a certain amount of hydrofluoric acid into the sodium fluoride synthesis reactor, and gradually add the sodium carbonate solution obtained in step (1) under sufficient stirring. When the pH of the reaction solution is 6-9 (when the pH is less than 6, a large amount of sodium bifluoride will dissolve in the aqueous solution during the reaction, and when the pH is greater than 9, excessive sodium carbonate will remain), stop adding the sodium carbonate solution. Since a large amount of gas will be generated during the addition process, the addition speed should not be too fast. After the addition, continue to stir and grow the crystal.

[0009] (3) Filter, wash and dry Centrifugal filtration, the filter cake is washed twice with deionized water, and the washing liquids are collected twice. The second washing liquid is used for the first washing of the next batch. The sodium fluoride mother liquor and the first washing water are retained and used in step (1). The washed sodium fluoride damp product is dried to obtain battery-grade sodium fluoride.

[0010] Preferably, the fluoride ion content in the water after mixing in step (1) is 1% to 1.5%.

[0011] Preferably, the amount of light sodium carbonate in step (1) is 9% to 10% of the weight of the deionized water (mother liquor) taken.

[0012] Preferably, in step (2), when the pH value of the reaction solution is 7-7.5, the addition of the sodium carbonate solution is stopped. Compared with the prior art, the present invention has the following beneficial effects: 1. The method provided by the present invention has low requirements on the purity of raw materials. By using inexpensive light sodium carbonate as raw material, the prepared sodium fluoride has a content of more than 99.9%, a yield of more than 94%, a total content of metal impurities of less than 20 ppm, and a moisture content of less than 100 ppm. Impurity ions such as calcium, iron, magnesium, and potassium meet the quality requirements of battery-grade sodium fluoride.

[0013] 2. The method provided by the present invention has a simple process flow, a simple impurity removal step for light sodium carbonate, and does not require complex steps such as resin adsorption and membrane separation, thereby reducing the cost of raw materials and energy consumption and improving the production efficiency of sodium fluoride.

[0014] 3. The sodium fluoride mother liquor and washing water produced in step (3) can be recycled, saving resources and complying with the green and environmentally friendly production concept.

[0015] 4. Compared with sodium fluoride prepared by conventional methods, the sodium fluoride prepared by the method provided by the present invention has good crystal form (particle size 75-85 microns), good fluidity, and is more convenient for downstream feeding and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a chart of the test results of sample content and impurity ion content in the embodiment and comparative example.

[0017] Figure 2 It is a graph of sample yield and particle size results of the examples. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical scheme and technical effect of the present invention more clear, the technical scheme of the present invention is further described below through specific implementation methods. Those skilled in the art should know that the embodiments are only to help understand the technical content and technical effect of the present invention and should not be regarded as limiting the present invention.

[0019] The sources of the raw materials in the following examples are as follows: light sodium carbonate was purchased from Shandong Haihua New Materials Co., Ltd., with a sodium carbonate content of 98%. 50% hydrofluoric acid was purchased from Zhejiang Sanmei Chemical Co., Ltd., electronic grade.

[0020] The desalted water is made by our company.

[0021] The above description only shows that the raw materials used in the embodiments of the present invention are purchased from mainstream manufacturers in the market, and does not represent that the raw materials must be produced by the above-mentioned manufacturers. As long as it is conventional raw material, the desired effect can be achieved without particular restrictions. In the present embodiment, specific conditions or operating methods are not described, indicating that operating conditions and methods are not limited, and can be according to conditions or operating methods commonly used in this area. Example

[0022] (1) At room temperature and normal pressure, add 1600L of deionized water to the dissolving kettle, then add 30Kg of 50% hydrofluoric acid and mix. While stirring thoroughly, slowly add 240kg of solid sodium carbonate; after adding the solid, stir and dissolve for 20 minutes, and then filter and collect the sodium carbonate solution.

[0023] (2) Add 150 kg of 50% hydrofluoric acid into the sodium fluoride synthesis kettle, and gradually add the sodium carbonate filtrate obtained in step (1) under sufficient stirring. When the pH of the reaction solution reaches 6.5, stop adding the sodium carbonate solution. Add the material for 2 hours, keep the kettle jacket cooled, and continue stirring and growing the crystal for half an hour after adding the material.

[0024] (3) Start centrifugal filtration when the temperature in the kettle reaches 30℃. Collect the mother liquor and wash the solid material twice with deionized water, using 100L of water each time. Collect the washing liquid twice and use the second washing liquid for the first washing of the next batch. After drying, collect the material and put it into the double cone drying. The drying temperature is controlled at 95~100℃ and nitrogen is used at 8m 3 / h, and after drying for 6 hours, battery-grade sodium fluoride was obtained. Example

[0025] (1) At room temperature and normal pressure, add 1600 L of the mother liquor from step (3) of Example 1 to a dissolving kettle. Slowly add 160 kg of solid sodium carbonate under full stirring; after adding the solid, stir and dissolve for 20 minutes, and then filter and collect the sodium carbonate solution.

[0026] (2) Add 120 kg of 50% hydrofluoric acid into the sodium fluoride synthesis kettle, and gradually add the sodium carbonate filtrate obtained in step (1) under sufficient stirring. When the pH of the reaction solution reaches 7, stop adding the sodium carbonate solution. The addition time is 2 hours, and the kettle jacket is kept cooled. After the addition, continue stirring and growing the crystal for half an hour.

[0027] (3) Centrifugal filtration was started when the temperature in the kettle reached 30°C. The mother liquor was collected, and the solid material was washed with the second washing liquid of Example 1 for the first time and with 100L of deionized water for the second time. The washing liquid was collected twice, and the second washing liquid was used for the first washing of the next batch. After drying, the collected material was put into a double cone drying, and the drying temperature was controlled at 95-100°C. 8m nitrogen was used. 3 / h, and after drying for 6 hours, battery-grade sodium fluoride was obtained. Example

[0028] (1) At room temperature and normal pressure, add 1600 L of the mother liquor from step (3) of Example 2 into a dissolving kettle. Slowly add 160 kg of solid sodium carbonate under full stirring; after adding the solid, stir and dissolve for 60 minutes, and then filter and collect the sodium carbonate solution.

[0029] (2) Add 120 kg of 50% hydrofluoric acid into the sodium fluoride synthesis kettle, and gradually add the sodium carbonate filtrate obtained in step (1) under sufficient stirring. When the pH of the reaction solution reaches 7, stop adding the sodium carbonate solution. The addition time is 2 hours, and the kettle jacket is kept cooled. After the addition, continue stirring and growing the crystal for half an hour.

[0030] (3) Centrifugal filtration was started when the temperature in the kettle reached 30°C. The mother liquor was collected, and the solid material was washed with the second washing liquid of Example 2 for the first time and with 100L of deionized water for the second time. The washing liquids were collected twice respectively, and the second washing liquid was used for the first washing of the next batch. After drying, the collected material was put into a double cone drying, and the drying temperature was controlled at 95-100°C. 8m nitrogen was used. 3 / h, and after drying for 6 hours, battery-grade sodium fluoride was obtained. Example

[0031] (1) At room temperature and normal pressure, add 1600 L of the mother liquor from step (3) of Example 3 to a dissolving kettle. Slowly add 160 kg of solid sodium carbonate under full stirring; after adding the solid, stir and dissolve for 20 minutes, and then filter and collect the sodium carbonate solution.

[0032] (2) Add 120 kg of 50% hydrofluoric acid into the sodium fluoride synthesis kettle, and gradually add the sodium carbonate filtrate obtained in step (1) under sufficient stirring. When the pH of the reaction solution reaches 7, stop adding the sodium carbonate solution. The addition time is 50 minutes, keep the kettle jacket cooled, and continue stirring and growing the crystal for half an hour after the addition.

[0033] (3) Centrifugal filtration was started when the temperature in the kettle reached 30°C. The mother liquor was collected, and the solid material was washed with the second washing liquid of Example 3 for the first time and with 100L of deionized water for the second time. The washing liquid was collected twice, and the second washing liquid was used for the first washing of the next batch. After drying, the collected material was put into a double cone drying, and the drying temperature was controlled at 95-100°C. 8m nitrogen was used. 3 / h, and after drying for 6 hours, battery-grade sodium fluoride was obtained.

[0034] Comparative Example (1) Add 120 kg of 50% hydrofluoric acid into the sodium fluoride synthesis kettle, and gradually add 160 kg of sodium carbonate solid while stirring thoroughly. When the pH of the reaction solution reaches 7, stop adding sodium carbonate solid. Add for 50 minutes, keep the kettle jacket cool, and continue stirring and growing crystals for half an hour after adding.

[0035] (2) Centrifugal filtration was started when the temperature in the kettle reached 30°C. The mother liquor was collected, and the solid material was washed with the second washing liquid of Example 3 for the first time and with 100L of deionized water for the second time. The washing liquids were collected twice respectively, and the second washing liquid was used for the first washing of the next batch. After drying, the collected material was put into a double cone drying, and the drying temperature was controlled at 95-100°C. 8m nitrogen was used. 3 / h, and after drying for 6 hours, sodium fluoride was obtained.

[0036] The sodium fluoride prepared in the above examples and comparative examples was weighed, its yield was calculated, and the particle size test, content test and impurity ion content test were performed. The test results are shown in the figure below Figure 1 and Figure Figure 2 shown.

[0037] Combination Figure 1 The data show that the sodium fluoride obtained by directly adding solid sodium carbonate in the comparative example has a low content and contains more impurity ions than the sodium fluoride obtained in the example.

[0038] Combination Figure 2 The data show that, in Example 1, deionized water was added with 30 kg of 50% hydrofluoric acid to dissolve sodium carbonate, and the mother liquor was used in Examples 2 to 4. Except for the dissolution of part of the material in Example 1 into the mother liquor, the average yield was 94.83%; the difference between Example 2 and Example 3 is that after adding the sodium carbonate solid in step (1), stirring for 20 minutes and 60 minutes has no effect on the result; the difference between Example 3 and Example 4 is the feeding speed of the sodium carbonate solution in step (2). If the feeding speed is too fast, the particle size will be slightly smaller. But the effect is not significant.

Claims

1. A method for preparing battery-grade sodium fluoride, It is characterized in that The following steps are involved: (1) Dissolving, filtering and removing impurities: Place an aqueous solution with a fluoride ion mass percentage of 0.1% to 1.8% in a dissolving kettle, and slowly add light sodium carbonate under full stirring, wherein the amount of light sodium carbonate added is 5% to 11.5% of the weight of the fluoride ion aqueous solution; after the light sodium carbonate is added, stir and dissolve for 20 minutes, filter, and collect the sodium carbonate solution; (2) Synthesis reaction: Add a certain amount of hydrofluoric acid into the sodium fluoride synthesis reactor, and gradually add the sodium carbonate solution obtained in step (1) under sufficient stirring. When the pH of the reaction solution is 6-9, stop adding the sodium carbonate solution. After adding the materials, continue stirring to grow the crystal; (3) Filter, wash and dry: The filter cake is centrifuged and filtered, and the filter cake is washed twice with deionized water, and the washing liquids are collected twice, and the second washing liquid is used for the first washing of the next batch; the sodium fluoride mother liquor and the first washing water are retained and used in step (1) as an aqueous solution with a fluoride ion mass percentage of 0.1% to 1.8%; the washed sodium fluoride damp product is dried to obtain battery-grade sodium fluoride.

2. A method for preparing battery-grade sodium fluoride according to claim 1, It is characterized in that The fluoride ion content in step (1) is 1% to 1.5% by weight.

3. A method for preparing battery-grade sodium fluoride according to claim 1, It is characterized in that In step (1), the amount of light sodium carbonate is 9% to 10% by weight of the aqueous solution.

4. A method for preparing battery-grade sodium fluoride according to claim 1, It is characterized in that When the pH value of the reaction solution in step (2) is 7-7.5, stop adding the sodium carbonate solution.

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